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The Effect of Magnification and Contrast on Reading Performance Journal of Eye Movement Research 10(2):5 The effect of magnification and contrast on reading performance in different types of simulated low vision Michael Christen MD Mathias Abegg MD, PhD Department of Ophthalmology, Department of Ophthalmology, Inselspital, Bern University Hospital, Inselspital, Bern University Hospital, and University of Bern, Switzerland and University of Bern, Switzerland Low vision therapy, such as magnifiers or contrast enhancement, is widely used. Scientific evidence proving its efficacy is scarce however. The objective of this study was to investi- gate whether the benefits of magnification and contrast enhancement depended on the origin of low vision. For this purpose we measured reading speed with artificially induced low vision in 12 healthy subjects in conditions of a simulated central scotoma, blurred vision and oscillopsia. Texts were either blurred, set in motion or blanked at the gaze position by using eye tracking and gaze contingent display. The simulated visual impairment was cali- brated such that all types of low vision caused equal reading impairment. We then tested the effect of magnification and contrast enhancement among the different types of low vision. We found that reading speed improved with increasing magnification and with higher con- trast in all conditions. The effect of magnification was significantly different in the three low vision conditions: The gain from magnification was highest in simulated blur and least in central scotoma. Magnification eventually led to near normal reading speed in all condi- tions. High contrast was less effective than high magnification and the effect of contrast enhancement was similar in all low vision conditions. From these results we conclude that the type of low vision determines the benefit that can be expected from magnification. Con- trast enhancement leads to similar improved reading speed in all low vision types. We pro- vide evidence that supports the use of low vision aids. Keywords: Eye tracking, low vision, reading, nystagmus Introduction Reading impairment is a main complaint of patients suffering from low vision. Hence improving reading speed Low vision is defined as an uncorrectable loss of vision is the primary therapeutic goal (Elliott et al., 1997). Low that restricts affected patients in their everyday life. The vision therapy has a long-standing tradition and is widely International Classification of Diseases assumes moderate provided. Its aim is it to enable and support low vision pa- | downloaded: 26.9.2021 to severe vision impairment with visual acuity below 6/18 tients in reading and other daily activities. In order to de- but better than 3/60 in the better eye with the best possible cide which low vision aids are beneficial for an individual correction (World Health Organization, 1992). According patient, near and distance visual acuity, contrast sensitivity to estimations of 2010, globally 191 million people suffer Michael Christen MD andMathias visual field Abegg are taken MD, into PHD account. Usually however it from low vision (Stevens et al., 2013). Major causes for Department of Ophthalmology, is difficultDepartment to predict of Ophthalmology, whether and how much an individual vision loss are cataract, age related macular degeneration, Inselspital, Bern University Hospital Inselspital,patient may Bern benefit University from low Hospital, vision therapy (Latham & diabetic retinopathy, glaucoma or refractive error (Bourne and University of Bern, Switzerland Tabrett,and University 2012; Legge,of Bern, Ross, Switzerland Isenberg, & LaMay, 1992; et al., 2014). Whittaker & Lovie-Kitchin, 1993). This may be due to the Low vision therapy, such as magnifiers or contrastscarce enhancement, evidence is from widely studies used. aboutScientific the efficacy of low vi- Received January 30,evidence 2017; Published proving May its 16,efficacy 2017. is scarce however. The objective of this study was to investi- Citation: Christen, M., & Abegg, M. (2017). The effect of magnifi- gate whether the benefits of magnification and contrastsion treatment, enhancement which depended has beenon the examined,origin with some ex- cation and contrast on reading performance in different types of sim- of low vision. For this purpose we measured readingceptions speed (Stelmack with artificially et al., 2008,induced 2016), low in small observa- ulated low vision. Journal of Eye Movement Research, 10(2):5. vision in 12 healthy subjects in conditions of a simulated central scotoma, blurred vision Digital Object Identifier: 10.16910/jemr.10.2.5 tional studies (Virgili, Acosta, Grover, Bentley, & Giaco- and oscillopsia. Texts were either blurred, set in motion or blanked at the gaze position by ISSN: 1995-8692 melli, 2013). Improvement of reading speed (Margrain, using eye tracking and gaze contingent display. The simulated visual impairment was cali- This article is licensed under a Creative Commons Attribution 4.0 brated such that all types of low vision caused equal2000; reading Nguyen, impairment. Weismann, We then & testedTrauzettel the -Klosinski, 2009) International license.effect of magnification and contrast enhancementand among quality the differentof life (Hinds types of et low al., vision. 