Short-term variation of autorefraction in Diabetic Macular Edema (DME) *

Abstract

Very few studies have investigated autorefraction in diabetic subjects presenting either with diabetic retinopathy (DR) and/ or diabetic macular edema (DME). To the best of our knowledge this is the first study using multivariate methods for investigating short-term autorefraction in a small sample of subjects diagnosed

with DME. Forty consecutive autorefractor measurements were taken over a short interval on each of seven diabetic subjects with varying stages of DME, and the results were compared to a smaller group of four diabetic control subjects without DME (reasons for the differences in sample sizes will be explained later). Measurements were obtained from both the right and left eyes of all subjects.  Subjects in the two groups were similarly matched according to duration of diabetes mellitus (DM), age and glycated hemoglobin (HbA1c) values. Normality of data distribution was mostly achieved with the removal of outliers (where necessary) until profiles of skewness, kurtosis, and standard mean deviation exhibited near-normal distribution. Thereafter, stereo-pair scatter plots with 95% surfaces of constant probability density (distribution ellipsoids) were generated and compared between the experimental and control subjects.

The diabetic subjects with DME demonstrated a larger spread of measurements in the eyes with the more severe DME, with the exception of one subject (subject 5). The volumes and orientation of the distribution ellipsoids also differed between the subject’s eyes. Some eyes with severe DME and poor visual acuity
displayed more stigmatic variation (for example, subjects 2 and 4), while others (subjects 1 and 3) displayed more ortho-antistigmatic variation or near oblique antistigmatic variation (subject 7).  In all experimental subjects, with the exception of subject 5, the eye with the more severe DME had a larger distribution ellipsoid
volume, indicating greater variation in autorefraction and thus it might be surmised that this paper provides some preliminary data to suggest that diabetic subjects with DME display greater short-term variation of refractive behaviour when compared to diabetic subjects without DME. Secondly, in diabetic subjects with
DME, eyes with the more severe DME or worse VA also display greater variation of refractive status. However, there seemed to be no distinctive or obvious pattern to the type of variation.

In addition, a suitable statistic in terms of a Cubic Root Difference (CRD) was introduced in this study to compare inter-ocular ellipsoidal volumes. This statistic is also useful for comparing variances between eyes, or between means for groups of eyes, and could be used in studies involving anisometropia,  et cetera.
Nevertheless, this study suggests that further investigation remains necessary before autorefraction can be used effectively in the early diagnosis, monitoring, and assessment of eyes with diabetic-related complications to the macular regions.