Reading is one of the most common goals in low vision rehabilitation.1 Children and young adults with low vision need to read during their education.2 Access to regular printed materials is important if it can be undertaken visually, so that children can learn in a way similar to their peers and not be limited to what is enlarged (large print material), recorded (audio books), or Braille material.
Usually, print size is the first impediment in reading for people with reduced visual acuity. These individuals need some form of magnification to resolve print sizes that are lower than their visual acuity threshold.3 Children and young people with low vision gain magnification naturally by reducing their reading distance (called relative distance magnification).4 However, many studies have shown that people with low vision have reduced accommodative response,5 – 9 which would be expected to reduce visual acuity for near-work tasks. Reduced accommodation response has been found in 86% of a heterogeneous low vision population and is particularly evident for close working distances.8 The simplest way to compensate for this reduced accommodative response in people with low vision is by the prescription of a reading addition in the form of bifocals, multifocals, or reading glasses. Some authors have discussed the possibility that a reading addition could be beneficial to improve reading performance in children and young adults with low vision.10 – 13 Leat12 suggested a clinical method to estimate a reading addition for young adults with low vision based on the person's expected amplitude of accommodation for his/her age. Alternatively, there may be no improvement because of the visual system's insensitivity to blur—the reduced visual acuity of these patients leads to an increased depth of focus and less need for accurate accommodation, in which case an addition would not improve their reading abilities. To the authors' knowledge, there is only one previous study to determine whether young adults with low vision will benefit from a reading addition.14 This study14 showed that reading acuity and the area under the reading speed curve (AUC) were improved with a reading addition determined by a dynamic retinoscopy technique for young adults with low vision.
The purpose of the present study is to apply three different methods of determining reading additions and the possible improvement in reading performance in children and young adults with low vision. The hypotheses of the study are that (1) there will be a difference in the dioptric power obtained by the three different methods, and (2) reading performance will be improved with a reading addition compared with no addition.
Participants were recruited from the Low Vision Clinic at the School of Optometry, University of Waterloo, Canadian National Institute for the Blind, Toronto, and the Vision Institute of Canada, Toronto. The inclusion criteria were as follows: age between 8 and 35 years; visual acuity between 6/12 to 6/120 inclusive, either monocularly in the better eye or binocularly, whichever was better; clear enough media so that the retinoscopy reflex could be seen; phakic; and able to read in English because all standard reading materials were in English. Participants with developmental delays or multiple challenges such as in Down syndrome were excluded, as this might interfere with performing the reading task. Those who were taking any medication that may affect their ocular accommodation were also excluded.
All participants underwent a battery of routine clinical tests, which included monocular distance logMAR visual acuity measured with by-letter scoring,15 near visual acuity with the Bailey-Lovie text chart at 12.5 cm, Pelli-Robson contrast sensitivity measured at 1 meter binocularly also with by-letter scoring,16 unilateral cover test to determine the presence of strabismus, distance static retinoscopy to measure the participant's refractive error with subjective refraction to refine the results, and measurement of the habitual reading distance while the participant held the Bailey-Lovie near text chart and looked at the 1M line held at their habitual distance for reading. Three methods were used to determine reading additions for each participant for a reading distance of 12.5 cm (8 D) and are described later. According to a previous study in our laboratory,14 12.5 cm was the most common reading distance for children and young adults with low vision. The study was approved and received full ethics clearance from the Office of Research Ethics, University of Waterloo.
The age-related reading addition assumed that children, like adults, can comfortably exert half of their amplitude of accommodation for reading.17 The following formula was applied:
The amplitude of accommodation was determined according to Hofstetter's formula,18 which gives the minimum amplitude of accommodation as 15 − (0.25 × age). This formula has gained general acceptance for clinical use. Millodot and Millodot17 showed that it is close to what is prescribed for presbyopes, and Leat12 suggested this formula be used to determine a reading addition for patients with low vision. Note that it is not usually feasible to measure the amplitude of accommodation subjectively in persons with low vision, as they will have difficulty determining a blur point. This also explains the choice of dynamic retinoscopy to determine the accommodative response, rather than any subjective technique.
