Measurement of the optic disc size has an important bearing on the evaluation of optic nerve diseases and anomalies. Accurate assessment of glaucomatous discs is very much dependent on the clinical judgment of the disc size, because the neuroretinal rim area is directly related to the disc area. The size of the disc may also be related to susceptibility to glaucoma. In the Blue Mountains Eye Study, larger optic disc size was found in patients with glaucoma.
1 Similarly, the Reykjavik Eye Study also reported larger disc size in patients with glaucoma.
2 In contrast, nonarteritic anterior ischemic optic neuropathy
3 and optic disc drusen
4 are more frequently found in small optic discs. In highly myopic eyes (< −8 D), the optic disc was found to be abnormally large whereas in highly hyperopic eyes it was abnormally small.
5 6 Of note, in eyes with moderate refractive error (between −8 and +4 D), it has been suggested that the optic disc size is independent of refractive error.
6 7 In a hospital-based study by Jonas
6 on Caucasian eyes, it was concluded that optic disc size depends on refractive error only when it is beyond −8 D in myopic eyes and +4 D in hyperopic eyes. A recent population-based study on Chinese eyes, the Beijing Eye Study, confirmed the same conclusion, suggesting that the disc size is independent of refractive error within the range of −8 to +4 D.
7 Nevertheless, there are other studies reporting that the optic disc size increased with myopia.
8 9 The Rotterdam Study showed that for each diopter of increase toward myopia, the disc area increased by 1.6%.
8 Measurements of optic disc size in previous studies were based on a fundus photograph. Planimetry, however, is limited by the fact that it is subjective and variable between observers. With the availability of the two modern optic disc imaging devices—the confocal scanning laser ophthalmoscope and the optical coherence tomograph—high reproducibility for optic disc measurements has been demonstrated.
10 11 12 13 14 In this study, the relationships between the optic disc size and axial length/refractive error were examined with the HRT 3 and the StratusOCT. Optic disc parameters measured by these two instruments were also compared.