In vivo cone imaging in age related macular degeneration by modified narrow angle Heidelberg Retina Angiograph (HRA2)

Abstract

 

Purpose

 

Currently there are no clear imaging end points in dry age related macular degeneration (AMD) and the use of many Adaptive Optics (AO) systems in the clinical setting is problematic owing to the time consuming nature of the measurements and the effects of age-related lens changes. It has previously been shown that retinal cones can be imaged in vivo using a narrow-scan angle HRA2 and that the counts are quite robust to the effects of media opacity (Anderson et al, ISIE 2014). In this exploratory study we measured cone density in patients with early AMD and compared that to previous histological and AO imaging data available in the literature.

 

Methods

 

Eight early AMD patients (mean age=74±6 years) were recruited with medium to large drusen. Inclusion criteria were: Snellen best corrected visual acuity of ≥6/9, refractive error <±6.00DS, astigmatism <1.25D and intraocular pressure <21mmHg. A modified HRA2 was used to obtain 3x3° images of the photoreceptor mosaic at four different oblique retinal locations, at 6° and 8° eccentricity from the fovea. Cones were identified and counted by image analysis using custom-designed software. The differences in cone packing density between early AMD patients and the previously established normal for location and eccentricity were explored using t-testing.

 

Results

 

Four patients had images taken at 6° and four at 8° of eccentricity. The mean cone density for all four meridians at 6° and 8° eccentricity was 7.1±0.2x10³ and 5.0±0.2x10³ cells/mm² respectively. Using unpaired t-tests, all the differences (as a function of eccentricity and meridian) were shown to be significant (p <0.01) when compared to previously reported normal data, for ages 50-65, by Song et al, IOVS, 2011 (figure 2).

 

Conclusions

 

There appears to be a reduced cone count in subjects with early AMD using the narrow scan angle HRA2. The technique seems to be capable of producing reliable images in subjects with early-to-moderate lens changes. References: RS Anderson et al. ISIE, ARVO 2014. H Song et al. Invest OphthalmolVis Sci. 2011;52:7376-7384<br /> CA Curcio et al. J Comp Neurol. 1990;292:497-523  

 

Retinal cone mosaic at 8° eccentricity using the modified HRA2

 

 

Cone density versus eccentricity plotted on graph with histology data from Curcio et al and AO data from group 2 Song et al