Direct Measurement of Optic Nerve Size with Ultra Widefield Digital Camera.
Andrew W. Arnold; Robin L. Grendhal; Richard K. Winkle; Robert W. Arnold
Alaska Children’s EYE & Strabismus
Introduction: The size of the optic nerve has important implications in pediatric ophthalmology(1), however reliable measurements with direct or indirect ophthalmoloscopy are complicated by lack of a direct reference and magnification-minification issues with refractive error.
Methods: We developed a method for efficient acquisition of fundus images with Optos California model (Optos, Dunfermline Scottland) in children as young as newborns. Refractive error and clinical diagnoses were recorded. Software allowed image zoom and direct linear measurement.
Results: 57 normal subjects had images for regression of horizontal optic nerve diameter regressed against refractive error: nerve size = 0.0002(spherical equivalent) + 1.66, r2= 0.0001. Normal subjects had horizontal diameters with mean of 1.66 ± 0.14 units. Clinical cases of optic nerve hypoplasia had diameters of 1.23 ± 0.30 units.
Discussion: Widefield imaging is optically different from conventional fundus imaging with respect to refractive error; we found independence. 96% of normal optic nerve horizontal diameters fall between 1.38 and 1.94 units.
Conclusion: Quick Ultra widefield fundus images with simple image analysis affords a practical way to quantitate optic nerve size with implications for optic nerve hypoplasia (2), amblyopia (3) and coloboma.
References: (1) HotchkissML,GreenWR.Opticnerveaplasiaandhypoplasia.J Pediatr OphthalmolStrabismus1979;16:225-40.
(2) Zeki S, GN D: Optic nerve hypoplasia in children. Br J Ophthalmol 1990, 74:300-304.
(3) Lempert P: Optic nerve hypoplasia and small eyes in presumed amblyopia. J AAPOS 2000, 4(5):258-266.