In the current study, we report a high frequency of narrow angles in PXF patients compared to the serially examined control patients (25.1% vs. 5%). The Middle Eastern region lacks population-based studies on the prevalence of narrow angles in the adult population for comparison, however, data from other ethnic groups suggests that it ranges from 2.2% in Whites  to 15.9% in Asians . A higher rate of narrow angle detection in PXF patients in the study population suggests that there is an association between PXF and clinically evident narrow anterior chamber angle.
Two prior studies have described the incidence of narrow angles in PXF patients. Out of 74 PXF patients, Roth M et al  found 3 (4.1%) cases of angle closure. Moreover, Gross FJ et al  reported five cases with a narrow angle (Shaffer grade two or less) in a review of 54 PXF patients (an incidence of 9.3%). The higher occurrence of narrow angles in our cohort (25.1%) compared to the reports by Roth M et al and Gross FJ et al might be explained by the racial difference between our patient population and theirs.
Several factors have been cited as causes of a narrow angle in PXF patients. First, laxity or degeneration of lens zonules may lead to decreased tension and subsequently a forward displacement of the lens . Secondly, several studies have suggested that certain ocular biometric characteristics (e.g. corneal thickness, AL, and ACD) in PXF patients may differ compared to healthy individuals [13, 14], thus, such difference may anatomically predispose to narrow angles. Finally, as it is well known from previous studies that the incidence of PXF increases with age  and that the anterior chamber angle is narrower in older individuals , it is possible that the high rate of PXF is attributed to the older age of affected patients.
The mean ACD in PXF patients was lower compared to the control group in our study (2.79 ± 0.4 vs. 3.05 ± 0.4, P < 0.0001), whereas the mean AL was comparable between both groups (23.3 ± 1.4 vs. 23.7 ± 1.0, P = 0.0714). This suggests that the anatomical difference between healthy eyes and eyes with PXF is at the level of the anterior segment and that PXF patients do not have shorter eyes compared to normal subjects. Therefore, the higher rate of narrow angles in PXF patients is possibly related to a larger or anteriorly displaced crystalline lens that may occur secondary to PXF-related zonular weakness. Another factor that is important to consider is the mean age of the PXF group in our study. PXF patients were older compared to the control group (72.6 ± 9.6 vs. 64.4 ± 8.5, P < 0.0001); thus, it is possible that crystalline lens enlargement occurring at a higher rate with advancing age contributed to a narrower angle which may explain the higher frequency of narrow angles in the older PXF group compared to the younger control group. Measurement of lens thickness in PXF patients is required to substantiate this hypothesis.
In binary logistic regression analysis of our data, PXF patients above 60 years were more likely to have narrow angles compared to younger patients (OR, 5.71; 95% CI, 1.01–32.27; P, 0.048). A finding that is consistent with previously published data correlating narrow angles with advanced age in normal individuals . Furthermore, we did not find a gender difference in the risk of narrow angles among PXF patients, which is in contrary with studies on healthy subjects that report a higher prevalence of angle narrowing among female patients .
The findings of our study must be carefully interpreted within the context of the following limitations. First, we recruited PXF patients from a tertiary care glaucoma clinic. This might have led to a referral bias, in that patients with narrow angles were most likely to be referred for further glaucoma workup. Secondly, the study sample constitutes a cohort of patients from the Saudi population, thus, findings cannot be directly extrapolated to other populations. Finally, due to machine unavailability, lens thickness measurements were not performed. Greater lens thickness is an important anatomical trait that is known to be a risk factor in the development of angle closure glaucoma . Thus, future studies documenting lens thickness measurements are required to further improve our understanding of the correlation between narrow angles and PXF.
In summary, narrow angles were more frequently encountered in PXF patients compared to controls. The higher frequency of narrow angles is most probably attributed to ocular biometric changes in the anterior segment of PXF eyes. Advanced age (> 60 years) was significantly associated with an increased likelihood of narrow angles.