Effects of Induced Astigmatism on Spectral Domain-OCT Angiography Quantitative Metrics

doi:10.1016/j.ajo.2020.07.005

American Journal of Ophthalmology

Volume 219, November 2020, Pages 49-58

https://doi.org/10.1016/j.ajo.2020.07.005 Get rights and content

Purpose

To analyze the effect of induced astigmatism on en-face spectral-domain optical coherence tomography angiography quantitative metrics.

Design

Prospective crossover study.

Methods

Normal eyes without astigmatism and with 0.75, 1.75, and 2.75 diopters (D) of with-the-rule (WTR) astigmatism were imaged using a 3 × 3-mm scan pattern SD-OCTA CIRRUS 5000 HD-OCT with AngioPlex (Carl Zeiss Meditec, Dublin, CA, USA). Quantitative parameters, including foveal avascular zone metrics, parafoveal vessel length density (VD), and perfusion density (PD) were corrected for magnification secondary to axial length and analyzed. Univariate linear regressions were performed within each eye to correlate quantitative metrics to the level of an induced astigmatic cylinder.

Results

Fifteen eyes from 15 patients were imaged. Every 1-D increase in induced WTR astigmatism was associated with a statistically significant decrease in VD and PD within all Early Treatment Diabetic Retinopathy Study inner ring quadrants; however, especially more so nasally (VD: 0.63; P < .001; PD: 0.0089; P = .001). For every 1-D increase in induced astigmatism, the resulting decrease in the inner ring superior quadrant was 12% greater for VD and 16% greater for PD versus that in the inferior quadrant. The resulting decrease in the inner ring nasal quadrant was 40% greater for VD and 48% greater for PD versus that in the temporal quadrant.

Conclusions

Increasing levels of induced WTR astigmatism correlated with globally diminishing VD and PD, was more symmetrical for vertical than horizontal quadrants, and was most pronounced nasally. This may be due to a high prevalence of horizontally oriented vessels nasally and the horizontal optical defocus induced by WTR astigmatism.

Section snippets

Methods

This prospective, crossover, single-center clinical practice cohort study received prospective approval from the Salus Institutional Review Board (Austin, Texas, USA). This study complied with the Health Insurance Portability and Accountability Act of 1996 and followed the tenets of the Declaration of Helsinki. All subjects signed a written informed consent before participating in the study.

Results

A total of 15 patients (15 eyes) who met the inclusion criteria were recruited for this study (Table 1). Average age was 40.9 years old, with a nearly equal distribution of right eyes versus left eyes (47% right eyes), and men versus women (47% men). All eyes were phakic, with an average axial length of 24.32 ± 1.3 mm; range: 22.72-27.10 mm), average spherical equivalent refractive error of −2.43 ± 2.91 D: range: −8 to +2.25 D), and an average SD-OCTA signal strength of 9.7 ± 0.6; range: 8-10).

Discussion

In this study, we evaluated the effect of induced WTR astigmatism on SD-OCTA quantitative metrics in healthy eyes with no intraocular pathologies. Each 1-D increase in induced WTR astigmatism resulted in a generalized decrease in both VD and PD across all subfields within the 3 × 3-mm scan area, but there was no significant effect on FAZ metrics. In the horizontal axis, VD and PD depression were greater in the nasal quadrants than the temporal quadrants. In the vertical axis, VD and PD

Conclusions

In conclusion, our study is the first to demonstrate the qualitative and quantitative effects of induced astigmatism on SD-OCTA SRL metrics. Measurements within the entire macula were affected by induced WTR astigmatism, with the largest effect found nasally. Astigmatic shifts were likely to confound both time-based and meridional cross comparisons of these measurements, especially in the presence of high astigmatic errors.

