Emely Z. Karam

Optical coherence tomography of the retinal nerve fibre layer in mild papilloedema and pseudopapilloedema

Aims: To determine the degree to which optical coherence tomography (OCT) can distinguish differences in retinal nerve fibre layer (RNFL) thickness between eyes with mild papilloedema, pseudopapilloedema, and normal findings. Methods: 13 patients with mild papilloedema, 11 patients with congenitally crowded optic nerves, and 17 normal subjects underwent neuro-ophthalmic examination, automated visual field testing, and fundus photography. Spinal fluid pressure measurements were obtained in a subgroup of five patients with pseudopapilloedema and 11 patients with mild papilloedema. Circular OCT scans using a diameter of 3.38 mm surrounding the optic disc were performed in each eye of patients and subjects. Fundus photographs were analysed by two observers who diagnosed crowding or papilloedema and graded amounts of swelling. Findings were assessed by descriptive statistics and variance analysis. Results: RNFL thickness was greater in the superior and inferior quadrants and showed a high degree of correlation between each group of patients and subjects. A statistically significant difference was found in mean RNFL thickness between both groups of patients with optic disc swelling and normal subjects. However, there was not a statistical difference in mean nerve fibre layer thickness between patients with papilloedema and those with congenitally crowded optic nerves. Conclusions: OCT demonstrates measurable differences in nerve fibre layer thickness between normal subjects and patients with either papilloedema or pseudopapilloedema. However, OCT does not appear to differentiate between those individuals with congenitally crowded optic nerves and those with mild papilloedema caused by increased intracranial pressure.

Clinical Applications of Optical Coherence Tomography in Optic Nerve Disease

Optical coherence tomography (OCT) is a relatively new technology that provides information about the retina, optic nerve, and nerve fiber layer (NFL) differently from other instruments. Newer versions of the OCT allow better resolution, which makes it useful for management of optic nerve disease. For neuro-ophthalmology, OCT methods employed for retinal as well as glaucoma analysis are used, because some optic nerve pathologies have macular complications, but also because many retinal conditions may mimic optic nerve disease. The tomograms used are radial, linear, and circular. Radial scans are made up of linear sections through the optic nerve in a clockwise manner that may provide information regarding the diameter of the optic disc, physiologic/pathologic excavation and swelling, and the integrity of the neuroretinal rim. In addition to radial scans of the macula, linear scans can be made horizontally through both the disc and the macula, which can supply some information regarding the relationship of optic nerve head pathology to macular pathology. Circular tomograms centered at the optic disc can be made with different diameters. Each of these circular tomograms is displayed in an unwrapped manner and can be interpreted in three different ways: (1) following each clock hour, which produces 12 measurements of the nerve fiber layer; (2) by quadrants, producing four different measurements of the nerve fiber layer; and (3) as an average of the nerve fiber layer thickness of all four quadrants. These values can provide information regarding segmental nerve fiber layer thinning and swelling, as well as overall nerve fiber layer thickness.