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N Tahhan, E Papas, R Du Toit, J Stern, A Kalliris, R Wong, B Holden; Corneal Topographic Change After Short Periods Of Reverse Geometry Rigid Gas Permeable Lens Wear . Invest. Ophthalmol. Vis. Sci. 2002;43(13):972.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Reverse geometry rigid gas permeable (RG-RGP) contact lenses are used to decrease myopia and can induce rapid changes in anterior corneal topography. We evaluated the topographic changes induced after 15 minutes and overnight RG-RGP wear and studied the possibility of predicting any overnight changes from the 15 min changes. Methods:Twenty subjects aged between 18 and 35 years, with myopia from -1.00 to -4.00 Dioptres (D) (cyl <-1.5D) wore RG-RGP (Boston XO) bilaterally for 15 min and then overnight. Corneal topography maps were taken at baseline (BL), after 15 min and after overnight RG-RGP wear using Eyesys 4.2. The amount of apical change (D) from BL, pattern of change ("bull's eye", "central island" or "smiley"), centration (mm) (horizontal=X, vertical=Y) and diameter (mm) of the treatment zone (TZ) region were recorded after each period of RG-RGP wear. Mean results for each subject were analyzed using Student paired t-tests and marginal homogeneity tests. Results:Significant apical flattening was seen at both 15 min (0.35 ± 0.29D; 95% CI 0.21 - 0.48) and after overnight (1.38 ± 0.41; 95% CI 1.19 - 1.58) RG-RGP wear when compared to BL. The correlation between the amount of apical change at 15 min vs overnight failed to reach significance. The pattern of change after 15 min did not predict the pattern of change seen after overnight. No significant change in TZ centration occurred overnight when compared to 15 min RG-RGP wear (p≷0.05) and a correlation was found for X (r=0.52; p<0.05). TZ diameter was consistently larger overnight vs 15 min (mean change 0.29 ± 0.68mm; 95% CI 0.51 - 0.08; p<0.05) and a correlation was again found (r=0.57; p<0.05). Conclusion:Our findings confirm that significant corneal topographic changes occur within a short period of RG-RGP wear. The data suggest that predictions are possible for overnight TZ diameter and horizontal centration after short periods of lens wear. However, for other variables, practitioners should not rely on results from 15 min RG-RGP wear as indicator of performance over longer periods.
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