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Andrew Carkeet, Barsha Lal, Scott A Read, David Alonso-Caneiro; Refractive ametropia induced by contact lenses changes OCT-A macular indices. Invest. Ophthalmol. Vis. Sci. 2021;62(8):46.
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© ARVO (1962-2015); The Authors (2016-present)
It is unclear how Optical Coherence Tomography Angiography (OCT-A) indices are influenced by refractive ametropia. This research used spherical contact lenses to vary refractive ametropia in healthy young participants and assessed whether OCTA indices changed in a way that could be predicted by changes in retinal image transverse magnification (TM).
11 participants (mean age 26 ± 5 years, 5M:6F) took part in the study. For each participant, spherical soft contact lenses (-6D to +6D in 2D steps) were used to vary spherical refractive error. This varies anterior surface power, but leaves axial length unchanged. For each condition, OCT-A measurements of macular vasculature were made using a Zeiss HD-OCT 5000OCT-A imaging system and the following indices generated: foveal avascular zone (FAZ) area, perimeter, circularity and vessel density and perfusion density, for the central 1mm zone. Optical modelling was also used to calculate TM based on biometry and autorefraction. TM of en face images was also empirically measured for each condition.
Empirical TM measures matched theoretical calculations, (regression slopes: mean 1.02, 95% CI 0.74 to 1.30). Without magnification correction, contact lens power had a significant effect on all OCT-A indices assessed (F6,60 from 2.39 to 8.51, p<0.05), and all OCT-A indices showed linear relationships with induced refractive ametropia that were significantly different from zero (magnitude t(10) > 3.79-7.93, p < 0.05). Corrected for TM, FAZ area (Fig 1) showed no relationship with induced refractive error (t(10) = 1.13, p = 0.28). FAZ perimeter and vessel density showed reduced but still significant relationships with refractive error even after correction for TM (t(10) > 2.77, p < 0.02).
This study is the first to demonstrate that refractive spherical ametropia affects OCT-A indices to an extent that may be clinically significant, with changes of up to 12%. Simple correction for transverse magnification can reduce but not fully compensate for the effect of refraction on most OCT-A indices tested. TM changes may also change perfusion density and vessel density measurements, by including different vessel beds in calculations as magnification changes.
This is a 2021 ARVO Annual Meeting abstract.
Figure 1. Linear regression between FAZ area and induced spherical refraction without TM correction (left frame) and with TM correction (right frame).
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