A Glossary of Vision-Related Terminology

10-degree visual field test (central 10-degree visual field test)
A test used in the diagnosis of glaucoma. The 10-degree visual field test assesses vision in the central 10 degrees of the visual field.

24-degree visual field test
A test used in the diagnosis of glaucoma. The 24-degree visual field test assesses vision in the central 24 degrees of the visual field.

**Angle (drainage canal)
The angle is where the front surface of the iris and the back surface of the cornea meet. Aqueous fluid drains from the eye through the angle and its various structures.
Suggested resource: "Understanding Glaucoma" on Glaucoma Research Foundation

Angle closure suspect
Someone who has risk factors for angle-closure glaucoma (also called closed-angle or narrow-angle glaucoma).

Angle-closure glaucoma (closed-angle glaucoma, narrow-angle glaucoma)
See "What Are the Different Types of Glaucoma?" on VisionAware.

**Anterior chamber 
The space between the outer surface of the iris and the innersurface of the cornea. The anterior chamber is filled with aqueous fluid.
NEI drawing of the eye

**Aqueous fluid (aqueous humor)
A clear, watery fluid produced by the ciliary processes and which is responsible for maintaining intraocular pressure. Aqueous fluid fills the anterior chamber and nourishes the cornea, iris, and lens.

Axon
In a nerve cell, the axon is a long thin structure that connects the nerve ending and the nucleus.

Bleb
A blister or bubble on the surface of the eye, made with a flap of tissue during a trabeculectomy, that will fill with aqueous fluid in order to facilitate the lowering of intraocular pressure. The fluid that collects in the bleb is slowly reabsorbed by the eye.
Suggested resource: "Trabeculectomy (Filtration Surgery) for Glaucoma" on WebMD

Canaloplasty
A surgical procedure wherein a small tube is inserted into the eye's drainage system in order to decrease intraocular pressure.
Suggested resource: "Treatments for Glaucoma" on VisionAware

Candidate gene
Any gene that is suspected to have a role in the cause of a disease.
Suggested resource: Candidate gene on MedicineNet

**Central vision
Central vision, as distinct from peripheral vision, results from focusing the eyes straight ahead. Central vision arises from stimulation of the fovea and the macular area. Central vision is the eye's sharpest vision and is responsible for tasks such as reading and discriminating fine detail and color.

Ciliary processes
Folds in the various vascular layers between the sclera and the retina. Responsible for producing aqueous fluid.

Cones (cone cells)
A type of photoreceptor cell found in the retina. Cone cells function in conditions of relatively bright light and assist with color vision and color differentiation.
Suggested resource: Cone cell on Wikipedia

Confocal scanning microscopy
An non-invasive optical imaging technique that results in high-resolution images that can be used in the detection of eye disease.
Suggested resource: Confocal laser scanning microscopy on Wikipedia

**Conjunctiva
A transparent mucous membrane that lines the inner surfaces of the eyelids and covers the sclera.

Contrast sensitivity 
The ability to distinguish facial features and to make distinctions between and among objects of similar tones (such as orange juice in an orange cup). Any eye problem can lead to a decrease in contrast sensitivity.
Suggested resource: "What Is Low Vision?" on Get Eye Smart

**Cornea 
The transparent covering of the iris, pupil, and anterior chamber, the cornea is responsible for most of the eye's optical power.
"Eye Health: Anatomy of the Eye" on VisionAware

Cup-to-disc ratio 
Ratio of the size of the optic disc cup to the horizontal diameter of the entire optic disc.

Cupping
When glaucomatous nerve fiber damage leads to an increase in the size of the optic disc cup relative to the optic disc.

Cytidine-5-diphosphocholine (citicoline)
A naturally occurring brain chemical that is used to treat a variety of diseases, including glaucoma.
Suggested resource: Citicoline on WebMD

Dilated eye exam
A painless exam that uses eye drops to enlarge (dilate) the pupils in order to allow more light to enter the eyes. Once the pupils are dilated, important tissues at the back of the eye—including the retina, the macula, and the optic nervecan be examined for signs of disease.
Suggested resource: "Leading Causes of Blindness" on NIH Medline Plus

**Dilation 
Widening of the pupil, allowing more light to enter the iris. Dilation is the eye's natural muscular response to dim light conditions, and can also be induced with certain drugs.