Dynamic Retinoscopy Technique
Dynamic retinoscopy was performed with the modified Nott technique as described in previous studies.8,19 – 21 This method determines the lag of accommodation. To stimulate an accommodative response, participants observed a near target, which was an internally illuminated box with high contrast pictures, letters, or numbers on each side of the box. This box was mounted on an amplitude rule marked in centimeters. The box could be placed at different dioptric distances from the participant (Fig. 1A). To maintain interest and accommodative effort, the box could be rotated to reveal different sides, and participants were asked to read the letters/numbers or describe the pictures. Dynamic retinoscopy was performed with the participants' habitual distance refractive correction in place. The eye chosen for dynamic retinoscopy was the non-strabismic eye or the eye with better visual acuity. Dynamic retinoscopy was performed on the meridian with the least amount of uncorrected hyperopia, i.e., the meridian that required the least accommodative effort. If the participant was non-strabismic with equal acuities, then the eye and meridian with the least amount of uncorrected hyperopia was chosen. The retinoscopist moved closer or further away until a neutral reflex was observed, and the lag of accommodation was measured as the dioptric difference between the distance of the target and the neutral position measured from the participant's eye. Accommodative response was measured with the target at 12.5 cm (8 D), which was the working distance used for all near testing.
The position of the participant's neutral reflex was noted. If the participant's neutral reflex fell within the lower limit of normal according to Leat and Mohr's normal age-related data for 8 D (Table 1),8 there was no reading addition determined by dynamic retinoscopy, and the reading measurements were done without a reading addition, i.e., reading addition of zero. However, if the participant's neutral reflex did not fall within these normal limits, plus lenses were added over the participant's distance refractive correction until the neutral reflex fell within the normal limits. The final reading addition determined by the dynamic retinoscopy technique was the lowest plus lens that gave an accommodative response within the normal limits.
The Bailey-Lovie near visual acuity text chart was fixed on a clipboard and held at 12.5 cm. Participants were asked to look at the 1M line, and a +1.00 D lens was introduced binocularly over the distance habitual refractive correction placed in a trial frame. Participants were asked to compare with and without the lens and to indicate which gave the sharper and clearer image. If the participant preferred the extra lens, it was incorporated into the trial frame and another +1.00 D lens was shown. The process was repeated until there was no further subjective improvement. Then it was refined in ±0.50 D steps. The reading addition determined by the subjective method was the least positive lens that led to the clearest image.
Reading charts were developed for this study from among a battery of standardized sentences supplied by Legge, similar to those in MNREAD charts.22 Each sentence had between 9 and 15 words and consisted of three lines of the same length of grade 3 difficulty. They were printed in Times New Roman font. The sentences were in a logarithmic size scale, and their range was from 1.8 logMAR to 0.116 logMAR (8 M to 0.16 M) in 0.1 logMAR steps, so that each chart had 18 sentences. Eight different sets were developed so that no sentence was repeated by any participant. They were printed on semi-gloss Canon paper by an i990 Canon printer at the maximum resolution of 4800 × 2400 dots per inch.
After determining the three different reading additions, participants were asked to read with each of the three reading additions and without a reading addition in random order. Charts were fixed on a clipboard, and a thread of 12.5 cm was used to measure the distance from the spectacle plane to the chart and keep it constant (Fig. 1B). Note that the participants were not allowed to hold the text themselves, as they would be likely to change the working distance. All sentences were covered with strips of the same semi-gloss white paper, and only uncovered one by one as the participant was asked to read. Participants were asked to read as quickly and accurately as possible. If they made a mistake, they were asked not to go back and correct themselves, but to continue to the end of the sentence. This process was repeated (with a different set of sentences) for each reading addition. Participants were timed with a stopwatch from the moment he/she read the first word of each sentence to the moment he/she read the last word of the sentence, and the errors were recorded.22
A demonstration set was used to explain the reading task, and the last sentence that was read correctly was considered as the approximate reading threshold. Reading commenced eight levels above this approximate threshold,23 starting with larger sentences and reading progressively smaller ones until the participant read more than 50% of the sentence wrong or could not read any other words in the sentence.
