WO2007057734A2

WO2007057734A2 - Photochromatic pinhole contact lenses

Info

Publication number: WO2007057734A2
Application number: PCT/IB2006/002994
Authority: WO
Inventors: Marinella Bergamaschi
Original assignee: Guerrieri, Roberto
Priority date: 2005-10-26
Filing date: 2006-10-25
Publication date: 2007-05-24
Also published as: ITBO20050647A1; WO2007057734A3

Abstract

The invention teaches the implementation of a contact lens that features large depth of focus and with a performance that is substantially independent of the specific diffraction problem of the viewer. The contact lens is based on the principle of pinhole optics applied to standard corrective contact lenses, even with no refractive power, and utilizes photochromatic materials characterized by a light absorption that increases with increasing levels of illumination.

Description

PHOTOCHROMATIC PINHOLE CONTACT LENSES

TECHNICAL FIELD

Corrective contact lenses have been prescribed by optometricians for several decades. The success of these lenses is related to their non invasive nature, when compared to standard glasses, and their easy use, once they are properly worn.

BACKGROUND OF THE INVENTION

However, contact lenses have problems that are shared with prescription glasses and others that are their own. Among the first, the use of contact lenses gives a substantial improvement to the acuity of sight in the proper conditions of use. As an example, a contact lens prescribed to cure a myopic condition gives excellent results when used to improve long distance vision, while in other conditions it produces discomfort to the user. Among the second class of problems, we include the difficulty in changing and/or removing lenses once they are worn. This difficulty makes more difficult to "rest" the eyes of the wearer, as it is possible with glasses that can be removed for a quick rest. Hence it is particularly important to have contact lenses that minimize the stress induced due to their usage.

There are two other markets where contact lenses could provide significant benefits, but where their adoption stresses the previous problems.

The first is the sport market, hi this important niche, we have active people who need to correct their vision problems without wearing glasses for several reasons and, at the same time, have several specific vision needs. Taking as example the sports based on the interaction with fast moving objects, such as tennis or volleyball, a pressing need is to have excellent field of view in very different conditions, e,g, when the ball is still remote and when it is close enough to be touched. At the same time, the very fast action of these sports makes it essential to have this adaptation as simple and natural as possible. This requirement pushes to its limits the technology of bifocal lenses. The other market of interest is characterized by the large masses of people living in countries where economic conditions make the availability of good optometricians unusual and the purchase of contact lenses, or glasses for that matter, specifically designed for a patient difficult. In these conditions, contact lenses whose performance is robust even in presence of complex refractive problems is very useful.

Although the popularity of eyeglasses for use in mono vision correction remains strong, considerable attention has been paid to the use of contact lenses in correcting the more difficult vision problems of presbyopic patients and patients suffering from pathological conditions. From this work, the commercial offering of multifocal contact lenses has emerged. However, the need for a training of the patient when these lenses are worn makes it necessary an additional effort to devise better corrective lenses.

Another type of vision correction device that has been attempted over the years is commonly referred to as "pinhole lenses". Two main categories of these lenses have been proposed over the years.

One is based on aperture-type pinhole approaches. These lenses are made of opaque plastic or glass to provide an absorbing periphery around the pinhole, which is made in such a way to guarantee its transparency. An example of this approach is found in patent US 3,794,414 where pinholes of different shapes are described with the inclusion of lateral apertures that should improve lateral vision. Unfortunately, the presence of radial slits induces diffraction effects that blur the resulting retinal image. Another and more recent approach adopts more sophisticated optical principles to attenuate the reduction of brightness of the retinal image. An example of this approach is found in patents US 6,899,424B2 and US 5,980,040. Here, the central pinhole is surrounded by a region that directs the light passing through it to a region substantially outside the pinhole focus on the retina. In this way, the reduction of retinal brightness is reduced and image sharpness maintained. The main drawback of this approach is that the resulting image has features that are not found in the common experience of the patient, such as discontinuities and other patterns. These lenses have been considered for correction of presbyopia, but have been rejected as reducing to an impractical extent the field of view and the brightness of the retinal image. Hence, solutions that solve the above issues of standard and pinhole contact lenses are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a section of pinhole lens. The annular ring, when dark, absorbs the light passing through it. In this case, the external diameter of the external annular region is the same of the lens itself and the pinhole is N-N'. Figure 2 shows a pinhole lens superimposed to a standard lens. It also shows the external diameter of the lens, the annular ring obtained using photosensitive materials and the central pinhole. The external diameter of the annular region can be the same of the lens itself.

