Randomised controlled trial of corneal vs. scleral rigid gas permeable contact lenses for keratoconus and other ectatic corneal disorders.

Purpose: To compare the comfort and visual performance of corneal rigid gas permeable contact lenses (CoL) and scleral rigid gas permeable contact lenses (SL) in participants with corneal ectasia, successfully wearing "habitual" CoL.

Methods: In a randomised controlled trial (RCT) with a 2 × 2 crossover, 34 participants were recruited and randomised into two groups. Group 1 (sequence AB), were fitted in period 1, with new CoL and after a 4-week washout period, in which habitual CoL were worn, were fitted with and crossed-over to SL, period 2. Group 2 (sequence BA), were first fitted with SL in period 1 and after a washout period of 4 weeks, crossed-over to new CoL, period 2. The median lengths in weeks of Periods 1 and 2 were: 17.5 (IQR 12.4) and 14.5 (IQR 6.2) respectively. The outcome measures for visual performance were best corrected visual acuity and the contrast sensitivity function. Vision related quality of life (Qol) was assessed using the National Eye Institute Visual Function Questioannaire-25 and reported subjective perception of vision (SPV) and reported subjective perception of comfort (SPC) scores, recorded on a scale from 1-10. The final outcome measure was the selection of the preferred lens type at the completion of the RCT.

Results: For the 30 who completed the trial, significantly higher SPC scores were found for SL compared to CoL (p = 0.002). Significantly higher SPC scores for CoL were found in participants who selected CoL as their preferred lens for future use, compared to those who selected SL (p = 0.009). All other outcomes exhibited no significant difference between the experimental lenses. There was no significant difference (p=0.86) in the proportion preferring CoL (53%) and SL (47%).

Conclusion: Significantly better comfort was reported for SL compared with CoL. Significantly higher comfort in CoL was found in those who preferred CoL, than those who preferred SL. Successful CoL wearers whose SPC in CoL is <7 are likely to achieve better comfort with SL. On average, successful CoL wearers found SL more comfortable and there are unlikely to be any significant visual or visual Qol advantage or disadvantage in refitting successful CoL wearers with keratoconus and other corneal ectasia disorders, with SL and vice versa.