Vergence prism adaptability was evaluated in subjects with high symptomatic and asymptomatic heterophoria and compared to individuals with a heterophoria within normal range (the control group). A computer haploscope was used to measure phoria values and changes in the eye position after introducing 6 prism diopters base out in front of the right eye. Phoria values were measured with a nonius paradigm every minute for a period of 10 minutes during adaptation. The results showed that subjects with symptomatic heterophoria are characterized by a lower rate of prism adaptation and adapted to a smaller extent with respect to the control group. The group with high but asymptomatic heterophoria showed prolonged adaptation time but after several minutes of binocular viewing the subjects were able to adapt to the prism to a level similar to the control group. These findings suggest that an impairment in the slow vergence control system may be responsible for the inability to fully reduce vergence effort, which results in poor vergence ranges and asthenopic symptoms during prolonged viewing.

Professional musicians are required to practice playing instruments for long hours, which often exerts significant impact on their health. Attention should be given to the specificity of playing each instrument, including uncomfortable and sustained body position and repetitive movements causing long-term strain of certain parts of the body. The aim of this study was to evaluate the impact of long-term playing wind and string instruments on the visual system. Ninety male and female subjects aged 15 to 30 years were included in the study and divided into two groups: musicians (Msc) and non-musicians (nMsc). Significantly less subjects in the Msc group had properly corrected vision, wore optical prescription recommended by an ophthalmologist/optometrist, and/or underwent any eye examination at all in their lifetime, even though more subjects in this group experienced certain asthenopic symptoms. Also, accommodative amplitude got statistically worse under dim illumination conditions, accommodative facility was significantly different between musicians and non-musicians, although there were no differences between the groups when tested in bright illumination. None of the music stands used by the study subjects met the respective standards concerning uniform illumination rates. Playing string and wind instruments is a challenge for the visual system due to the forced body and head positions, and asymmetry between the visual plane and the plane of regard as well as non-uniform illumination in the working environment. However, conditions such as correct working distance and proper tilt of the music stand may be beneficial to the visual system. It is the role of optometrists to properly educate their patients about the importance of appropriate vision correction, especially in dim light and under adverse working conditions and to communicate the impact of such conditions on the visual system.