The reading addition lenses were taped onto the participant's habitual spectacles, so as to minimize the weight. If he/she did not have spectacles, the lenses were placed in a trial frame. The first experimenter positioned the reading lenses and controlled the position of the text. The timing and recording of errors was undertaken by a second person who was naïve regarding the reading addition used. He/she marked every word that was read incorrectly and noted the total time needed to read each sentence in seconds.
Analysis of MNREAD Sentences
Reading speed in correct words per minute was calculated by counting the words that were read correctly for each print size.22 The average of reading speed for each print size from the two sets was taken as the correct words per minute and its logarithm plotted as a function of print size. Maximum reading speed and critical print size (CPS) were determined by an iterative process.22 The mean and the standard deviation (SD) of the highest three adjacent data points were calculated. The lower 95% range was calculated by the mean minus 1.96 × SD to check which data points of reading speed fell within the 95% range.22 Those that fell within that range were included in a recalculation of the mean and SD (Fig. 2). This process was repeated until no further points fell within the 95% range.22 The reading speed plateau was defined by the points that fell within this range, and the maximum reading speed was the average of all these data points. CPS was the smallest print size that fell within the reading speed plateau.
MNREAD reading acuity was calculated as a proportion of errors that were made in each sentence, and each sentence was given a weight of 0.1 logMAR. The reading acuity threshold was calculated as the smallest print size attempted + (0.1 × total number of errors as a proportion of the number of words at each level).22
The AUC was calculated as a measure of the total reading performance across different print sizes. The reading speeds were calculated in log units, and the AUC was the sum of the geometrical area under all data points across the reading speed curve (Fig. 2). Note that the right-hand end of the curve always extended to the same point on the X axis for all reading additions (each subject always started reading with the same size of text), so that an extension of the range that would increase the AUC would only be due to a change in threshold at the left side of the curve.
Data were analyzed using the Statistical and Graphical Software (SYSTAT 13, Chicago, IL) and Microsoft Excel. Differences in reading performance measurements were analyzed by one-way repeated measures analysis of variance (ANOVA) followed by Dunnett's test for the post hoc testing, using the “no addition” condition as the comparison group. Reading performance measurements included maximum reading speed, CPS, AUC, and MNREAD reading threshold. A probability of 0.05 indicated statistical significance for all analyses. Univariate regression and multivariate forward multiple step-wise regression analysis with 0.05 to enter and 0.15 to remove was conducted to study which visual factors, if any, predicted any improvement in reading performance.
Twenty-eight participants with low vision took part in the study (Table 2). The mean age was 16.4 (SD ± 6) years and 46% were female. The most common causes of low vision across participants were nystagmus (50%) and albinism (20%). The mean distance visual acuity of the tested eye was 0.78 ± 0.21 logMAR. The near visual acuity with the Bailey-Lovie near chart ranged between 0.30 and 1 with a mean of 0.77 ± 0.22 logMAR. There were six participants who already had a reading addition. Maximum reading speed without a reading addition ranged between 53 to 270 wpm (mean 173 ± 66 wpm). Critical print size without a reading addition ranged between 0.33 and 1.4 logMAR (mean 0.94 ± 0.27). The mean MNREAD acuity threshold without a reading addition was 0.72 ± 0.22 logMAR and ranged between 0.21 and 1.03 logMAR.