Direct ophthalmoscopy
An exam that uses a direct ophthalmoscope to shine a beam of light through the pupil in order to see the internal structures of the eye.
Suggested resource: "Ophthalmoscopy" on MedlinePlus
Image of a direct ophthalmoscope from NEI on Flickr

Drainage canal
See angle.

**Eyelid 
Structure that covers the front of the eye. The eyelids protect the eyes, limit the amount of light entering the pupil, and distribute tear film over the exposed surface of the cornea.

Filtering surgery
See trabeculectomy.

Fourier-Domain optical coherence tomography
Extremely high-resolution, high-speed medical imaging technique that uses broadband light to generate images that can be used in the detection of eye disease.
Suggested resource: "Ultrahigh-resolution, high-speed, Fourier domain optical coherence tomography and methods for dispersion compensation" on OpticsInfoBase

**Fovea
Central pit in the macula that produces sharpest vision. Contains a high concentration of cones and no retinal blood vessels.
"Eye Health: Anatomy of the Eye" on VisionAware

Functional vision
How well an individual processes the visual information in his or her environment in order to go about daily tasks.
Suggested resource: "What Is a Low Vision Examination?" on VisionAware

Fundus 
The fundus is the part of the interior of the eye that is visualized through the pupil during an eye examination. It includes the retinaoptic disc , and the macula.
Suggested resource: Fundus, retinal, on MedicineNet

Glaucoma
See "What Are the Different Types of Glaucoma?" on VisionAware.

Gold shunt implant
A device implanted to reduce intraocular pressure associated with glaucoma.

**Gonioscopy 
Examination of the anterior chamber angle through a gonioscope.

Gonioscope (goniolens)
A special type of lens that uses a prism or a mirror to allow an examiner to visualize the angle of the eye.

Humphrey Field Analyzer
Computerized instrument for performing an exam to identify loss of vision anywhere in the visual field. The pattern of vision loss indicated by the Humphrey can be used to diagnose eye disease.

Indirect Ophthalmoscopy
An exam that uses an indirect ophthalmoscope to visualize the back of the eye. The examiner may use a blunt probe to apply pressure to the eyeball during the exam.
Suggested resource: "Ophthalmoscopy" on MedlinePlus

**Intraocular pressure (IOP) (tension)
Fluid pressure inside the eye.

**Iris
Pigmented tissue lying behind the cornea that gives color (such as blue, brown, or hazel) to the eye. The iris controls the amount of light entering the eye by varying the size of the pupil.
"Eye Health: Anatomy of the Eye" on VisionAware

Iris sphincter
The muscle that contracts or expands the iris in order to decrease or increase the size of the pupil.
Suggested resource: Free Dictionary

Laser iridotomy
A surgical procedure used to treat closed-angle glaucoma. In the procedure, a tiny hole is created through the iris in order to increase the flow of aqueous fluid to the angle.
Lens
A circular, transparent structure located in the front of the eye, behind the pupil. The lens helps focus light on the retina.
"Eye Health: Anatomy of the Eye" on VisionAware
Suggested resource: Lens (anatomy) on Wikipedia

Linkage analysis
A method of genetic research used to hunt for and test genes.
Suggested resource: Linkage analysis on MedicineNet

Low vision specialist
See a description of a low vision specialist on VisionAware.

**Macula 
Small central area of the retina surrounding the fovea. The area responsible for the most acute central vision.
"Eye Health: Anatomy of the Eye" on VisionAware

Microperimetry 
An exam that precisely identifies areas of impaired retinal function by mapping measured retinal sensitivity onto an image of the fundus.
Suggested resource: "Expanded Role for Microperimetry in Visual Rehabilitation" on American Academy of Ophthalmology

Modifier genes
Genes that influence the expression of another gene.
Suggested resource: "Modifier Genes" on the Mendelian Genetics page at North Dakota State University

Multifocal visual-evoked potentials
A technique used in glaucoma detection that can simultaneously measure visual evoked potentials in multiple regions of the visual field.
Suggested resource: "The Role of the Multifocal Visual Evoked Potential (MFVEP) Latency in Understanding Optic Nerve and Retinal Diseases" on National Library of Medicine

Narrow angle
See "What Are the Different Types of Glaucoma?" on VisionAware.

