Quantitative assessment of the effect of fasting on macular microcirculation: an optical coherence tomography angiography study

Evaluating macular and optic nerve changes during Ramadan fasting by optical coherence tomography angiography-a prospective before-and-after study

PURPOSE

During Ramadan, millions of Muslims fast from sunrise to sunset. Fasting influences the hormonal system, sympathetic activity, blood circulation, and metabolic pathways. Because of these changes, we employed optical coherence tomography angiography (OCTA) to investigate the effects of fasting on the macula and optic nerve.

METHODS

In this prospective before-and-after study, both eyes of 45 participants were examined. Vascular characteristics of the macula and optic nerve head were evaluated in the morning and evening, once before Ramadan and once on the 20th day of Ramadan.

RESULTS

Compared to the non-fasting condition, fasting significantly reduced inner parafoveal retinal thickness in both eyes and total foveal retinal thickness in the left eye in the morning and evening. Fasting in the morning also considerably reduced inner foveal retinal thickness in both eyes and total parafoveal retinal thickness in the right eye. Fasting significantly reduced central choroidal flow (1 mm) in both eyes in the evening (all p-values are < 0.05). In the morning, there were significant increases in the foveal avascular zone (FAZ) area (p-value = 0.006) and deep parafoveal vascular density in the left eye (p-value = 0.001).

CONCLUSION

Fasting alters both the macular characteristics and the optic nerve head, as seen in OCTA, although it did not affect participants' vision. However, further research is needed before reaching a broad conclusion.

Investigation of the short-term effects of water drinking test on the eye using Optical Coherence Tomography Angiography in young healthy male subjects

PURPOSE

To evaluate the acute effects of the water drinking test (WDT) on the eye using optical coherence tomography angiography (OCTA) on healthy young male subjects.

METHODS

The study included 25 eyes of 25 male subjects. Selected parameters of the retinal vasculature were measured, including macular flow indices, foveal avascular zone, and vessel densities (VDs) of the macula using OCTA. The measurements were taken on the first day without drinking water at 0 min, 30 min and 60 min, then repeated on the second day before drinking water at 0 min, and after drinking water at 30 min and 60 min. The Paired Samples t-test and repeated measures One-way analysis of variance test were used in the statistical analyses.

RESULTS

The repeated measures analysis of variance test using Bonferroni adjustment demonstrated a significant increase in superficial and deep foveal VD following WDT (p <0.001 for both). Intraocular pressure, retinal nerve fiber layer thickness, foveal avascular zone, flow area of choriocapillaris, flow area of outer retina, foveal non-flow area of superficial layer, and retinal thickness measurements showed no significant changes following WDT.

CONCLUSIONS

WDT is associated with temporary flow modifications in superficial and deep foveal vascular plexus in young male subjects.

Corneal morphology correlates with choriocapillaris perfusion in myopic children

AIMS

The present study investigated the difference in choriocapillaris (CC) perfusion between different AL/K ratio groups with similar spherical equivalent refraction (SER) and analyzed factors affecting CC perfusion.

METHODS

This cross-sectional study included 129 children with low-to-moderate myopia. Axial length (AL), average K-reading (Ave-K), and SER were measured. Choroidal vascularity, including the total choroidal area (TA), choroidal luminal area (LA), stromal area (SA), choroidal vascularity index (CVI), CC flow voids (FVs), and FVs%, was obtained using optical coherence tomography angiography.

RESULTS

Participants with similar SER were divided into two groups (high AL/K ratio, n = 57; low AL/K ratio, n = 72). The high AL/K group had lower LA, TA, and CVI (P < 0.01) and lower FVs (inner ring and fovea, P < 0.05) and FVs% (outer ring, inner ring, and fovea, P < 0.05). The AL/K ratio and FVs% were negatively correlated in the outer ring (r =  - 0.174, P < 0.05) and inner ring (r =  - 0.174, P < 0.05). The Ave-K and inner FVs (r = 0.178, P < 0.05), outer FVs% (r = 0.175, P < 0.05), and inner FVs% (r = 0.196, P < 0.05) were positively correlated. In stepwise multiple regression for the outer ring, the horizontal CVI was related to FVs (β = 0.175, P < 0.05), and the vertical CVI was related to FVs% (β = 0.232, P < 0.01). Independent risk factors associated with inner FVs area were vertical CVI (β = 0.329; P < 0.001) and SER (β =  - 0.196, P < 0.05); FVs% was also associated with vertical CVI (β = 0.360, P < 0.01) and SER (β =  - 0.196, P < 0.05).