Reading Performance with Reading Additions—Whole Group
Repeated measures ANOVA [4 × (no addition + 3 reading additions)] showed that there was no significant difference in reading performance between any of the reading additions for any of the reading performance measures [maximum reading speed, CPS, MNREAD acuity threshold or the AUC (p > 0.05)]. There were two distinct groups according to age; 23 participants aged 8 to 19 years and 5 aged 25 to 32 years. Note that the oldest participant was 32 years old, although our inclusion criterion was age of up to 35 years. As there may have been a different pattern with respect to age, a separate analysis was conducted on the younger group of the participants (it was not possible to do this for the older group, as there were insufficient numbers). A repeated measures ANOVA [4 × (no addition + 3 reading additions)] for each of the measures of reading performance showed that there was no significant difference in reading performance with any of the reading additions (p > 0.05).
Reading Additions and Performance of Reading Additions—Participants with Normal Accommodation Excluded
Twelve participants had normal accommodation at 12.5 cm. Repeated measures ANOVA was conducted excluding these participants, who might not need an addition of any kind because of their normal accommodation. Repeated measures ANOVA showed that there was no significant difference between the reading addition powers.
One-way repeated measures ANOVA [4 × (no addition + 3 reading additions)] showed a significant effect of reading addition on the logarithm of the AUC. Dunnett's test, using no addition as the comparison group, showed a significant increase in the AUC with all the reading additions (F = 5.67, p = 0.0310; F = 5.89, p = 0.028; and F = 5.90, p = 0.028 for the age-related, subjective, and retinoscopy additions, respectively; Fig. 3). ANOVA also showed a significant effect of reading addition on MNREAD threshold. Dunnett's test showed that the MNREAD acuity threshold was lower (better) with the age-related, subjective, and retinoscopy additions (F = 7.67, p = 0.014; F = 5.72, p = 0.030; and F = 5.31, p = 0.036, respectively; Fig. 4). There was no significant difference in the AUC or threshold between the three additions (repeated measures ANOVA, p > 0.05). There was no significant effect of reading addition on CPS or maximum reading speed (p > 0.05).
There was no significant difference between the reading addition powers for the AUC and threshold (repeated measures ANOVA, F = 0.43, p = 0.95), and there was a significant correlation between all three reading powers (r = 0.48, r = 0.70, and r = 0.62, p < 0.05 for correlations between the age-related and subjective, age-related and retinoscopy, and subjective and retinoscopy addition, respectively).
Thus, there was a modest average improvement in the AUC (0.12 log units) and reading acuity threshold (0.055 log units) for the participants with reduced accommodation. These are small average differences (to compare, one line on a logMAR acuity chart is 0.1 log units), but it was also noted that there was a large variability between participants. Some showed an apparent clear improvement in reading performance with reading additions and some did not show such clear improvement. This variability would tend to mask the results when considered as a whole. So it is instructional to look at individual data. Fig. 5A is an example of a participant who showed a clear improvement in all measures of reading performance (maximum reading speed, CPS, AUC, and MNREAD acuity threshold) with all reading additions. Another participant (Fig. 5B) showed an improvement with all reading additions in CPS, AUC, and MNREAD acuity threshold but not in maximum reading speed. Some participants showed an improvement in reading performance with two or only one reading addition. Fig. 5C is an example of a participant who showed an improvement in reading performance with all the reading additions compared with no addition. Fig. 5D is an example of a participant who showed a definite improvement in all reading performance measures with the age-related reading addition. This individual improvement is emphasized by the fact that three participants or their parents requested a prescription of the reading glasses that they used during the study.
Fig. 5E, F are examples of participants who did not show an obvious improvement in reading performance. In fact, they had better reading performance without an addition compared with any of the three reading additions.
