Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/0008—Introducing ophthalmic products into the ocular cavity or retaining products therein
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/007—Methods or devices for eye surgery
  • A61F9/0079—Methods or devices for eye surgery using non-laser electromagnetic radiation, e.g. non-coherent light or microwaves
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/33—Heterocyclic compounds
  • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
  • A61K31/495—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having six-membered rings with two or more nitrogen atoms as the only ring heteroatoms, e.g. piperazine or tetrazines
  • A61K31/505—Pyrimidines; Hydrogenated pyrimidines, e.g. trimethoprim
  • A61K31/519—Pyrimidines; Hydrogenated pyrimidines, e.g. trimethoprim ortho- or peri-condensed with heterocyclic rings
  • A61K31/525—Isoalloxazines, e.g. riboflavins, vitamin B2
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K41/00—Medicinal preparations obtained by treating materials with wave energy or particle radiation ; Therapies using these preparations
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N5/00—Radiation therapy
  • A61N5/06—Radiation therapy using light
  • A61N5/0613—Apparatus adapted for a specific treatment
  • A61N5/062—Photodynamic therapy, i.e. excitation of an agent
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P27/00—Drugs for disorders of the senses
  • A61P27/02—Ophthalmic agents
  • A61P27/10—Ophthalmic agents for accommodation disorders, e.g. myopia
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/007—Methods or devices for eye surgery
  • A61F9/008—Methods or devices for eye surgery using laser
  • A61F2009/00861—Methods or devices for eye surgery using laser adapted for treatment at a particular location
  • A61F2009/00872—Cornea
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/007—Methods or devices for eye surgery
  • A61F9/013—Instruments for compensation of ocular refraction ; Instruments for use in cornea removal, for reshaping or performing incisions in the cornea

Definitions

• the invention pertains to systems and methods for corneal cross-linking with pulsed light, especially when a cross-linking agent is applied to stabilize desired shape changes generated in corneal tissue.
• LASIK Laser-assisted in-situ keratomileusis
• LASIK eye surgery an instrument called a microkeratome is used to cut a thin flap in the cornea. The cornea is then peeled back and the underlying cornea tissue ablated to the desired shape with an excimer laser. After the desired reshaping of the cornea is achieved, the cornea flap is put back in place and the surgery is complete.
• thermokeratoplasty provides a noninvasive procedure that applies electrical energy in the microwave or radio frequency (RF) band to the cornea.
• the electrical energy raises the corneal temperature until the collagen fibers in the cornea shrink at about 60°C.
• the onset of shrinkage is rapid, and stresses resulting from this shrinkage reshape the corneal surface.
• application of energy according to particular patterns including, but not limited to, circular or annular patterns, may cause aspects of the cornea to flatten and improve vision in the eye.
• One aspect of the present disclosure relates to a method for controlling activation of Riboflavin applied to an eye.
• the method includes applying the Riboflavin to a selected region of a cornea of the eye and initiating cross-linking activity in the selected region by activating the Riboflavin with pulsed light illumination.
• the pulsed light illumination has an irradiance, a dose, and an on/off duty cycle.
• the irradiance, the dose, and the on/off duty cycle are adjusted in response to a determination of photochemical kinetic pathways for Riboflavin cross-linking activity to control photochemical efficiency.
• a further aspect of the present disclosure relates to a system for controlling cross- linking in corneal tissue.
• the system includes an applicator for applying a cross-linking agent to a selected region of a cornea.
• the system also includes a light source configured to initiate cross-linking activity in the selected region by activating the cross-linking agent.
• the light source is configured to deliver at least one of pulsed light illumination and continuous wave illumination.
• the pulsed light source has an irradiance, a dose, and an on/off duty cycle. The irradiance, the dose, and the on/off duty cycle are adjusted in response to a determination of photochemical kinetic pathways for the cross-linking activity to control photochemical efficiency and achieve a desired amount of cross-linking in the cornea.
• the continuous wave illumination corresponds with absorption peaks of the cross-linking agent.
• the system further includes a monitoring system configured to monitor the amount of cross- linking in the cornea. The irradiance, the dose and the on/off duty cycle are optionally further adjusted in response to the monitored amount of cross-linking in the cornea.
• Yet another aspect of the present disclosure relates to a method of controllably applying cross-linking therapy to an eye.
• the method includes analyzing a cornea of the eye to determine a desired change in a biomechanical characteristic for the eye.
• the method further includes achieving the desired change in the biomechanical characteristic for the eye by adjusting, in response to a determination of photochemical kinetic pathways of cross- linking activity in the eye, at least one parameter selected from: an irradiance of pulsed light illumination to be applied to the cornea, a dose, a duration of an exposure cycle of the pulsed light illumination, and a duration of a dark cycle of the pulsed light illumination.
• the method additionally includes activating the cross-linking agent by delivering the pulsed light illumination to the cornea according to the at least one adjusted parameter.
• a further aspect of the present disclosure relates to a system for dynamically controlling an amount of cross-linking in a cornea.
• the system includes an applicator for applying a cross-linking agent to a cornea.
• the system further includes a pulsed light source configured to activate the cross-linking agent.
• the pulsed light source has an irradiance, a dose, and an on/off duty cycle. The irradiance, the dose, and the on/off duty cycle are adjusted based on a desired amount of cross-linking in the cornea.
• the system additionally includes a delivery device configured to provide oxygen to a surface of the cornea.
• An additional aspect of the present disclosure relates to a method for controlling cross-linking in corneal tissue.
• the method includes applying a cross-linking agent to a cornea and activating the cross-linking agent with pulsed light illumination.
• the pulsed light illumination has an irradiance, a dose, and an on/off duty cycle.
• the method also includes monitoring an amount of cross-linking in the cornea and adjusting the irradiance, the dose, and the on/off duty cycle in response to the monitored amount of cross-linking in the cornea.
• the method further includes delivering oxygen to a surface of the cornea.
• FIG. 1 provides a block diagram of an example delivery system for delivering a cross-linking agent and an activator to a cornea of an eye in order to initiate molecular cross- linking of corneal collagen within the cornea.
• FIG. 2A illustrates a graph of depletion and gradual replenishment of oxygen below a ⁇ corneal flap saturated with 0.1% Riboflavin during 3mW/cm continuous wave (CW) irradiation.
• FIG. 2B illustrates a graph of oxygen recovery under a ⁇ corneal flap saturated with 0.1% Riboflavin during 30 mW/cm pulsed irradiation.
• FIG. 3 illustrates a graph of absorbance of reduced Riboflavin before and after 30 mW/cm CW irradiation for 3 minutes.
• FIG. 4A illustrates a graph of fluorescence or Riboflavin samples at 450nm.
