ELECTRORETINOGRAPHY IN GLAUCOMA DIAGNOSIS
Abstract: Glaucoma is a progressive optic neuropathy, and structural damage to the optic nerve is directly responsible for loss of vision. The importance of structure and function in glaucoma is relevant for diagnostic and prognostic purposes. In addition to clinical examination and pressure monitoring, several diagnostic modalities may be used to gather information on the relative health of the eye. For instance, fundus photographs are used to observe and monitor the optic nerve (for analysis of structure), while visual field testing provides insight into the functional losses a patient may be experiencing due to his or her glaucoma. Both tests provide important pieces of information, despite their output and interpretation being highly subjective. In recent years, optical coherence tomography (OCT) has become an important tool for assessing glaucoma. Studies indicate that loss of ganglion cells at the optic nerve may be observable on OCT before functional vision loss is demonstrated on visual fields. Another diagnostic modality, the electroretinogram (ERG), has great utility for detecting the earliest signals of glaucoma, even before they are visible on OCT. Electroretinography is a minimally invasive technique that provides a direct, objective assessment of retinal function. The pattern reversal ERG (PERG) and the photopic negative response (PhNR) of the cone-driven full-field provide objective measures of retinal ganglion cell function and are all sensitive to glaucomatous damage. Recent studies demonstrate that a reduced PERG amplitude is predictive of subsequent visual field conversion (from normal to glaucomatous) and an increased rate of progressive retinal nerve fiber layer thinning in suspect eyes, indicating a potential role for PERG in risk stratification. Converging evidence indicates that some portion of PERG and PhNR abnormality represents a reversible aspect of dysfunction in glaucoma. This study evaluates the characteristics of PERG in patients with suspected glaucoma.