Prediction of Improvement with Reading Additions
The logarithm of the AUC and the MNREAD acuity threshold were improved with the reading additions in participants with abnormal accommodation response. To study if reading performance measured by maximum reading speed, CPS, AUC, or the MNREAD acuity threshold could be predicted by various factors measured in the study, univariate and multivariate regression analyses were undertaken. The factors considered as predictors were distance visual acuity, near visual acuity measured with the Bailey-Lovie text chart, contrast sensitivity, accommodative response, and the age of the participant. Results of both univariate and multivariate analyses showed that the improvement in reading performance with any of the reading additions was not predicted by any of these factors (p > 0.05), after Bonferroni correction for multiple comparisons.
Finally, participants were separated into those who had a clear improvement with reading additions and those who did not. Eleven participants showed a clear improvement in reading performance with at least two reading additions, and one participant had a very definite improvement with one addition. Analysis of these individuals' data showed that all, but one, of these participants had reduced accommodation for their age. There were no other significant differences, e.g., visual acuity, age, or contrast sensitivity, between those who showed a clear improvement and those who did not (p > 0.05, paired t-test). Of the six who already were wearing a reading addition, three were in the group that showed this clear improvement. Among the rest of the participants (17/28) who did not show a definite improvement with reading additions, there were some with normal and some with abnormal accommodation, i.e., some participants who had no improvement in reading performance had abnormal accommodation.
To the authors' knowledge, this is the first study to compare different methods of determining reading additions and to investigate their effect on reading performance. It is also one of the few studies reported in the literature on reading speed in children and young adults with low vision.
Maximum reading speed without an addition ranged between 53 wpm to 270 wpm (mean 173 ± 66 wpm). Lovie-Kitchin et al.,23 in a study of reading performance in children with low vision, reported similar, but slightly lower, reading speed rates; 28 wpm to 254 wpm was the range of maximum oral reading rate and their mean was 146.5 ± 61.2 wpm. A reading speed of more than 80 wpm is sufficient for fluent reading24 and is considered adequate for grades 4 to 6 in children with low vision.25 In the current study, all participants except one had a reading speed of more than 80 wpm. The only participant who had a reading speed <80 wpm obtained 53 wpm, which is considered “spot” reading and only adequate for activities of daily living.24 Mangold and Mangold26 reported that 60 wpm is needed for grade 3 level. This participant had one of the lowest contrast sensitivity measurements in the group (0.95 contrast sensitivity), which may explain his slow reading rate compared with the rest of the group. This participant may need other methods that are not vision dependent to access textual information, such as Braille or audio.
Similar to the report of Leat and Mohr,8 participants with low vision were frequently found to have abnormal accommodation response compared with age norms. In the present study, 60% of the participants had abnormal accommodation response, compared with 86% reported by Leat and Mohr. This difference may be explained by the way in which abnormal accommodation was defined. In the present study, abnormal accommodation was defined as an accommodation response that did not fall within the normal range at an 8 D demand. In the Leat and Mohr study, accommodation response was measured at four different accommodative demands, and the mean error of accommodative response and the slope of the accommodative response were calculated. If the mean accommodative error and/or the slope did not fall within the normal limits according to age, accommodative response was said to be reduced.
The first research question in this study was whether different methods to determine reading additions would give different dioptric powers of the reading addition. For the group with reduced accommodation, there was no significant difference between the additions, which were significantly correlated. The means were 2.58, 2.50, and 2.47 D for the age-related, subjective, and retinoscopy addition, respectively. Thus, at present, we are not able to answer the question of which of these methods is optimal, or indeed whether there is one that is optimal. They all gave similar improvements in average reading performance as measured by the AUC and thresholds.
The second research question was whether reading performance would improve with any of the reading additions. This was not found to be true across the group as a whole. This might be due to the 12 participants who had normal accommodation who did not require a reading addition (by dynamic retinoscopy) or who were less likely to benefit from one. Once they were removed, significant improvements were found.
For the sub-group of participants who had abnormal accommodation, the AUC was greater with all three reading additions compared with no addition. We suggest that the AUC is a useful measure of reading performance, as it is an indication of the total reading performance across different print sizes, as would be encountered in real life situations. Thus, children and young adults with low vision tend to have better overall reading performance with reading additions compared with no addition.
