The Eye Care Advocate

Dilated Fundus Examination (Dilated Eye Examination)

Apr 10, 2026

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A dilated fundus examination involves using eye drops to enlarge the pupil, allowing the optometrist an unobstructed, wide-angle view of the internal structures at the back of the eye.

Linguistic Context:
Type: Noun. UK Usage: Spelt “Dilated Fundus Examination.” Often referred to as “getting your eyes dilated.”

A dilated fundus examination is a crucial diagnostic procedure for fully evaluating the health of the posterior segment (back) of the eye. By instilling mydriatic eye drops, typically tropicamide, the optometrist paralyses the iris sphincter muscle, causing the pupil to widen significantly.

This bypasses the eye’s natural reflex to constrict under bright lights. A dilated pupil provides the practitioner with an expanded field of view, allowing for a thorough, 3D inspection of the peripheral retina, the macula, and the optic nerve head using a binocular indirect ophthalmoscope or a slit-lamp biomicroscope.

This procedure is clinically essential for detecting peripheral retinal tears, diabetic retinoscopy, or evaluated other causes of reduced vision, although patients will experience temporary blurred near vision and increased sensitivity to light afterwards.

Frequently Asked Questions About the Dilated Fundus Examination

What is a dilated fundus exam and why is it necessary?

A dilated fundus examination is a procedure where your optometrist uses special eye drops to widen your pupils. This is done to get a clear, unobstructed view of the fundus (the back of the eye).

While a standard test looks through a small “keyhole,” dilation opens the “door,” allowing the clinician to thoroughly inspect the retina, optic nerve, and blood vessels for early signs of disease like retinal tears, tumours, or diabetic changes that might be hidden in the less easy to examine areas.

Why do the eye drops make my vision so blurry and sensitive to light?

The drops work by temporarily relaxing the muscles that constrict your pupil (make your pupil small) and those that help you focus. Because your pupil is stuck “wide open,” your eye is flooded with too much light, causing glare and photophobia (sensitivity to light).

Simultaneously, because the focusing muscle (the ciliary muscle) is relaxed, you lose the ability to see things clearly up close. This is perfectly normal and shows the drops are working effectively to allow a thorough clinical check.

How long do the effects last and can I drive afterwards?

For most people, the effects of the drops last between 4 to 6 hours, though some people may remain slightly dilated for up to 24 hours.

You are strongly advised not to drive until your vision has returned to normal and the glare has subsided. In the UK, the College of Optometrists notes that your legal vision for driving is likely compromised during this time.

It is always a good idea to bring sunglasses to your appointment to help with the light sensitivity on the way home.

What are the primary mydriatic agents used in the UK and what are their mechanisms?

The most common agent is Tropicamide (0.5% or 1.0%), an antimuscarinic that works by blocking the parasympathetic receptors in the sphincter pupillae muscle, causing it to relax.

Clinicians often use Phenylephrine (2.5%) in combination; this is a sympathomimetic that stimulates the dilator pupillae muscle. Using both allows for maximum mydriasis, especially in patients with dark irides or those who are difficult to dilate.

How do you screen a patient for the risk of acute angle-closure before dilating?

Before instilling drops, you must perform gonioscopy, or a Van Herick assessment at the slit lamp to estimate the depth of the anterior chamber angle. If the peripheral anterior chamber depth is less than 1/4 of the corneal thickness (Grade 2 or less), there is a significant risk that dilating the eye could trigger an acute angle-closure glaucoma attack by physically “bunching up” the iris into the drainage angle.

You should also check for a history of narrow angles or previous episodes of ocular pain in dim light.

Medical Disclaimer: This glossary entry is intended for informational and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. If you are experiencing changes in your vision or ocular discomfort, please consult a qualified optometrist or your primary care provider immediately.

UK Authority Resources & Clinical Guidelines:
NHS England | NICE Guidelines | The College of Optometrists | Association of Optometrists (AOP) | General Optical Council (GOC)