General Medical Information

Ophthalmoscopy

Jean Edwards Holt

The final part of a general eye examination is ophthalmoscopy. It is used to evaluate the internal structures of the eye, primarily the retina, retinal blood vessels, and optic nerve. A direct ophthalmoscope is used for this examination and provides an upright ×15 magnified image. There is great limitation of the field of view and the information obtained if the examiner is viewing through a small pupil. A 3-mm pupil gives only a 4-degree field of view, but a 7-mm pupil allows a 30-degree field of view. Therefore, routine dilation of the pupils with 0.5% or 1% tropicamide or 2.5% phenylephrine is recommended with the following exceptions: known narrow-angle glaucoma, neurologic or neurosurgical observation, and some types of intraocular lens implants after cataract surgery. In rare instances, dilation of the pupil can precipitate an attack of acute angle-closure glaucoma that was previously unsuspected. This should not be considered a contraindication. Because this form of glaucoma is rare and can be managed effectively, the benefits of improved ophthalmoscopy through dilated pupils outweigh the risks.
The examiner holds the ophthalmoscope in the right hand and uses the right eye to examine the patient’s right eye. With the pupil dilated, reflected light from the ocular fundus produces a clear red reflex when viewed through the ophthalmoscope with a +6 lens at a distance of approximately 1 foot (0.3 m). Any alteration in the red reflex indicates abnormality in one of the optical structures of the eye and is always important. The patient’s eye is then approached as closely as possible as the power of the lens in the ophthalmoscope is reduced until the optic disk comes into focus. The nerve head should be evaluated for color, sharpness of margins, and appearance of the central depressed area known as the cup. Systematic examination of the retinal vessels and background then is performed. The macular region deserves special attention for patients with vision loss.