CONCLUSION

With a similar SER, myopic eyes with a higher AL/K ratio maintained more CC perfusion and lower CVI, which may indicate rapid myopic progression. Low K-reading eyes had more CC perfusion and less CVI, which may explain the relatively poor myopia control efficacy in the clinic.

Evaluation of the different thresholding strategies for quantifying choriocapillaris using optical coherence tomography angiography

Background

In this paper, we evaluate the different thresholding strategies that have been used for the quantification of the choriocapillaris (CC) and explore their repeatability and the interchangeability of the measurements resulting from its application.

Methods

Observational study. Eighteen eyes from nine healthy volunteers aged >18 years were imaged four consecutive times with a SD-OCTA system (Heidelberg Engineering, Germany) using a 10°×10° high-resolution protocol centered on the fovea. Projection artifacts were removed, and the CC was bracketed between 10 and 30 µm below Bruch's membrane. For the quantification of CC, we used four flow deficits (FD) parameters: FD number, mean FD size, total FD area and FD density. We performed a systematic review of literature to collect the thresholding methods that have been used for the quantification of CC. The CC quantification parameters were then evaluated after applying each of the thresholding strategies. Intraclass correlation coefficient (ICC) and Pearson's correlation analysis were used to compare the repeatability and interchangeability among the different thresholding strategies for quantifying the CC.

Results

A total of 72 optical coherence tomography angiography (OCTA) examinations were considered. The systematic review allowed us to conclude that three local thresholding strategies (Phansalkar, mean and Niblack) and three global thresholding strategies (mean, default, Otsu) have been used for CC quantification. These strategies were evaluated in our observational study. We found a high agreement within the same method in the quantification of FD number, mean FD size, total FD area and FD density but a poor agreement with different strategies. Local strategies achieved a significantly superior ICC than global ones in CC quantification.

Conclusions

In conclusion, the interchangeability of the CC quantification using different thresholding strategies is low, and direct comparisons should not be performed. Local thresholding strategies are significantly superior to global ones for quantifying CC and should be preferred. There is an unmet need for a uniform strategy to quantify CC in future studies.

The effect of religious fasting and dehydration at Ramadan on choroidal thickness and Retinal vessel densities, measured with optical coherence tomography angiography

AIM

To investigate the effect of religious fasting and dehydration at Ramadan on choroidal thickness and vessel density in the superficial and deep vascular plexuses with OCTA.

METHODS

The choroidal thickness, and superficial and deep vessel density indices of fasting healthy subjects were measured with an OCTA device, and compared with non-fasting measurements.

RESULTS

The study included 70 eyes of 35 healthy subjects with a mean age of 42.86 ± 8.3 years. The measured choroidal thickness, superficial vessel density index and deep vessel density index were 288.89 ± 67 µm, 40.56% and 41.43%, respectively when measured in the fasting period, compared to 284.62 ± 65 µm, 40.41% and 41.41%, respectively when measured in the non-fasting period. The choroidal thickness under the fovea center was found to be significantly higher in the fasting period than in the non-fasting period (p = 0.014). The mean total choroidal thickness was found to be reduced in the non-fasting period, although not to a statistically significant degree (p > 0.05). An analysis of the mean total superficial and deep vascular plexuses revealed no statistically significant difference (p = 0.368, p = 0.938 respectively).

CONCLUSION

Although a significant increase was noted in central choroidal thickness in the fasting period, no significant change due to fasting was observed in the superficial and deep capillary plexuses. The choroidal layer may vary in thickness due to fasting-related metabolic factors, while retinal vessels are more stable against such effects.