Abstract
Abstract: :
Objective: To correlate measures of the retinal nerve fiber layer with disc diameter, using scanning laser polarimetry (GDx). Patients and Methods: GDx was performed in 33 eyes of 17 patients presenting with a papillary hypoplasia, incidentally discovered during routine fundoscopic examination. For each eye, the thickness of the RNFL was measured within a 10–pixels–wide band located concentrically with the disc margin at 1.7–disc diameters. The circular band was adjusted for disc size. The cross sectional area of the nerve fiber layer and its four 90 degree quadrants was calculated. Each patient underwent a complete ophthalmologic examination and visual field testing. Results: Patients’ mean age ± S.D. was 44.8 ± 12.6 years. Best corrected visual acuity was 25/25 in 26 eyes, 20/25 in 6 eyes and 10/25 in the remaining eye. Optic disc size ranged from 1mmto 2.13 mm. Disc size was positively correlated with the cross sectional area of RNFL (p<0.05). Twenty–two eyes, whose optic nerve size ranged between 1.01 and 1.95 mm, showed a reduced RNFL thickness (between 0.39 and 0.529 mm). However, 9 eyes with a small optic disc showed normal RNFL thickness (0.538–0.607 mm). In contrats, one eye with normal sized disc ( 2.17 mm2), presented with a reduced number of axons (0.527 mm). Discussion: The diagnosis of optic nerve hypoplasia, can be difficult on routine clinical examination. Diagnostic clues include subnormal diameter of the optic nerve head as well as a deficiency of retinal ganglion cells and optic nerve axons. However, few observations of disc hypoplasia providing a quantitative assessment of nerve fiber layer were reported, and, to our knowledge, none were based on healthy subjects. Using the GDx, we were able to quantify non–invasively the nerve fiber layer. We found that, indeed, as a rule, hypoplastic optic disc contained a reduced number of axons. However, interestingly, some small discs contained a high amount of axons. Conclusion: Small optic disc size is not consistently associated with a subnormal amount of optic nerve axons. Our observation emphasize the importance diagnostic of quantifying the neurofiber layer and to distinguish normal and hypoplastic optic nerve.
Keywords: imaging/image analysis: clinical • neuro–ophthalmology: optic nerve • nerve fiber layer