Assessment of impact of soft contact lens power on fit

Authors:
Andrew Coates¹, Christina Olner², Chithra Dhanabalan², Debarun Dutta¹
1. Optometry and Vision Science Research Group, Aston University, UK
2. Coopervision Manufacturing Limited, Fareham, UK 

Study sponsored by CooperVision Manufacturing Limited
 

Purpose: 
With increasing ranges of available soft contact lenses (CL), it can be challenging having the exact CL prescription in clinical practice which may impact patient experience and require additional, valuable appointments. This study aims to evaluate if there is a difference in outcomes when using exact CL prescription (Exact-RX) on fitting compared to using a CL power within ±2.00DS of Exact-RX.
 

Methods: 
A prospective, randomised, cross-over, open-label, controlled study was conducted, following ethics approval. Participants wore their Exact-RX daily disposable (DD) spherical or toric soft CL (somofilcon A, CooperVision, Inc.) and a second CL (±0.50 to ±2.00DS with the correct cylinder power and axis component) in random order, switching after 15-30 minutes. A series of investigations were conducted: OSDI questionnaires, subjective logMAR VA , ocular comfort, corneal coverage, centration, post-blink movement (up-gaze), horizontal lag, push-up test, and overall fit impression. Right eye data were analysed using paired t-test or Wilcoxon signed-ranked test based on data normality.  
 

Results: 
Thirty participants (50% females; 12 toric lenses) with mean age 31.2±9.7 years, mean sphere -1.24±1.79DS and -0.73±0.63DC were included. Mean OSDI score pre-CL wear was 20.85±14.80, BCVA (logMAR) with Exact-RX and ±2.00DS CL (with over-refraction) was -0.13±0.08 and 0.11± 0.12 (p=0.230) respectively. There was no difference in comfort (8.4±1.1 and 7.9±1.1; p=0.051), corneal coverage, horizontal centration (+0.02±0.07 and +0.06±0.09mm;p=0.500), vertical centration (+0.02±0.07mm and +0.02±0.07; p=0.064), post-blink movement (0.36±0.12 and 0.37±0.11mm; p=0.500), horizontal lag (57.2±18.3% and 56.5±18.3%; p=0.444), push-up tightness (-0.37±0.49 and -0.33±0.48; p=0.513) respectively. Both CL prescriptions had identical overall fit impression (optimum=21, slightly-tight=9 participants).
 

Conclusion: 
DD CL with the same material and specifications (except for sphere power within ±2.00DS) exhibited no difference in fitting patterns. Eye care professionals may fit and assess CL of the same type within ±2.00DS, reflecting the original fitting characteristics and prescription of the correct CL, which may save additional time during fitting appointments.