• FIG. 4B illustrates a graph of relative fluorescence of cross-linked Riboflavin flaps at different Riboflavin concentrations and depths.
• FIGs. 5A-5C illustrate graphs of force versus displacement curves for porcine cornea for various soak times and UVA illumination scenarios.
• FIG. 6 illustrates a graph of fluorescence versus wavelength for porcine cornea 200 ⁇ flaps for various UVA illumination scenarios.
• FIG. 7A illustrates a graph of cross-linking measured by fluorescence of the digested corneal flap at 450 nm for various UVA illumination scenarios.
• FIG. 7B illustrates a graph of force versus displacement curve for porcine cornea for various UVA illumination scenarios.
• FIG. 8A illustrates an example approach for stabilizing or strengthening corneal tissue by applying a cross-linking agent according to aspects of the present invention.
• FIG. 8B illustrates an example approach for stabilizing or strengthening corneal tissue by applying Riboflavin as a cross-linking agent according to aspects of the present invention.
• FIG. 9A illustrates an example device that may be employed to supersaturate a cross-linking agent with 0 2 according to aspects of the present invention.
• FIG. 9B illustrates an example approach for stabilizing or strengthening corneal tissue by applying supersaturated Riboflavin as a cross-linking agent according to aspects of the present invention.
• FIG. 10A illustrates an example device that may be employed to supersaturate a carrier gel with 0 2 according to aspects of the present invention.
• FIG. 10B illustrates an example approach for stabilizing or strengthening corneal tissue by mixing Riboflavin with a gel supersaturated with 0 2 according to aspects of the present invention.
• FIG. IOC illustrates an example approach for stabilizing or strengthening corneal tissue by applying a gel supersaturated with 0 2 according to aspects of the present invention.
• FIG. 11A illustrates an example device that may be employed maintain a steady state of 0 2 above the eye to expose the cornea to higher concentrations of 0 2 according to aspects of the present invention.
• FIG. 11B illustrates another example device that may be employed to maintain a steady state of 0 2 above the eye to expose the cornea to higher concentrations of 0 2 according to aspects of the present invention.
• FIG. l lC illustrates an example approach for stabilizing or strengthening corneal tissue by applying a state of 0 2 above the eye to expose the cornea to higher concentrations of 0 2 .
• FIG. 12 illustrates an example approach for stabilizing or strengthening corneal tissue by monitoring cross-linking activity in real time and controlling the amount of 0 2 exposure to achieve desired rates of cross-linking according to aspects of the present invention.
• the delivery system 100 includes an applicator 132 for applying the cross-linking agent 130 to the cornea 2.
• the delivery system 100 includes a light source 1 10 and optical elements 1 12 for directing light to the cornea 2.
• the delivery system 100 also includes a controller 120 that is coupled to the applicator 132 and the optical elements 1 12.
• the applicator 132 may be an apparatus adapted to apply the cross-linking agent 130 according to particular patterns on the cornea 2.
• the applicator 132 may apply the cross-linking agent 130 to a corneal surface 2A (e.g., an epithelium), or to other locations on the eye 1. Particularly, the applicator 132 may apply the cross-linking agent 130 to an abrasion or cut of the corneal surface 2 A to facilitate the transport or penetration of the cross-linking agent through the cornea 2 to a mid-depth region 2B.
• a corneal surface 2A e.g., an epithelium
• the applicator 132 may apply the cross-linking agent 130 to an abrasion or cut of the corneal surface 2 A to facilitate the transport or penetration of the cross-linking agent through the cornea 2 to a mid-depth region 2B.
• the initiating element is ultraviolet-A ("UVA") light
• UVA ultraviolet-A
• the UVA light may be applied continuously (continuous wave or CW) or as pulsed light, and this selection has an effect on the amount, the rate, and the extent of cross-linking. If the UVA light is applied as pulsed light, the duration of the exposure cycle, the dark cycle, and the ratio of the exposure cycle to the dark cycle duration all have an effect on both the rate of cross-linking and the amount of resulting corneal stiffening.
• cross-linking agent concentration a concentration of cross-linking agent in a significant role in cross-linking
• temperature a temperature of the cornea
• specific conditions of the cornea e.g., if any previous treatments have taken place
• other factors and parameters e.g., other parameters and parameters.
• aspects of the present disclosure relate to determining the effect of each of these parameters on the rate and the amount of cross-linking, as well as the interrelations of these parameters among each other to optimize the conditions to achieve the desired amount, rate, and location (on the cornea 2) of corneal stiffening.
• aspects of the present disclosure relate to monitoring the corneal response to a change in one or a plurality of parameters and adjusting the one or the plurality of parameters based on the received feedback.
• the devices and approaches disclosed herein may be used to preserve desired shape or structural changes following an eye therapy treatment by stabilizing the corneal tissue of the cornea 2.
• the devices and approaches disclosed herein may also be used to enhance the strength or biomechanical structural integrity of the corneal tissue apart from any eye therapy treatment.
• the optical elements 112 may include one or more mirrors or lenses for directing and focusing the light emitted by the light source 110 to a particular pattern on the cornea 2 suitable for activating the cross-linking agent 130.
• the light source 110 may be a UVA light source that may also alternatively or additionally emit photons with greater or lesser energy levels than ultraviolet light photons.
• the delivery system 100 also includes a controller 120 for controlling the operation of the optical elements 112 or the applicator 132, or both. By controlling aspects of the operation of the optical elements 112 and the applicator 132, the controller 120 can control the regions of the cornea 2 that receive the cross-linking agent 130 and that are exposed to the light source 110.
• the controller 120 can control the particular regions of the cornea 2 that are strengthened and stabilized through cross-linking of the corneal collagen fibrils.
• the cross-linking agent 130 can be applied generally to the eye 1, without regard to a particular region of the cornea 2 requiring strengthening, but the light source 110 can be directed to a particular region of the cornea 2 requiring strengthening, to thereby control the region of the cornea 2 wherein cross-linking is initiated by controlling the regions of the cornea 2 that are exposed to the light source 110.
• aspects of the present invention relate to modulating the specific regimes of the applied light to achieve a desired degree of corneal stiffening in selected regions of the cornea 2.
• Another controller may be used to control the operation of the optical elements 112, and thereby control with precision the delivery of the light source 110 (i.e., the initiating element) to the cornea 2 by controlling any combination of: wavelength, bandwidth, intensity, power, location, depth of penetration, and duration (the duration of the exposure cycle, the dark cycle, and the ratio of the exposure cycle to the dark cycle duration) of treatment.
• the function of the controller 120 can be partially or wholly replaced by a manual operation.
