[Comparison of three optical coherence tomography devices, one time-domain and two fourier-domain, for the estimation of the retinal nerve fibre layer thickness]

Morphometric characteristics of the optical disc and thickness of retinal nerve fibre layer using Cirrus 5000 optical coherence tomography in healthy patients attending the National Institute of Ophthalmology

OBJECTIVE

To describe the morphometric characteristics and thickness of the retinal nerve fibre layer (CFNR) in healthy patients using optical coherence tomography.

METHODS

A cross-sectional and descriptive study was conducted on a total of 184 eyes of 184 people of mestizo origin enrolled after a complete ophthalmological evaluation at the National Institute of Ophthalmology, Lima-Peru. The morphometric parameters of the optic disc and thickness of the CFNR were measured by optical coherence tomography ZEISS CIRRUS™ HD-OCT Model 5000 (Carl Zeiss Inc., Dublin, CA, EE.UU). Megalopapilla was defined as: area of the optical disc greater than 2.5 mm² and area greater than the mean plus 2 standard deviations.

RESULTS

The areas obtained were: optical disc of 2.21±0.43mm², neuroretinal ring of 1.37±0.25mm², 0.84±0.48mm² cup; mean cup/disc ratio of 0.58±0.16, vertical cup/disc ratio of 0.55±0.15, and a CFNR thickness of 100.30±8.54μm. The prevalence of megalopapilla, being considered as a disc area greater than 2.5mm² and 3.07, was 24% and 4%, respectively. When comparing megalopapilla with normal discs, the area of the ring (P=.08) and thickness of CFNR (P=.73) did not show statistically significant differences.

CONCLUSION

The mean disc area was 2.21±0.43mm² with a CFNR thickness of 100.30±8.54μm. The prevalence of megalopapilla was 24% and 4%, considering a disc area greater than 2.5 mm² and 3.07 mm², respectively. These results show that the megalopapilla and normal discs are similar in terms of ring area and CFNR thickness.

Comparison of Retinal Thickness Measurements between the Topcon Algorithm and a Graph-Based Algorithm in Normal and Glaucoma Eyes

PURPOSE

To assess the correlation and agreement between the Topcon built-in algorithm and our graph-based algorithm in measuring the total and regional macular thickness for normal and glaucoma subjects.

METHODS

A total of 228 normal eyes and 93 glaucomatous eyes were enrolled in our study. All patients underwent comprehensive ophthalmic examination and Topcon 3D-OCT 2000 scan. One eye was randomly selected for each subject. The thickness of each layer and the total and regional macular thickness on an Early Treatment of Diabetic Retinopathy Study (ETDRS) chart were measured using the Topcon algorithm and our three-dimensional graph-based algorithm. Correlation and agreement analyses between these two algorithms were performed.

RESULTS

Our graph search algorithm exhibited a strong correlation with Topcon algorithm. The macular GCC thickness values for normal and glaucoma subjects ranged from 0.86 to 0.91 and from 0.78 to 0.90, and the regional macular thickness values ranged from 0.79 to 0.96 and 0.70 to 0.95, respectively. Small differences were observed between the Topcon algorithm and our graph-based algorithm. The span of 95% limits of agreement of macular GCC thickness was less than 28 μm in both normal and glaucoma subjects, respectively. These limits of total and regional macular thickness were 15.5 μm and 23.1 μm for normal subjects and 29.1 μm and 46.4 μm for glaucoma subjects, respectively.

CONCLUSION

Our graph-based algorithm exhibited a high degree of agreement with the Topcon algorithm with respect to thickness measurements in normal and glaucoma subjects. Moreover, our graph-based algorithm can segment the retina into more layers than the Topcon algorithm does.