Addition lens alleviates reading-induced ocular stress.

BACKGROUND: Near tasks have been associated with binocular stress to induce myopia. The aim of this study was to investigate the effects of accommodation on reading-induced near heterophoria. METHODS: We measured the near heterophoria of 22 young adults before and after 30 minutes of reading. The reading task comprised a column of local English newsletter studied monocularly at 33 cm. One of three addition lenses (that is, 0.00 D, +1.50 D and +3.00 D) was randomly incorporated into the optical prescription. The difference in near heterophoria between the pre- and post-reading task was recorded. The experiment was completed on separate days for the other lens powers. RESULTS: Reading for 30 minutes with a plano lens addition (control) increased the near heterophoria by 3.81 +/- 0.95 prism dioptres (SEM) toward exo-deviation (p < 0.002). Addition of a +3.00 D lens significantly decreased the reading-induced exophoric shift to 1.36 +/- 0.55 prism dioptres (SEM). Similarly, a +1.50 D lens reduced the exophoric shift to 3.14 +/- 0.85 prism dioptres (SEM) but the difference was not statistically significant when compared with the control. CONCLUSIONS: The results showed that close work might cause eye strain via the extraocular muscles. Incorporation of plus lens into the optical correction caused a power-dependent reduction in the stress, that is, smaller exophoric shift. Whether binocular stress contributes to myopia and its response to addition lens therapy deserve further investigation.