• the embodiments described herein may initiate cross-linking in the cornea according to an annular pattern defined, for example, by a thermokeratoplasty applicator
• the initiation pattern in other embodiments is not limited to a particular shape. Indeed, energy may be applied to the cornea in non-annular patterns, so cross-linking may be initiated in areas of the cornea that correspond to the resulting non-annular changes in corneal structure. Examples of the non-annular shapes by which energy may be applied to the cornea are described in U.S. Application Serial No. 12/113,672, filed on May 1, 2008, the contents of which are entirely incorporated herein by reference.
• Embodiments may also employ aspects of multiphoton excitation microscopy.
• the delivery system e.g., 100 in FIG. 1 delivers multiple photons of longer wavelengths, i.e., lower energy, that combine to initiate the cross-linking.
• longer wavelengths are scattered within the cornea 2 to a lesser degree than shorter wavelengths, which allows longer wavelengths of light to penetrate the cornea 2 more efficiently than shorter wavelength light. Shielding effects of incident irradiation at deeper depths within the cornea are also reduced over conventional short wavelength illumination since the absorption of the light by the photosensitizer is much less at the longer wavelengths. This allows for enhanced control over depth specific cross-linking.
• each photon may be employed, where each photon carries approximately half the energy necessary to excite the molecules in the cross-linking agent 130 that release radicals (Riboflavin or photosensitizer and oxygen).
• radicals Radiboflavin or photosensitizer and oxygen.
• a cross-linking agent molecule simultaneously absorbs both photons, it absorbs enough energy to release reactive radicals in the corneal tissue.
• Embodiments may also utilize lower energy photons such that a cross-linking agent molecule must simultaneously absorb, for example, three, four, or five, photons to release a reactive radical.
• the probability of the near-simultaneous absorption of multiple photons is low, so a high flux of excitation photons may be required, and the high flux may be delivered through a femtosecond laser.
• aspects of the present disclosure can be employed to reduce the amount of time required to achieve the desired cross-linking.
• the time can be reduced from minutes to seconds. While some configurations may apply the initiating element (i.e., 2
• the total dose of energy absorbed in the cornea 2 can be described as an effective dose, which is an amount of energy absorbed through an area of the corneal surface 2A.
• the effective dose for a region of the corneal surface 2A can be, for
• the effective dose described can be delivered from a single application of energy, or from repeated applications of energy.
• aspects of the present disclosure provide systems and methods for delivering pulsed light of specific duty cycle and frequency, especially when a cross-linking agent is applied to stabilize desired shape changes generated in corneal tissue.
• Corneal cross-linking with Riboflavin is a technique that uses UVA light to photoactivate Riboflavin to stabilize and/or reduce corneal ectasia, in diseases such as keratoconus and post-LASIK ectasia. Corneal cross-linking improves corneal strength by creating additional chemical bonds within the corneal tissue.
• systems and methods generate pulsed light by employing a digital micro-mirror device (DMD), electronically turning a light source on and off, and/or using a mechanical or opto-electronic (e.g., Pockels cells) shutter or mechanical chopper or rotating aperture.
• DMD technology may be used to modulate the application of initiating light spatially as well as a temporally.
• a controlled light source projects the initiating light in a precise spatial pattern that is created by microscopically small mirrors laid out in a matrix on a semiconductor chip, known as a DMD. Each mirror represents one or more pixels in the pattern of projected light. The power and duration at which the light is projected is determined as described elsewhere.
• pulsed light may be generated in any suitable manner.
• Riboflavin is deactivated (reversibly or irreversibly) and/or photo-degraded to a greater extent as irradiance increases. When Riboflavin absorbs radiant energy, especially light, it undergoes photosensitization. There are two major photochemical kinetic pathways for Riboflavin photosensitization, Type I and Type II. Some of the major reactions involved in both the Type I and Type II mechanisms are as follows: [0045] Common Reactions for Type I and Type II Mechanisms
• Rf represents Riboflavin in the ground state.
• Rf i represents Riboflavin in the excited singlet state.
• Rf 3 represents Riboflavin in a triplet excited state.
• Rf " is the reduced radical anion form of Riboflavin.
• RfH " is the radical form of Riboflavin.
• RfH 2 is the reduced form of Riboflavin.
• SH is the substrate. SH "+ is the intermediate radical cation.
• S " is the radical.
• S ox is the oxidized form of the substrate.
• Rf ox is deuteroflavin (7,8-dimethyl-10- (formylmethyl)isoalloxazine) having UVA absorption and sensitizer properties similar to those of Riboflavin (and unlike those of RfH 2 ).
• Riboflavin is excited into its triplet excited state Rf 3 as shown in reactions (1) to (3). From the triplet excited state Rf 3 , the Riboflavin reacts further, generally according to Type I or Type II photomechanical mechanisms.
• Type I mechanism above is favored at low oxygen concentrations, and Type II mechanism is favored at high oxygen concentrations.
• the substrate reacts with the sensitizer excited state to generate radicals or radical ions, respectively, by hydrogen atoms or electron transfer.
• the excited sensitizer reacts with oxygen to form singlet molecular oxygen. The singlet molecular oxygen then acts on tissue to produce additional cross-linked bonds.
• Oxygen concentration in the cornea is modulated by UVA irradiance and temperature and quickly decreases at the beginning of UVA exposure.
• the oxygen concentration tends to deplete within about 10-15 seconds for irradiance of 3mW/cm (as shown, for example, in FIG. 2 A) and within about 3-5 seconds for irradiance of 30mW/cm .
• Utilizing pulsed light of a specific duty cycle, frequency, and irradiance, input from both Type I and Type II photochemical kinetic mechanisms may be optimized to achieve the greatest amount of photochemical efficiency.
• utilizing pulsed light allows regulating the rate of reactions involving Riboflavin.
• the rate of reactions may either be increased or decreased, as needed, by regulating, one of the parameters such as the irradiance, the dose, the on/off duty cycle, Riboflavin concentration, soak time, and others.
• additional ingredients that affect the reaction and cross-linking rates may be added to the cornea.
• One aspect of the present disclosure relates to achieving photon optimization by allowing deactivated (reduced) Riboflavin to return to ground state Riboflavin in Type I reactions and allowing for reduced rate of oxygen uptake in Type II reactions where better photon conversion efficiency occurs.
• the rate of return of deactivated (reduced) Riboflavin to ground state in Type I reactions and the rate of oxygen uptake in Type II reactions is determined by a number of factors. These factors include, but are not limited to, on/off duty cycle of pulsed light treatment, pulse rate frequency, irradiance, and dose. Moreover, the Riboflavin concentration, soak time, and addition of other agents, including oxidizers, affect the rate of oxygen uptake. These and other parameters, including duty cycle, pulse rate frequency, irradiance, and dose are optimized to achieve optimal photon efficiency and make efficient use of both Type I and Type II photochemical kinetic mechanisms for Riboflavin photosensitization. Moreover, these parameters are optimized in such a way as to achieve an optimum chemical amplification effect.
