AU2002216737A1 - Zero compression microkeratome cutting head assembly - Google Patents

Description

ZERO COMPRESSION MICROKERATOME CUTTING HEAD

ASSEMBLY

Background of the Invention

I. Field of the Invention

The present invention relates to the field of ophthalmic microkeratomes and,

more particularly, to microkeratome cutting head assemblies for cutting a corneal

flap to prepare a patient's eye for refractive surgery.

II. Description of the Related Art

The use of microkeratomes in creating a corneal flap for preparing an eye for

refractive surgery such as laser-assisted instuikeratomileusis (LASIK) are well

known. Typically, a microkeratome cuts a flap of corneal tissue by movement of a

blade (either oscillating or non-oscillating) across a cornea of a patient's eye. The

movement of the blade against the cornea typically stops before the corneal flap

becomes detached from the cornea. Such microkeratomes are well known and their

movement may be arcuate, as described in U.S. Patent 5,624,456, titled Automatic

Surgical Device For Cutting a Cornea, by Johann Hellenkamp which is incorporated

herein by reference. However, a microkeratome may also translate a blade across

the cornea in a linear straight-line fashion which is well-known in the art. It is common for known microkeratomes to applanate, or flatten-out, the cornea of patient's eye before the cutting blade of the microkeratome begins to

create the flap. This applanation causes the cornea to form a flat surface so that the

flat blade may create a proper thickness of cut in the cornea and provide a surgeon

with a properly sized flap thickness and diameter.

What has not been appreciated until now is the relationship between a cutting

blade's forward cutting edge and the trailing portion of an applanation member of a

microkeratome cutting head assembly. When forming a corneal flap, it is important

to prevent damage to the greatest extent possible to the thin epithelial layer of the

cornea. Any damage to the epithelial layer of the cornea can cause discomfort and temporarily diminish sight of a patient. In this regard, it is believed that if the

forward cutting edge is not positioned properly with respect to the trailing portion of the applanation member, compression of the corneal flap can occur resulting in

damage to the epithelial layer of the created corneal flap.

Therefore, there is a need to ensure that compression of the created corneal flap is reduced to minimize potential epithelial damage to the corneal flap. Brief Description of the Drawings

FIG. 1 is an elevational view of a microkeratome cutting head assembly, in

accordance with the present invention;

FIG. 2 is a partial view of a prior art microkeratome cutting head assembly;

and

FIG. 3 is a partial view of a microkeratome cutting head assembly, in

accordance with the present invention.

Detailed Description of the Preferred Embodiment

Microkeratome cutting head assembly 10 is shown in FIG. 1 and includes an

applanation member 12, a cutting blade 14, and a recessed area 16 for accepting a

corneal flap cut by assembly 10. Applanation member 12 includes trailing portion

18 having a curved section presenting apex 20. Cutting blade 14 has a forward

cutting edge 22 and a nominal length 24, in addition to a blade holder 26 for

securing the blade within cutting head assembly 10.

Dashed circle 28 generally defines the area which is illustrated in FIGS. 2

and 3 below and is a particular concern to the present invention. In use, cutting head assembly 10 moves across a cornea of a patient's eye

where cutting edge 22 contacts the cornea and begins to form a corneal flap which is

held within recess 16 as assembly 10 moves across the patient's cornea. The formed corneal flap is preferably between

120 micron and 200 microns thick, depending on a patient's corneal topography, the required refractive correction, and the particular assembly 10 chosen.

FIG. 2 shows a prior art microkeratome cutting head assembly having a trailing portion 30 with an apex 32 defined by line 34 that is positioned relative to

cutting blade 36 where a forward cutting edge 38 of blade 36 extends beyond line

34. This results in compression of cornea 40 as shown in shaded areas 42. In

testing, using a computer model simulation, the compression of the corneal flap 44

has been calculated to be approximately 10.9 microns with a blade of nominal

length. This compression rose to 28 microns for a blade length within specification limits but longer than nominal. A shorter than nominal blade length resulted in a

compression of approximately 1.7 microns.

This is in contrast to a microkeratome cutting head assembly, in accordance

with the present invention, such as that shown in FIG. 3. FIG. 3 shows apex 20 aligned with forward cutting edge 22 along line 46 which defines the apex 20 of trailing portion 18. As can be seen, a cornea 48 cut by the cutting head assembly of

FIG. 3 does not compress the created corneal flap 50 and therefore, minimizes any

chance of epithelial or other damage to the flap 50 that may have otherwise been

caused by compression. The epithelial layer of cornea 48 can be said to be the

darkest portion 52.

In testing with a computer model, with a cutting head assembly such as

shown FIG. 3, using a cutting blade having a nominal length a compression of 0

microns was calculated. This is compared to the 10.9 microns of compression in the

prior art. A more stark contrast can be found when blades of longer than nominal

length are compared. Testing showed that such a longer blade resulted in

compression of just 3.2 microns. This is compared to the 28 micron compression of

a longer than nominal blade in the prior art. Therefore, not only does a nominal

blade eliminate compression but a blade of longer than nominal length causes much

less compression than is true of a longer blade in the prior art. This reduced

sensitivity to variations in blade length also helps minimize the risk of epithelial

damage during operation of microkeratome cutting head assembly 10. It is

preferred, that the forward cutting edge 22 be placed within +/- 5° relative to apex 20

to minimize compression of flap 50, as shown by lines 54. If edge 22 is placed beyond the preferred +/-5° from apex 20, the compression of flap 50 begins to be significant.

It will be appreciated that the predetermined distance defined by apex 20 and

edge 22 determines the thickness of the flap created.

Not withstanding the preferred embodiments specifically illustrated and

described above, it will be appreciated that various modifications and variations of

the instance invention are possible in light of the description set forth above and the

appended claims, without departing from the spirit and scope of the invention.

Claims (9)

What is Claimed Is:

1. A microkeratome cutting head assembly comprising:

a cutting blade having a nominal length and presenting a forward cutting

edge;

an applanation member for applanating a cornea of an eye and including a

trailing portion having a cured section presenting an apex; and

wherein the forward cutting edge of the cutting blade of the nominal length is

positioned relative to the apex, such that the forward cutting edge and

the apex together define a desired thickness of a flap to be created

from the cornea, such that the flap is essentially not compressed,

thereby minimizing damage to the flap.

2. The assembly of claim 1 wherein the flap thickness is between 120 microns

and 200 microns.

3. The assembly of claim 1 wherein the forward cutting edge is positioned

within five degrees relative to the apex.

4. A microkeratome cutting head assembly comprising:

a cutting blade having a forward cutting edge;

an applanation member for applanating a cornea of an eye and including a trailing portion spaced a predetermined distance from the forward

cutting edge; and

wherein the trailing portion includes a curved section having an apex such

that a distance between the forward cutting edge and the apex defines

the predetermined distance.

5. The assembly of claim 4 wherein the predetermined distance is between 120

microns and 200 microns.

6. The assembly of claim 4 wherein the forward cutting edge is positioned within five degrees relative to the apex.

7. A microkeratome head assembly comprising:

a cutting blade having a nominal length and presenting a forward cutting

edge; and

an applanation member for applanating a cornea of an eye and including a

trailing portion having a curved section presenting an apex wherein

the apex and the forward cutting edge cooperate to define a distance

which creates a given corneal flap thickness to be formed from the

eye, such that any compression of the corneal flap will be minimized

during operation of the microkeratome head assembly.

8. The assembly of claim 7 wherein the distance between the apex and the

forward cutting edge is between 120 microns and 200 microns.

9. The assembly of claim 7 wherein the forward cutting edge is positioned

within five degrees relative to the apex.