lenses are contraindicated because a small portion of the cornea supports most of the weight of the lens. This may result in a stress to the tissue that could aggravate the corneal epithelial defect and / or generate scarring. The mini-scleral lenses represent an improved option, where cornea-lens touch is absent with a limited amount of fluid layer. In addition, they are smaller than scleral lenses and are therefore easier to handle and less intimidating for young patients to insert into their eyes. 8
Lens trials
The patient was fitted successfully with a relatively new LDRGP on the market( One Fit P & A, Tyro 97
Blanchard Laboratories, Sherbrooke, Quebec.). The apical clearance and peripheral edge of this mini-scleral lens are designed to correct regular ametropia( high refractive errors, astigmatism, dryness related to con-tact lens wear( P & A profile) and are very successful in correcting irregu-lar corneas( KC profile). The fitting process is simple and easy to learn. They are proven as easy to wear and as comfortable, once properly fitted, as a soft lens. 11 Based on the fitting guide, the initial base curve is selected 0.3 mm steeper than flat K, to provide a central clearance of 150 µ m after 30 minutes of wear. This can be directly assessed at the slit lamp, using the known or esti-mated corneal thickness( 555 µ m on average), by comparing the width of the space between the lens and the cornea( the green fluorescein layer) to the slit width of the cornea. 12
Figure 2 – Similar appearance of the One Fit lens on another pediatric patient. One can appreciate the diameter of the lens, exceeding the visible cornea by at least 1mm.
This can be efficiently re-evaluated at subsequent follow-up visits. The lens diameter should exceed the cornea by at least 1 mm in every quadrant( Figure 2). The lens should offer no resistance on push-up, compression( blanching of the con-junctival vessels) or impingement( pinching of the conjunctival tissue resulting in staining). 8 The lens is inserted into the eye once it has been filled with fluid( non preserved saline solution or artificial tears). With LDRGP wear, the need for topical ocular lubricants during the day can be substantially decreased because the fluid inside the lens constantly surrounds and lubricates the cornea. It was recommended that the patient wear the contact lenses the majority of the time with the option of spectacle wear when the lenses were removed. The final prescription was made with the following parameters: + 4.25 OD and + 3.75 OS with base curves of 7.80 mm and diameters of 14.0 mm OU. The lenses were made of Tyro 97, a fluoro-silicone material with a Dk of 97 and a wetting angle of less than 10 degrees. This was the only contact lens, among all that were attempted, that satisfied both the physiological requirements of the ocular surface and the visual needs of the patient. In theory, the lifespan of these lenses is two years. An example of a One Fit lens in a pediatric patient can be appreciated above.( Figure 2)
With these lenses, the visual acu-ity was OD 6 / 7.5 + 2 and OS 6 / 6-1. After educating the patient and her parents on handling and cleaning the lenses, they were dispensed. According to a study conducted in 2008 by Gungor et al, there are no age restrictions in scleral lenses. 13 Nevertheless, fitting a patient of this young age did not come without its
46 Vol 75 | No 2 2013 C a n a d i a n J o u r n a l o f O p t o m e t r y | R e v u e c a n a d i e n n e d’ o p t o m é t r i e