Purpose:
To evaluate if optic disc shape predisposes to the development of focal damage to the neuroretinal rim(NRR), as manifest by either a focal notch or acquired pit of the optic nerve (APON).
Methods:
A total of 79 digital optic nerve head (ONH) sequential stereophotographs (20 degree fields, 567×768 pixels) were taken from 44 subjects with normal tension glaucoma ((NTG, median age 75.5 years; range 29 to 91 years). The diagnosis of the APON/ focal thinning of the NRR was made on by slit lamp biomicroscopy. Three expert observers independently viewed the images using a standard PC and Z–screen monitor with custom software (StereoDX 2.0). Disc areas, major axis, minor disc axis, major and minor axis of least inertia, ratio of major to minor disc axis (1.0 = circular, >1.0 elliptical)were evaluated as explanatory for the presence of focal damage.
Results:
Eyes with diffuse NRR loss were classified as controls (n=48), those with local NRR notching (n=16) and those with APONs (n=13). 35 subjects has bilaterel disease and 9 were unilateral. Patient demographics are shown below. We noted a trend for the ratio of the major to minor disc axis to increase with the development of notches and APONs. However this did not reach significance. Logistic regression analysis in which the presences of a notch or APON as the dependent variables did not demostrate a statistically significant relationship with factors characterising the shape of the optic disc.
Conclusions:
Digital stereoplanimetry is a useful tool for the characterisation of optic disc shape. For the sample in this study we could not find evidence to support the hypothesis that optic disc shape influences the presence of focal neuroretinal rim damage.
Keywords: optic disc • imaging/image analysis: clinical • shape and contour