The Apaeros™ Retinal Imaging System generates images that allows the user to identify individual photoreceptors. Through third party software, Apaeros™ enables the operator to measure various properties of retinal cone physiology.

Images of cone photoreceptors demonstrating increase in cone size from near fovea (left) moving temporally out.

Since Apaeros™ can image these attributes, the system has enabled various investigative studies, specifically:

• Increasing severity of Diabetic Retinopathy associated with decrease in cone regularity
• Diabetic Macular Edema associated with cone mosaic changes, cone reflectance and decreased regularity of cone spacing ​
• Photoreceptor disruption in Diabetic Macular Ischemia

The Apaeros™ AOSLO has been used as part of a study to characterize hard retinal drusen using both confocal and multiply scattered light imaging techniques. The study benefited from AO imaging because the increase in lateral resulotion allowed…”distinction between lesions of difference size and shape, which could potentially be related to lesion growth.”⁵

Multiply-Scattered Light Images (top) and Confocal images (bottom) showing small hard drusen of varying sizes and appearance (round, oval, lobular).⁵

Apaeros™ offers the capability to identify micro aneurysms (MA) which are undetectable by other retinal imaging modalities.² Operators can examine vascular retinal planes in vivo with cell-scale resolution. This may enable researchers to explore retinal pathology developments, effects on visual acuity, and response to treatment.

From the listed capabilities above, Apaeros™ has enabled various investigative studies. The results of these studies have shown:

• MA wall hyper-reflectivity on AOSLO images is significantly associated with larger MA size and the presence of retinal inner layer disorganization.
• The presence of a MA lumen clot correlates with larger MA size, but not with neural retinal changes on Spectral Domain Optical Coherence Tomography (SDOCT)
• For MA’s located within 500 µm of the foveal center, the presence of wall hyper reflectivity is associated with worse VA, even after adjusting for MA size or inner layer disorganization.²

With the use of Computational Fluid Dynamics (CFD) analysis to estimate the perfusion parameters through MA structural information obtained with Apaeros, a third party flow solver was used to simulate steady-state and time-dependent fluid flow. These findings suggest that morphology and CFD estimation of perfusion parameters may be useful tools for determining the likelihood of clot presence in individual diabetic MAs.⁸

Three MAs imaged by AOSLO superimposed on a digital fundus photograph from an eye with diabetic retinopathy.

The hypothesis that deep capillary plexus (DCP) ischemia is associated with abnormalities of cone photoreceptor layer in DMI was confirmed, using the Apaeros™ AOSLO. It was found that areas of photoreceptor abnormalities found in AOSLO images corresponded to abnormalities of the photoreceptor lines on SD-OCT scans in some eyes, while these photoreceptor changes in AOSLO images were not detectable on OCT scans in others.³

AOSLO montage stitched from 2˚ x 2˚ images with location of B-scans (yellow dotted lines) and enlarged inset (blue box). Inset: 1˚ x 1˚ AOSLO image from montage.³

Bright hyperreflective lesions on AOSLO throughout the course of multiple evanescent white dot syndrome (MEWDS) could be correlated to the hyperreflective dots of foveal granularity on infrared imaging. During the acute phase of MEWDS, extrafoveal hyperreflective dots were also visible on AOSLO and infrared and were associated with accumulations of hyperreflective material above the retinal pigment epithelium on spectral domain optical coherence tomography.

Infrared (A), contrast enhanced IR (B), and AOSLO (C) images correlating foveal granularity on IR with Jampol dots on AO in the eye of a patient, marked with white arrowheads in (B and C).

Apaeros™ also has the added capability to obtain data which can be used to measure small-vessel blood flow. Through a combination of imaging, instrument optimization and third-party post-processing software, quantitative measurements can be obtained.

​Method 1:

While stopping the horizontal scan over a blood vessel, blood velocity can be measured by tracking erythrocytes moving across a scanning line. The steeper the slope, the slower the erythrocyte. This capability has allowed researchers to produce a blood velocity profile for retinal vessels.^{4, 7}

Slope is inversely proportional to velocity.

