| Abstract |
Purpose: The assessment of visual performance is achieved in optometric practice by the measurement of visual acuity (VA) which constitutes the most essential part of visual perception. The properly constructed UoC charts developed in the University of Crete (Plainis et al., 2007) represent modified ETDRS charts of letter recognition used in a wider range while the Landolt-C and Illiterate-E optotypes belong to visual acuity charts based on symbol resolution. The main purpose of this study was to assess the identification of these different optotypes in a normal group and in patients with vision loss.
Methods: The repeatability of visual acuity was assessed using the modified UoC chart of letter recognition (recognition acuity) and the Landolt-C, Illiterate-E charts of symbol resolution (resolution acuity) in two different conditions; in normal vision and in vision loss situations. The legibility of the optotypes of these charts was evaluated by the following experiment;
Experiment; Visual acuity of 80 people was assessed; of 22 students (40 eyes) of the University of Crete, 15 people (30 eyes) of the working team of the Optics and Vision Institute and 3 people (6 eyes) working in the Hospital of Heraklion in Crete (age range 23-42) with normal vision who represented the first group of the study and of 25 patients (age range 46-83) who represented the second group with vision loss. During the study, two more subgroups occurred; that of vision loss as a result of cataract and of vision loss caused by various retinopathies. All the under evaluation groups were tested with the modified UoC charts (chart 1 for RE, chart 2 for LE) and the charts with the Landolt-C (chart 3) and the Illiterate-E (chart 4) optotypes used for both eyes. The charts were installed in the standard light box at a 4m distance. Visual acuity score was derived from the calculation of missed letters up to the last readable line. All the charts were viewed in random order. Subjects were tested with their habitual spectacle correction.
Results: For right eyes, the difference in visual acuity scores was -0.05 logMAR (-2.4 letters) between the UoC and the Landolt-C chart in normal vision conditions and -0.14 logMAR (-6.9 letters) in vision loss conditions, -0.02 logMAR (1 letters) between UoC and Illiterate-E charts in both evaluated conditions, while the mean difference of visual acuity measurements between the Landolt-C and Illiterate-E charts ranges up to 0.02 logMAR (1 letter) και 0.12 logMAR (5.9 letters) respectively. Following the same process for left eyes, the mean difference in visual acuity scores was -0.03 5
logMAR (-1.4 letters) between the UoC and the Landolt-C chart in normal vision conditions and -0.13 logMAR (-6.5 letters) in vision loss conditions, -0.01 logMAR (0.5 letter) and -0.04 logMAR (-2 letters) respectively between UoC and Illiterate-E charts, while the difference of visual acuity measurements between the Landolt-C and Illiterate-E charts ranges up to 0.02 logMAR (1 letter) και 0.09 logMAR (4.7 letters) respectively. The evaluation of vision acuity repeatability in the two subgroups of vision loss (patients suffering from cataract/retinopathies) led to the following results; for right eyes the mean difference in visual acuity scores between the UoC charts Landolt-C charts was -0.17 logMAR in the cataract subgroup and -0.13 logMAR in the retinopathies-group, -0.04 logMAR and -0.03 logMAR respectively between the UoC and Illiterate-E charts, while the mean difference of visual acuity measurements between the Landolt-C and Illiterate-E charts ranges up to 0.13 logMAR και 0.10 logMAR (4.7 letters) respectively.
Conclusions: The overall pattern of results suggests that the evaluation of visual acuity greatly differs between the UoC and Landolt-C charts and between Landolt-C and Illiterate-E charts, when it is assessed in different vision conditions (normal vision and vision loss), while it does not differ between UoC and Illiterate-E charts. Moreover, it is also concluded that visual acuity scores do not differ between the chosen pairs of charts (UoC-Landolt C, UoC-Illiterate E, Landolt C-illiterate E) when visual acuity is evaluated in the different pathological conditions of vision loss (cataract and retinopathies). What was basically shown was that the two specific pathological conditions do not have an effect on the mean difference of visual acuity values measured using the pairs of visual acuity charts.
|
Αξιολόγηση της αναγνωρισιμότητας διαφορετικών οπτότυπων σε φυσιολογικό πληθυσμό και σε ασθενείς με χαμηλή όραση