Neuron
A cell that transmits and responds to electrical and chemical signals.
Suggested resource: Neuron on MedicineNet

Neuroprotection
Protection, salvage, or recovery of the nervous system and related structures that are damaged or likely to be damaged in the course of a disease.
Suggested resource: "Neuroprotection and neurodegenerative disease" on PubMed

Neuroprotective agents (for glaucoma)
Drugs used to prevent retinal ganglion cell death.
Suggested resource: "Neuroprotection in glaucoma" on National Library of Medicine

Neuroretinal rim
The part of the optic nerve that contains ganglion cells.

Notching
An area of reduction in the width of the neuroretinal rim.
Suggested resource: "Presence of an optic disc notch and glaucoma" on PubMed

Ocular hypertension 
Intraocular pressure that is above the normal range, with no detectable changes in vision or damage to the structure of the eye.
Suggested resource: "What Is Ocular Hypertension?" on Get Eye Smart

Ologen
An implant that promotes wound healing after glaucoma surgery.
Suggested resource: Body Organ Biomedical Corporation

Open-angle glaucoma
See "What Are the Different Types of Glaucoma?"on VisionAware.

Ophthalmoscope
Device used to illuminate and magnify the interior of the eye in order to assess eye health and detect signs of disease. An ophthalmoscope may consist of a separate light (sometimes worn on the examiner's head like a miner's light) and handheld microscope, or may be a single unit that the patient looks into during an exam.
Suggested resource: "Ophthalmoscopy" on MedlinePlus

Optic disc
See optic nerve disc.

Optic disc cup (physiologic cup)
Depression found in the center of the optic nerve disc.

**Optic nerve
Largest sensory nerve of the eye; carries impulses for sight from the retina to the brain.
"Eye Health: Anatomy of the Eye" on VisionAware

**Optic nerve disc (optic disc, optic nerve head)
Ocular end of the optic nerve. Where the retinal nerve fibers exit from the eye and where the blood vessels enter.

Optic nerve head
See optic nerve disc.

Optic neuropathy
An eye disease that is characterized by damage to, or destruction of, the optic nerve.
Suggested resource: Free Dictionary

Optical system 
The optical system of the eye is composed of the cornea, the lens, the iris, and the retina.
Suggested resource: Journal of Optometry
"Eye Health: Anatomy of the Eye" on VisionAware

Pachymetry
A procedure that uses ultrasonic waves to measure the thickness of the cornea.
Suggested resource: "Facts About Glaucoma" on NEI

Paracentral scotomas 
Blind spots adjacent to the macula.

**Perimetry
Method of charting the visual field in order to detect damage to sensory visual pathways. Perimetry uses objects of various sizes and light intensities to test vision while the eye remains stationary.

**Peripheral vision
Side vision, as distinct from central vision. Vision elicited by stimuli falling on retinal areas distant from the macula.

Perkins Tonometer 
A handheld device that measures intraocular pressure.

Photoreceptor cell
A type of cell responsible for the conversion of light into a representation of the visual world. In the eye, rods and cones are two types of photoreceptor cells.
Suggested resource: Photoreceptor cell on Wikipedia

Physiologic cup
See optic disc cup.

**Pupil
Black circular opening in the center of the iris that changes its size in order to regulate the amount of light that enters the eye.
"Eye Health: Anatomy of the Eye" on VisionAware

**Retina 
Light-sensitive nerve tissue in the eye that converts images from the eye's optical system into electrical impulses that are sent along the optic nerve to the brain. The retina forms a thin membranous lining of the rear two-thirds of the eyeball.
"Eye Health: Anatomy of the Eye" on VisionAware

Retinal functional imaging
Non-invasive functional imaging technology used to visualize the retina.
Suggested resource: "Retinal functional imager (RFI): non-invasive functional imaging of the retina" on PubMed