• the on/off duty cycle is between approximately 100/1 to approximately 1/100; the irradiance is
• the pulse rate is between approximately 0.1 Hz to approximately 1000 Hz.
• the on/off duty cycle is between approximately 1000/1 to approximately 1/1000; the irradiance is
• the laser source may be an adjustable pulsed source, an LED system, arc sources or incandescents at very long on-time duty cycles, or any other suitable sources.
• Pulse rates of 0.1 Hz to approximately 1000 Hz or 1000 Hz to approximately 100,000 Hz may be chosen based on the photochemical kinetics as detailed by Kamaev et al., Investigative Ophthalmology & Visual Science, April 2012, Vol. 53, No. 4, pp. 2360-2367 (April 2012), which is incorporated herein by reference in its entirety.
• the pulse length may be long - on the order of one or several seconds - or short - on the order of fractions of a second.
• pulsed light illumination can be used to create greater or lesser stiffening of corneal tissue than may be achieved with continuous wave illumination for the same amount or dose of energy delivered.
• Light pulses of suitable length and frequency may be used to achieve optimum chemical amplification.
• FIG. 2A illustrates a graph of depletion and gradual replenishment curve of dissolved oxygen below a ⁇ thick porcine corneal flap, saturated with 0.1% Riboflavin during 3 mW/cm UVA irradiation at 25°C.
• the oxygen concentration (mg/L) fell to zero at about 15 seconds and gradually started to increase after approximately 10 minutes, getting back to approximately one-tenth its starting value after 30 minutes.
• FIG. 2B illustrates a graph of oxygen recovery under a 100 ⁇ thick corneal flap.
• the corneal flap was saturated with 0.1% Riboflavin during 30 mW/cm UVA irradiation.
• the irradiation was pulsed at a 3 second on / 3 seconds off cycle. Riboflavin drops were added to the cornea every 90 seconds. In this example, it took about 3 minutes for the oxygen concentration to gradually start increasing and about 6 minutes for the oxygen concentration to increase to 0.1 mg/L.
• UVA radiation is stopped shortly after oxygen depletion, oxygen concentrations start to increase (replenish) as shown in FIGs. 2 A and 2B.
• Excess oxygen may be detrimental in corneal cross-linking process because oxygen is able to inhibit free radical photopolymerization reactions by interacting with radical species to form chain-terminating peroxide molecules.
• the pulse rate, irradiance, dose, and other parameters may be adjusted to achieve an optimized oxygen regeneration rate. Calculating and adjusting the oxygen regeneration rate is another example of adjusting the reaction parameters to achieve a desired amount of corneal stiffening.
• Dissolved free oxygen is significantly depleted not only at the position of the oxygen sensor and below, but also throughout the corneal flap above. Oxygen content may be depleted throughout the cornea, by various chemical reactions, except for the very thin corneal layer where oxygen diffusion is able to keep up with the kinetics of the reactions. This diffusion-controlled zone will gradually move deeper into the cornea as the reaction ability of the substrate to uptake oxygen decreases.
• Oxygen measurements in the cornea suggest that the predominant photosensitizing mechanism for cross-linking with Riboflavin is the Type I pathway after a very short initial Type II photochemical mechanism at the start of the illumination with UVA light. More than halfway through the period of illumination, the oxygen concentration in the cornea slowly increases, as shown in FIGs. 2A and 2B above, to a concentration at which a Type II mechanism may begin to play an additional role.
• Reduced Riboflavin undergoes an oxidation reaction as shown in equation (6) above.
• the oxidation of reduced Riboflavin by molecular oxygen is irreversible, autocatalytic, and involves generation of free radicals that can initiate radical polymerization (as in case of vinyl monomers, acrylamide with bis(acrylamide), etc.).
• the autocatalytic oxidation of reduced Riboflavins by oxygen is accounted for by the reactions described in Massey, V., Activation of molecular oxygen by flavins and flavoproteins, J. Biol. Chem. (1994), 269, 22459-22462.
• Oxygen is the naturally occurring oxidizer and is used as the oxidizer according to aspects of the present disclosure. According to further aspects of the present disclosure, oxygen and/or other oxidizers are utilized; such oxidizers may be added to the formulation or administered to the cornea in a suitable way.
• reduced Riboflavin may be soaked in a suitable agent that contains oxygen and is able to oxidize the reduced Riboflavin.
• Vitamin B12 may be added in any suitable manner to the reduced Riboflavin and/or to the cornea.
• Vitamin B12 contains a Cobalt molecule that is capable of holding oxygen, thereby creating an oxygen storage reservoir.
• the reduced Riboflavin may be super-saturated with Vitamin B12 or another suitable oxygen carrying agent.
• the suitable agent, such as Vitamin B12 may be provided in conjunction with application of pulsed light. The proper level of oxygen can be maintained with various reversible oxygen carriers. See Yang N., Oster G. Dye-sensitized photopolymerization in the presence of reversible oxygen carriers. J. Phys. Chem. 74, 856-860 (1970), the contents of which are incorporated entirely herein by reference.
• Corneal stiffening may be applied to the cornea according to particular patterns, including, but not limited to, circular or annular patterns, which may cause aspects of the cornea to flatten and improve vision in the eye. For example, more or less corneal stiffening may be desired on the outer edges of the cornea as opposed to the center of the cornea. Aspects of the present disclosure relate to achieving more corneal stiffening on the outer diameter of the cornea and gradually decreasing the amount of corneal stiffening from the outer diameter toward the center of the cornea. Other aspects of the present disclosure relate to selecting regions of the cornea that require more corneal stiffening based on a predetermined set of characteristics and applying more corneal stiffening to those selected regions by varying the regime of the pulsed light.
• pulsed light may be applied with different irradiance, dose and/or different duty cycle to different areas of the cornea, leading to areas of differing levels of corneal stiffening or corneal stiffening gradients.
• Varying the regime of the pulsed light to achieve a desired level of corneal stiffening is another example of adjusting the parameters of the cross-linking reaction to achieve specific, targeted results.
• varying the regime of the pulsed light to achieve a desired level of corneal stiffening at selected regions of the cornea allows for more precise and accurate control of the shape changes in the eye.
• Riboflavin RFH 2 (with two hydrogen atoms supplied to the aromatic nucleus by the side chain) can be produced by anaerobic photolysis of Riboflavin
• FIG. 3 a graph illustrating absorbance for 0.2 mm light path of an initial sample of Riboflavin versus absorbance for 0.2 mm light path of reduced Riboflavin
• the absorbance of the initial sample is about 0.543, while the absorbance of the irradiated sample is about 0.340.
