Reviewing ocular specialty testing
Familiarize yourself with anterior and posterior testing in your practice
Electrooculography and electroretinography (EOG/ERG) are detailed posterior testing methods that can assist in diagnosis and determining progression of retinal disease processes.
Electrooculography measures corneal-retinal potential, the correlation between the front and the back of the eye. Electrodes are attached by the canthi, and small eye movements register the potential and measure the eye’s position.
EOG is used to test the retinal pigment epithelium. The Arden ratio, which is the ratio of the light peak to the dark trough, determines a normal or abnormal test result. An Arden ratio of 1.8 or greater is considered “normal,” subnormal is 1.65 to 1.80, and below 1.65 is abnormal and cause for further investigation. Diseases such as Best’s disease, retinitis pigmentosa, and Stargardt’s disease can cause an abnormal test result in electrooculography.
Electroretinography measures electrical responses of retinal cells contributing to the diagnosis of retinitis pigmentosa and other retinal degenerations. ERG consists of putting electrodes around the eyes and the skin of the eye, the patient is then exposed to light stimuli, dark adapted for 20 minutes to induce rod cell functioning, and light adapted again. The activity of the rod/cone system indicates deviations in the retinal function. By observing the A-wave and B-wave of the test, doctors can diagnose a variety of retinal disorders.
Visual evoked potential (VEP) testing is a measurement of the neurological activity of the eye’s visual system. VEP testing utilizes visual stimuli to “evoke” an electrical response from the brain. Various patterns and contrasts coupled with electrodes on the skin can be useful in the monitoring of optic neuritis in conditions such as multiple sclerosis or in cases of traumatic brain injuries (TBI).
Specialty testing is crucial in modern eyecare practice, and the role of the ophthalmic technician is integral in diagnosing, treating, and observing ocular diseases. Whether a technician is involved in specialty testing directly or merely exposed to it through working closely with the physicians, an overall concept of diagnostic testing is needed to assist in comprehensive patient care.