The meridian effect on the cortical magnification factor for visual word form identification

Legibility Assessment of Visual Word Form Symbols for Visual Tests

For a reliable visual test, it is important to evaluate the legibility of the symbols, which depends on several factors. Previous studies have compared the legibility of Latin optotypes. This study developed a visual function test based on identification visual capacity for a Chinese reading population. The legibility of word symbols was assessed with three methods: (1) Identification of the contrast thresholds of the character sets, (2) patterns of confusion matrices obtained from analysis of the frequency of incorrect stimulus/response pairs, and (3) pixel ratios of bitmap images of Chinese characters. Then characters of similar legibility in each character set were selected. The contrast thresholds of the final five character sets and the Tumbling E and Landolt C optotypes were evaluated. No significant differences in contrast threshold were found among the five selected character sets (p > 0.05), but the contrast thresholds were significantly higher than those of the E and C optotypes. Our results indicate that combining multiple methods to include the influences of the properties of visual stimuli would be useful in investigating the legibility of visual word symbols.

Detecting Visual Function Abnormality with a Contrast-Dependent Visual Test in Patients with Type 2 Diabetes

In addition to diabetic retinopathy, diabetes also causes early retinal neurodegeneration and other eye problems, which cause various types of visual deficits. This study used a computer-based visual test (Macular Multi-Function Assessment (MMFA)) to assess contrast-dependent macular visual function in patients with type 2 diabetes to collect more visual information than possible with only the visual acuity test. Because the MMFA is a newly developed test, this study first compared the agreement and discriminative ability of the MMFA and the Early Treatment Diabetic Retinopathy Study (ETDRS) contrast acuity charts. Then symbol discrimination performances of diabetic patients and controls were evaluated at 4 contrast levels using the MMFA. Seventy-seven patients and 45 controls participated. The agreement between MMFA and ETDRS scores was examined by fitting three-level linear mixed-effect models to estimate the intraclass correlation coefficients (ICCs). The estimated areas under the receiver operating characteristic (ROC) curve were used to compare the discriminative ability of diseased versus non-diseased participants between the two tests. The MMFA scores of patients and controls were compared with multiple linear regression analysis after adjusting the effects of age, sex, hypertension and cataract. Results showed that the scores of the MMFA and ETDRS tests displayed high levels of agreement and acceptable and similar discriminative ability. The MMFA performance was correlated with the severity of diabetic retinopathy. Most of the MMFA scores differed significantly between the diabetic patients and controls. In the low contrast condition, the MMFA scores were significantly lower for 006Eon-DR patients than for controls. The potential utility of the MMFA as an easy screening tool for contrast-dependent visual function and for detecting early functional visual change in patients with type 2 diabetes is discussed.