Reading Additions in Children and Young Adults with Low Vision – Effects on Reading Performance

Abstract

Reading is one of the most important activities in most people’s life. For children, reading is a window to knowledge, good educational achievement and better job opportunities in the future. Thus reading fluency is a very important factor in the child’s education. Children and young adults with low vision usually use a close working distance to gain relative distance magnification. Unlike adults, they have active accommodation. Many studies, however, have shown that children and young adults with low vision have reduced accommodation response compared to the norms of their age. Reading additions (high plus lenses) can correct for this reduction in accommodation and may be an optimum method of prescribing magnification in younger adults with low vision. There have been no studies to verify the best method of prescribing reading additions in young adults with low vision and few studies of their effect on reading performance. This is the first study to compare different methods to determine reading additions and their effect on reading performance in young adults with low vision. The aims of the present study are 1) to investigate if three different methods to determine reading additions would lead to significantly different dioptric powers 2) to determine which method (if any) would lead to better reading performance. Reading performance was assessed by measuring the maximum reading speed, critical print size (CPS), print size threshold and the area under the reading speed curve. This was an experimental study involving thirty participants with low vision aged between 8 to 35 years. Participants were recruited from the Low Vision Clinic at the School of Optometry, University of Waterloo, Canadian National Institute for the Blind (CNIB) and the Vision Institute of Canada. All participants underwent a routine clinical examination including distance visual acuity, near visual acuity, Pelli-Robson contrast sensitivity, unilateral cover test, static retinoscopy, subjective refraction and measurement of the habitual reading distance. A questionnaire was used to determine their usage of any low vision aids, their perceived difficulty with reading and time spent reading. Reading additions were determined by 1) an objective method using Nott dynamic retinoscopy 2) an age-based formula 3) a subjective method based on the participant’s response to lenses. Reading tasks and dynamic retinoscopy were conducted at a fixed working distance of 12.5cm. Reading performance was assessed using MNREAD-style reading charts with each of the reading additions and without a reading addition, in a random order. Sentences were arranged in way that no sentence was repeated by the same participant. Participants were timed with a stop watch in order to calculate the reading speed in correct words per minute (CWPM). Reading speeds were plotted against print size to calculate the maximum reading speed, the critical print size, MNREAD threshold and the area under the reading speed curve. The participant’s mean age was 16 (± 6) years. There were equal number of males and females. The mean distance visual acuity of the tested eye ranged from 0.357 to 1.184 logMAR with a mean of 0.797 ± 0.220 logMAR. The near visual acuity ranged between 0.301 to 1.301 logMAR with a mean of 0.80 ± 0.26 logMAR. There were six participants who already had a reading addition. Maximum reading speed ranged between 52 to 257 wpm (165 ± 61 wpm). Critical print size ranged between 0.325 to 1.403 logMAR (0.965 ± 0.279 logMAR). Repeated measures ANOVA on the whole group showed that there was a significant difference between the reading additions (p=0.001). The retinoscopy reading addition power was significantly lower than the age add (p=0.002) and the subjective add (p=0.038). Repeated measures ANOVA did not show any improvement of any of the reading measures with the reading additions compared to without the reading addition. A re-analysis was undertaken excluding participants who had normal accommodation at 12.5cm. The results of repeated measures ANOVA showed that there was no significant difference in the dioptric powers obtained by the three methods, although, all reading addition power were significantly greater than zero (t-test <0.0005). There was a significant difference in the area under the reading speed curve (p=0.035), which was greater with the subjective addition than with no reading addition (p=0.048). The MNREAD threshold significantly improved with the age addition compared to no addition (p=0.012). There was a large variability between the participants in their response to a reading addition. Analysis of individual data showed that some participants showed a clear improvement in reading performance with a reading addition. Other participants did not demonstrate any obvious improvement in reading performance with reading additions. Of those participants who showed an improvement, all but one participant had abnormal accommodation. However, not all participants who did not show an improvement had normal accommodation. Univariate analysis and forward step-wise linear regression analysis were used to investigate if any improvement in reading performance and the habitual reading performance without a reading addition could be predicted by factors that were measured in the study. These factors included distance visual acuity, near visual acuity, contrast sensitivity, lag of accommodation, age, time spent on reading each day, perceived difficulty of reading regular print and whether or not the participant received training for the usage of his/her low vision aids. Improvement in reading performance could not be predicted by any of these factors. Habitual reading performance without a reading addition was correlated with some factors. Univariate analysis showed that critical print size was associated with MNREAD threshold (r=0.904. p<0.0005), distance visual acuity (r=0.681, p<0.0005) and contrast sensitivity (r=-0.428, p=0.018) and MNREAD threshold without an addition was associated with the contrast sensitivity (r=-0.431, p=0.017,) and distance visual acuity (r=0.728, p<0.0005). Difficulty of reading correlated with near visual acuity (Spearman correlation coefficient=0.620, p=0.0009), MNREAD threshold (Spearman correlation coefficient=0.450, p=0.02) and maximum reading speed (Spearman correlation coefficient=-0.472, p=0.014). Time spent on reading each day correlated with the area under the reading speed curve (Spearman correlation coefficient=0.659, p=0.0024). The multiple regression analysis showed that MNREAD threshold was best predicted by distance visual acuity (R=0.728, p <0.0005), critical print size could be predicted by distance visual acuity (R=0.681, p <0.0005) and age (R=0.748, p=0.022) and the power of the subjective addition could be predicted by age (R=0.583, p=0.001) and near visual acuity (R=0.680, p=0.028). There was evidence that a reading addition improved reading performance as measured by the area under the curve and MNREAD (reading acuity) thresholds, but this was not predicted by any visual factor, except that all those who gained improvement had poor accommodation. Therefore, it is recommended that an eye care practitioner should demonstrate a reading addition in a low vision assessment of children and young adults, particularly with patients who have reduced accommodation.