New study finds association between myopic progression and reading position

It is not better to sit up straight to read, a long-term study has concluded. Finnish researchers Olavi Pärssinen and Markku Kauppinen published their results in Acta Ophthalmologica this month.¹

Who, as a child, was not issued with an ominous warning that reading in an awkward position, under the bedclothes or lolling about on the floor, would "ruin your eyes"? It has long been a popular belief that myopia can be caused by an improper reading posture, by reading too close or by reading in dim light, perhaps with a torch in bed. As long ago as 1864, it was suggested that myopia could be caused by a stooped reading position and use of a horizontal, rather than sloped, writing surface.

“There is substantial epidemiological evidence of a connection between myopia and reading, without accepted proof of the mechanisms behind this connection”, Professor Pärssinen explained. “Reading is a complex neurophysiological process involving not only accommodation and convergence but also keeping the fixation and regulating saccadic eye movements by varying the tension of six extraocular muscles. The pressure between lids and eye may also vary in reading, not only because of anatomical differences but also with differences in posture and the alignment of the eyes. All of these factors may gradually have an influence on scleral stretching, which is the anatomical change behind myopic progression.”

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This long-term study, analysing the connections between myopia and posture, distance and gaze angle when reading, is part of a trial that began in the early 1980s by recruiting 240 schoolchildren (119 boys and 121 girls; mean age 10.9 years) with previously untreated myopia to a randomised clinical trial of three treatments – continuous use, distance use only or bifocals. No previous studies have compared reading posture at the onset and during the progression of myopia.

Annual examinations were conducted for three successive years, after which time ordinary fully corrected spectacles were prescribed and continuous use recommended. The next clinical follow-up, in which nearly three-quarters of patients participated, came after a further 10 years when they were in their early 20s. Examinations at all visits included biomicroscopy, ophthalmoscopy and biometric measurements, and measurement of intraocular pressure. Habitual reading distance and gaze direction were also measured.

A structured questionnaire was used to record average daily time spent reading and performing other types of close work outside school; time spent watching television, playing sports and on outdoor activities; and data on parents’ myopia.²

Reading posture

Mean spherical equivalent at baseline was highest in those who sat to read, as was myopic progression across all follow-up visits. Myopic progression from baseline to their early 20s was lowest for those who reported reading lying on their backs, by a difference of 0.96 D and 1.38 D for men and women, respectively, compared with progression in those who read in a seated position. Overall, there was about one-third less myopic progression in those reading on their backs compared with those whose reading posture was sitting.

Reading angle and distance

The children were asked to select their habitual reading posture from sitting down, lying on their back, lying on their stomach and varying.

About half of the respondents varied their reading posture, while about one-third of them preferred to sit to read.

Twenty children reported lying on their back as their habitual reading posture at the initial visits, 11 of whom answered a follow-up questionnaire in 2015. The questionnaire asked ‘As far you remember, what was your preferred reading posture during childhood?’ and ‘What is your current preferred reading posture?’. Five respondents still preferred to read lying on their back, while the remainder reported a sitting or varied posture.

Of course, reading for schoolwork and in a professional capacity is mainly performed in a sitting position; reading in other positions is generally possible only when at leisure. The answers to this new questionnaire support the view that many of those who read lying down as children continue to do so as they grow.

Related: High myopia: Global pandemic with genetic and environmental causes

Reading angle

The researchers found a tendency towards more myopic progression with a steeper downward angle of gaze when reading.

Although correlations between reading angle and myopic progression at the initial three yearly visits were mainly insignificant, the mean reading angle of the last two childhood follow-ups correlated with myopic progression in the subjects’ early 20s.

Elongation of the eye has been suggested to result from the influence of the extraocular muscles.³ It is known that different gaze directions cause different tensions in the extraocular muscles, and also that eyelid pressure influences the shape of the cornea, depending on angle of gaze.

Gaze direction was measured with an angle scale, starting at zero if the eyes were looking horizontally ahead. The posture of the head during reading was not recorded.

Reading distance

The correlation between spherical equivalent and reading distance was the only myopia parameter that showed significant differences between the sexes. Higher myopia was associated with a shorter reading distance in girls at the last two of the three yearly follow-ups, but not at other visits. However, it seems logical that myopes might hold their reading material close, especially when not using spectacles, so it is difficult to conclude whether the association is causal.

In male subjects a correlation was observed at the fourth visit (early 20s) only, the direction of which opposed that seen in the younger girls: higher myopia was connected with a longer reading distance. It is possible that this was because they had been advised at the childhood visits to adopt a longer reading distance.

“Larger follow-up studies including a wide distribution of refraction and controlling factors connected with reading, such as reading speed, intensity, pauses, etc, are warranted”, concluded Professor Pärssinen. “Based on our results, one can at least say that there is no need to prohibit children lying down to read.”

References

O Pärssinen and M Kauppinen. Acta Ophthalmol 2016. doi: 10.1111/aos.13148.

O Pärssinen, M Kauppinen and A Viljanen. Acta Ophthalmol 2014; 92: 730-739.

A Ghosh, et al. Invest Ophthalmol Vis Sci 2012; 53: 6465-6471.