Quantitative evaluation of the optic nerve head in early glaucoma

Abstract

Aims-Progressive loss of neuroretinal rim tissue is known to occur early in glaucoma and measurement of the neuroretinal rim area is possible by magnification corrected analysis of optic disc photographs (planimetry). This study was performed to determine whether the facility to distinguish between glaucomatous and normal optic discs could be improved upon by: (a) taking into account the known relation between optic disc size and neuroretinal rim area, and (b) measuring rim area in a number of segments, in order to detect focal changes. Methods-Planimetric examination of the optic disc photographs of 88 control subjects and 51 patients with early visual field defects was performed. In the control group, multiple linear regression analysis was performed between neuroretinal rim area and optic disc area, age, sex, eye side, refraction, and keratometry. This was repeated for the whole disc and for each of twelve 30 degree segments. Normal ranges were defined by the 98% prediction intervals of the regression analysis and the sensitivity and specificity for correct identification of optic discs in the two groups determined. Results-Multiple linear regression demonstrated significant associations between the neuroretinal rim area and optic disc area and age in normal subjects. Sensitivity and specificity for glaucoma diagnosis, using the cut oV derived from the 98% prediction intervals, was 37.7% and 98.9% respectively when total neuroretinal rim area alone was considered, and 88.7% and 94.3% respectively when the 30 degree segments were included. The most frequent pattern of neuroretinal rim loss was diVuse, followed by thinning in more than one sector and then by thinning in the inferotemporal sector alone. Conclusions-This method of optic disc analysis enables the examiner to identify glaucomatous optic discs at the stage of early perimetric loss with a high degree of precision. Optic disc photography is simple, and fundus cameras are widely available. This method for glaucoma case identification may therefore be suitable for the primary care setting as well as hospital practice. (Br J Ophthalmol 1998;82:352-361) Primary open angle glaucoma is the term given to a progressive optic neuropathy, occurring in the absence of other discernible ocular or extraocular disease, and for which the major risk factors are raised intraocular pressure and older age. A functional deficit, measurable as visual field loss, is associated with the morphological changes that occur at the optic nerve head and retinal nerve fibre layer. Several clinical studies have demonstrated that these morphological changes are frequently apparent before functional loss can be detected with conventional perimetry.

Optic Disk Size and Glaucoma

“…There is consistent evidence, regardless of the measurement technique that rim area increases with increasing disk size. 21,22,24,31,48,49,79,86,110 This raises the question, as to whether large disks have more optic nerve fibers than small disks. A larger number of nerve fibers may represent a larger anatomical reserve in various optic neuropathies including glaucoma.…”

Glaucoma screening in Western Cameroon

“…Thus the whole screening is based on morphological criteria of the inspection of the optic nerve head (ONH), using criteria in accordance with the literature [6][7][8][9][10][11][12][13], and completed by measurements of the intraocular pressure (IOP). The criteria are defined in the next section.…”

Combining optical coherence tomography with visual field data to rapidly detect disease progression in glaucoma: a diagnostic accuracy study

“…[14][15][16] The optic nerve and neural rim can be examined with imaging technology to quantify the degree of structural damage; the association between image-based measurements of neural rim and RNFL loss and VF damage is well recognised [17][18][19][20][21] and the spatial relationship between the structural damage and VF loss has been established. 13,22 Imaging-based quantitative measurements have diagnostic utility [23][24][25][26][27][28][29] and numerous publications support the ability of imaging-based measurements to identify glaucoma deterioration. [30][31][32][33][34][35][36][37][38][39][40] Progressive structural change has been shown to be useful as a predictor of subsequent VF loss.…”