Purchase this article with an account.
Chris Dickinson, Wei Lin; The effect of a prolonged near vision task on near vergence in a non-clinical population. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5412.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Many individuals report eyestrain after prolonged periods of near work, especially using a display screen. This study investigated whether there was a change in the binocular status of individuals, and any link to subjective fatigue, after a prolonged near vision task (NVT).
Visually-normal individuals aged 8-35 years, with no visual problems, subjectively rated their visual fatigue on a scale from 1 “no perceptible visual fatigue” to 7 “extreme visual fatigue”. Near dissociated phoria, near associated phoria, near fusional vergence, near point of convergence (NPC) break and recovery, and vergence facility were measured. All measures were taken at baseline, after 1 hour of distance viewing (0h), and then at the end of each of 3 hours of near work (1h, 2h and 3h) presented on a computer screen at 30cm.
There were 34 participants: 53% (n = 18) were myopes (12 spectacle wearers and 6 contact lens wearers); the remainder were emmetropes. The mean age was 27.4 (4.6) years, and 50% were male.Subjects were divided retrospectively into those who had NPC break > 10 cm (Group 1: n=9), at 0h, and those with NPC ≤10cm (Group 2: n=25).In Group 1, NPC break and recovery, statistically significantly receded by 6.6 (5.6) cm (p = 0.008) and 7.3 (6.6) cm (p = 0.011) respectively, during the NVT, and there was a statistically significant eso-shift of 3.3 (1.5) Δ in dissociated phoria after the NVT (p< 0.001). In Group 2, the change in NPC break 0.6 (1.7) (p=0.083) and the eso-shift of 0.7 (2.2) Δ (p = 0.144) were not significant. Mean changes in near associated phoria, vergence facility and near fusional vergence, after the NVT were not significant in either group.The NVT had a statistically significant fatigue effect with a mean increase of the scores of 1.78 (95% CI: 0.69-2.87) and 1.14 (95% CI: 0.68-1.60) respectively for Group 1 (p = 0.006) and Group 2 (p <0.001). The increases of the NPC break and visual fatigue score over the NVT, showed a moderate correlation in Group 1 (r = 0.41, p = 0.275), but this was negligible in Group 2 (r = 0.02, p = 0.924).
The near horizontal vergence system can be affected by the type of prolonged NVT which is commonly performed by young adults, particularly in individuals who already have one of the signs of convergence insufficiency. However the NVT also causes increased subjective fatigue in individuals with a normal horizontal vergence system.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
This PDF is available to Subscribers Only