2003; Lamoureux et al., https://doi.org/10.7892/boris.108243 We found that reading speed improved with increasing magnification and with higher con- 1 trast in all conditions. The effect of magnification was significantly different in the three low vision conditions: The gain from magnification was highest in simulated blur and least in central scotoma. Magnification eventually led to near normal reading speed in all condi- source: tions. High contrast was less effective than high magnification and the effect of contrast enhancement was similar in all low vision conditions. From these results we conclude that the type of low vision determines the benefit that can be expected from magnification. Con- trast enhancement leads to similar improved reading speed in all low vision types. We pro- vide evidence that supports the use of low vision aids.. Keywords: eye tracking, low vision, reading, nystagmus (noch zwei weitere..) Journal of Eye Movement Research Christen, M., & Abegg, M. (2017) 10(2):5 The effect of magnification and contrast on reading performance 2007) could be found. In a randomized trial Stelmack et al Experimental Setup showed that training and instruction enabled significantly Reading texts were presented on a 21” CRT-monitor better performance than provision of low vision aids alone (ViewSonic G220fb) with a refresh rate of 100Hz and a (Gary S. Rubin, 2016; Stelmack et al., 2016). The great resolution of 1024 to 768 pixels. Participants viewed stim- majority of studies focused on patients with macular dis- uli binocularly from a distance of 0.5m. One screen pixel ease causing a central scotoma. However low vision may corresponded thus to a visual angle of 0.045° (=146 sec- have a great variety of causes, which raises the question onds of arc). Eye movements were recorded using an Eye- whether all kinds of low vision respond equally to low vi- Link 1000 eye-tracking system (SR Research, Missis- sion support, irrespective of the cause. sauga, Canada) with a sampling rate of 2000Hz. To stabi- To investigate this we compared the effect of magnifi- lize the head position a chin and forehead rest was used. cation and contrast enhancement on reading performance On the chin rest a microphone was attached to record the in three different types of low vision. Measurements were participants’ voice. performed in healthy subjects with a computer based sim- To simulate a central scotoma, a white disc covering ulation of low vision diseases. This approach gave us the the reading text at the center of gaze was displayed (illus- possibility to compare directly and within subjects the dif- trated in figure 1). For this, we used the technique of gaze ferent low vision types and furthermore we could avoid contingent display, which is a function of the Eye- bias induced by comorbidities that may be found in real Link1000 system (Sheldon, Abegg, Sekunova, & Barton, low vision patients. Low vision types tested in this study 2012; Simpson, Abegg, & Barton, 2011). To simulate were simulated blurred vision, simulated oscillopsia and blurred vision, texts were blurred with a mean filter from simulated central scotoma. the software ImageJ 1.46 (Public domain, National Insti- tutes of Health, USA; figure 1). The mean filter replaces Methods each pixel value in an image with the mean value of all Subjects pixels within a given radius. To simulate oscillopsia, read- ing texts were set in motion with a sinusoidal movement Twelve healthy subjects with a mean age of 27 years (illustrated in figure 1). The movement pattern consisted (range 25-31 years) took part in the experiment. All were of two overlaid sine functions, one with an amplitude of native German speakers. All subjects had a visual acuity 70 pixels horizontally and the other with an amplitude of equal or better than 20/20, tested at 0.5m. The study was 40 pixels vertically resulting in excursion of 140 pixels conducted with approval of the local ethic committee (6.4°) horizontally and 80 pixels (3.6°) vertically. Bern, Switzerland and all the subjects gave informed con- sent in accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki). Figure 1. Illustration of the low vision types. Left panel, shows simulated central scotoma, middle panel shows simulated blurred vision and right panel illustrates simulated oscillopsia. To ensure all types of simulated low vision lead to the same reduced visual acuity in all subjects, a calibration was performed with adjustments of the scotoma size, the blur radius and the frequency of the oscillopsia. 2 Journal of Eye Movement Research 10(2):5 Experimental Protocol ceiling effect (data not shown). For contrast we used the range possible with our CRT screen. To test the effect of The three different simulated low vision conditions magnification a scale with a step size of 0.1 log unit were tested in separate experimental blocks.
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