Macular Cone Abnormalities in Behçet's Disease Detected by Adaptive Optics Scanning Light Ophthalmoscope

BACKGROUND AND OBJECTIVE

Investigations of morphological changes in photoreceptors in Behçet's disease (BD) using adaptive optics scanning light ophthalmoscope (AOSLO) are lacking. The authors aimed to evaluate macular cone density and regularity in BD patients with or without a history of uveitis with good visual acuity (VA).

PATIENTS AND METHODS

The authors included 16 patients (29 eyes) with BD and 12 healthy volunteers (12 eyes) as controls. All subjects had VA of 20/20 or higher. Subjects underwent AOSLO to evaluate the photoreceptor status including cone density (numbers/mm²) and proportion of hexagonal Voronoi domains.

RESULTS

Hyporeflective patches that were not detected in color fundus photograph or optical coherence tomography were observed by AOSLO in BD patients both with and without past uveitis history; these were not detected in the control group. Cone density was significantly reduced in BD patients with a history of uveitis compared to controls (P = .002). The proportion of hexagonal Voronoi domains was significantly reduced in BD eyes both with and without history of uveitis relative to controls (P < .001).

CONCLUSION

Macular photoreceptor damage was observed in BD patients with and without a history of uveitis. [Ophthalmic Surg Lasers Imaging Retina. 2021;52:218-225.].

Outer Plexiform Layer Elevations as a Marker for Prior Ocular Attacks in Patients With Behcet's Disease

Purpose

Patients with Behcet's disease frequently have abnormal focal outer plexiform layer (OPL) bumps, which compress the inner nuclear layer. This study investigates the clinical relevance of these OPL elevations in Behcet's disease patients.

Methods

Thirty-one consecutive patients (59 eyes) with Behcet's disease in remission and with available optical coherence tomography (OCT) images were included. The number of OPL bumps was counted using spectral-domain OCT images. The relationships between the number of bumps and visual acuity (VA), retinal thickness, choroidal thickness, disease duration, number of prior ocular attacks, and photoreceptor layer status (including external limiting membrane [ELM] and ellipsoid zone [EZ] continuity) were examined.

Results

Eyes with more severe EZ or ELM disruptions had lower VA, more ocular attacks, and thinner retinas. Additionally, EZ line and ELM line status were significantly correlated with the number of OPL elevations. Eyes with OPL elevations had poorer VA, longer disease duration, more ocular attacks, and thinner retinas than those without OPL elevations. Additionally, the number of OPL elevations was strongly correlated with the number of ocular attacks in eyes with a preserved photoreceptor layer (R = 0.720, P < 0.0001).

Conclusions

The number of OPL elevations was associated with the number of prior ocular attacks in eyes with preserved photoreceptor layers. Therefore, OPL elevations may be a marker of prior posterior ocular attacks, which is important when determining how best to manage Behcet's uveitis.

Correlation of retinal arterial wall thickness with atherosclerosis predictors in type 2 diabetes without clinical retinopathy

AIMS

To evaluate retinal arterial wall thickness (WT) using high-resolution retinal imaging in patients with type 2 diabetes and assess its correlation with risk factors for arteriosclerosis.

METHODS

Outer diameter, inner diameter and WT of the retinal artery were measured using adaptive optics scanning laser ophthalmoscopy in 28 patients with type 2 diabetes without clinically apparent diabetic retinopathy and normal volunteers. Laboratory values and intima-media thickness (IMT) in the common carotid artery were measured.

RESULTS

Retinal arterial WT was significantly greater in patients with type 2 diabetes than in controls (p=0.02). There was a significant correlation of retinal artery WT with IMT in patients with diabetes (r=0.40, p=0.04). WT in patients with diabetes was positively correlated with haemoglobin A1c (HbA1c) (r=0.49, p=0.001), total cholesterol (r=0.47, p=0.002) and low-density lipoprotein cholesterol (r=0.47, p=0.003).

CONCLUSIONS

Microvasuclar thickness was greater in patients with diabetes than in controls. Furthermore, WT was positively correlated with HbA1c, total cholesterol and low-density lipoprotein cholesterol levels and IMT in the diabetic group. These results suggest that retinal artery wall measurements can be potential surrogate markers of early diabetic microangiopathy.

Enhanced-Resolution Optical Coherence Tomography Imaging

PURPOSE

The effect of the enhanced-resolution imaging (ERI) technique on optical coherence tomography (OCT) images was evaluated.

