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What role do accommodation and binocular vision issues play in eyestrain symptoms?

Posted on January 15th 2023 by Ailsa Lane research paper.png

Paper title: Is reading rate in digital eyestrain influenced by binocular and accommodative anomalies?

Authors: Robert Yammouni (1), Bruce J.W.Evans (2)

  1. Neville Chappell Research Clinic, Institute of Optometry, 56-62 Newington Causeway, London, SE1 6DS, UK
  2. Division of Optometry & Visual Sciences, City, University of London, Northampton Square, London, EC1V 0HB, UK

Date: Sep 2021

Reference: Yammouni R, Evans BJW. Is reading rate in digital eyestrain influenced by binocular and accommodative anomalies? J Optom. 2021 Jul-Sep;14(3):229-239.  [Link to open access paper]


Digital eye strain (DES) is a collective term for ocular symptoms such as headaches, tired eyes and blurred vision that may arise from using digital devices. External symptoms1-5 may be related to dry eye and tear film issues such as burning, tearing and irritation. Internal factors may be due to refraction, accommodation, or binocular vision anomalies.6,7 Differing diagnostic criteria for DES give prevalence estimates ranging from 31 to 69%.2

Accommodation and binocular vision anomalies have been linked to asthenopia and digital eyestrain.8,9  This study aimed to discover the prevalence and influence of internal factors on DES, and if low powered positive lenses worn to relieve accommodative and binocular vision issues can increase a reading rate score.

The 107 study participants, aged between 20 and 40yrs, completed the validated Computer Vision Syndrome questionnaire (CVS-Q) and were found to be experiencing DES with a score of 6 or more.  After a full eye examination, their reading rate was assessed with low-powered addition lenses (+0.50, +0.75 and +1.25) using the Wilkins Rate of Reading Test (WRRT). The control lens was plano. The WRRT score shows the rate at which random test words are read per minute with an average of two readings. A percentage was calculated for the fastest score compared to the control lens.

Associations were explored between binocular and accommodative functions and the WRRT rate, the fastest lens and the CVS-Q scores. These relationships were also considered in terms of how accommodative and binocular anomalies may be diagnosed.

A previous study by the same authors10 found that a low-addition power of +0.75D was subjectively preferred by study participants and gave the best improvement with WRRT.

This study found that compared to the control lens, 88% of the participants read faster with the adds. The improvements were small, though, with one-quarter reading at least 10% faster with adds and only 8% reading at least 15% faster. Research cited in both children and adults has "found the 15% criterion to be most appropriate" for improvement - in this small group of nine adults, seven had reduced amplitude of accommodation compared to their age expected norm.

Within the study group, there was a high number of participants with either at least one subnormal accommodative function (77%) and one subnormal vergence function (93%). However, the WRRT and CVS-Q scores were found to have little correlation with binocular and accommodation functions, regardless of the diagnostic method used.

There was also a small number of participants (5%) who had an eso-fixation disparity on the near Mallett unit. Further analysis showed this prevalence to be higher than expected and the add powers may be relieving a decompensated near esophoria.

What does this mean for my practice?

Low add power lenses were preferred by many digital device users who were symptomatic of DES in this study, despite accommodative and binocular functions not being strongly associated with DES symptoms.

  • This suggests DES may be combination of causes, particularly where dry eye has been shown to have an inverse relationship with reading rates11,12
  • Many of the study participants (80%) still preferred low add powers despite a low association with WRRT and CVS-Q scores.

DES symptoms should be investigated with a full eye examination in case of underlying binocular or accommodative issues. A small number of patients may have an eso-fixation disparity on the near Mallett unit and benefit from a low add power.

Previous studies have found a 15% increase in the WRRT can be a significant improvement for children who have issues reading.

  • The participants in this study were adults, but children can also present with reading difficulties. Near esophoria has been associated with asthenopia and myopia development and progression in children13

This suggests that identifying and correcting binocular anomalies, with or without DES symptoms, is best practice for myopes and pre-myopes.  Find out more about identifying pre-myopes here.

What do we still need to learn?

Limitations of this study include:

  • a lack of control group with no DES symptoms.
  • A potential for a placebo effect with a low power such as +0.50, particularly for participants in their early twenties or low adds simply gave a relaxing effect on accommodation.

The CVS-Q can estimate the severity of DES but is unable to differentiate between symptoms due to external or internal factors.

  • Further research into external causes of DES such as light flicker, blue light exposure, and pupil effects will give a deeper understanding of the influence of each and how sever they have to be to be significant enough for scoring on the CVS-Q.


Title: Is reading rate in digital eyestrain influenced by binocular and accommodative anomalies?

Authors: Robert Yammouni, Bruce J W Evans

Purpose: Symptoms experienced when using digital devices are known as digital eyestrain (DES) or computer vision syndrome. They can be categorised as either external (associated with dry eye) or internal (related to refractive, accommodative, or binocular vision anomalies). In a large cohort of adults with DES, we investigate the prevalence of binocular and accommodative anomalies, contrasting different diagnostic approaches, to evaluate potential mechanisms for the benefit from +0.75D addition lens that has been previously reported

Methods: Participants (20-40y) were selected using the Computer Vision Syndrome Questionnaire (CVS-Q) tool as suffering with DES. A comprehensive eye examination was given to each participant, and this paper concentrates on "internal factors", detected with a refraction and comprehensive testing of binocular and accommodative functions. The effects of low-powered addition lenses (+0.50D, +0.75D, +1.25D; and plano controls) were assessed by double-masked testing with the Wilkins Rate of Reading Test (WRRT) and by subjective preference.

Results: As previously reported, most participants showed a subjective preference for one of the three convex lenses we used, with +0.75D chosen most frequently. Performance at the WRRT was significantly improved with +0.50D and +0.75D, but not +1.25D. Using a variety of diagnostic criteria, there were no strong associations between WRRT results or CVS-Q scores and any binocular or accommodation functions. The one finding of significance is that a disproportionate number of participants who benefited from adds had an eso-fixation disparity on the near Mallett unit, although this only affected 5% of the population.

Conclusions: DES is a collection of diverse symptoms that have a multifactorial aetiology. In the sample described here, binocular, and accommodative anomalies do not seem to be a major cause of DES. Nevertheless, in view of the multifactorial aetiology it is recommended that patients with the symptoms of DES are assessed with a comprehensive eye examination. Patients with an esophoric fixation disparity on the near Mallett unit are particularly likely to benefit from near additions.

[Link to open access paper]

Meet the Authors:

About Ailsa Lane

Ailsa Lane is a contact lens optician based in Kent, England. She is currently completing her Advanced Diploma In Contact Lens Practice with Honours, which has ignited her interest and skills in understanding scientific research and finding its translations to clinical practice.

Read Ailsa's work in the SCIENCE domain of

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