Figure 3 Two annular rings are obtained using photosensitive materials around the central pinhole. The external diameter of the external annular region can be the same as that of the lens itself. Figure 4 shows the effect of pinhole size on FOV.

BEST MODE OF CARRYING OUT THE INVENTION

A lens with pinhole effect obtained using suitably shaped photochromic materials is described in this section. The optical behavior of this lens can be explained referring to Figure 1 and relying on standard geometrical optics.

The light produced by a point O goes through the lens and reaches the focal point F. If the retina were located here, vision would be sharp. If there is a refractive defect of the lens, the model changes as if the retina were located along line R-R'. In this case, vision is blurred and the sharp spot becomes a larger area whose size is A-A'. The introduction of a pinhole that reduces the aperture of the lens from M-M' to N-N' reduces the blur area from A-A' to B-B'. At the same time, the amount of available light is reduced proportionally to the reduction of the lens area not covered by the absorbing material. If the light were correctly focused on the retina, the sharpness of vision would not be affected, but the image would be darker.

The same description applies also to the actual case of a non-totally absorbing material. In this case, some light would pass through the absorbing region and the image produced on R-R' would be a region with high luminosity (B-B') and a lower luminosity region (A-A'). hi this case, blurring would be reduced in a continuous way, providing a smooth trade-off between image brightness and sharpness. A unique property of this invention is that the smooth transition of photochromatic materials from transparency to full absorption allows us to implement a pinhole whose size can be smaller than the one used in literature, based on pinholes with a fixed diameter.

It is clear from these considerations that the design of a pinhole system requires a trade-off between several contrasting issues. First of all, a small pinhole increases the perceived acuity of the image, since it reduces light arriving from lateral sections of the scene. On the other hand, a small pinhole drastically reduces the amount of light perceived by the viewer. This drawback is particularly significant in poor lighting conditions. The pupil takes different sizes when light intensity is different. Its diameter can range from 2 to 6 mm according to the light conditions and its dynamics is reduced when the viewer is older. The optical analysis of the sizing of the pinhole shows that the best performance is obtained in presence of strong illumination with a diameter of about 1 mm. This pinhole size is small enough to produce significant effects in terms of correction of refractive problems and large enough to avoid excessive light diffraction. However, this pinhole size would introduce an unacceptable reduction of illumination of up to 36 times when light is dim and pupil would be fully dilated. At the same time, a small pinhole introduces diffraction effects that limit the benefit of the technology.

When illumination is intense, pinhole lenses provide excellent performance in terms of better depth of field (DOF) and reduced accommodation effort. However, their performance degrades significantly with reduced illumination. On the other hand, the performance of standard lenses is not affected by illumination intensity, but requires accommodation efforts when the viewer is focusing on an image located outside the appropriate DOF.

This invention merges the two technologies, pinhole-based and standard refractive lenses. In general, the refractive lens can be without any refractive power or can have some refractive power. In this case, the refractive power would be prescribed by a trained optometrician to reduce the main refractive defects of the eye.

This invention exploits the properties of photochromatic materials. These materials have an absorbance that increases with increasing light conditions.

This invention teaches how to design a lens such that when light is abundant, the photosensitive material absorbs light and creates the pinhole effect. From this standpoint, light reduction is tolerated since in any case there is abundant light. In this case, maximum performance is achieved in terms of DOF and acuity. When light is dim, the absorption and the pinhole effect are reduced. The trade-off between resolution and light reduction changes, giving an adaptive response.

Photochromatic materials are in common use in the field of prescription lenses. In this invention, however, the need for a smooth transition from transparent to absorbing conditions is lessened when compared with the previous application.

