Variability in Human Cone Topography Assessed by Adaptive Optics Scanning Laser Ophthalmoscopy.
OBJECTIVE
To assess between- and within-individual variability of macular cone topography in the eyes of young adults.


METHODS
Observational case series.


METHODS
Cone photoreceptors in 40 eyes of 20 subjects aged 19-29 years with normal maculae were imaged using a research adaptive optics scanning laser ophthalmoscope. Refractive errors ranged from -3.0 diopters (D) to 0.63 D and differed by <0.50 D in fellow eyes. Cone density was assessed on a 2-dimensional sampling grid over the central 2.4 mm × 2.4 mm. Between-individual variability was evaluated by coefficient of variation (COV). Within-individual variability was quantified by maximum difference and root mean square (RMS). Cones were cumulated over increasing eccentricity.


RESULTS
Peak densities of foveal cones are 168 162 ± 23 529 cones/mm(2) (mean ± SD) (COV = 0.14). The number of cones within the cone-dominated foveola (0.8-0.9 mm diameter) is 38 311 ± 2319 (COV = 0.06). The RMS cone density difference between fellow eyes is 6.78%, and the maximum difference is 23.6%. Mixed-model statistical analysis found no difference in the association between eccentricity and cone density in the superior/nasal (P = .8503), superior/temporal (P = .1551), inferior/nasal (P = .8609), and inferior/temporal (P = .6662) quadrants of fellow eyes.


CONCLUSIONS
New instrumentation imaged the smallest foveal cones, thus allowing accurate assignment of foveal centers and assessment of variability in macular cone density in a large sample of eyes. Though cone densities vary significantly in the fovea, the total numbers of foveolar cones are very similar both between and within subjects. Thus, the total number of foveolar cones may be an important measure of cone degeneration and loss.
Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama.
Tianjiao
T
Zhang
Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama.
Pooja
P
Godara
Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama.
Ernesto R
ER
Blanco
Department of Epidemiology, University of Alabama at Birmingham, Birmingham, Alabama.
Russell L
RL
Griffin
Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama.
Xiaolin
X
Wang
Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama.
Christine A
CA
Curcio
Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama. Electronic address: zhanghua@uab.edu.
Yuhua
Y
Zhang
D000328:Adult; D002452:Cell Count; D005260:Female; D005584:Fovea Centralis / Q000166:cytology; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D009887:Ophthalmoscopy / Q000379:methods*; D015203:Reproducibility of Results; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology*; D041623:Tomography, Optical Coherence / Q000379:methods*; D014792:Visual Acuity; D055815:Young Adult