Abstract
Purpose: :
To investigate the optic-nerve disc size and its distribution amongst normal Japanese subjects with Heidelberg Retinal Tomography (HRT-II).
Methods: :
Total 547 normal subjects (male:female =221:326, mean age 48.7±14.4 years old) who visited Glaucoma Clinic in Kyoto Prefectural University of Medicine from March 2005 to September 2007 were enrolled. All subjects were diagnosed as normal by glaucoma specialists, after kerato-, refractometry, frequency doubling perimetry (N-20 program). HRT-II measurement was performed in clinical setting and optic-nerve disc area and rim area were calculated. Additional inclusion criteria were bilateral phakic eyes, refractive error within ±5.0 diopter. Optic-nerve disc / rim sizes were classified as follows; normal (1.68-2.82 / 1.20-1.78 mm2), small (<1.68 / 1.20 mm2), or large (>2.82 / 1.78 mm2), using the optic-nerve disc / rim area referring to the normal score of HRT-II, respectively.
Results: :
Right and left mean optic-nerve disc area / rim area in normal Japanese subjects was 1.91±0.45 / 1.42±0.29 mm2 and 1.88±0.46 / 1.40±0.31 mm2, respectively. There was no significant difference in disc or rim area between right and left, and between male and female . There was a good correlation between the disc and rim area (R2=0.49; male, 0.48; female). Forty-five percent of the subjects had normal optic disc size in both eyes, while 50% had a small disc in either right or left eye. There was no significant correlation between age and optic-nerve disc area. As for the rim area, 48% of the subjects had normal rim area in both eyes, while 36% had a small area in either eye. Considering the combination of both disc and rim area, 25% of the subjects showed out of the normal range in either eye.
Conclusions: :
In normal Japanese subjects, the incidence of small optic-nerve discs in at least one eye was 50%. This study proved that racial differences should be taken consideration when analyzing the optic disc morphology.
Keywords: optic disc • imaging/image analysis: clinical