Retinal ganglion cell (RGC)
A type of neuron that transfers visual information from the eye to  brain. RGCs transmit information from the retina to a variety of locations in the brain.
Suggested resource: Ganglion Cell on EyeWire

Retinal nerve fiber layer
The retinal nerve fiber layer is composed of RGC axons, and constitutes the innermost layer of the fundus. The layer transmits impulses to the optic disc.
Suggested resource: "Retinal Nerve Fiber Layer" on the Managed Care Eye Institute of the University of Minnesota

Rods, rod cells
A type of photoreceptor cell found in the retina. Rods function in lower light conditions and assist with color vision and color differentiation.
Suggested resource: Rod cell on Wikipedia

Scanning laser ophthalmoscopy (SLO) 
An imaging technology that uses laser light to illuminate the retina.
Suggested resource: Heidelberg Engineering

**Schlemm's canal 
Circular channel that carries aqueous fluid from the anterior chamber of the eye to the bloodstream.

**Sclera 
The "white of the eye." Opaque, fibrous, protective outer layer of the eye that is directly continuous with the cornea in front and with the sheath covering the optic nerve behind.

**Slit-lamp ophthalmoscopy
Exam performed by shining a beam of light through the pupil using a slit-lamp ophthalmoscope in order to view the internal structures of the eye. The patient sits in a chair for the exam.
Suggested resource: "Ophthalmoscopy" on MedlinePlus

Spectral domain optical coherence tomography (SD-OCT)
A noninvasive imaging technique that uses reflected laser light to visualize the layers of the retina.
Suggested resource: "Spectral Domain Optical Coherence Tomography in Glaucoma" on EyeWiki

Stereoscopic photograph
Two photographs taken at different angles that, when viewed simultaneously (with a different photograph in front of each eye), appear 3-dimensional. 
Suggested resource: Stereoscopic photograph on Free Dictionary

Tear film 
The protective coating that protects and lubricates the eye. The tear film is composed of three layers: an oily layer, a watery layer, and a layer of mucus.
Suggested resource: "Dry Eye" on VisionAware

Tension
See intraocular pressure.

Titanium-sapphire laser
Type of laser used to open the angle of the eye.

Tono-Pen
Instrument used to measure intraocular pressure.

**Tonometry 
Measurement of intraocular pressure.

Trabectome
A surgical procedure to remove a small portion of the eye's trabecular meshwork in order to improve drainage.
Suggested resource: "What Are the Different Treatments for Glaucoma?" on VisionAware

**Trabecular meshwork
Mesh-like structure inside the eye that filters aqueous fluid and controls its flow into Schlemm's canal.

Trabeculectomy (filtering surgery)
A surgical procedure where a small incision is made in the sclera (the white of the eye). Fluid slowly leaks from this incision into a bleb in the conjunctiva. The procedure decreases intraocular pressure by allowing fluid to bypass blockages in the trabecular meshwork.
Suggested resource: "What Are the Different Treatments for Glaucoma?" on VisionAware

**Visual acuity 
Assessment of the eye's ability to distinguish object details and shape, using the smallest identifiable object that can be seen at a specified distance (usually 20 feet or 16 inches).

**Visual field 
Full extent of the area visible to the eye when looking straight ahead.

Visual field loss 
An area of vision loss in part of the usual visual field. Can occur due to disease or disorders of the eye, optic nerve, or brain. There are several types of field defects.

Visual cortex  
The area of the brain that receives and processes mpulses from the optic nerves.
Suggested resource: Visual cortex on Dictionary.com

Visually evoked potential (visually evoked response, visually evoked cortical potential)
Electrical impulses caused by visual stimuli. Measurement of visually evoked potentials is used to determine how well the visual pathways are functioning.
Suggested resource: "Visually Evoked Potentials by Donnell J. Creel" on Webvision

Vitreous (vitreous humor, vitreous body, vitrea)
The clear gel that fills the space between the lens and the retina.
"Eye Health: Anatomy of the Eye" on VisionAware





**Excerpted or adapted from: Cassin, B. (2011). Dictionary of Eye Terminology. Triad Communications: Gainesville, FL. Reprinted with permission.

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