What Does a Dilated Fundus Exam Show?

You’re leaving your eye doctor’s office. The light sensitivity is unbearable. Your only reprieve is to wear those dreaded disposable sunglasses they gave you. Is this pupil dilation really necessary? Can’t an eye exam show sufficient detail without this torture?

Key takeaways:
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    Although the effects of having your pupils dilated are not pleasant, a dilated fundus exam is a very important part of having your eyes checked.
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    The inner structures of the eye, including the retina, macula, and optic nerve, are not adequately visualized without pupil dilation.
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    In order to properly screen for diseases like glaucoma, macular degeneration, and retinal detachment, a dilated fundus exam is necessary.

What Is a dilated fundus exam?

The term dilated fundus exam describes a procedure that’s done as part of an eye examination.

Dilation refers to the use of eye drops to open up the pupils. By pharmacologically enlarging your pupil size, the eye doctor can get a better view into your eyes. Normal pupil size is too small to allow for a sufficient look at all the structures inside the eyes.

The fundus is the interior surface of the eye, including the retina, macula, and optic nerve. These structures are difficult to visualize without pupil dilation.

What structures are visualized in a dilated fundus exam?

Crystalline lens.The crystalline lens is the clear lens located behind the iris in the eye. Early in life, the crystalline lens enables you to focus on nearby objects. With age, the crystalline lens loses its flexibility, making it more difficult to see things up close.

Vitreous. The vitreous is the clear jelly-like fluid that fills the inside of the eyeball.

Retina. The retina is the tissue that lines the back wall inside the eye. This is where light-sensing rods and cones are found. This layer of cells detects light and transmits these signals to the brain via the optic nerve. If the eye were a camera, the retina would serve as the film.

Macula. The macula describes a distinct central portion of the retina. Although small, the macula serves a very important role. It provides clear and detailed central vision. Whenever we look at something, we’re aligning our macula to that target. The macula is densely packed with cones, providing sharp vision.

Optic nerve. The optic nerve is a cable that transmits signals from the retina to the brain to allow for vision.

What diseases does a dilated fundus exam show?

Crystalline lens disorders. The crystalline lens, often referred to as the lens, is where cataracts develop. Cataracts are a clouding of the lens that develops with age, causing increasing glare and a decline in the clarity of vision. There are various types of cataracts, which progress at different rates. One may develop a single type of cataract, or a combination of the various types. Once cataracts are having a significant impact on vision, surgical intervention is recommended.

Vitreous disorders. The vitreous can develop floaters, which look like spots, threads, squiggles, or cobwebs in one’s vision. Floaters can be a harmless nuisance, or a symptom of a more serious eye condition. The appearance of new floaters warrants a dilated fundus exam.

Retinal diseases. Many different diseases can affect the retina. Among these are:

  • Diabetic retinopathy.
  • Hypertensive retinopathy.
  • Retinal vein occlusion.
  • Retinal artery occlusion.
  • Retinal tear, hole, or detachment.
  • Retinitis pigmentosa.

Many of these conditions are treatable.

Macular diseases. Many different diseases can affect the macula. Among these are:

  • Macular degeneration (dry or wet).
  • Diabetic retinopathy.
  • Macular pucker.
  • Macular hole.
  • Macular edema.

Many of these conditions are treatable.

Optic nerve diseases

The most common group of diseases that affects the optic nerve is glaucoma. Glaucoma is often (but not always) associated with increased eye pressure. In glaucoma, the optic nerve shows changes in its cup size. The cup is the central portion of the optic nerve, and it is generally quite small relative to the nerve’s overall size. When the cup is relatively large, the suspicion of glaucoma increases. There are other tests that are used to help make the diagnosis. Glaucoma is treatable, though any existing vision loss is not reversible. The earlier it’s caught, the better.

An eye check-up is not complete without a dilated fundus exam. Dilation opens up the pupils, enabling an eye doctor to take a better look at all the structures inside the eye, including the lens, vitreous, retina, macula, and optic nerve.

Although a doctor can view these tissues without dilating the pupils, their view is very limited through a small opening.

Many diseases can impact these tissues, so it’s important that your eye doctor gets a thorough look at them.

Thankfully, it’s not too often that pupil dilation is required. A dilated fundus exam is commonly recommended to be done annually, though this varies depending on the patient’s ocular and family history. Ultimately, you’ll want to follow your doctor’s recommendation for your eyes specifically.


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