Abstract
Purpose :
In subjects with pathological myopia, age-related macular degeneration (AMD), and diabetic macular edema (DME), there can be significant elevation of the photoreceptor layer due to subretinal fluid and neovascularization. The photoreceptor layer elevation leads to optical defocus and could significantly impact the visual acuity measurements, when the habitual refraction must be used. For example, clinical trials for AMD or DR treatments have different criteria, e.g., 1,2,3 lines of logMAR or 5,10,15 letters gained or lost in VA compared to baseline (e.g., STAIRWAY Phase 2, DRCR Protocol V, DRCR Protocol T). We instigated the effect of refractive status on errors in the classification of individual patients due to residual refractive error caused by photoreceptor layer elevation.
Methods :
Previously, we simulated the photoreceptor layer elevation using plus lenses in normally sighted adults (N= 44, Age = 32 +/- 13 yr, 21-71 yr). All the subjects performed a 4 alternative forced-choice visual acuity task under four conditions: refractive correction, +0.75 D, +1.50 D, and +2.25 D over the correction. We showed that the 95 % confidence limits for the +2.25 D lens condition were larger (3-10 letters) compared to the no plus lens condition (3-5 letters), with the +1.50 D condition intermediate (3-7 letters). Large confidence limits can lead to misclassification of individual patients in clinical trials. Using the reduced Indiana model eye, we modeled the change in induced refractive error across different refractive conditions.
Results :
The one surface model demonstrated a difference across refractive status for the induced refractive error, sufficient to cause misclassification of patients according to their visual acuity. The induced refractive error was greatest for eyes with short axial lengths. An eye with an 18 mm axial length had +2.33 D of induced refractive error for a 550-micron photoreceptor layer elevation, such as found in pigment epithelial detachments. In contrast, an eye with a 30 mm axial length reached only 1.76 D of induced refractive error for 1000 microns of photoreceptor elevation.
Conclusions :
The induced refractive error modeled from the photoreceptor layer elevation is sufficient to cause misclassification of the visual acuity of some patients. The size of the error in visual acuity depends not only on the photoreceptor layer elevation but also on the refractive condition or axial length.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.