A comprehensive eye test is a routine, non-invasive appointment designed to achieve two goals. The first is to determine if you need corrective lenses or if your current prescription requires an update to achieve the clearest possible sight. The second involves a thorough check of the internal and external health of your eyes to screen for potential diseases that often develop without noticeable symptoms.
Initial Functional Tests
The eye examination begins with a conversation about your medical and personal history. This helps the doctor understand any risk factors you may have, covering your general health, current medications, family history of eye diseases like glaucoma, and any visual symptoms you may be experiencing.
Next, a visual acuity test measures how clearly you see, typically involving reading letters off a chart twenty feet away. This test establishes your baseline vision clarity, often expressed as a fraction like 20/20, indicating normal vision. The clarity of your vision is initially checked both with and without your current corrective lenses, if applicable.
The doctor also assesses how well your eyes work together as a synchronized pair. This involves tests of eye muscle coordination, where you follow a moving target to check for smooth and accurate tracking. A preliminary check of your peripheral vision helps detect potential blind spots that could signal issues with the optic nerve or other parts of the visual pathway.
Refining the Prescription
Following the initial checks, the process moves to determining the precise lens power needed to correct any refractive error. Refraction is the physical process where light bends as it passes through the cornea and lens to focus an image onto the retina. If the eye’s shape is irregular, the light focuses incorrectly, resulting in conditions like nearsightedness, farsightedness, or astigmatism.
The doctor often starts with an objective measurement, using an automated device that shines light into the eye to estimate the required correction. This estimate then leads to the subjective refinement phase, the part of the exam where you sit behind the large, multi-lensed instrument called a phoropter. This device allows the doctor to quickly switch between different corrective lenses while asking, “Which is clearer, lens one or lens two?”.
By asking you to compare minute changes in clarity, the doctor fine-tunes the prescription.
Prescription Components
The final prescription contains three main components for each eye: the sphere, which corrects nearsightedness or farsightedness; the cylinder, which corrects astigmatism; and the axis, which indicates the orientation of the astigmatism correction.
Internal Eye Health Check
A significant part of the exam focuses on screening for diseases by examining both the front and back structures of the eye. The doctor uses a specialized microscope, called a slit lamp, to get a magnified view of the eyelids, cornea, iris, and lens, checking for issues like dry eye, inflammation, or the early formation of cataracts.
Another procedure is tonometry, which measures the intraocular pressure (IOP) as a screening test for glaucoma. This pressure is caused by the fluid inside the eye and is measured either with a gentle puff of air against the cornea or by momentarily touching the anesthetized eye surface with a small sensor. Normal eye pressure ranges between 10 and 21 mm Hg.
To inspect the retina and optic nerve, the doctor may use special eye drops to temporarily widen the pupils (dilation). This provides a much wider view of the internal back section of the eye, which is especially important for detecting conditions like diabetic retinopathy, macular degeneration, or signs of glaucoma damage. While the drops cause temporary light sensitivity and blurred near vision, dilation is crucial for identifying diseases in their earliest, most treatable stages.
Reviewing Results and Next Steps
Once all measurements and health assessments are complete, the doctor reviews the findings with you. This summary covers the clarity of your vision, any refractive errors found, and the overall health of your eyes, including the results of the glaucoma screening and the retinal check.
If a change in vision correction is required, the doctor provides the final prescription. They also discuss the recommended frequency for your next eye test, which is often annual or biennial, depending on your age and risk factors. If signs of an eye disease were detected, the doctor will outline the next steps, such as a referral to a specialist or scheduling follow-up testing.