​Method 2:

Spatially shifted raster scan. By scanning two separate beams over the area of interest and spatially shifting the beams by a known amount, the velocity of individual erythrocytes can be directly measured.⁶

Apaeros™ also has the added capability to obtain data which can be used to visualize small-vessel blood flow. Through a combination of imaging and Boston Micromachines post-processing software, qualitative measurements can be observed.

Using the standard deviation of a series of images reveals features that are otherwise not detectable using singular images. With this technique, small vessel blood flow detection is enhanced.

Apaeros™ also enables multiply scattered light imaging through the use of variable sized and placed apertures. By varying aperture size and location, a tradeoff can be made between resolution and contrast, enabling enhancement of different types of features. Below is a demonstration of imaging a micro aneurysm and surrounding vasculature with the different imaging modes of the Apaeros™ Retinal Imaging System.

Microaneurysms

Optic Nerve Images

Using the standard deviation of a series of images reveals features that are otherwise not detectable using singular images.  With this technique, small vessel blood flow detection is enhanced.

Standard Deviation calculation of a series of images enables visualization of blood flow

Improves detection of blood flow through small vessels

In addition to imaging modality tools, the Apaeros™ Retinal Imaging System has implemented usability enhancements such as a programmable fixation target, image stabilization, on-the-fly dewarping, retinal stimulation, dynamic pupil detection, and the use of an integrated database for image capture storage. Other custom options are available.

REFERENCES:

1. Changes in Cone Density, Reflectivity and Regularity Assessed by AOSLO in Diabetic Retinopathy. J Lammer, A Ahmed, S Prager, M Cheney, SA Burns, PS Silva, LP Aiello, JK Sun, Beetham Eye Institute, Joslin Diabetes Center
2. Structural Characteristics of Microaneurysms on AOSLO and Surrounding Neural Retinal Pathology in Diabetes. JK Sun, PS Silva, SA Burns, LP Aiello, Joslin Diabetes Center, Department of Ophthalmology, Harvard Medical School
3. Adaptive Optics Reveals Photoreceptor Disruption in Diabetic Macular Ischemia. PL Nesper, F Scarinci, JM Simonett, AA Fawzi, Department of Ophthalmology, Northwestern University, Feinberg School of Medicine
4. Noninvasive Measurements and Analysis of Blood Velocity Profiles in Human Retinal Vessels. Zhangyi Zhong et al IOVS, June 2011, Vol. 52, No. 7
5. Multimodal imaging of small hard retinal drusen in young healthy adults. Pedersen HR, et al. Br J Ophthalmol 2018;102:146–152.
6. Rapid high resolution imaging with a dual-channel scanning technique. A de Castro, G Huang, L Sawides, T Luo, SA Burns, Opt. Lett. 41, 1881-1884 (2016)
7. Retinal Blood Velocity and Flow in Early Diabetes and Diabetic Retinopathy Using Adaptive Optics Scanning Laser Ophthalmoscopy. Palochak, C.M.A., et al., J Clin Med, 2019. 8(8).
8. Estimation of Diabetic Retinal Microaneurysm Perfusion Parameters Based on Computational Fluid Dynamics Modeling of AOSLO. Bernabeu, M.O., et al., Front Physiol, 2018.
9. Visualization of Photoreceptors in Birdshot Chorioretinopathy Using AOSLO: A Pilot Study. Khanna, S., et al., Ocul Immunol Inflamm, 2017. 25(5): p. 610-620.
10. AOSLO and Multimodal Imaging of Peau D’Orange in Pseudoxanthoma Elasticum. Onishi, A.C., P.L. Nesper, and A.A. Fawzi, Ophthalmic Surg Lasers Imaging Retina, 2017. 48(5): p. 436-440.
11. Characterization and Correlation of “Jampol Dots” on Adaptive Optics with Foveal Granularity on Conventional Fundus Imaging. Onishi, A.C., et al., Retina, 2019. 39(2): p. 235-246.aging