• RFH 2 is autoxidizable and in the presence of oxygen yields the highly light- sensitive fluorescent and absorbing (445 nm) Deutero flavin (7,8-dimethyl-10- (formylmethyl)isoalloxazine).
• Reduced Riboflavin solutions can be prepared under nitrogen by irradiation of Riboflavin with visible light in the presence of EDTA and stored in absence of oxygen. Reaction with oxygen completes during hundreds of msec (depending on the initial conditions), proceeds via free radicals (as described in Massey), and is able to initiate polymerization of vinyl monomers. The rate of the reaction with oxygen may be increased by dissolving oxygen in a flavin solution instead of in water.
• RFH 2 was prepared by irradiation of Riboflavin solutions (with and without EDTA, 1% EDTA, 0.1% Riboflavin) and saturated with argon (to displace oxygen) in a shallow sealed quartz cuvette. Then, in the absence of additional UV light, porcine corneal flaps were immediately placed in those solutions. After 1-2 min this procedure was repeated with a fresh solution containing RFH 2 several times. Corneal flaps then were washed with distilled water, digested with papain buffer, and their fluorescence was measured.
• the reducing agents may include, but are not limited to, EDTA, ascorbic acid, sugars, amines, amino acids, and any combination thereof. This is another example of modifying the parameters of the cross-linking reaction to achieve a desired level of cross-linking with the corneal fibrils.
• Riboflavin concentrations between about 0.001% Riboflavin to about 1.0 % Riboflavin may be utilized.
• Example 2 Measurement of the Collagen Linked Fluorescence in Cross-Linked Corneal Flaps at Depths of 100 ⁇ m and 200 ⁇ m
• Porcine whole globes (SiouxPreme Packing Co., Sioux City, IA; shipped in saline solution packed in ice) were warmed to room temperature (25°C). The corneas were then de- epithelialized with a dulled scalpel blade and 0.1, 0.25, or 0.5% riboflavin solution in 0.9% saline was applied to the top of each cornea during 20 minutes before cross-linking.
• Corneas were pan-corneally irradiated with a top hat beam (3% root mean square) for a determined amount of time with 365-nm light source (UV LED NCSU033B[T]; Nichia Co., Tokushima, Japan) at the chosen irradiance (3 or 30 mW/cm ) which was measured with a power sensor (model PD-300-UV; Ophir, Inc., Jerusalem, Israel) at the corneal surface.
• 365-nm light source UV LED NCSU033B[T]; Nichia Co., Tokushima, Japan
• a power sensor model PD-300-UV; Ophir, Inc., Jerusalem, Israel
• Corneal flaps (each 100 ⁇ thick, one after another) were excised from the eyes with aid of Intralase femtosecond laser (Abbott Medical Optics, Santa Ana, CA). The average thickness of the corneal flaps was calculated as a difference between the measurements before and after the excision from the eyes with an ultrasonic Pachymeter (DGH Technology, Exton, PA). The flaps were washed with distilled water until Riboflavin in the washing waters was not detectable by absorbance measurement at 455 nm (Thermo Scientific Evolution 300/600 UV-Vis Spectrophotometer, Thermo Fisher Scientific, Waltham, MA).
• FIG. 4B Fluorescence of the excised samples, which was a relative value to the non-cross- linked samples with the same thickness, is illustrated in FIG. 4B. It is shown that the corneal fluorescence after cross-linking (all samples were exposed to the same UVA dose, 5.4 J/cm ) is greater for samples exposed to UVA for a longer duration with lower irradiance and lower concentration of Riboflavin. Corneal fluorescence is also greater at first 100 ⁇ than at the next 100 ⁇ in the cornea. The highest corneal fluorescence was observed at the first 100 ⁇ for the sample that was soaked in 0.1% Riboflavin solution and irradiated at 3 mW/cm .
• porcine eyes Upon arrival, porcine eyes have excess muscle tissue that was removed and placed in saline in the incubator (set to 37°C) for 30 minutes. Eyes were then de-epithelialized and placed in a 0.1% Riboflavin solution for 20 minutes at 37°C. Eyes were removed from solution and physiological IOP was applied. Eyes were then placed under a UVA source and shutter system and irradiated according to the indicated protocol as shown in FIGs. 5A-5C. Riboflavin drops were applied every 1.5 minutes during UVA application. After being irradiated, the corneal thickness was measured with a pachymeter. The sample was then placed under the femto second laser and a -200 ⁇ flap was cut.
• the flap was positioned in a biaxial materials tester (CS-BIO TESTER 5000, CellScale, Waterloo, ON Canada) and stretched until failure. The sample was then rinsed with distilled water and frozen for future papain digestion and fluorescence analysis.
• CS-BIO TESTER 5000 CellScale, Waterloo, ON Canada
• FIG. 5A illustrates force versus displacement curves for porcine cornea for various soak times and UVA illumination scenarios.
• FIG. 5A illustrates results of experiments that show dissimilar biomechanical stiffness of the 0.25% Riboflavin sample 2 irradiated with 3 mW/cm continuous wave illumination vs. the sample 3 irradiated with
• the biomechanical stiffness of the 0.25 % Riboflavin sample 6 irradiated with 30 mW/cm pulsed light with a 3 seconds on / 3 seconds off duty cycle was similar to the biomechanical stiffness of 0.25 % Riboflavin sample 7 irradiated with 60 mW/cm pulsed light with a 2 seconds on / 4 seconds off duty cycle for a total 5.4 J/cm dose delivered to each sample.
• the biomechanical stiffness of the 0.1 % Riboflavin sample 8 irradiated with 30 mW/cm pulsed light with a 3 seconds on / 3 seconds off duty cycle was higher than both the samples 6 and 7.
• the biomechanical stiffness of the Riboflavin sample 5 irradiated with 30 mW/cm continuous wave illumination for a total 35.1 J/cm dose delivered was higher than that for samples 6, 7, 3, 4, and 1 (control sample with 0.25% Riboflavin concentration) and lower than that for sample 2.
• Sample 4 was soaked with Riboflavin for 30 minutes, while all the other samples were soaked with Riboflavin for 1 hour.
• FIG. 5A illustrates the effect of varying different parameters on corneal cross- linking. Different parameters - irradiance, continuous wave vs. pulsed illumination, on/off duty cycle of pulsed light illumination, Riboflavin concentration, and other parameters - all have an effect on biomechanical stiffness.