The idea is further clarified considering now Figure 2. The diameter of the lens 2 is set by standard considerations, well known to those versed in this discipline and is about 8 to 9 mm. When light intensity is low, the pupil is dilated and its size is about 5 to 6 mm. In these situations, the photochromatic material 4 is transparent and the lens behaves as the underlying refractive lens. When the photochromatic material has uniform properties, it can be either used to absorb light in the region of the lens surrounding a central spot 5 whose size is about 1 mm or to have it shaped as an annular ring 4 that surrounds the central pinhole and whose external diameter is smaller than that of a dilated pupil. In this case a reasonable size of the external diameter is about 4 mm. This choice leaves a portion of the lens 3 transparent in an annular region that surrounds it. The advantage of this second, more complex, choice is that the residual absorption of the photochromatic material is avoided in parts of the pupil that are exposed only when light intensity is low. Another, more important, advantage of this specific variation is of cosmetic nature. In fact, the absorbing material would cover a much smaller region of the eye, reducing its visual impact.

If the photochromatic material can have different sensitivities in different regions of the lens, this invention teaches to add at least an additional ring 7 of lower photochromic sensitivity between the external annular region 6 and the internal pinhole 5. In this case region 6 features a stronger photochromic effect that region 7. Hence, given the same intensity of light, region 6 is darker than region 7. The behavior of the lens when light is dim is the same as before. With increasing light, the external annular structure becomes darker before the internal one, creating a first pinhole having diameter of about 1.5-2 mm as in Fig. 3. With additional light, the internal annular ring becomes dark, creating now a pinhole whose diameter is about 1 mm. Those skilled in the art immediately recognize that this technique allows to create an "artificial pupil" whose diameter is reduced as soon as light intensity is increased.

The reduced Field of View (FOV) is another problem of pinhole lenses. This point can be clarified considering Figure 4 which shows a section of a pinhole 5 and light rays 8 and 8' passing through it. The thickness of the photochromatic region 9 influences the FOV angle A since A=I 80 - 2*atan(h/d), where h is the thickness of the opaque material and d is the pinhole diameter and the distance between point N-N' in Fig. 1. Hence, a thinner opaque layer and a larger pinhole diameter improve the FOV. In this invention, FOV is the same of that of the standard refractive lens when illumination is low.

The same description applies to the case of a lens such as the one shown in Fig. 3. The only difference would be that the reduced transparent area in Fig. 1 called N-N' would change its size as function of the light intensity of the image.

Hence, if the diffraction effects are neglected, the previous description avoids the specific consideration of the refractive power associated to the lens. This can be done since the behavior of the lens is not modified. Hence, this technology can be combined with any refractive lens.

Additionally, the lens described so far can benefit from any advance in lens manufacturing that avoids Ultra Violet (UV) rays from reaching the eye.

The proper functioning of the lens requires the availability of a material with high absorbing activity. This blocking activity is more than what is likely required by the common usage of sunglasses. Hence, such a material could be used to create an absorbing layer that covers the pinhole. Due to its reduced absorbing capabilities, it provides a sunglass-like action, without interfering with the optical principles described so far.

Claims

1. A contact lens, with or without optical power, characterized in that at least one first region, covering part of the pupil, has photochromic properties, and at least a second region located on the pupil is transparent or at least has light absorbance substantially lower than that of the first region.

2. Contact lens, as in claim 1, characterized in that the first region has an annular shape.

3. Contact lens, as in claim 1 or 2 , characterized in that the first region is smaller than the lens.

4. Contact lens, as in any of claims 1 - 3, characterized in that the first region has a light absorbance that decreases moving toward the first region.

5. Contact lens, as in claim 1, characterized in that it absorbs UV radiation.

6. Contact lens, as in claim 2, characterized in that it includes at least an additional ring of different photochromic sensitivity between the external annular region and the internal pinhole.

7. Contact lens, as in claim 6, characterized in that the photochromic sensitivity of the least one additional ring is lower of the photochromic sensitivity of the external annular region.