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Los pacientes con formas avanzadas de RP muestran menor VD en el área macular que los controles sanos. Estas diferencias están presentes en todos los cuadrantes del DVP y en 3 de ellos en el SVP.
To describe the changes in vessel density (VD) using optical coherence tomography angiography (OCTA) of the different sectors in the macular area between retinitis pigmentosa (RP) patients and controls.
Observational case-control study. We initially included 22 patients with RP and 21 controls. We obtained 6x6 OCTA images of the macular area using Angio-OCT SS-DRI-Triton 1.22 (Topcon, Japan), together with visual acuity, biomicroscopy, visual field and optical coherence tomography examination. We compared the VD values in both groups for both superficial (SVP) and deep vascular plexus (DVP). Correlation between VD and macular thickness was also calculated.
The mean visual field index (VFI) in the RP group was 26.11% (±17.29). VD was significantly lower in the RP group compared with healthy controls in all sectors of the DVP (Superior 43.48±3.79 vs 48.86±2.62, P<.0001; Nasal 40,52±4.30 vs 46,01±3.23, P=.0002; Inferior 42.76±5.26 vs 50.10±3.36, P<.0001; Temporal 40.42±4.46 vs 46.09±2.91, P=.0001) and in all but nasal sector in the SVP (Superior 39.86±4.46 vs 46.47±2.61, P<.0001; Nasal 40.35±4.56 vs 44.09±2.87, P=.0067; Inferior 40.74±4.61 vs 46.58±3.26, P=.0002; Temporal 39.98±5.07 vs 44.78±3.28, P=.0024). Correlation between VD and macular thickness was positive and significant (RP: r=.59, P=.043; controls r=.51, P=.018).
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Citation Excerpt :
This may be due to limited sensitivity of OCTA to detect the small physiological changes in capillaries related to caffeine intake, which could differ from pathological changes, such as those observed in diabetic retinopathy,4142 high myopic choroidal neovascularization,11 or age‐related macular degeneration.4344 Jung et al.45 reported that amount of astigmatism could influence OCTA vessel length density and perfusion area density at different quadrants. It could be due to optical blur across different meridians because current OCTA systems incorporate only spherical lens to compensate refractive errors.
To monitor effect of caffeine on vasculature of the inner retina of high myopes
This was a crossover, self‐control, randomized trial. Healthy young high myopes were recruited to take 200 mg of caffeine capsule and placebo capsule, randomly assigned in two visits separated by at least one week. Superficial retinal vasculature in terms of vessel length density (VD) and perfusion area density (PD) was captured and monitored using a spectral domain optical coherence tomography angiography (OCTA) machine. After baseline measurements, blood pressure (BP), intraocular pressure (IOP), and subfoveal choroidal thickness (ChT) were also monitored at 30‐min intervals till 3 h.
Eighteen subjects (6 male, 24.3 ± 3.1 years) completed the study. After taking the caffeine capsule, there was a significant increase in BP (p < 0.01), and reduction in ChT (p < 0.01), with no change in IOP (p = 0.36). VD demonstrated a trend of reduction at the central 1‐mm circle, and 1‐3 mm annulus (p < 0.01) following the ETDRS grid. Reduction trend of PD appeared at the central 1‐mm circle, 1‐3 mm annulus, and the entire 3‐mm circle (p < 0.01). Compared with baseline, VD and PD reductions were significant 180 min after taking the caffeine capsule at the central 1‐mm circle, but the reduction was small (VD: by 1mm^-1; PD: by 1%). Changes in other regions were not significant.
The current study found significant reduction in VD and PD after taking 200 mg of caffeine capsule. Such a small amount of alteration may be clinically irrelevant.
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Prospective crossover study.
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Original ArticleEffects of Induced Astigmatism on Spectral Domain-OCT Angiography Quantitative Metrics

Purpose

Design

Methods

Results

Conclusions

Section snippets

Methods

Results

Discussion

Conclusions

Prog Retin Eye Res

Ophthalmology

J Fr Ophtalmol

Am J Ophthalmol

Ophthalmol Retina

Diagn Pathol

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Acta Ophthalmol

Branch retinal artery occlusion imaged with spectral-domain optical coherence tomographic angiography

JAMA Ophthalmol

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Original Article
Effects of Induced Astigmatism on Spectral Domain-OCT Angiography Quantitative Metrics