As a patient or patient support person, it can be overwhelming and confusing when doctors and technicians start using words and terms that are unfamiliar. Of course, a professional with good bedside manner will clue you in or take time time to answer any and all questions (if not, keep looking for another doctor). This page contains definitions of tools, tests and terminology that I’ve come across. Basic components of the eye are found here.

Tools and Tests

The Amsler Grid is a tool used to detect vision problems resulting from damage to the macula (the central part of the retina) or the optic nerve. The patient stares at a grid of straight lines and notes any irregularities. Check out All About Vision’s Instructions. Also check digital stores for digital applications of the Amsler Grid.

Fluorescein Angiography (FA or Intravenous (IVFA) ) is a medical imaging technique in which a fluorescent dye (sodium fluorescein) is injected into the bloodstream. The dye highlights the blood vessels in the back of the eye, specifically the retina, in order for them to be photographed. Not recommended during pregnancy.

Fundus photography is high contrast, high resolution imaging of the back, interior portion of the eye. It is used to inspect anomalies associated to diseases that affect the eye, and to monitor their progression.

Indocyanin Green (ICG) Angiography is a medical imaging technique, much like IVFA, in which a fluorescent dye is injected into the bloodstream. Indocyanin green fluoresces in the infrared spectrum and highlights the the choroid layer, in order for it to be photographed.

Optical Coherence Tomography (OCT) is a non-invasive imaging test. OCT uses light waves to take cross-section pictures of the retina which allows the ophthalmologist to map and measure the thickness of each of the layers of the retina.

Pachymetry is a test to measure the thickness of the cornea. A probe called a pachymeter is placed on the front of the eye to measure thickness. Corneal thickness has the potential to influence Interocular Pressure.

Perimetry tests the visual field. This creates a map of the eye to determine the extent of a patient’s complete field of vision (i.e. are there blind spots). The Humphrey Visual Field (HFV) Test consists of a center fixation light and blinking test lights in the peripheral (side) vision. The person being tested presses a button eat time a light is perceived. The Goldmann Visual Field Test is done with a moving target controlled by a trained technician.

The Snellen Eye Chart is the classic visual acuity (vision) test developed by Herman Snellen that starts with the big letter “E” on top with letters getting progressively smaller towards the bottom. Read about the Snellen chart and get a copy on All About Vision’s Eye Test page.

Tonometry is a test that measures Intraocular Pressure (IOP). First, eye drops are used to numb the eye. Then a doctor or technician uses a device called a tonometer to measure the inner pressure of the eye by pressing on the eye; the force with which the eye pushes back is used to estimate the pressure inside the eye. The most common type of tonometry test is called the Goldmann Applanation Tonometry Test, which is bar attached to a microscope. Although a bit less accurate, another common tonometry test is the Tono-Pen, a handheld device that’s shaped like a large pen. It provides a digital readout of eye pressure. The patient should make an effort to breathe normally during this test as holding breathe can influence the IOP. The normal range for pressure is 12-21 mm Hg (millimeters of mercury,).


Anterior Chamber Flare occurs when inflammation in the front of the eye causes the breakdown of vessels in the blood–aqueous barrier. This increases the number of cells and protein concentration in the aqueous humor via leakage, creating a cloudiness (flare) when a light is shone in the eye. Anterior Chamber Flare is a diagnostic indicator of uveitis. It can be examined with slit-lamp or Optical Coherence Tomography. Read Anterior Chamber Cell Grading by Optical Coherence Tomography.

The Blood-Retina Barrier (BRB) is composed of both an inner and an outer barrier in which the cells are joined tightly together. Molecules are selectively allowed to diffuse across the membrane to nourish (inner BRB) and protect (outer BRB) the retina and maintain retinal homeostasis. 

Dyschromatopsia is the interference with or deficiency in accurate color vision.

Exudate is fluid that leaks out of blood vessels into nearby tissues. The fluid is made of cells, proteins, and solid materials. Exudate may ooze from cuts or from areas of infection or inflammation. 

Granulomatous is a term sometimes used to classify anterior uveitis. Granulomatous uveitis is characterized by a grainy appearance due to keratic precipitates.

HLA-B27 Gene (Human Leukocyte Antigen B27) is a genetic marker for proteins that differentiate between the body’s healthy cells and foreign invaders. Although the mechanism is unknown, it is strongly associated with auto immune diseases including anterior uveitis. Read HLA-B27 Syndromes.

Keratic precipitates are clumps of white blood cells deposited on the corneal epithelium (layer protecting the cornea). These cellular deposits are a sign of inflammation and a diagnostic indicator of uveitis. Keratic precipitates (KP) start out white and round and become irregular and faded with age. If the KP stick together, large large yellow KP formed and termed mutton-fat KP.

Metamorphopsia is a visual defect that causes linear objects, such as lines on a grid, to look curvy or rounded (distorted). It’s caused by problems with the eye’s retina, and, in particular, the macula.

Müller cells, or Müller glia, are a type of retinal glial cells (cells that support neurons (nerve cells)), first recognized and described by Heinrich Müller.

An Ophthalmologist is a medical doctor who specializes in eye care including diagnosis, management, and surgery of ocular diseases and disorders. An optometrist performs eye exams and writes prescriptions for corrective lenses. An optician fills the prescriptions.

Photopsia is perceived flashes of light in the field of vision that may characterize activity in the eye.

Retinal Pigment Epithelium (RPE) is the pigmented cell monolayer just between the retina and the choroid that nourishes retinal cells.

Retinal striae are concentric lines on the surface of the retina, which appear after spontaneous or surgical retinal reattachment.

Retinal vasculitis is inflammation of the retina cells in which there is evidence of ocular inflammation and retinal vascular changes.

Scotoma is a partial loss of vision or blind spot in an otherwise normal visual field.

Synechiae are adhesions formed between adjacent structures within the eye usually as a result of inflammation. Anterior synechiae occurs when the iris adheres to the cornea; posterior synechiae occurs when the iris adheres to the lens. The occurrence of synechiae is a diagnostic indicator of uveitis.

Visual Acuity is sharpness of vision, measured by the ability to discern letters or numbers at a given distance according to a fixed standard.