الفهرس 
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Abstract
Glaucoma is one of the major causes of irreversible blindness worldwide. It is a group of optic neuropathies with distinctive gradual damage of the retinal ganglion cells (RGCs) and their axons that form the retinal nerve fiber layer (RNFL). As glaucoma advances, it results in specific changes in the optic nerve head (ONH) associated with visual field (VF) loss.
The precise pathophysiology of glaucomatous optic neuropathies is not fully understood. Many mechanisms are involved in the pathogenesis of POAG. Glaucomatous optic nerve damage is highly related to elevated IOP. However, the VF loss may continue to worsen in some patients with normal or even low IOP. Vascular elements are suggested to be involved in glaucoma. The vascular theory states that glaucoma is accompanied by ocular hypoperfusion. Early diagnosis and proper management of glaucoma can prevent permanent damage and subsequent visual loss.
Clinical diagnosis and follow-up of glaucoma are carried out by the evaluation of both functional changes in the VF via standard automated perimetry (SAP), and structural changes in the RNFL via optical coherence tomography (OCT). Fast non-invasive quantitative evaluation of the retinal and choroidal microvasculature can be obtained by optical coherence tomography angiography (OCTA). This recent technique images the microcirculation by using an intrinsic contrast agent based on the flowing red blood cells in the small blood vessels.
This study was conducted to evaluate vascular parameters in the form of macular vessel density provided by OCT-A changes in early POAG eyes and to compare their diagnostic abilities in discriminating early POAG eyes from healthy eyes.
The current study included a total of 40 eyes of 22 individuals. The subjects were divided into 2 age-matched groups according to their VF findings and structural parameters assessed by the OCT. The control group included 20 eyes of 10 normal subjects, and the early POAG group included 20 eyes of 12 patients.
The control group included normal persons with IOP ranging from 12 to 20 mmHg, no previous history of increased IOP, reliable normal VF, normal ONH appearance, intact NRR, and normal RNFL thickness. Early glaucoma is defined as patients who have at least 2 of the following criteria in at least one eye: (a) IOP more than 21 mmHg, (b) ONH appearance or RNFL abnormality suggestive of glaucoma, i.e., enlarged or asymmetric C/D ratio, NRR notching or narrowing, disc hemorrhages, or suspicious alterations in the RNFL, and (c) VF defect matching with early glaucoma criteria according to the HPA glaucoma grading scale.
The research control subjects and patients were recruited, examined, and evaluated in the Minia University Hospital’s outpatient Ophthalmology clinic, from March 2021 to April 2022. All patients underwent history taking and full ophthalmological examination. They were subjected to automated perimetry and optical coherence tomography imaging.
All the OCT structural parameters, including both RNFL thickness (average, superior, and inferior) and GCC thickness (total, superior, and inferior), were significantly decreased in the early POAG than in the control group.
Concerning the perimetric functional parameters, both the VF mean deviation (MD) and the visual field index (VFI) were significantly decreased, while the VF pattern standard deviation was significantly increased in the early POAG group compared to the control group.
The OCTA parameters of the superficial macular capillary plexus (SCP) vessel density were significantly decreased in the early POAG eyes compared to normal eyes. The whole image vessel density (wiVD) is 42.9 ± 3% in the early POAG eyes vs 48.2 ± 1.9% in the normal eyes (P = 0.0001). The foveal VD is 24.9 ± 7.1% in the early POAG eyes vs 30.5 ± 4.5% in the normal eyes (P = 0.041). The parafoveal VD is 45.7 ± 4.4% in the early POAG eyes vs 50.6 ± 2.7% in the normal eyes (P = 0.001). As well, all the sectorial SCP VD parameters were significantly lower in the early POAG eyes compared to the healthy eyes.
Concerning the VD of the deep macular capillary plexus (DCP), there was no significant change in all of its parameters between the healthy and POAG groups (P > 0.05), except for the temporal VD which was slightly decreased in the early glaucomatous eyes compared to the normal eyes (P = 0.042).
As regards the correlations between the OCTA findings, the structural and the functional parameters; the current study found that there were statistically significant positive correlations (R + and P < 0.05) between the SCP wiVD, and the total RNFL thickness, the average GCC thickness, as well as the visual field MD. The total RNFL thickness had the strongest linear relationship with the wiVD of SCP, followed by the VF MD and GCC thickness. On the other hand, the VD of the DCP showed positive but insignificant correlations (R + and P > 0.05) between the DCP wiVD and both the average RNFL thickness and the total GCC thickness. However, there was a slightly significant positive correlation (R + and P = 0.05) between the DCP wiVD and the visual field MD.
To study the accuracy of GCC thickness, RNFL thickness, and VD as diagnostic tools and their ability to discriminate early glaucomatous from healthy eyes; area under the receiver operating characteristic (AUROC) curve values were estimated. A value of 1.0 indicates perfect discrimination, while 0.5 indicates chance discrimination.
This study represented that the total GCC thickness had an AUROC value of 0.938 (P < 0.001), with 81% sensitivity and 100% specificity at a cutoff point of 91.7. The average RNFL thickness had an AUROC value of 0.926 (P < 0.001), with 81% sensitivity and 100% specificity at a cutoff point of 90. The wiVD of the superficial capillary plexus had an AUROC value of 0.94 (P < 0.001), with 95.24% sensitivity and 80% specificity at a cutoff point of 47.11. The wiVD of the deep capillary plexus had an AUROC value of 0.652 (P > 0.05), with 100% sensitivity and 40% specificity at a cutoff point of 58.69.
Conclusions:
In conclusion, the current study has shown that:
1. Patients with early POAG have significantly decreased superficial macular VD parameters when compared to normal subjects.
2. The superficial macular wiVD has significant correlations with both the structural and the functional glaucoma parameters.
3. The superficial macular wiVD shows a comparable diagnostic accuracy to the GCC thickness and the RNFL thickness. This ensures the significance of the assessment of the macular microcirculation parameters in cases of POAG.