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