New Insights on Choroidal Vascularity: A Comprehensive Topographic Approach

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Quantitative shadow compensated optical coherence tomography of choroidal vasculature

Conventionally rendered optical coherence tomography (OCT) images of the posterior segment contain shadows which influence the visualization of deep structures such as the choroid. The purpose of this study was to determine whether OCT shadow compensation (SC) alters the appearance of the choroid and the apparent choroidal vascularity index (CVI), an OCT-derived estimated ratio of luminal to total choroidal volume. All scans were shadow compensated using a previously published algorithm, binarized using a novel validated algorithm and extracted binarized choroid to estimate CVI. On 27 raw swept-source OCT volume-scans of healthy subjects, the effect of SC on CVI was established both qualitatively and quantitatively. In shadow compensated scans, the choroid was visualized with greater brightness than the neurosensory retina and the masking of deep tissues by retinal blood vessels was greatly reduced. Among study subjects, significant mean difference in CVI of -0.13 was observed between raw and shadow compensated scans. Conventionally acquired OCT underestimates both choroidal reflectivity and calculated CVI. Quantitative analysis based on subjective grading demonstrated that SC increased the contrast between stromal and luminal regions and are in agreement with true tissue regions. This study is warranted to determine the effects of SC on CVI in diseased eyes

Semi-automated quantification of hard exudates in colour fundus photographs diagnosed with diabetic retinopathy

Background: Hard exudates (HEs) are the classical sign of diabetic retinopathy (DR) which is one of the leading causes of blindness, especially in developing countries. Accordingly, disease screening involves examining HEs qualitatively using fundus camera. However, for monitoring the treatment response, quantification of HEs becomes crucial and hence clinicians now seek to measure the area of HEs in the digital colour fundus (CF) photographs. Against this backdrop, we proposed an algorithm to quantify HEs using CF images and compare with previously reported technique using ImageJ. Methods: CF photographs of 30 eyes (20 patients) with diabetic macular edema were obtained. A robust semi-automated algorithm was developed to quantify area covered by HEs. In particular, the proposed algorithm, a two pronged methodology, involved performing top-hat filtering, second order statistical filtering, and thresholding of the colour fundus images. Subsequently, two masked observers performed HEs measurements using previously reported ImageJ-based protocol and compared with those obtained through proposed method. Intra and inter-observer grading was performed for determining percentage area of HEs identified by the individual algorithm. Results: Of the 30 subjects, 21 were males and 9 were females with a mean age of the 50.25 ± 7.80 years (range 33-66 years). The correlation between the two measurements of semi-automated and ImageJ were 0.99 and 0.99 respectively. Previously reported method detected only 0-30% of the HEs area in 9 images, 30-60% in 12 images and 60-90% in remaining images, and more than 90% in none. In contrast, proposed method, detected 60-90% of the HEs area in 13 images and 90-100% in remaining 17 images. Conclusion: Proposed method semi-automated algorithm achieved acceptable accuracy, qualitatively and quantitatively, on a heterogeneous dataset. Further, quantitative analysis performed based on intra- and inter-observer grading showed that proposed methodology detects HEs more accurately than previously reported ImageJ-based technique. In particular, we proposed algorithm detect faint HEs also as opposed to the earlier method

Change in choroidal vascularity in acute central serous chorioretinopathy

Purpose: This study aims to compare the effect of laser photocoagulation or observation on choroidal vascularity in acute central serous chorioretinopathy (CSCR). Methods: A retrospective analysis of 30 patients with acute CSCR treated either with laser photocoagulation (16 eyes) or sham laser (14 eyes) was performed. Demographic details, visual acuity (VA) assessment, and other relevant clinical data were considered from baseline to the 3rd and 6th month follow-up visits. Participants with chronic CSCR and missing follow-up or inadequate data were excluded. Choroidal analysis including choroidal thickness and choroidal vascularity index (CVI) assessment was done for each visit using Spectral Domain (SD) Optical Coherence Tomography (OCT) images. Results: In laser arm group, there was a statistically significant change in VA, contrast sensitivity and central macular thickness (CMT) and neurosensory detachment (NSD) (P 0.05) at both the visits. In sham laser group, similarly, there was a significant improvement in VA, contrast sensitivity, CMT, and CVI (P < 0.05) at the 3rd and 6th month visits. There was significant reduction in NSD at the 3rd month; however, it was not statistically significant at the 6th month visit. SFCT did not change significantly at both the visits. There was no significant difference for the changes in parameters between the groups at the 6th month. Regression analysis showed no significant correlation with final VA with any of the baseline parameters. Conclusion: Early laser photocoagulation does lead to change in choroidal morphology, though insignificant, in comparison to observation. The present data, yet again, support no additional benefit of early laser photocoagulation in acute CSCR

