Updated by Sefy Paulose, M.D., March, 2022

From the National Eye Institute (NEI): The Difference between Screening and Comprehensive Dilated Eye Exams in Detecting Glaucoma

The U.S. Preventive Services Task Force released its final recommendation statement on screening for open-angle glaucoma. The task force found that there was not enough evidence to determine the accuracy and effectiveness of glaucoma screening in primary care settings for adults who do not have vision problems. Based on this lack of clear evidence, the task force could not make a recommendation for or against screening adults for glaucoma at this time (July 2013).

Statement from NEI

Statement by Dr. James Tsai, chair of the Glaucoma Subcommittee for the National Eye Institute’s National Eye Health Education Program: “While the task force concluded that there was insufficient evidence to prove that widespread glaucoma screening reduces blindness risk or improves quality of life, this recommendation does not mean that comprehensive dilated eye examinations are not important for preventing vision loss among Americans.”

More than 3 million Americans are living with glaucoma, Nearly 2 percent of Americans over age 40 (2.7 million in total) have open-angle glaucoma, a leading cause of blindness that has no early warning signs. However, early diagnosis and treatment can prevent vision loss.

Glaucoma screening is a method for assessing an entire population for glaucoma, including those without visual symptoms and those who are not at higher risk for developing glaucoma. In addition, screening usually detects only one risk factor for developing glaucoma: elevated eye pressure. However, because of individual differences in normal eye pressure and the various forms of the disease, this method by itself is not sufficient for an accurate diagnosis of glaucoma.

Dilated Eye Exams Are Important for Prevention of Vision Loss

By contrast, a comprehensive dilated exam looks at the back of the eye to detect subtle changes of the optic nerve in patients without any visual symptoms, thereby potentially leading to early detection of the disease.

Dilated eye exams are especially recommended every one to two years for people who are at higher risk for glaucoma, including African Americans age 40 and older, everyone over age 60 (especially Mexican Americans), and those with a family history of glaucoma. The task force found that early treatment for glaucoma is effective in keeping visual field defects from getting worse and this is very important for preserving vision.

What Will Happen at My Eye Appointment?

Because glaucoma can begin to develop without noticeable symptoms, the best way to protect your sight from glaucoma is to have regular comprehensive eye examinations to assess your eye pressure, optic nerve health, thinning of the cornea, and other signs of potential problems. An ophthalmologist or optometrist diagnoses glaucoma by doing a comprehensive medical eye examination, which should include all of the following components:

A Health and Medication History

  • Your overall heath and that of your immediate family
  • The medications you are taking (prescription and over-the-counter)
  • Questions about high blood pressure (hypertension), diabetes, smoking, and sun exposure

A Vision History

  • How well you can see at present, including any recent changes in your vision
  • Eye diseases that you or your family members have had, including macular degeneration and glaucoma
  • Previous eye treatments, surgeries, or injuries
  • The date of your last eye examination

Visual Acuity Testing

a phoropter

  • Distance and near vision acuity tests to determine the sharpness or clarity of your reading and distance vision
  • Testing your vision with different lenses (sometimes contained in a machine called a phoropter), pictured at right) to determine if your vision can be improved or corrected with regular glasses or contact lenses. This can indirectly help your doctor determine the size of your eye to determine whether you are at risk for particular types of glaucoma.

Basic Visual Field Testing

  • This test is done to determine how much side (or peripheral) vision you have and how much surrounding area you can see.
  • The most common type of visual field test in a regular eye exam is called a confrontation field test. This test measures only the outer edge of the visual field and will not reveal changes in early glaucoma. See Perimetry (below) to learn about more detailed and precise visual field testing for glaucoma.