• a DMD may be used for illumination. With the DMD one can perform topography guided cross-linking as described, for example, in U.S. Patent Application No. 13/438,705, filed April 3, 2012, and U.S. Patent Application No. 13/051,699, filed March 18, 2011, the contents of which are incorporated entirely herein by reference.
• the algorithms associated with the topography may be created using several different spatial and temporal irradiance and dose profiles.
• These spatial and temporal dose profiles may be created using continuous wave illumination but may also be modulated via pulsed illumination by pulsing the illumination source under varying frequency and duty cycle regimes as described above.
• the DMD may be able to modulate different frequencies and duty cycles on a pixel by pixel basis to give ultimate flexibility using continuous wave illumination.
• both pulsed illumination and modulated DMD frequency and duty cycle combinations may be combined. This allows for specific amounts of spatially determined corneal cross-linking.
• This spatially determined cross-linking may be combined with dosimetry, interferometry, optical coherence tomography (OCT), corneal topography, etc., for real-time modulated corneal cross-linking.
• OCT optical coherence tomography
• corneal topography etc.
• the pre-clinical patient information may be combined with finite element biomechanical computer modeling to create patient specific pre-treatment plans.
• complex biomechanical stiffness patterns may be imparted to the cornea to allow for various amounts of refractive correction.
• These refractive corrections may include combinations of myopia, hyperopia, astigmatism, irregular astigmatism, presbyopia and complex corneal refractive surface corrections because of ophthalmic conditions such as keratoconus, pellucid marginal disease, post-lasik ectasia, and other conditions of corneal biomechanical alteration/degeneration, etc.
• a specific advantage of the DMD system and method is that it allows for randomized asynchronous pulsed topographic patterning, creating a non-periodic and uniformly appearing illumination which eliminates the possibility for triggering photosensitive epileptic seizures or flicker vertigo for pulsed frequencies between 2 Hz and 84 Hz as described above.
• Flicker vertigo is an imbalance in brain-cell activity caused by exposure to low-frequency flickering (or flashing) of a relatively bright light. It is a disorientation-, vertigo-, and nausea-inducing effect of a strobe light flashing at 1 Hz to 20 Hz, which corresponds approximately to the frequency of human brainwaves.
• the effects are similar to seizures caused by epilepsy (particularly, photosensitive epilepsy), but are not restricted to people with histories of epilepsy.
• websites provided by federal agencies are governed by section 508 of the Rehabilitation Act. The Act says that pages shall be designed to avoid causing the screen to flicker with a frequency between 2 Hz and 55 Hz.
• FIG. 5B illustrates force versus displacement curves for samples of porcine cornea irradiated with pulsed light having various exposure times, as well as a curve for a sample irradiated with continuous wave illumination, and a curve for a control sample.
• All the samples that were irradiated with pulsed light had a 0.1% Riboflavin concentration and were irradiated with 30 mW/cm pulsed light with a 3 seconds off cycle and a varied exposure ("on") cycle.
• the sample 2 having a 4.5 second exposure cycles had slightly lower biomechanical stiffness than samples 3 or 1.
• the duration of the exposure cycle affects the amount of corneal stiffening at the same irradiance and dark phase duration. Therefore, aspects of the present disclosure affect the displacement per unit force ratio. This is yet one more parameter that may be altered in optimizing cross-linking.
• FIG. 5C illustrates force versus displacement curves for samples of porcine cornea illuminated with pulsed light having varied dark phase durations, as well as curves for samples irradiated with continuous illumination, and a curve for a control sample.
• the sample 2 having 0.25%> Riboflavin concentration irradiated with 3 mW/cm continuous wave illumination had the lowest biomechanical stiffness out of samples 1 and 3-7.
• the duration of the dark phase affects the amount of corneal stiffening even at the same irradiance and exposure duration. This is yet one more parameter that may be altered in optimizing cross-linking.
• the graphs in FIGs. 5A-5C show that varying different parameters - applying pulsed instead of continuous wave illumination, varying on/off duty cycles, irradiance, dose, Riboflavin concentration, and soak times - all have an effect on biomechanical stiffness. These parameters may be modified in such a way as to achieve an optimum or desired amount of corneal stiffness anywhere on or within the cornea.
• Corneas were pan-corneally irradiated with a top hat beam (3% root mean square) for a determined amount of time with 365-nm light source (UV LED NCSU033B[T]; Nichia Co., Tokushima, Japan) at the chosen irradiance of 30 mW/cm with either continuous wave illumination or pulsed illumination 3 seconds on/3 Seconds off.
• Corneal flaps (200 ⁇ thick) were excised from the eyes with aid of Intralase femtosecond laser (Abbott Medical Optics, Santa Ana, CA). The average thickness of the corneal flaps was calculated as a difference between the measurements before and after the excision from the eyes with an ultrasonic Pachymeter (DGH Technology, Exton, PA).
• FIG. 6 a graph of fluorescence versus wavelength curves is shown. At 455 nm, fluorescence was the highest - about 20,000 counts/s - for the sample irradiated with 30mW/cm pulsed light illumination with a 3 seconds on / 3 seconds off cycle. The fluorescence for the sample irradiated with 30mW/cm continuous illumination was about 40% less, or about 12000 counts/s. This is yet another example demonstrating that applying pulsed light illumination as opposed to continuous wave illumination affects cross- linking in the cornea.
• Example 5 Cross-linking Measured by Fluorescence of Digested Corneal Flaps at 450 nm
• Pig eyes from an abattoir (SiouxPreme, Sioux City, IA) were rinsed in saline. Eyes were cleaned and the epithelium was removed. Eyes were placed on a stand in the middle of a large beaker filled part way with water with a tube bubbling compressed oxygen into the water. The oxygen was turned on at certain times during the experiment to create a humid oxygenated environment for the eye. Eyes were soaked for 20 minutes with 0.1% Riboflavin, dH 2 0 solution in an incubator set at 37°C by using a rubber ring to hold the solution on top.
• Corneas were pan-corneally irradiated with a top hat beam (3% root mean square) for a determined amount of time and irradiance (3 minutes CW at 30 mW/cm with one drop of solution added every 30 seconds, or 30 minutes CW at 3 mW/cm with one drop of solution added every minute, or 9 minutes for pulsed light - 1.5 seconds on / 3 seconds off - using a shutter system (Lambda SC Smart Shutter, Sutter Instrument, Novate, CA) at 30 mW/cm with one drop of solution added every minute) with a 365-nm light source (UV LED NCSU033B[T]; Nichia Co., Tokushima, Japan). The irradiance was measured with a power sensor (model PD-300-UV; Ophir, Inc., Jerusalem, Israel) at the corneal surface.
• a power sensor model PD-300-UV; Ophir, Inc., Jerusalem, Israel
• Corneal flaps (approximately 380 ⁇ thick) were excised from the eyes with aid of Intralase femtosecond laser (Abbott Medical Optics, Santa Ana, CA). The average thickness of the corneal flaps was calculated as a difference between the measurements before and after the excision from the eyes with an ultrasonic Pachymeter (DGH Technology, Exton, PA). The flaps were washed with distilled water 15 times and then dried in a vacuum until the weight change became less than 10% (Rotary vane vacuum pump RV3 A652-01- 903, BOC Edwards, West Wales, UK).
• Each flap (2 mg) was digested for 2.5 h at 65°C with 2.5 units/ml of papain (from Papaya latex, Sigma) in 1 ml of papain buffer [lx PBS (pH 7.4), 2 mM L-cysteine and 2 mM EDTA].
• the fluorescence of the papain buffer was taken into account by measuring fluorescence in the absence of tissue and subtracting this value from the fluorescence of the samples.
• FIG. 7A illustrates a graph of the amount of cross-linking measured by fluorescence of the digested corneal flaps at 450 nm. Eyes were de-epithelized, soaked for 20 minutes with 0.1% Riboflavin, put in a regular air environment or a humid oxygenated environment, and illuminated with 30 mW/cm 2 or 3 mW/cm 2 of UV light for 3 minutes CW with one drop of solution every 30 seconds, or 30 minutes CW with one drop of solution every minute, or 9 minutes pulsed (1.5 seconds on / 3 seconds off) with one drop of solution every minute. The following treatments shown in Table 2 below were applied to each of the samples shown in FIG. 7A:
• 3 mW CW Eyes were illuminated with 3mW/cm 2 CW of UV light for 30 minutes.
• Pulsed Light Eyes were illuminated with 30mW/cm 2 of pulsed UV light (1.5 seconds on / 3 seconds off) for 9 minutes with oxygen on during soak and UV exposure.
• a humid oxygenated environment with pulsed UV light greatly increases the amount of cross-linking taking place in the cornea.
• Applying a combination of Riboflavin and ultraviolet (UV) light sterilizes a surface of the cornea.
• the Riboflavin acts as a photosensitizer that increases the absorption of UV light.
• the resulting absorption of UV light can induce DNA and RNA lesions, and as a result, is effective in killing viruses, bacteria, and other pathogens in the field.
• a humid oxygen environment and pulsing UV light increase the amount of cross- linking to a certain degree when done separately, while they increase the amount of cross- linking to a significantly greater extent when done in conjunction.
• Increased cross-linking involves creation of an increased number of radicals. Radicals help to eliminate harmful bacteria present in the eye. Accordingly, a humid oxygenated environment and pulsing UV light result in more efficient elimination of viruses, bacteria, and other pathogens in the cornea, creating a sterile environment while minimizing any damage or other unwanted effects in the tissue. This is yet another example demonstrating that applying pulsed light illumination as opposed to continuous wave illumination affects the amount of cross-linking in the cornea.
• FIG. 7B illustrates force versus displacement curves for samples of porcine cornea illuminated with pulsed light of irradiance with oxygen, as well as curves for samples irradiated with continuous illumination, and a curve for a control sample.
• oxygen may be applied during the cross-linking treatments in a number of different ways as discussed in U.S. Application No. 12/909,228, the contents of which are incorporated entirely herein by reference.
• a treatment such as thermokeratoplasty or LASIK surgery
• the corneal tissue is treated with a cross-linking agent 222.
• the cross-linking agent may be applied directly on the treated tissue and/or in areas around the treated tissue.
• the cross-linking agent may be an ophthalmic solution that is broadly delivered by a dropper, syringe, or the like.
• the cross-linking agent may be selectively applied as an ophthalmic ointment with an appropriate ointment applicator.
• the cross-linking agent 222 is then activated in step 230 with an initiating element 232.
• Activation of the cross-linking agent 222 may be triggered thermally by the application of microwaves or light from a corresponding energy or light source.
• the resulting cross-linking between collagen fibrils provides resistance to changes in corneal structure.
• Riboflavin is applied as a cross-linking agent 222' to the corneal tissue in step 220.
• light from an UV light source may be applied as an initiating element 232' in step 230 to initiate cross-linking in the corneal areas treated with Riboflavin.
• the UV light initiates cross-linking activity by causing the applied Riboflavin to release reactive oxygen radicals in the corneal tissue.
• the Riboflavin acts as a sensitizer to convert 0 2 into singlet oxygen which causes cross-linking within the corneal tissue.
• 0 2 content is very low compared to the atmosphere.
• the rate of cross-linking in the cornea is related to the concentration of 0 2 when it is irradiated with photoactivating light. Therefore, it may be advantageous to increase or decrease the concentration of 0 2 actively during irradiation to control the rate of cross-linking until a desired amount of cross-linking is achieved.
• An approach according to aspects of the present invention involves supersaturating the Riboflavin with 0 2 .
• a higher concentration of 0 2 is delivered directly into the cornea with the Riboflavin and affects the conversion of 0 2 into singlet oxygen when the Riboflavin is exposed to the photoactivating light.
• the Riboflavin 222' may be stored in a closed vessel, e.g., a vial, 300 under increased 0 2 pressure 305.
• the increased 0 2 pressure 305 results in a higher equilibrium concentration of 0 2 in the Riboflavin 222'.
• the walls 310 of the vessel 300 are preferably opaque or otherwise prevent visible, UV, or other light from entering the vessel interior 301 to minimize the degradation of the Riboflavin 222'. Accordingly, referring to FIG. 9B, the step 215 supersaturates the Riboflavin 222' with 0 2 so that a supersaturated Riboflavin 222' is applied in step 220.
• a gel e.g., a methylcellulose gel
• a gel 421 may be stored in an interior 401 of a closed vessel, e.g., a vial, 400 under increased 0 2 pressure 405.
• the increased 0 2 pressure 405 results in a higher equilibrium concentration of 0 2 in the gel 421.
• the gel can then act as a carrier for 0 2 .
• step 216 saturates a gel 421 with 0 2
• step 217 mixes the supersaturated gel 421 with the Riboflavin 222', so that a mixture 422 containing the Riboflavin 222' and the supersaturated gel 421 is applied in step 220.
• step 216 saturates a gel 421 with 0 2
• step 225 applies the gel 421 to the cornea after the Riboflavin 222' has been applied to the cornea.
• the gel 421 increases the presence of 0 2 when the Riboflavin 222' is activated with the UV light.
• a steady state of 0 2 may be maintained at the surface of the cornea to expose the cornea to a selected amount of 0 2 and cause 0 2 to enter the cornea.