Qualitative comparison of choroidal vascularity measurement algorithms

Purpose: To compare the accuracy of manual and automated binarization technique for the analysis of choroidal vasculature. Methods: This retrospective study was performed on a total of 98 eyes of 60 healthy subjects. Fovea-centered swept source optical coherence tomography (SS-OCT) scans were obtained and choroidal area was binarized using manual and automated image binarization technique separately. Choroidal vessel visualization in the binarized scans were subjectively graded (grades 0–100) by comparing them with the original OCT scan images by two masked graders. The subjective variability and repeatability was compared between two binarization method groups. Intergrader and intragrader variability was estimated using paired t-test. The degree of agreement between the grades for each observer and between the observers was evaluated using Bland–Altman plot. Results: The mean accuracy grades of the automatically binarized images were significantly (P < 0.001) higher (93.38% ± 1.70%) than that of manually binarized images (78.06% ± 2.92%). There was a statistically significant variability and poor agreement between the mean interobserver grades in the manual binarization arm. Conclusion: Automated image binarization technique is faster and appears to be more accurate in comparison to the manual method

Choroidal Vascularity in Non-arteritic Anterior Ischaemic Optic Neuropathy

This study evaluates the peripapillary choroidal vascularity in eyes with non-arteritic anterior ischaemic optic neuropathy (NAION) and compares it with the vascularity of healthy fellow eyes and age-matched subjects. The peripapillary choroidal vascularity index (CVI), a new tool of measurement, was calculated using horizontal swept-source optical coherence tomography scans. CVI was calculated using a previously validated automated algorithm. CVI in NAION and fellow eyes of NAION patients were compared with age-matched eyes of healthy individuals using Kruskal–Wallis test. A total of 20 eyes of 20 patients with acute unilateral NAION with healthy fellow eyes (20 eyes) and 40 eyes of 40 healthy patients were included in the study. The average age of patients with NAION was 56 ± 8 and 55 ± 7 years in age-matched healthy controls. NAION eyes had a significantly lower CVI than age-matched controls in both nasal and temporal areas. NAION nasal CVI was 0.47 ± 0.47 compared to 0.62 ± 0.04 in controls (p < 0.001). NAION temporal CVI was 0.45 ± 0.48 compared to 0.58 ± 0.04 in controls (p < 0.001). Temporal CVI was 0.45 ± 0.48 in NAION eyes and was significantly lower than counterpart healthy fellow eyes 0.48 ± 0.02 (p = 0.007). In conclusion, NAION eyes have significantly reduced vascularity in the peripapillary area. CVI is lower in the nasal and temporal of the optic disc compared to healthy individuals. This may suggest those with smaller CVI are more prone to ischaemia from reduced vascularity resulting in NAION

Comparison of different settings for yellow subthreshold laser treatment in diabetic macular edema

Abstract Background To assess the safety and efficacy of two subthreshold parameters (5 and 15% duty cycle (DC)) compared to standard ETDRS (early treatment of diabetic retinopathy study) continuous wave (CW) laser. Methods In this prospective randomized study, 30 eyes from 20 patients with non-center involving macular edema were randomized into 3 different groups: 5% DC, 15% DC and CW navigated modified ETDRS laser treatment. Titration in subthreshold groups was performed with 30% of the threshold power, decided with microsecond pulses. CW laser was titrated to a barely visible burn. All patients underwent microperimetry, thickness measurements and visual acuity examinations at baseline, 6 weeks and 12 weeks post treatment. Results At three months follow up, retinal sensitivity was significantly reduced in the CW group by − 2.2 dB whereas in both subthreshold groups, retinal sensitivity increased by 2.4 dB for 5% and 1.9 dB for 15% DC with no significant difference. Retinal volume (mm3) decreased in both subthreshold groups by 0.08 ± 0.3 and 0.12 ± 0.11 in 5 and 15% DC group respectively. Whereas the CW group showed volume increase of 0.55 ± 0.92 (p = 0.02 and 0.01 for 5 and 15% DC groups). Visual acuity remained stable in all 3 groups (− 0.7 letter in 5% DC; 2.11 letters in 15% DC and 0.88 in CW with no significant difference). Conclusion Subthreshold microsecond laser was shown to be safe and effective with both 5 and 15% DC as compared to conventional photocoagulation with ETDRS parameters. The 15% DC setting trended to achieve better anatomical, visual and functional outcomes. Trial registration Retrospectively registered (NCT03571659, 06/26/2018)