An Eye Health Evaluation

  • A pen light is used to assess for an relative afferent pupillary defect, which can indirectly help your doctor determine if there is a nerve dysfunction in one eye as compared to the other eye
  • A tonometer, machine used to check pressure, is used to assess the amount of aqueous humor or pressure within your eyes. There are various ways and instruments to measure the pressure inside your eyes including a machine that ejects a puff of air, a pen-like probe that taps the surface of your eye, or a tool on the slitlamp itself that taps the surface of your eye. Your doctor might also refer to this pressure as intraocular (“within the eye”) pressure, or IOP.
  • A special microscope, called a slit lamp, is used to examine the anterior segment of the eye (front third of the eyeball), including the cornea, pupil, iris, lens, and aqueous drainage structures. If there is concern for a blocked aqueous drainage system, your doctor may
  • A dilated eye (or fundus) examination that can be achieved with the use of special lenses will allow your doctor to see inside your eye and examine the retina and optic nerve. Your doctor might choose to use eye drops to see the retina and optic nerve more clearly.

Additional Tests for Glaucoma

If your eye doctor suspects that you may have glaucoma, you will need to undergo additional testing that can help your doctor make a more definitive diagnosis of glaucoma:


  • Examining the drainage system of the eye is an important aspect of the assessment for glaucoma as decreased drainage of the fluid (aqueous humor) can increase eye pressure. This drainage system, or drainage angle, is formed between your cornea and iris. As it is located around a “corner” of your cornea, the doctor will not be able to see this structure by looking directly into your eye.
  • In order to view the drainage system of the eye, a mirrored contact lens test called a gonioscopy must be done. To do this exam, the doctor will numb the surface of your eye with an anesthetic drop. Then a lens, called a gonioscope, is placed on the surface of your eye like a large contact lens. The doctor will have you look straight ahead, then use the slit lamp to look through the lens and assesses the angle.


  • This test uses a probe that emits an ultrasonic wave to measure the thickness of your cornea. Thicker than normal corneas can give IOP readings that are inaccurately high, while thinner than normal corneas can give IOP readings that are inaccurately low.
  • To measure your corneal thickness, the doctor will numb the surface of your eye with an anesthetic drop. Then will have you look straight and touch the tip of the pachymeter probe to the surface of your cornea. The probe emits a painless ultrasound wave that measures your corneal thickness.


  • As glaucoma progresses, the optic nerve thins. This is able to be assessed by your doctor subjectively by looking at the optic nerve and measuring the thinning of nerve itself. However, your doctor may want to assess this objectively with a machine that measures the thickness of the optic nerve. This test is done through a non-invasive imaging test called an Optical Coherence Tomography, or OCT.
  • The technician or ocular photographer will have you rest your head on a chinrest and look straight at a target. The machine will then focus on your optic nerve and scan the area in order to measure the thickness of each direction. Your doctor will be able to view these results and assess progression of glaucoma by comparing this results with any past or future test results.


  • This test measures and maps your visual fields. Perimetry testing can draw a map of your visual fields and show you where you may have lost vision, especially your peripheral (or side) vision, which is the vision usually affected by early damage to the optic nerve from glaucoma.

the Humphrey Field Analyzer

  • The most commonly used test for perimetry is the Humphrey Field Analyzer (pictured at right). The machine resembles a large bowl. One eye is covered with a patch and the other eye remains stationary and focused straight ahead. Small white lights of varying sizes and intensities will flash at different locations around the bowl. You will be instructed to press a button whenever you see a flashing light. By recording which lights you see and which ones you do not, it creates a map of your visual field.

More Information

Talk With Your Doctor About Glaucoma | National Eye Institute (nih.gov)

For more detailed and patient-centered information about ophthalmoscopy, tonometry, pachymetry, perimetry, OCT, and gonioscopy, check Discovering the Sneak Thief: Diagnosing Glaucoma in VisionAware’s new Patient’s Guide to Living with Glaucoma and El descubrimiento del ladrón silencioso: El diagnóstico de glaucoma in Guía del Paciente: Vivir con Glaucoma.

Glaucoma: Facts & Figures | BrightFocus Foundation