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Peri-operative Investigations
Published in Pradeep Venkatesh, Handbook of Vitreoretinal Surgery, 2023
Fluorescein angiography, although invasive and associated with certain side effects, remains a useful and affordable investigation to assess the integrity of the retinal vascular bed. In the situation of non-availability of OCT angiography, it is useful for the surgeon to assess the status of the foveal avascular zone by fluorescein angiography. The presence of foveal ischemia is a poor prognostic indicator for the recovery of satisfactory vision following surgery for complications of diabetic retinopathy. This must be explained to the patient before obtaining consent for surgical intervention. In addition, fluorescein angiography may also reveal significant ischemia of the retina in other regions too, even in the absence of neovascularization. In this situation, it may be safer to first undertake retinal photocoagulation [if media permits] at least 4–6 weeks before planned surgery. This is likely to reduce the risk of postoperative complications such as severe fibrinoid reaction and anterior hyaloidal fibrovascular proliferation. Postoperatively too, it is useful to undertake fluorescein angiography within the first 4–6 weeks following surgery for complications of either diabetic retinopathy or retinal vasculitis. This would allow the detection of missed or subclinical neovascularization, and if present, prompt laser augmentation can avert recurrence of severe vision loss due to rebleed.
Retinal image enhancement and analysis for diabetic retinopathy assessment
Published in Ahmad Fadzil Mohamad Hani, Dileep Kumar, Optical Imaging for Biomedical and Clinical Applications, 2017
Ahmad Fadzil Mohamad Hani, Hanung Nugroho, Lila Iznita Izhar, Nor Fariza Ngah
Instead of varied contrast, the contrast between retinal vessels and background is very low. Low contrast occurs particularly around retinal capillaries that are mostly located in the centre of the retina known as macular region. The retinal capillaries and vessels surrounding the macular region are of very low contrast since they are located in the choroidal layer underneath the macular pigment and the RPE, which contains melanin that absorbs light. Due to the small contrast between retinal blood vessels and the background in retinal fundus pictures, it is not easy to find out the retinal vasculature that can be utilized to identify macular region, foveal avascular zone (FAZ) and existence of pathology. Diverse and small contrast conditions in colour retinal fundus pictures generally reduces image quality and leads to inaccuracy of segmentation of retinal blood vessels and pathology detection; thus, leading to reduced accuracy, sensitivity and specificity in the diagnosis of the retinal-related diseases.
SKILL Ocular angiography
Published in Sam Evans, Patrick Watts, Ophthalmic DOPS and OSATS, 2014
Areas of the retina or vessels that do not fluoresce as brightly as adjacent tissue of the same type are said to be ‘hypofluorescent’. These areas may be physiological (foveal avascular zone [FAZ] 450–600 μm) or pathological. Pathological areas of hypofluorescence may be due to poor vascular filling or the masking of deeper structures. Vascular hypoperfusion is related to capillary non-perfusion (seen as wedges of hypofluorescence in the retinal capillary bed) or retinal vessel non-perfusion. The masking of the fluorescence of deeper layers by non-perfusing overlying structures is an important cause of hypofluorescence and is most commonly due to pre- or intraretinal haemorrhage. It is important to identify the level of the blood – pre-retinal masking defects obscure retinal vessels, while intraretinal haemorrhages do not.
Retinal arcades in posterior microphthalmos: biometric correlation
Published in Clinical and Experimental Optometry, 2023
Ramesh Venkatesh, Pranjal Mishra, Harshita Nahata, Nikitha Gurram Reddy, Naresh Kumar Yadav, Jay Chhablani
In this study, there was an increase in the capillary vessel densities at the foveal region and a decrease in foveal avascular zone area in PM eyes. Also, in the current study, there was a significant correlation between foveal vessel density and foveal avascular zone area on optical coherence tomography angiography with axial length. The possible explanation for this finding is as follows. The superficial capillary plexus is anatomically located within the nerve fibre layer, ganglion cell layer, and inner plexiform layer and the deep capillary plexus within the inner nuclear layer and outer plexiform layer.19 This study showed thicker central retinal layers in eyes with PM compared to the controls. As a result, higher vessel densities were seen in eyes with PM. Similar optical coherence tomography angiography descriptions have been mentioned in a previous study of the authors on PM and in other studies published recently.9,11–13
Retinal imaging biomarkers of neurodegenerative diseases
Published in Clinical and Experimental Optometry, 2022
Eirini Christinaki, Hana Kulenovic, Xavier Hadoux, Nicole Baldassini, Jan Van Eijgen, Lies De Groef, Ingeborg Stalmans, Peter van Wijngaarden
Building on studies of retinal photography in AD, numerous research groups have turned to macular OCT-A in the search for biomarkers of the disease. Amongst an array of parameters, several studies have identified decreased retinal vessel density, reduced perfusion density and enlarged foveal avascular zones in people with AD relative to controls without the disease.71–73 Other studies have identified reduced choroidal thickness in people with AD.74 A recent meta-analysis of 14 cross-sectional OCT-A studies identified enlarged foveal avascular zones, reduced parafoveal superficial and whole vessel density (defined as the foveal avascular zone and the surrounding areas) in people with AD compared with controls without the disease.73 Findings for MCI and preclinical AD were more mixed and no significant differences between these groups and control participants were found in the meta-analysis.73 Significant heterogeneity in case definitions, device types, imaging protocols and image processing methods, including those used for retinal vessel network segmentation, may account for some of the observed variability in study findings, prompting calls for standardisation of protocols.46,73 Consideration of comorbid ocular disease and axial length is also important to reduce confounding.73 Furthermore, given the interplay between cerebrovascular disease and AD, an assessment of cerebrovascular disease burden with neuroimaging should accompany biomarkers of AD (CSF or PET) in studies of OCT-A in the disease.7
Imaging Amblyopia: Insights from Optical Coherence Tomography (OCT)
Published in Seminars in Ophthalmology, 2019
Eric D. Gaier, Ryan Gise, Gena Heidary
There have been 5 published OCT-A studies in amblyopia to date.39–43 Of those that examined the macular superficial capillary plexus, three have identified a reduction in vessel density associated with amblyopia compared to fellow eyes and/or controls.39,42,43 One study found no difference in vessel density in this segment.40 Among studies examining the deep capillary plexus, two reported a reduction in vessel density42,43 and one found no difference.40 The foveal avascular zone was found to be of similar size in two-thirds studies40,43 and enlarged in one study.39 Two studies examined the choriocapillaris using OCT-A, with one showing an increase in vessel density41 and the other showing no difference.43 Currently, spectral domain-based OCT-A is limited to imaging the choriocapilaris and cannot sufficiently image the choroid itself.