PURPOSE. To examine the changes in unaided visual acuities (UVA), contrast sensitivity (CS) and central corneal thickness associated with a reverse geometry design orthokeratology lens worn overnight for a 3-month treatment period. METHOD. Eight subjects (ages 21 to 43) with myopia less than 3.00D and astigmatism less than 1.00D were fitted with reverse geometry OK lenses (OK B & D Series, Contex Inc., Sherman Oaks, CA). During this period, the lenses were worn overnight and removed during the day. Data was collected once before treatment (baseline) and then at 0, 4, 8 and 12 hrs following the removal of OK lenses after overnight wear at 1 day, 1 wk, 1 mo., and 3 mos. Unaided logMAR visual acuities were measured with Bailey-Lovie charts. Log CS was measured using the Pelli-Robson chart at 5 m. Central 3 mm corneal thickness was measured using Orbscan.
RESULTS. At Day 1, mean UVA and CS at 0 hr improved significantly (p<0.05) from baseline (UVA: OD 0.56 to 0.0125, OS 0.4225 to-0.0525; CS: OD 0.57 to 1.52 , OS 0.94 to 1.60). However, these values deteriorated from 0 to 12 hrs (UVA: OD .205 OD, OS .0925; CS: OD 1.24, OS 1.36), although still better than baseline. However, at 1 wk. mean UVA and CS improved again (UVA: OD -0.115, OS-0.0875, CS: OD 1.69, OS 1.65) and remained unchanged throughout the day. The results at 1 and 3 mos. were similar to those at 1 wk. For all test visits, the mean central corneal thickness increased by approx. 20mm at 0 hr and returned to baseline at 4 hrs and was not significantly altered thereafter. Neither mean UVA nor CS was significantly correlated with central corneal thickness changes.
CONCLUSIONS. With overnight wear of reverse geometry design orthokeratology lenses, maximum unaided visual improvement is achieved by 1 week. We believe the increase in central corneal thickness at 0 hr is the result of edema following sleep. However, the lack of expected central corneal thinning with Orbscan is likely due to the large variability of thickness measurements and therefore, do not reflect the noted visual improvements in this study. Future studies will analyze central corneal thickness changes using other techniques