Purpose: To assess the effects of scleral expansion band (SEB) segments on accommodative amplitude (primary measure), along with near and distance vision, refraction, pupil size and function, keratometry, axial length, intraocular pressure, contrast sensitivity, stereopsis, and other parameters (secondary measures) in a cohort of 29 emmetropic, presbyopic patients.
Design: Multicenter, prospective, nonrandomized, unmasked clinical trial in which the nonoperated eye served as the control.
Methods: Four polymethylmethacrylate segments were surgically implanted in quadrantic scleral pockets created in the dominant eye of 29 emmetropic patients who were between the ages of 51 and 60 (mean age 54). Patients were examined preoperatively and up to 6 months postoperatively. The aforementioned tests were performed on the operated and control eye of each patient. Data were analyzed using two-sided rank tests. Medians, means, and standard deviations are provided for all measurements.
Results: Accommodative amplitude was measured monocularly using a near-point "push" technique from both a 70-cm and 30-cm starting point. An increase in accommodative amplitude of surgical eyes by +1.7 +/- 1.5 diopters and +1.5 +/- 1.2 diopters, at these two testing distances, respectively, was noted at 6 months postoperatively (P <.0001). A smaller increase was also seen in control eyes (+1.2 +/- 1.1 diopters and +1.3 +/- 1.2 diopters, respectively). There was notable intercenter variation in gains in accommodation, with three of seven centers showing significant improvement in near-point accommodative amplitudes relative to the others (P =.0003). There was a median improvement of uncorrected near acuity in surgical eyes by 0.3 logarithm of the minimal angle of resolution (logMAR) at 30 and 40 cm and by 4 lines at 20 cm, with the difference in near acuity improvement at 6 months between SEB eyes and control eyes statistically significant at 20 cm (P <.030). Changes in spherical equivalence, axial length, and central keratometry readings were not statistically significant. There were no reports of anterior segment ischemia or malignant glaucoma. Adverse effects were limited to a transient elevation of intraocular pressure in one patient and misalignment of individual SEB segments, due to inadequate scleral pocket formation, in three patients. Only one SEB segment in one eye was replaced. It appears that the thickness and uniformity of the scleral belt loop is critical to the proper positioning and efficacy of the SEB segments.
Conclusion: While the safety profile of SEB segments for the treatment of presbyopia was high, a modest improvement in near vision was noted in approximately half the patients using subjective methods of testing. The mechanisms that underlie improvement in near vision in the nonoperated eye await explanation. This may be due to a centrally controlled consensual response, potentiated convergence generating increased intravitreal pressure and hydraulic lift of the vitreo-zonular-lens diaphragm, or artifact from current testing techniques. Future studies of the SEB procedure should address the issue of intercenter variation by further standardizing and automating specific aspects of the surgical technique, as well as incorporating objective testing methods into the study design.