Faculty Collaboration Database

Repeatability of in vivo parafoveal cone density and spacing measurements. Optom Vis Sci 2012 May;89(5):632-43

Date

04/17/2012

Pubmed ID

22504330

Pubmed Central ID

PMC3348369

DOI

10.1097/OPX.0b013e3182540562

Scopus ID

2-s2.0-84861102023 (requires institutional sign-in at Scopus site)   123 Citations

Abstract

PURPOSE: To assess the repeatability and measurement error associated with cone density and nearest neighbor distance (NND) estimates in images of the parafoveal cone mosaic obtained with an adaptive optics scanning light ophthalmoscope (AOSLO).

METHODS: Twenty-one participants with no known ocular pathology were recruited. Four retinal locations, approximately 0.65° eccentricity from the center of fixation, were imaged 10 times in randomized order with an AOSLO. Cone coordinates in each image were identified using an automated algorithm (with or without manual correction) from which cone density and NND were calculated. Owing to naturally occurring fixational instability, the 10 images recorded from a given location did not overlap entirely. We thus analyzed each image set both before and after alignment.

RESULTS: Automated estimates of cone density on the unaligned image sets showed a coefficient of repeatability of 11,769 cones/mm(2) (17.1%). The primary reason for this variability appears to be fixational instability, as aligning the 10 images to include the exact same retinal area results in an improved repeatability of 4358 cones/mm(2) (6.4%) using completely automated cone identification software. Repeatability improved further by manually identifying cones missed by the automated algorithm, with a coefficient of repeatability of 1967 cones/mm(2) (2.7%). NND showed improved repeatability and was generally insensitive to the undersampling by the automated algorithm.

CONCLUSIONS: As our data were collected in a young, healthy population, this likely represents a best-case estimate for corresponding measurements in patients with retinal disease. Similar studies need to be carried out on other imaging systems (including those using different imaging modalities, wavefront correction technology, and/or image analysis software), as repeatability would be expected to be highly sensitive to initial image quality and the performance of cone identification algorithms. Separate studies addressing intersession repeatability and interobserver reliability are also needed.

Author List

Garrioch R, Langlo C, Dubis AM, Cooper RF, Dubra A, Carroll J

Authors

Joseph J. Carroll PhD Director, Professor in the Ophthalmology and Visual Sciences department at Medical College of Wisconsin
Robert F. Cooper Ph.D Assistant Professor in the Biomedical Engineering department at Marquette University

MESH terms used to index this publication - Major topics in bold

Adult
Cell Count
Female
Follow-Up Studies
Fovea Centralis
Humans
Male
Middle Aged
Ophthalmoscopy
Reference Values
Reproducibility of Results
Retinal Cone Photoreceptor Cells
Retinal Diseases
Young Adult