• the photoactivating light can then be applied to a cornea with the desired 0 2 content.
• a ring 500 is placed on the eye 1 to supply 0 2 to the cornea 2 during irradiation.
• the ring 500 includes one or more ports 502 that direct a steady flow of 0 2 to the cornea 2, which has been treated by Riboflavin.
• the flow applies 0 2 at high pressure against the cornea 2, so that more 0 2 is available during the irradiation of the Riboflavin in the corneal tissue.
• the ring 500 may optionally be held in place by suction.
• FIG. 11B illustrates, in another embodiment, an enclosure 510 receiving a supply of 0 2 through a port 512 is placed on the eye to establish a steady state of 0 2 .
• the enclosure 510 may be held in place by a suction ring 512.
• the enclosure 510 may be a cup-like structure.
• the enclosure 510 maintains the 0 2 at a higher pressure, e.g., higher than ambient, against the surface of the cornea 2.
• the concentration of 0 2 within the enclosure 510 and above the surface of the cornea 2 can approach 100%.
• the 0 2 within the enclosure 510 makes more 0 2 to be available for the irradiation of the Riboflavin in the corneal tissue.
• At least a portion of the walls 514 of the enclosure 510 may be translucent to allow photoactivating light to pass through the enclosure 510 to irradiate the cornea 2 and activate the Riboflavin applied to the cornea 2.
• the light source may be disposed within the enclosure.
• the enclosure 510 may also include a valve that allows the gas to be released.
• step 227 establishes a steady state of 0 2 above the corneal surface before the photoactivating light 232' is applied in step 230 to initiate cross-linking with the Riboflavin 222'.
• the rate of cross-linking may be monitored in real time and the concentration of 0 2 may be dynamically increased or decreased to achieve a desired amount of cross-linking.
• corneal tissue is treated with Riboflavin 222' in step 220.
• a first amount of 0 2 is provided above the corneal surface to introduce 0 2 to the corneal tissue and establish a first concentration of 0 2 in the cornea during irradiation.
• the devices described with reference to FIGS. 11A and 1 IB may be employed to change the amount of 0 2 is provided above the corneal surface.
• the Riboflavin 222' is then activated in step 230 with UV light 232'.
• step 240 the amount of cross-linking resulting from the activation of the Riboflavin 222' is monitored.
• One technique for monitoring the cross-linking employs polarimetry to measure corneal birefringence and to determine the structure of the corneal tissue.
• the technique measures the effects of cross-linking on corneal structure by applying polarized light to the corneal tissue.
• the corneal stroma is anisotropic and its index of refractions depends on direction.
• the cornea behaves like a curved biaxial crystal with the fast axis orthogonal to the corneal surface and the slow axis (or corneal polarization axis) tangential to the corneal surface.
• a light beam emerging from the living eye after a double pass through the ocular optics contains information on the polarization properties of the ocular structures (except optically inactive humours).
• the technique of using birefringence to monitor the structural changes resulting from cross-linking is described further in U.S. Provisional Patent Application No. 61/388,963, filed October 1, 2010, the contents of which are entirely incorporated herein by reference.
• a controller employing conventional computer hardware or similar processing hardware, can be used to monitor the amount of cross-linking.
• Such hardware may operate by reading and executing programmed instructions that are stored or fixed on computer-readable media, such as conventional computer disk.
• the controller may be coupled to, and automatically control, the device(s) that provide the 0 2 above the corneal surface.
• step 250 Based on the information from the real time monitoring in step 240, step 250 provides a second amount of 0 2 above the eye to introduce another amount of 0 2 to the corneal tissue and expose the cornea to a second concentration of 0 2 during irradiation with UV light 232' in step 260. Steps 240, 250, and 260 may be repeated any number of times to change the concentration of 0 2 during irradiation to control the rate of cross-linking dynamically.
• the first amount of 0 2 in step 228 may be greater than the second amount of 0 2 in step 250, or vice versa. Changing the cornea's exposure from the first concentration to the second concentration changes the rate of cross-linking in the corneal tissue as desired. If the information from step 240 indicates that the first amount of 0 2 is too low, step 250 provides a second amount of 0 2 that is greater than the first amount of 0 2 . On the other hand, if the information from step 240 indicates that the first amount of 0 2 is too high, step 250 provides a second amount of 0 2 that is greater than the first amount of 0 2 . It may be necessary to remove the first amount of 0 2 , e.g., from the enclosure 510, before providing the second amount of 0 2 in step 250.
• step 250 may introduce a non-0 2 element or substance above the corneal surface.
• nitrogen gas (N 2 ) may replace the 0 2 supplied by the devices 500 and 510 shown in FIGS. 11A and 1 IB.
• the photoactivating light 332' may include, for example, UV light or green light.
• cross-linking treatments described herein may be applied in combination with any eye therapy that may require additional stabilization of the corneal tissue.
• cross-linking treatments are combined with astigmatic keratotomy eye surgery (AK).
• AK is a surgical procedure for correcting astigmatism, where incisions are made in the steepest part of the abnormally shaped cornea to relax the cornea into a rounded shape.
• AK is often employed in combination with cataract surgery. The resulting shape change from AK can be stabilized with cross-linking treatment.
• cross-linking treatments may be combined with radial keratotomy (RK), which is a surgical procedure for correcting myopia, where radial incisions are made to the cornea to make corrective shape changes.
• RK radial keratotomy
• the effect of applying the cross-linking agent may also allow smaller incisions to be used during AK or RK.
• Riboflavin concentration concentration, conditions on the cornea, temperature, presence of oxidizing agents, the type of illumination applied to activate the Riboflavin, the irradiance, the dose, the on/off duty cycle of the applied illumination, as well as other factors.
• a number of these factors are interrelated, in other words, changing one factor may have an unexpected effect on another factor.
• aspects of the present disclosure relate to determining the effect of each of these parameters on the rate and the amount of cross-linking, as well as the interrelations of these parameters among each to optimize the conditions to achieve the desired amount, rate, and location of corneal stiffening.
• aspects of the present disclosure relate to monitoring the corneal response to a change in one or a plurality of parameters and adjusting the one or the plurality of parameters based on the received feedback.
• the embodiments described above may employ stepwise on/off pulsed light functions, it is understood that other functions for applying light to the cornea may be employed to achieve similar effects.
• light may be applied to the cornea according to a sinusoidal function, sawtooth function, or other complex functions or curves, or any combination of functions or curves.
• the function may be "substantially" stepwise where there may be more gradual transitions between on/off values.
• irradiance does not have to decrease down to a value of zero during the off cycle, and may be above zero during the off cycle. Effects of the present disclosure may be achieved by applying light to the cornea according to a curve varying irradiance between two or more values.

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