METHODS

A total of 5 healthy subjects and 20 patients diagnosed with various eye diseases were recruited into the study. ERI, a novel image processing technique, was accomplished by using super-resolution technology, and was assessed by objectively and subjectively comparing the image quality among three different image groups: images enlarged without bicubic interpolation (NONE), with bicubic interpolation (IP), and with ERI.

RESULTS

ERI showed a higher ratio of the detailed variance to the background variance than NONE, whereas no significant difference was detected between NONE and IP. The mean opinion score of 5 experienced retinal specialists for ERI was significantly higher than that for IP.

CONCLUSIONS

ERI generated a sharper image and clearly visualized small objects. Additionally, it is effective in enhancing OCT image quality.

Effects of age and blood pressure on the retinal arterial wall, analyzed using adaptive optics scanning laser ophthalmoscopy

The wall-to-lumen ratio (WLR) of the vasculature is a promising early marker of retinal microvascular changes. Recently, adaptive optics scanning laser ophthalmoscopy (AOSLO) enabled direct and noninvasive visualization of the arterial wall. Using AOSLO, we analyzed the correlation between age and WLR in 51 normal subjects. In addition, correlations between blood pressure and WLR were analyzed in 73 subjects (51 normal subjects and 22 hypertensive patients). WLR showed a strong correlation with age (r = 0.68, P < 0.0001), while outer diameter and inner diameter did not show significant correlation with age in the normal group (r = 0.13, P = 0.36 and r = −0.12, P = 0.41, respectively). In the normal and hypertensive groups, WLR showed a strong correlation with systolic and diastolic blood pressure (r = 0.60, P < 0.0001 and r = 0.65, P < 0.0001, respectively). In conclusion, AOSLO provided noninvasive and reproducible arterial measurements. WLR is an early marker of morphological changes in the retinal arteries due to age and blood pressure.

Potential measurement errors due to image enlargement in optical coherence tomography imaging

The effect of interpolation and super-resolution (SR) algorithms on quantitative and qualitative assessments of enlarged optical coherence tomography (OCT) images was investigated in this report. Spectral-domain OCT images from 30 eyes in 30 consecutive patients with diabetic macular edema (DME) and 20 healthy eyes in 20 consecutive volunteers were analyzed. Original image (OR) resolution was reduced by a factor of four. Images were then magnified by a factor of four with and without application of one of the following algorithms: bilinear (BL), bicubic (BC), Lanczos3 (LA), and SR. Differences in peak signal-to-noise ratio (PSNR), retinal nerve fiber layer (RNFL) thickness, photoreceptor layer status, and parallelism (reflects the complexity of photoreceptor layer alterations) were analyzed in each image type. The order of PSNRs from highest to lowest was SR > LA > BC > BL > non-processed enlarged images (NONE). The PSNR was statistically different in all groups. The NONE, BC, and LA images resulted in significantly thicker RNFL measurements than the OR image. In eyes with DME, the photoreceptor layer, which was hardly identifiable in NONE images, became detectable with algorithm application. However, OCT photoreceptor parameters were still assessed as more undetectable than in OR images. Parallelism was not statistically different in OR and NONE images, but other image groups had significantly higher parallelism than OR images. Our results indicated that interpolation and SR algorithms increased OCT image resolution. However, qualitative and quantitative assessments were influenced by algorithm use. Additionally, each algorithm affected the assessments differently.

Adaptive optics assisted visualization of thickened retinal arterial wall in a patient with controlled malignant hypertension

Purpose

We aimed to visualize the retinal arterial wall thickness, assisted by noninvasive adaptive optics scanning laser ophthalmoscopy (AO-SLO).

Methods

The arterial wall thickness was measured and compared between one normal subject and one patient suffering from malignant hypertensive retinopathy.

Results

Increased arterial wall thickness was revealed with a newly developed AO-SLO system, in a retinal artery of 1-papilla diameter temporal inferior to the optic disc. The average wall thickness, with hypertension, was 18.7 μm, and the wall-to-lumen ratio was 0.44, both bigger than normal.

Conclusion

AO-SLO enabled us to evaluate the retinal wall thickness in the hypertensive patient. The arterial walls were thickened compared with normal. AO-SLO may facilitate future noninvasive study of arterial walls in human medicine.