Retinal and choroidal changes in steroid-associated central serous chorioretinopathy

Abstract Background To evaluate the retinal and choroidal alterations in steroid-associated central serous chorioretinopathy (CSC) in comparison to idiopathic CSC. Methods In this retrospective cohort study, swept source optical coherence tomography scans of eyes with steroid-associated CSC (group A) were compared with the same in idiopathic CSC (group B). The key features included central subfield retinal thickness, subfoveal choroidal thickness, subfoveal large choroidal vessel diameter, subretinal deposits, retinal pigment epithelial irregularities, double layer sign, hyperreflective dots, intraretinal fluid, and choroidal vascularity index (ratio of choroidal luminal area and total choroidal area, measured on a high definition horizontal 9 mm OCT B-scan. Results There were 20 eyes in group A and 30 in group B. Group A had a higher female proportion (60 vs. 16.67%; P < 0.01) and higher bilaterality (30 vs. 6.67%; P = 0.03). The height of neurosensory detachment was lower in group A (153.1 ± 175.70 µm vs. 312.9 ± 223.06 µm; P < 0.01). There was no significant difference in the prevalence of subretinal deposits, retinal pigment epithelial irregularities, pigment epithelial detachments, double layer sign, outer retinal layer disruption, and intraretinal fluid. Hyperreflective dots (HRDs) were less common in group A (15 vs. 46.67%; P = 0.03). The subfoveal choroidal thickness (P = 0.65) and subfoveal large choroidal vessel diameter (P = 0.78) were comparable. There was a trend towards a higher choroidal vascularity index (CVI) in group A (A: mean, 82%, 95% CI, 66–99%; B: mean, 58%, 95% CI, 57–59%; P = 0.10). Conclusion Steroid-associated CSC has a marginally higher CVI and less common association with HRDs as compared to idiopathic CSC

Choroidal vascular analysis in myopic eyes: evidence of foveal medium vessel layer thinning

Abstract Purpose To analyse morphologic features of the choroid in Non-pathological myopic eyes using spectral-domain (SD) optical coherence tomography (OCT). Methods Retrospective analysis of enhanced depth SD-OCT images of Non-pathological myopic eyes in comparison with age-matched healthy controls was performed. Choroidal thickness (CT) and large choroidal vessel thickness (LCVT) were measured at the fovea, 750 µm nasally from fovea (N750) and 750 µm temporally (T750) from fovea. Medium choroidal vessel thickness (MCVT) was calculated by subtracting LCVT from CT. Choriocapillaris was encompassed by MCVT, given its reduced thickness. Linear regression analysis evaluated the relationship between age and axial with CT, LCVT and MCVT. Results The study group comprised 42 eyes of 31 patients (mean age 46.13 ± 15.63; 15 females). Control group included 57 eyes of 34 patients (mean age of 42.3 ± 15.29; 24 females). Mean axial length in myopic eyes and control group was 26.57 ± 1.27 and 23.59 ± 0.99 mm respectively. Myopic eyes showed significant thinning of MCVT and CT at all locations (p  0.05). With each decade, thinning of up to 37 µm in CT was noted along with thinning of LCVT (up to 22.6 µm) and MCVT (up to 25 µm). Each mm increase in axial length caused 38.2 µm thinning of choroid along with LCVT (30 µm). Conclusion Significant thinning of MCVT was noted in non-pathological myopic eyes in comparison to healthy subjects. It appears that MCVT has stronger relationship with age and axial length