Ophthalmoscopy is an examination of the back part of the eyeball (fundus), which includes the retina, optic disc, choroid, and blood vessels.

Direct ophthalmoscopy: You will be seated in a darkened room. The examiner performs this common examination by projecting a beam of light from an ophthalmoscope, through the pupil, to view the back of the eyeball. An ophthalmoscope is an instrument about the size of a flashlight, with a light source and a disk of rotating lenses.

The magnification obtained by using the direct ophthalmoscope occurs because the eye itself is a simple magnifier. The rotating lenses incorporated in the instrument are used to correct the focusing error of the examiner or the patient being examined.

Slit-lamp ophthalmoscopy: You will be seated at the same instrument used in examining the front part of the eye. An additional lens will be held close to the eye to enable the doctor to see the interior part of the eye (the fundus). This has the advantage of a three-dimensional view in addition to the magnification of direct ophthalmoscopy. The view is much wider than that of direct ophthalmoscopy, but not as wide as indirect ophthalmoscopy.

Indirect ophthalmoscopy: You will either lie or sit in a semi-reclining position. The examiner performs this examination by holding the eye open. The examiner wears an instrument on the head resembling a miner's light. While holding the eye open and using a hand-held instrument, the examiner shines a very bright light into the eye. Some pressure may be applied to the eyeball using a small, blunt instrument, and you will be asked to look in various directions.

This examination takes between 5 and 10 minutes. The bright light will be uncomfortable, but the test is not painful. This examination requires more skill and time than the other forms of ophthalmoscopy, but has the advantage of allowing the doctor to see the entire retina.

Indirect ophthalmoscopy and slit-lamp ophthalmoscopy are performed after eye drops are placed to dilate the pupils. Direct ophthalmoscopy can be performed with or without dilation of the pupil.

The dilating drops may impair focusing of the eyes for several hours. Therefore, arrangements should be made for someone else to drive after the examination. Wearing sunglasses or tinted lenses will make the patient with dilated pupils more comfortable.

You should tell the examiner if you:

• Are allergic to any medications
• Are taking any medications
• Have glaucoma or a family history of glaucoma

Direct ophthalmoscopy: As the scope is focused, a clicking sound will be heard. The bright light shone into the eyeball may cause brief after-images to be seen.

Indirect ophthalmoscopy: The light is brighter with indirect ophthalmoscopy, so the sensation of seeing after-images may be greater. Pressure put on the eyeball by the blunt instrument may be slightly uncomfortable, but should not be painful. The fundus can usually be seen through cataracts.

If eyedrops are used, they may produce a brief stinging sensation when put in the eyes and a medicinal taste in the mouth caused by the medication draining from the tear ducts into the throat.

Ophthalmoscopy is performed as part of a routine physical or complete eye examination. It is used to detect and evaluate symptoms of retinal detachment or eye disease such as glaucoma. Ophthalmoscopy is also performed if diabetes, hypertension, or other vascular disease is suspected.

The retina, blood vessels, and the optic disc should appear normal to the examiner.

The exam can reveal eye diseases, such as cloudy vitreous, detached retina, optic nerve problems, macular degeneration, and changes caused by glaucoma. High blood pressure and many systemic diseases can also be detected.

Additional conditions under which the test may be performed:

• CMV retinitis
• Diabetes
• Hypertensive retinopathy
• Macular degeneration
• Melanoma of the eye
• Optic neuritis
• Retinal detachment

The test itself involves no risk. The dilating eye drops may rarely produce nausea, vomiting, dryness of the mouth, flushing, dizziness, or an attack of narrow-angle glaucoma. If the latter is suspected, drops generally are not used.

Since it can detect the initial stages and early effects of many serious diseases, ophthalmoscopy is a most valuable test. It is considered to be 90-95% accurate. In addition to specific eye diseases, ophthalmoscopy can detect heart and blood vessel diseases (particularly high blood pressure), brain disease, and diabetes.

Yanoff M, Duker JS, Augsburger JJ, et al. eds. Ophthalmology. 2nd ed. St. Louis, Mo: Mosby; 2004:1461-1462.

Ruamviboonsuk P, Wongcumchang N, Surawongsin P, Panyawatananukul E, Tiensuwan M. Screening for diabetic retinopathy in rural area using single-field, digital fundus images. J Med Assoc Thai. 2005 Feb;88(2):176-80.