In current clinical work, doctors usually focused on features suggesting neural tissue loss on the ONH and surrounding area to assess the glaucomatous structural changes. However, in addition to the changes that occur in ONH and cpRNFL, another retinal region, macula has been proposed to be a potential location for glaucoma evaluation . There is hardly any large vessel in macula, and which shape is generally less variable than ONH. Additionally, RGCs are located intensively within macula . Meanwhile, RGC cell body exists is large enough that any such loss should theoretically be easiest to detect in macular region . These are the reasons that we focus on macular area in this study.
Formerly，GCC thickness is the only data that investigators could get in previous studies which concerned on macular area. Vessels and blood flow in macular, which can reflect macular function, were not available before the appearance of OCTA. OCTA can provide value of MVD by its included software automatically. So in our current study, we measured the MVD by OCTA in a group of patients with unilateral APAC. In eyes with history of APAC, we observed that changes of morphological characterstics and vessel density in macular were similar to the results obtained by our team about the changes on peripapillary retina using OCTA . Meanwhile, MVD in control eyes was similar to that in healthy subjects , which suggested the attenuated microvascular network in the case group was caused by APAC.
Few studies concerned the vascular morphology and blood perfusion in PACG. Gao et al. reported PACG individuals had narrower retinal arteries and veins by measuring of retinal vessel diameter from digitized photographs . It is deduced that ocular blood flow may be temporarily blocked by mechanical oppression, and microcirculation system would re-open and regenerate after IOP was controlled. However, in our study, we found that macular microcirculation system is irreversible damaged which can be interpreted as even IOP was lowered to normal level and keep stable for years. It is further demonstrated in our study that blood flow decrease was not temporary manifestation under extremely high IOP but a result of extensive damage of microvascular system.
We observed that MVD was markedly linked to BCVA and GCC than any other glaucomatous parameters, suggesting that a more prominently reduced MVD is associated with more severe visual impairment. FAZ and visual acuity have the close correlation, and significant capillary dropout from FAZ region may cause severe visual loss. So we considered the macular microvascular network atropy, depressed MVD, enlargement of intercapillary spaces and FAZ area might be the indicator of poor visual prognosis in patients with attack of APAC.
Several studies have shown that macular measurements have good glaucoma diagnostic capabilities as RNFL and ONH parameters[15,17]. Kim et al. reported that the macular GCC and cpRNFL thicknesses showed similar diagnostic performances in detecting different severity of glaucoma.Therefore, we believe the close correlation between the MVD and GCC thickness suggests that MVD meatured by OCTA might also be useful in monitoring the progression, severity and prognosis of glaucoma, further studies are required to draw the conclusion.
In the present investigation, we chose the patients with unilateral PACG, whose one eye had symptoms of APAC attack while the follow eye with no APAC evidence, as subjects for study. Self-control study might eliminate the effect of age, gender, and systemic disease which may interfere the conclusion about vascular factor in the pathological process of glaucoma, and made results of our study more reliable .
There are several limitations in our study. First, the relatively limited number of patients enrolled. Second, more eyes had cataract extraction or trabeculectomy history in case group. There is no data about influence of these surgeries on MVD. Third, the time sequence of macular microcirculation abnormalty and other glaucomatous change could not be concluded in present study. Finally, all the examination and measurements were operated in a non-masked fashion. Because OCTA give the report automatically, it is deduced that the effect of mask on measurements may be limited.