The genesis of the GRSTM Biometric Scleral Lens came about in response to the acute need for a better method of fitting complex eyes. The uniqueness of each and every eye demanded a radically different approach from the trial-and-error process that has dominated the field for decades. A key limitation has been the absence of adequate imaging technologies. Whereas corneal topography has come to dominate the field of corneal lenses, comparable imaging techniques for the sclera have been elusive. They say that necessity is the mother of invention, and that certainly applied to our situation. Dr. Gemoules had been following the development of optical coherence tomography (OCT) for a number of years, and decided to investigate the potential of this technology. This research culminated in an article published in March 2007 entitled: A Novel Method of Fitting Scleral Lenses from High Resolution Biometry (Eye & Contact Lens: Science and Clinical Practice). This method is currently patent-pending.

The ability to design a contact lens surface that has a specific relationship with the underlying surface of the eye distinguishes our lenses from all other scleral lenses. Sophisticated software allows us to design lenses using a series of geometrical shapes, or sags. Once the lens has been designed, the numerical data is then exported to a spreadsheet or table, which then becomes part of the lens specification. This final specification is sent to the lab for fabrication using modern CNC lathing equipment. Figure 2 shows a proposed lens shape on a post-LASIK eye. The chosen design is a reverse geometry in order to minimize both the lens power and higher order aberrations. The optical zone was created large enough to accommodate the patient’s scotopic pupil size. Figure 3 shows the actual lens on the patient’s eye. The posterior surface of the lens is outlined in yellow. Note how closely the actual lens fit is to the proposed design. Figure 4 shows the actual fluorescein pattern of the lens on the eye.

The design template of the GSL Biometric Lens is limited only by the manufacturing capability of the manufacturing equipment. The basic design comprises the following:

1. Posterior Optical Zone
The posterior optical zone comprises the base curve(s) of the lens. This may be taken from topography “K” readings, or may be determined directly from the Visante images.
2. Anterior Optical Zone
This zone is determined by the posterior optical zone and the prescription, as well as other factors such as pupil size.
3. Transitional Zone(s)
The Transitional Zone(s) is/are those that permit the contour of the lens to conform to the desired vault depth and geometry.
4. Landing Zone
The Landing Zone takes the surface of the lens to the sclera.
5. Haptic Zone(s)
The Haptic Zone(s) define the scleral bearing surface of the lens.

After a minimum settling time, the lens should show the following fitting characteristics:

• The clearance over the corneal apex should be a minimum of 100m, with modest peripheral clearance.
• Good centration and minimal movement with blink.
• There is an absence of focal scleral compression of the haptic.
• Absence of air bubbles in the fluid reservoir.
• Absence of significant lens imprint on the bulbar conjunctiva following wear.
• Lens edge does not impinge on elevated structures on the bulbar conjunctiva such as pingueculum, pterygium, scars, etc.

Fitting Process

1. Obtain corneal topographies.
2. Obtain a minimum of two OCT scans per eye.
3. Design lens using image analysis software.
4. Transmit order to lab along with special instructions.
5. Evaluate lenses on the eyes.
6. Repeat process until the optimal fit has been achieved.

It may be necessary to fabricate several lenses to achieve the desired fit, depending upon the degree of difficulty. The process depends entirely upon the skill of the lens designer and not the comprehensiveness of the in-house library of fitting lenses.