Funduscopy is an examination of the fundus, the back part of the eye’s interior, including the retina. It illuminates the back of the eye for examination by using a beam of light projected through an instrument called a funduscope.

Funduscopy is a valuable tool for detecting diabetic retinopathy, a common complication of diabetes. Early diagnosis and treatment of diabetic retinopathy can prevent vision loss and blindness. Funduscopy can also be used in diagnosing other eye conditions, such as glaucoma. It can be performed as part of a general physical examination or a dilated pupil examination.

The major types of funduscopy include:

• Direct funduscopy. A test that allows the physician to examine the eye magnified up to 15 times. It produces an upright (unreversed) image.
  
  
• Indirect funduscopy. A test that allows the physician to examine the eye magnified up to two to five times. It produces an inverted (reversed) image.
  
  
• Slit-lamp funduscopy. Also known as binocular funduscopy or stereo funduscopy, it allows the physician to view the eye through two eyepieces and to obtain a three-dimensional image. It can produce an inverted and reversed image with a lens held by the ophthalmologist, or an upright image using a lens placed on the front surface of the eye.

Patients who undergo funduscopy generally feel little or no discomfort, and there are no major risks associated with the test. However, because the pupils are dilated (widened) in some forms of funduscopy, patients may be advised not to drive after the procedure and to arrange for a ride home.

Funduscopy is an examination of the back part of the eye’s interior (fundus). Also known as ophthalmoscopy, it can help detect damage that is the earliest sign of diabetes in some patients. It features an instrument called a funduscope (or ophthalmoscope), which contains a mirror and lenses that are used to examine the inside of the eye. It is performed to look for damage caused by diabetic retinopathy or other eye diseases.

Using this procedure, the physician can examine the fundus, which is composed of the:

• Retina. The light-sensitive nervous tissue lining the inner eye and connected to the brain via the optic nerve. The central part of the retina that produces sharp, central vision is known as the macula.
  
  
• Optic disc. The end of the optic nerve, viewed on cross section, where it enters the eye. Because there is no retina where it enters the back of the eye, it creates a blind spot in the retina. The brain normally learns to ignore this area of the retina without vision.
  
  
• Choroid. Dark-brown vascular coat of the eye between the sclera (tough, white, fibrous outer envelope of tissue covering most of the eye) and the retina.
  
  
• Blood vessels.

Funduscopy may be performed as part of a dilated pupil exam. Regular examination of the eyes is crucial to the long-term health of people with diabetes. A person with diabetes is 25 times more likely to become blind than a person who does not have diabetes, according to the American Academy of Ophthalmology. Other tests may also be performed, such as tonometry, which measures the pressure inside the eye, and perimetry, which assesses peripheral (side) vision

There are three major types of funduscopy:

• Direct funduscopy. It allows the examiner to see the eye magnified up to 15 times and produces an upright (unreversed) image. Physicians and nurse practitioners can perform direct funduscopy. Here, the examiner is “looking at the trees, not the forest.”
  
  
• Indirect funduscopy. Allows the physician to examine the eye magnified two to five times. It produces an inverted and reversed image. This gives a more complete view of the retina, and takes more specialized skill than a direct funduscopy. As a result, it is usually performed by an ophthalmologist. Indirect funduscopy affords the physician a wide view of the fundus to identify lesions that can be seen in greater detail later. Here, the ophthalmologist is “looking at the forest, not the trees.”

  

• Slit-lamp funduscopy. Provides a magnified, three-dimensional view of the parts of the eye. Though the test is often used to look at the front part of the eye, special lenses can also be placed on the cornea to view deeper structures of the eye such as the fundus. Slit-lamp funduscopy provides a clearer view of the optic nerve (nerve that transmits signals from the eye to the brain) and the center of the fundus than indirect funduscopy. It is performed by an ophthalmologist or optometrist, often as part of a dilated pupil examination.

Funduscopy usually takes place in a physician’s office or clinic. The test requires little or no preparation on the part of patients. If the test involves eye drops that dilate (widen) the pupil, they should bring sunglasses and, as instructed by the office, may need to arrange for transportation home.

Patients should inform their physician if they:

• Are allergic to any medications
• Are taking any medications at the time of testing
• Have glaucoma (eye disease that affects the optic nerve) or a family history of the disease

In addition, certain eye problems may interfere with obtaining accurate test results. These include:

• Incomplete pupil dilation
• Cataracts (clouding of the eye’s lens or capsule)
• Cloudiness of the liquid (aqueous humor) or gel (vitreous humor) inside the eye

The way in which the test unfolds depends upon the type of funduscopy being performed:

• Direct funduscopy. Eye drops may be administered to dilate (widen) the pupil (the opening in the iris, which is the colored part of the eye) just before testing. Patients sit in a darkened room and are asked to stare straight ahead at a distant spot. A beam of light from a funduscope is projected through the pupil, allowing the physician to see the back of the eye’s interior. A clicking sound will be audible as the scope is being adjusted, and the bright light may cause the patient to see after-images.
  
  This examination takes just a few minutes. During the exam, the physician will move very close to the patient’s face. Patients should do their best to hold their eyes steady without blinking. Direct funduscopy examines the central retina.
  
  
• Slit-lamp funduscopy. Eye drops are administered to dilate the pupil just before testing. The patient remains seated at the same instrument used to examine the front part of the eye. A separate lens is held close to the eye, allowing the physician to view the fundus (back of the inner eye). This technique provides a stereoscopic view that is much wider than the view afforded by direct funduscopy.
  
  
• Indirect funduscopy. In some but not all cases, eye drops are administered to dilate the eye just prior to testing. The patient either lies down or is seated in a reclining position. The physician wears an instrument on the head that resembles a miner’s light. The physician holds open the patient’s eyelids and shines a bright light into it. A small, blunt instrument is sometimes used to apply pressure to the eye, and the patient is asked to look in various directions. This helps bring the front portion of the fundus into view.
  
  The light in this test is more intense than with direct funduscopy, so after-images are even more likely. The patient’s vision will seem dark and/or unusually colorful following the test. The test takes more time than the others (five to 10 minutes), but it also allows the physician to see the entire retina.

If the exam reveals a problem, the physician may recommend additional testing, regular monitoring, medication such as prescription eye drops, or procedures such as photocoagulation or vitrectomy.

Dilation of the eyes may impair the patient’s ability to visually focus for up to a few hours and will make the eyes very sensitive to light. Patients may be advised not to drive after the test. People should wear sunglasses when outside in the hours after testing.

There are no major risks associated with funduscopy. The bright light used may cause minor discomfort for some patients. In addition, eye drops may cause a slight stinging sensation and a medicinal taste in the mouth as medication drains from the tear ducts into the throat.

In rare cases, the eye drops can cause more substantial reactions, such as:

• Nausea or vomiting
• Dizziness
• Dryness of the mouth
• Flushing
• Sudden increase in pressure inside the eye (acute angle-closure glaucoma)

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about funduscopy:

1. Will funduscopy show if I have diabetic retinopathy?
   
   
2. Can it be used to detect glaucoma, cataracts or other eye diseases?
   
   
3. Which type of funduscopy should I have?
   
   
4. Do I need to do anything to prepare for the test?
   
   
5. Could I find the test uncomfortable, or is it painless?
   
   
6. What do my test results show?
   
   
7. What treatments will follow if the test shows a problem?
   
   
8. How often should I have this test?
   
   
9. What other eye tests might I need, and how often?
   
   
10. Is it safe for me to drive afterward, or do I need a ride?