Abstract
Purpose: :
Transverse magnification varies with the eye's refractive error, and we have previously shown that magnification may affect the reported size of lateral retinal dimensions measured with optical coherence tomography (Johnson et al., ARVO, 2009). In longer myopic eyes with increased magnification, thicker regions surrounding the foveal pit might be included in a central ‘1 mm’ scan and thus may affect the reported central 1 mm thickness. We examined the effect of contact lens wear on measured retinal thickness over a range of myopic refractive errors in an effort to determine if the slight differences in retinal magnification that result from contact lens wear are associated with differences in reported central retinal thickness.
Methods: :
Twenty two soft contact lens wearers were recruited; data for right eyes are reported here but similar results were observed in left eyes. Spherical equivalent refractive errors measured with an aberrometer ranged from -1.1 to -11.2 D (mean ± SD = -5.31 ± 2.51). Axial lengths measured with a Zeiss IOL Master ranged from 23.63 to 29.10 mm (mean ± SD = 25.62 ± 1.26). Retinal thickness of the macular region was measured with and without contact lens correction, using an Optovue RTVue FD-OCT and the MM6 scan pattern that consists of twelve 6-mm rotational line scans through the fovea. Retinal thickness is reported for the central 1 mm, the parafoveal ring from 1 to 3 mm diameter and the perifoveal ring from 3 to 6 mm diameter.
Results: :
Mean central 1mm foveal thickness was 245.8 ± 16.3mm without contacts and 241.1 ± 15.0mm with contacts (p = 0.001 in a paired t-test). The mean parafoveal thickness was 310.5 ± 13.2mm without contacts and 308.5 ± 12.8mm with contacts (p = 0.048, paired t-test). The mean perifoveal thickness was 268.8 ± 13.2mm without contacts and 267.9 ± 11.9mm with contacts (p > 0.05, paired t-test). The reduction in central 1 mm thickness with contact lenses was more apparent with increasing myopia.
Conclusions: :
The reported central 1 mm retinal thickness was significantly reduced when contact lenses were worn, probably due to slight minification of the OCT scan. The reduction of this effect outside the central 1mm is consistent with magnification. Slight changes in the scan lateral dimension would be most likely to affect measures where the thickness changes rapidly, such as near the foveal pit slope, rather than where the thickness changes gradually, such as in the parafovea and perifovea.
Keywords: imaging/image analysis: clinical • refraction • retina