The improvement in reading acuity with the three reading additions answers the question that Leat and Mohr posed.8 They suggested that we cannot be sure whether (a) correcting the large lag of accommodation would improve the near visual acuity of observers with low vision due to improved retinal focus, or (b) they would not gain improvement because of their decreased sensitivity to blur and increased depth of focus.27,28 This increased depth of focus could help them to tolerate their decreased accommodation28 and a more in-focus image would give no improvement, i.e., they may not benefit from a reading addition.8 The results of the present study showed that some children and young adults with low vision do not accommodate sufficiently accurately, despite their increased depth of focus. Despite their increased depth of focus, they had better reading acuity with a reading addition.
Improvement in reading performance was not predicted by any of the factors that were used in the formal univariate and multivariate regression analyses. However, when the participants were separated into those who obtained a significant obvious improvement in reading performance with at least two reading additions and those who did not, all but one of the participants who showed a clear improvement had abnormal accommodative response at 12.5 cm. Of the participants who did not show such clear improvement, some had reduced and some had normal accommodation. Thus, if accommodation is normal, there is unlikely to be an improvement with a reading addition. If it is reduced, a reading addition may give improvement. Poor accommodation was the only factor that could predict if people with low vision might obtain improved reading performance from a reading addition.
Limitations of the Study
Being the first study to investigate the effectiveness of correcting the potential blur that results from reduced accommodation at near distances that young people with low vision experience, there are some limitations of the study. First, due to the age-range of participants, there would have been some diversity in reading ability and comprehension, while the grade level of the reading material (grade 3) was the same for all. We do not feel, however, that this significantly influenced our results, as first, even the youngest participants were at least of grade 3 level (one was 9, one was 10, and four were 11 years of age), and second, each participant was compared against him/herself, rather than against others. Second, reading comprehension was not measured in the present study, although this is the ultimate purpose of the reading process. In this study, we have only attempted to measure the more basic attribute of reading speed, with the assumption that good reading speed and accuracy are basic requirements for accessing text. Future studies might also consider reading comprehension. Third, the sample size was small, which may have limited our ability to find predictive and associated factors or to find differences in the reading additions. However, despite this, a significant main effect was found—reading performance could be demonstrated to be improved for the group of participants with reduced accommodation.
Clinical Recommendations and Conclusions
Reading performance measured by the AUC and reading acuity improved with the all reading additions compared with no addition in the sub-group with reduced accommodation. This indicates that during a clinical low vision evaluation of children and young adults with low vision, either (a) accommodation should be measured, followed by an assessment with a reading addition if accommodation is reduced, or (b) a reading addition should be trialed in all patients.
As the person ages, his/her accommodation becomes reduced further. So even if a reading addition is not required in early life, it should be demonstrated again as it might be accepted later in life.
From the present results, we cannot determine which would be the optimal method for determining a reading addition to apply clinically. In this study, the immediate benefit of a reading addition was measured. The impact after a period of sustained reading may be different, and a clinician may decide to prescribe an addition even in the absence of measurable improvement in reading performance if she/he thought that reading duration and comfort could be extended. Further research in this area is indicated.
School of Optometry
University of Waterloo
200 University Ave W
Waterloo, Ontario N2L 3G1, Canada
We thank Dr Deborah Gold for help in recruiting participants from the Canadian National Institute for the Blind, Dr Lois Calder for help in recruiting participants from the Vision Institute of Canada, and Lisa Chan for help in collecting the data. Balsam Alabdulkader was supported by King Fahad Medical City, Saudi Arabia, during the majority of this project and by King Saud University, Riyadh, during the manuscript preparation phase.
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Keywords:© 2012 American Academy of Optometry
low vision; reading; visual impairment; accommodation; reading addition