The relationship between the treatment zone diameter and visual, optical and subjective performance in CRTTM lens wearers

Abstract

Abstract: : Purpose:To investigate the stability of the treatment zone (TZ) during Corneal Refractive Therapy over one month of lens wear, and to determine the relationship between the treatment zone diameter (TZD) and visual performance. Methods:23 myopic subjects wore Corneal Refractive Therapy (CRT^TM HDS, Dk=100) lenses overnight and removed their lenses on awakening. High/Low contrast visual acuity, subjective visual performance using an analogue scale, refractive error, aberrations (LADARWave^TM), and corneal topography were measured at baseline, immediately after lens removal on the first day and 14 hours later and these were repeated on day 4, 10 and 28. The TZD was defined by the change in curvature from negative to positive and vice versa, using the tangential difference map from the Atlas ^TM topographer. Results: The average diameter (±SE) of the flat zone ranged from 3.11±0.13mm to 3.61±0.09 mm, and from 7.40±0.15mm to 7.91±0.12mm for the total (steep+ flat) zone over the study duration. The flat zone became significantly smaller (p<0.001), while the overall diameter remained constant (p=0.886) throughout the day. From day 4 onwards, the overall TZD was constant (all p>0.116), but the flat zone diameter was only stable from day 10 onwards (p=0.449). There were significant positive correlations between the TZD and the achieved prescription, subjective vision and spherical aberration (r=0.743–0.926, all p<0.05). There were significant negative correlations between the total zone diameter and high/low contrast visual acuity (r=–0.913, p=0.002; r=–0.918, p=0.001). There were also negative correlations between the flat zone diameter and high/low contrast visual acuity (r= –0.652, p=0.080; r=–0.701, p=0.053). Conclusions:The CRT^TM TZ changed during the first 10 days. Its diameter was associated with visual acuity, achieved prescription, spherical aberration, and subjective vision. The TZ is a useful indicator of visual, optical and subjective performance of CRT^TM lenses.

Keywords: contact lens • cornea: clinical science • imaging/image analysis: clinical