Background and Objective
Age-related macular degeneration is one of the leading causes of vision loss in the developed world. As the disease progresses, the central part of the retina, called the macula, is compromised leading to a disruption of both structure and visual function. In this study, we investigate the disruption of macular photoreceptor cells in vivo as a function of disease stage in patients with the dry form of age-related macular degeneration AMD.
Materials and Methods
An investigational confocal Adaptive Optics Scanning Laser Ophthalmoscope (AO-SLO) was used to obtain high resolution images of the macular photoreceptor mosaic in patients previously diagnosed with AMD. Four patients were selected as representative cases, comprising each of the four clinical stages of AMD progression.
Results
AO-SLO imaging revealed slight disruption in the photoreceptor mosaic in early stage AMD due to focal drusen formation and identified several small drusen deposits that were not observed with standard clinical imaging techniques. An increase in photoreceptor disruption was visualized within the macula in direct correlation with the stage of AMD progression leading to a decrease in visual acuity. Large coalescent drusen and areas of geographic atrophy in advanced stage dry AMD exhibited a significant decrease in visible photoreceptor density. Significant decrease in photoreceptor counts (~35–50%) were observed when comparing earlier stages of AMD progression (Category I & II) to later stages of the disease (Category III & IV).
Conclusions
This study demonstrates the capabilities of adaptive optics retinal imaging to monitor disruption of individual photoreceptor cells as a function of disease progression yielding valuable diagnostic findings in early stage AMD beyond what can be learned about the health of photoreceptors using conventional retinal imaging techniques.
We characterized image quality in optical coherence angiography (OCA) en face planes of mouse cortical capillary network in terms of signal-to-noise ratio (SNR) and Weber contrast (Wc) through a novel mask-based segmentation method. The method was used to compare two adjacent B-scan processing algorithms, (1) average absolute difference (AAD) and (2) standard deviation (SD), while varying the number of lateral cross-sections acquired (also known as the gate length, N). AAD and SD are identical at N = 2 and exhibited similar image quality for N<10. However, AAD is relatively less susceptible to bulk tissue motion artifact than SD. SNR and Wc were 15% and 35% higher for AAD from N = 25 to 100. In addition data sets were acquired with two objective lenses with different magnifications to quantify the effect of lateral resolution on fine capillary detection. The lower power objective yielded a significant mean broadening of 17% in Full Width Half Maximum (FWHM) diameter. These results may guide study and device designs for OCA capillary and blood flow quantification.
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