Neuroretinal Rim Size, Shape, and Perfusion
Overview
A careful evaluation of the neuroretinal rim is critical in diagnosing early glaucoma, monitoring for glaucomatous progression, and differentiating between glaucomatous and nonglaucomatous optic neuropathy. In glaucoma, the neuroretinal rim shape is an indicator of the stage of disease and a strong indicator for glaucomatous visual field loss.
Pearls
Neuroretinal rim size:
The neuroretinal rim is one of the most important variables1 to accurately diagnose glaucoma earlier and detect progression sooner.
Similar to optic disc size and optic cup size, there is high interindividual neuroretinal rim area variability within the normal population and significant overlap between normal eyes and glaucomatous eyes.
Neuroretinal rim area is directly proportional to the optic disc area
For more accurate diagnosis, divide the optic disc into sectors.
There is preferential loss of neuroretinal rim in the inferior and superior optic disc regions in the early to moderate stages of the disease.
Rim area is greatest with no disc cupping; less with temporal flat/sloping of the optic cup, and least in eyes with circular, steep disc cupping.
Rim area and disc area correspond to optic disc size, optic fiber count, and total area of the lamina cribrosa pores.
The nerve fibers within the neuroretinal rim are retinotopically arranged.
Axons from ganglion cells close to the optic disc are arranged more centrally in the optic disc, whereas axons from cells in the retinal periphery are located at the optic nerve head margins.
Neuroretinal rim shape:
Because of the normal vertical oval shape of optic disc and the normal horizontal oval shape of the optic cup, the neuroretinal rim usually follows “ISNT rule.”
Inferior neuroretinal rim width is usually most broad, then superior neuroretinal rim, and then nasal neuroretinal rim, with the temporal neuroretinal rim usually being the thinnest sector.
Helpful in diagnosing patients with ocular hypertension or early glaucoma prior to visual field defects.
Characteristic shape is highly critical in the diagnosis of early glaucomatous optic nerve damage in patients with ocular hypertension prior to white-on-white visual field defects.
The shape of the neuroretinal rim is positively associated with the following:
The diameter of the retinal arterioles: wider in the inferior temporal (IT) arcade than in superior temporal (ST) arcade.
The visibility of the retinal nerve fiber layer bundle pattern: usually greatest visibility in the IT sector than the ST sector.
The laminar cribrosa morphology: the largest pores, and therefore the least amount of interpore connective tissue, are found in the inferior and superior regions as compared with the temporal and nasal sectors.
Glaucomatous neuroretinal rim damage:
The neuroretinal rim commonly shows preferential rim loss, depending on the stage of the disease:
