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

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 symptoms^1-5 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.

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 rates^11,12
• 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.

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

[Link to open access paper]