Comparison of contact lenses and spectacles in terms of fusion amplitude in myopic patients

Objective: To compare contact lenses and spectacle lenses with respect to fusion amplitude width by measuring convergence, divergence and vertical fusional vergence amplitudes. Material and Method: A total of 40 volunteers aged between 20-40 years who had no pathological findings except for refractive error, anisometropia or a deviation greater than 5 prism diopter on prism cover test, and who had normal vision in both eyes, and a spherical refractive error ranging between -1.00 and -5.50 D, and a refractive cylinder less than ±0.50 D were enrolled in this study. Convergence, divergence and vertical vergence amplitudes were measured in near and far distances (0.33 m ve 6 m) with both spectacles and contact lenses. Results: The mean diopter of the spectacle lenses was significantly higher than that of the contact lenses in both left and right eyes (p<0.05). The fusion restoration point for convergence at 0.33 m was significantly higher with the spectacle lens compared to that with the contact lens (p=0.026). The measurement of the fusional convergence amplitude at 6 m revealed no difference between the spectacle lens and the contact lens in terms of fusion break and fusion restoration. Similarly, with regards to fusional divergence amplitudes, fusion break points and fusion restoration points at 0.33 and 6 meters were not significantly different between contact lenses and spectacles (p>0.05). Vertical fusion ampitudes measurements at 0.33 m and 6 m yielded no significant differences between spectacles and contact lenses with regards to fusion break point (p>0.05). Conclusion: The only significant difference between the spectacle lens and the contact lens in terms of fusion amplitude was that the fusion restoration was higher with the spectacle lens at 0.33 m, which could be attributed to participants' being myopes and the base-in prismatic effect of the spectacle lens. In light of these findings, spectacles appear to be superior to contact lens in terms of alleviating symptoms in patients with convergence insufficiency due to exophoria in clinical practice. Keywords: Divergence, Spectacles, Contact lens, Convergence, Vergence