In order to correct the refractive error, the evaluation of accommodative and binocular system parameters is indispensable especially in myopic astigmatism while prescribing either spectacle or contact lens (6). The early detection of non-strabismic binocular vision-related disorders in a patient wearing both spectacle and soft contact lenses may prevent near vision problems like headache, asthenopia and blurred vision, and progression of refractive error (9). In our study, we found a greater value of near point of convergence while wearing soft contact lens meaning that receded of near point of convergence with soft contact lens. Accommodative lag is the most common binocular vision disorder in a clinic (1). In our study, the mean value of lag of accommodation was found to be higher at 0.81 ± 0.36 Ds in contact lens wear than spectacle wear at 0.77 ± 0.28 Ds in both eyes with a statistically significant p-value at- 0.03. This result was agreed by the study done by (10) which suggested that accommodative insufficiency due to decreased accommodative function creates a lag of accommodation that causes reduced accommodative effort. When soft contact lenses are worn for a longer period of time, the amplitude of accommodation is decreased due to the higher value of lag of accommodation (11). Values of relative accommodations had been used in several studies in a secondary way for diagnosing non-strabismic binocular dysfunctions. Any binocular vision dysfunction had not been clearly associated with the variation in the result of NRA and PRA values (12). Our study found a higher value of both NRA and PRA in both eyes but only PRA showed statistical significance at a p-value- 0.035 Ds. A similar study was done previously suggesting that PRA values can be elevated in a patient with convergence insufficiency (13). The higher value of NRA may cause accommodative insufficiency and convergence excess although statistically, one must not rule out other anomalies when there is a high result of NRA. In general, a high value of PRA can distinguish between the disorders related to accommodative excess and the others. So, even small change in clinical value of accommodation, convergence and PRA may indicate a reduction in the ability of the eyes to focus at near, which can lead to symptoms such as eye strain, blurred vision, and headaches, particularly when reading or doing close work. However, the clinical significance of this change depends on the individual patient and their specific visual needs and symptoms.
Generally, the correlation between different accommodative and vergence parameters in binocular vision is important for diagnosing, managing, and understanding binocular vision disorders, as well as guiding treatment planning, assessing visual function, and conducting research. In order to correlate between different accommodative and vergence parameters, our study showed that patient wearing spectacle and contact lenses the accommodative facility, and accommodative amplitude were strongly correlated with Pearson correlation coefficient 0.78, 0.73, respectively and the lag of accommodation, NRA, PRA, PFV, and NFV were moderately positively correlated with Pearson correlation coefficient 0.78, 0.73, 0.53, 0.67, 0.61, 0.50 and 0.61 with significance level 0.01 (2-tailed) respectively. This finding was supported by the previous study done by (2) and suggested that with the use of contact lenses, statistically, significant correlations exist between NRA and accommodative lag (r = 0.63, p < 0.01). This study showed a high correlation between the accommodative facility and accommodative amplitude r = 0.78 and r respectively. Our study indicates that as the value of the accommodative facility and accommodative amplitude increase in the spectacle wearer, the value of AF and AA will also increase in the contact lens wearer. The good correlation between the different accommodative and fusional vergence parameters is due to some accommodative parameters like; NRA, PRA, BAF, and Lag of accommodation which indirectly measures the positive and negative fusional vergence (14). So, from this study, we can conclude that there are some statistically significant changes in the accommodative and vergence parameters when a myopic patient who is wearing spectacles shifts to contact lenses.