Changes in Corneal Thickness in Keratoconic Eyes With Variation in Scleral Contact Lens Central Clearance

The purpose of this study is to investigate changes in the corneal thickness of scleral contact lens wearers in a keratoconic (KC) population and compare to age-matched controls. The hypothesis is that scleral contact lens wear is associated with low levels of corneal hypoxia including measurable changes in corneal thickness.

This will be a prospective, dispensing study design. The study will involve up to 20 keratoconic participants and up to 20 age matched controls. Participants will attend 1 screening/fitting visit wearing their habitual contact lenses where the two test lens designs (350 and 450microns) will be fitted. There will then be a delivery visit for each design (randomly selected) and a single follow up visit after 8-10 hours of scleral lens wear, three weeks later. A washout period of a minimum of 48 hours will be applied between the cross-over of each lens design. Lenses to be worn in this study will be made of Boston XO material and are approved by Health Canada. The lenses will have a diameter of 14.8-17.0mm with a high and low sagittal depth in the corneal zone. As to which of the two lenses is being assessed, both the investigator and the participant will be masked as the assistant will provide the lenses in an unlabeled case. Masking the investigator will prevent bias when measuring corneal thickness and analyzing the data. The objectives of this study are to take a sample of keratoconic and control participants, fit them in scleral lenses, and to measure topographic corneal thickness after 8-10 hours of scleral lens wear after three weeks of wear, to compare two instruments in the measurement of corneal thickness, and to compare the effects of varying central corneal clearance of the scleral lens on corneal thickness. Secondary objectives include comparing ocular physiological outcomes between the two test lens designs. Corneal thickness will be altered post scleral lens wear compared to pre-lens wear and the amount of alteration will correlate to the fitting characteristics in the central zone of the scleral lenses.