Retinal microstructural changes in eyes with resolved branch retinal vein occlusion: an adaptive optics scanning laser ophthalmoscopy study

PURPOSE

To assess macular photoreceptor abnormalities in eyes with resolved branch retinal vein occlusion (BRVO) using adaptive optics scanning laser ophthalmoscopy (AO-SLO).

DESIGN

Prospective observational cross-sectional case series.

METHODS

After complete resolution of macular edema and retinal hemorrhage, 21 eyes (21 patients) with BRVO underwent full ophthalmologic examination and imaging with optical coherence tomography (OCT) and a prototype AO-SLO system. Cone density and spatial mosaic organization were assessed using AO-SLO images.

RESULTS

Regular parafoveal cone mosaic patterns were clearly visualized with the prototype AO-SLO imaging system in the BRVO-unaffected side. However, in the side of the retina previously affected by the BRVO, cone mosaic patterns were disorganized and dark regions missing wave-guiding cones were apparent. Additionally, retinal capillaries were dilated, no longer had a uniform caliber, and had less direct paths through the retina. In the affected side, parafoveal cone density was significantly decreased, compared with the corresponding retinal area on the unaffected side (P < .001). Furthermore, the hexagonal Voronoi domain ratio and the nearest-neighbor distances were significantly lower than in the unaffected side (P < .05). These parameters were also correlated with photoreceptor layer integrity in the parafovea.

CONCLUSIONS

After BRVO-associated retinal hemorrhage and macular edema resolved, affected parafoveal cone density decreases and the cone mosaic spatial arrangement is disrupted, becoming more irregular. These cone microstructural abnormalities may extend to parafovea in the BRVO-unaffected side.

Adaptive optics-assisted identification of preferential erythrocyte aggregate pathways in the human retinal microvasculature

Purpose

To characterize human parafoveal blood flow using adaptive optics scanning laser ophthalmoscopy (AO-SLO).

Methods

In 5 normal subjects, erythrocyte aggregate distributions were analyzed on 3 different days. Erythrocyte aggregates were described as a “dark tail” in AO-SLO. The characteristics of the pathways with dark tail flow in the parafovea were measured. Additionally, the tendency for dark tail flow before and after bifurcations was analyzed to study the blood flow in detail.

Results

Average velocity in parent vessels with dark tail flow was 1.30±0.27 mm/s. Average velocity in daughter vessels with dark tail flow was 1.12±0.25 mm/s, and the average velocity of plasma gaps in daughter vessels without dark tail flow was 0.64±0.11 mm/s. Downstream from the bifurcations, the velocity in vessels with dark tail flow was higher than that in those without it (p<0.001), and the branching angles of vessels with dark tail flow were smaller than those of vessels without it (p<0.001).

Conclusions

Images from the AO-SLO noninvasively revealed pathways with and without dark tail flow in the human parafovea. Pathways with dark tail flow in the daughter vessels generally had faster flow and smaller bifurcation angles than daughter vessels without dark tail flow. Thus, AO-SLO is an instructive tool for analyzing retinal microcirculatory hemodynamics.

Image quality improvement in adaptive optics scanning laser ophthalmoscopy assisted capillary visualization using B-spline-based elastic image registration

PURPOSE

To investigate the effect of B-spline-based elastic image registration on adaptive optics scanning laser ophthalmoscopy (AO-SLO)-assisted capillary visualization.

METHODS

AO-SLO videos were acquired from parafoveal areas in the eyes of healthy subjects and patients with various diseases. After nonlinear image registration, the image quality of capillary images constructed from AO-SLO videos using motion contrast enhancement was compared before and after B-spline-based elastic (nonlinear) image registration performed using ImageJ. For objective comparison of image quality, contrast-to-noise ratios (CNRS) for vessel images were calculated. For subjective comparison, experienced ophthalmologists ranked images on a 5-point scale.

RESULTS

All AO-SLO videos were successfully stabilized by elastic image registration. CNR was significantly higher in capillary images stabilized by elastic image registration than in those stabilized without registration. The average ratio of CNR in images with elastic image registration to CNR in images without elastic image registration was 2.10 ± 1.73, with no significant difference in the ratio between patients and healthy subjects. Improvement of image quality was also supported by expert comparison.

CONCLUSIONS

Use of B-spline-based elastic image registration in AO-SLO-assisted capillary visualization was effective for enhancing image quality both objectively and subjectively.