---
title: "Understanding eye tests | Eye Health Guide"
description: "What happens at an eye exam, how long it takes, why eyes are dilated, and what OCT, pressure checks and visual field tests look for, in plain language."
url: https://eyehealthguide.org/eye-care/understanding-eye-tests/
source: Eye Health Guide
licence: "General information only. Cite the URL and the named medical reviewer."
---

Eye care guide

# Understanding eye tests

Medical reviewer [Mr Mohamed Mohyudin](https://eyehealthguide.org/reviewers/mohamed-mohyudin/)· Last recorded site review July 6, 2026

### About this review

This page inherits the site’s previous review record. A separate, current article sign-off has not yet been recorded.

[How review works](https://eyehealthguide.org/reviewers/) · [Official biography & credentials](https://mohamedmohyudin.co.uk/author/mohamed-mohyudin/)

Quick answer

A routine eye test usually takes 20 to 30 minutes and checks vision, glasses need and basic eye health. A full exam may add a pressure test for glaucoma, photographs or OCT scans of the retina, and visual field testing. Dilating drops widen the pupil so the optometrist can see the back of the eye clearly; they blur near vision for a few hours.

### On this page ⌄

1. How long an eye exam takes
2. Common tests explained
3. Why eyes are dilated
4. OCT and visual field tests
5. Frequently asked questions

## How long an eye exam takes

A standard sight test with history, vision charts and refraction often fits in 20 to 30 minutes. First visits, contact lens fittings or full dilated health checks can take 45 minutes or longer.

## Common tests explained

Each part of the exam looks for different problems.

- Vision chart: measures clarity at distance and near
- Refraction: finds your glasses or contact lens prescription
- Eye pressure (tonometry): a quick puff or touch test for glaucoma risk
- Slit-lamp exam: magnified view of the front of the eye
- Retinal exam: looking at the optic nerve and blood vessels at the back

## Why eyes are dilated

Dilating drops temporarily widen the pupil so the retina and optic nerve can be seen in detail. This helps detect glaucoma, macular disease and diabetic changes early. Side effects include light sensitivity and blurred near vision for several hours — bring sunglasses and avoid driving if unsure.

## OCT and visual field tests

OCT (optical coherence tomography) is a non-contact scan of the retina's layers, useful for macular degeneration, glaucoma and diabetic eye disease. Visual field testing maps peripheral vision and is important in glaucoma monitoring. Neither usually hurts; OCT takes seconds per eye.

## Frequently asked questions

### How long does an eye exam take?

Most routine tests take 20 to 30 minutes. A first visit or full dilated exam with OCT or visual fields can take longer.

### Why do opticians dilate your eyes?

Dilation lets them see the retina and optic nerve clearly to check for glaucoma, macular problems and diabetic changes. It temporarily blurs near vision and increases light sensitivity.

### What is an OCT eye scan?

OCT is a quick, painless scan that images the layers of the retina. It helps detect and monitor conditions such as macular degeneration, glaucoma and diabetic retinopathy.

Your next step

## Take this to your appointment

Write down what has changed, when it started, your current medicines and the questions you want answered. Take these to your eye-care appointment.

Sudden loss of sight, severe eye pain or a dark curtain across vision needs immediate assessment. Do not wait to complete a worksheet.

## Trusted sources

For general background, these organisations provide eye-health information. This list is further reading, not a record that they reviewed this article.

- [NHS — Health A to Z](https://www.nhs.uk/conditions/)
- [Moorfields Eye Hospital NHS Foundation Trust](https://www.moorfields.nhs.uk/)
- [American Academy of Ophthalmology — EyeHealth](https://www.aao.org/eye-health)
- [National Eye Institute (NIH)](https://www.nei.nih.gov/)
- [College of Optometrists — Look After Your Eyes](https://lookafteryoureyes.org/)
- [World Health Organization — Eye care, vision impairment and blindness](https://www.who.int/health-topics/blindness-and-vision-loss)