Abstract
Purpose: To compare the effects of age and near phoria on interpupillary distance measured at far (FIPD) and near (NIPD) using the Viktorin's and pupillometer (PD-5) methods.
Methods: Interpupillary distance (IPD) by Viktorin's method and the corneal reflex pupillometer (PD-5) method, as well as near heterophoria by the Saladin near point card, were each obtained on 133 randomly selected normal subjects aged 20-67 years. Comparison within and between techniques, influence of age on IPD, and near heterophoria were assessed.
Results: The mean FIPD varied significantly from the NIPD (P < 0.001 for both methods). Overall, FIPD ranged from 56-73 mm, and NIPD ranged from 50-70 mm. For FIPDs of 55 mm, 63 mm, and 71 mm, the corresponding NIPDs were less by 3.9 mm, 4.4 mm, and 5.0 mm, respectively, which were measured by Viktorin's method, and 4.0 mm, 4.6 mm, and 5.2 mm, respectively, measured by the PD-5 method. Between methods, the limits of agreement were: -3.9 mm and 3.2 mm (P < 0.05) for FIPD, and -3.1 mm and 2.9 mm (P < 0.05) for NIPD. Both IPDs varied significantly across age groups (P , 0.0001). Post hoc analysis revealed a significant variation (P < 0.01 in both techniques) only in the comparison between age groups 16-25 years and 41-67 years. The mean difference was -2.2 mm (-4.0 mm to -0.3 mm) and -2.8 mm (-4.7 mm to-1.0 mm) for Viktorin's method for FIPD and NIPD, respectively. For PD-5, the corresponding values were -1.3 mm (-3.2 mm to 0.4 mm) and -1.7 mm (-4.1 to -0.5 mm). Also, the near phoria differed significantly (P < 0.0001) across age groups and correlated positively with age (r(2) = 0.27, P , 0.0001) and NIPD (r(2) > 0.04; P < 0.03, both techniques).
Conclusion: The difference between FIPD and NIPD (about 4.4 mm in Arab males) was observed independent of the technique used. The Viktorin's and the PD-5 methods of IPD assessment resulted in similar values, and therefore, could be interchangeably used. However, caution is advised in cases of high power refractive corrections as the difference could vary from -4 mm to +3 mm (FIPD) and -3 mm to +3 mm (NIPD). Both IPDs have demonstrated an increase until the patients are in their early 40s, and a slight decrease has been observed thereafter. Age and NIPD were significantly associated with heterophoria in our subjects.