Eye Care Definitions

santa-rosa-eye-definitionsThese are simple eye care definitions and general information for common eye-related terms that we often use in our office. Explanations are then expanded based on the individual circumstances for each patient. If you wish more extensive web-based eye terminology before or after your examination in our office, review these resources:

Glossary of Eye Care Terms

Eye Care Glossary of Terms

Glossary of All Eye & Vision Conditions

Diagram of the Eye

And of course Wikipedia.


Anatomy, Front to Back:

Eyebrows: Small hairs above the eyelids that provide shade for the eyes, wick moisture away from the eye area and assist with facial expressions.

Eyelids: Structure in front of the eyes that act like a windshield wiper to clear debris and excess moisture from the front of the eyeball. The eyelids also contain some tissue to help protect the eyes, various glands to supplement the tears, muscles for the blinking action and blood vessels to provide oxygen to the cornea when the eyelids are closed.

Tears: The fluid layer on the eye that helps keep the eye moist and nourished and provides a smooth surface for clear vision. The tears have three main components: a mucin layer is directly on the eye and helps smoothly spread the main watery layer over the eye, and a very thin lipid/fatty molecule layer on top to help slow evaporation.

Sclera: The white layer of the eye that provides much of the eye structure.

Conjunctiva: Thin clear covering over the sclera and inside part of the eyelids.

Cornea: The clear front surface of the eye. The curvature of the cornea is very influential in determining the amount and type of eyeglass prescription your eye needs.

Anterior Chamber: The area between the cornea and iris that is filled with a fluid called aqueous humor.

Iris: Tissue that contains two sets of muscles to allow your pupil to get bigger or smaller to allow more or less light into the eye. The iris is what determines your eye color.

Pupil: Hole in the middle of the iris where light enters the eye. The pupil generally looks black because most of the light entering the eye is absorbed inside the eye.

Lens: Nearly clear, lens-shaped tissue behind the iris and pupil that is able to change shape to allow focusing from distance to near. The lens grows like an onion, layer by layer, getting thicker over time. The lens becomes a cataract when it becomes more cloudy or develops opacities.

Vitreous: A gelatinous material that fills the back chamber of the eye. It is mostly water with a protein support matrix.

Retina: The nerve lining inside the back part of the eye that allows you to see. It contains photoreceptors (rods for black & white vision; cones for color vision) and other nerves to process and transmit information to the brain.

Macula: The central, detail vision part of the retina. Contains mostly cone photoreceptors.

Choroid: Tissue between the retina and sclera that provides structural support and much of the blood supply for the retina.

Optic Nerve Head: Where the optic nerve connects to the eye. The information transmitting nerves of the retina gather at the optic nerve head to enter the optic nerve.

Optic Nerve: The information from the retina travel along the optic nerve into the brain. Information from the temporal (ear-side) retina travel along the temporal side of the optic nerve. Information from the nasal side of the retina travel along the nasal side of the optic nerve which crosses over to the other side of the brain to travel with the information from the temporal retina of the opposite eye. This allows information from the left side of the visual field from both eyes to go to the right side of the brain, and vice versa.

Visual Cortex: The back part of the brain where most of the visual processing takes place.


Common Conditions:

Myopia (Near-sightedness): You can see near easier than you can see far. The cornea is relatively too sharply curved &/or the eye is too long.

Hyperopia (Far-sightedness): You can see far easier than you can see near. The cornea is relatively too flat &/or the eye is too short.

Astigmatism: The cornea is more sharply curved in some directions (meridians) than in others; more of a football shape than a baseball shape. This makes vision blurry and distorted at far and near.

Presbyopia: Loss of the ability to naturally focus from distance to near. This happens as the lens inside the eye becomes too thick and has difficulties in changing shape.

Dry Eye: Condition in which one or more of the tear system components are not working properly resulting in irritated, inflammed eye surfaces. There are many potential causes for this.

Cataract: The lens inside the eye becomes more cloudy, less clear. There are several different types of cataracts. Symptoms may include glare, halos, muted colors and blurry vision.

Macular Degeneration: The central vision area of the retina degenerates which can result in poor detail vision. Generally, there is a slowly progressive dry form and a rapidly progressive wet form of macular degeneration.

Glaucoma: Multi-factorial, silent loss of retinal vision cells in the eye. Eye pressure is only one potential factor, and glaucoma can occur &/or progress with average or lower eye pressure.

Acute Glaucoma: Damage to the retina due to a sudden large increase in eye pressure that often has symptoms such as eye pain, redness, halos around lights and/or eye bulging.

Retinal Detachment: A condition in which the retina is detaching from the choroid. There can be a partial or full detachment. Early to partial retinal detachments can occur with very minor to no symptoms and is one reason to have your eyes dilated during an eye exam. Possible symptoms include flashes of light, floaters, a curtain or veil closing in your vision, blurry vision &/or vision loss.

Diabetic Retinopathy: With long-term or advanced diabetes retinal blood vessels can become leaky. In the early stages this may be without symptoms but detectable during an eye exam. If this condition progresses, symptoms such as blurry &/or distorted vision, floaters and double vision may occur. Further progression can result in vision loss and blindness.


Eye Care Procedures:

For a description of most parts of an eye exam: Santa Rosa Eye Exam

Refraction: Testing to determine what eyeglass lens power is required for best corrected visual acuity. An autorefractor is a computerized machine that can estimate the lens power without a response from the patient. This estimate helps by providing a starting point for the manual methods, usually involving a phoropter (the device with many lens choices).

Binocular Vision Testing: An assessment of how well the eyes to work together to attain clear vision, depth perception and stereo vision.

Anterior Segment Evaluation: Using a biomicroscope and other devices to observe the health of anterior eye structures such as the eyelids, cornea, iris and lens.

Dry Eye Evaluation: Along with using a biomicroscope to observe the amount, quality and flow of the tears on the eye, the tear production can be measured with special filter paper. Also, certain dyes can be used to help evaluate the tears and drying effects on the eye surface.

Posterior Segment Evaluation: Using a biomicroscope in tandem with a handheld magnifying lens to evaluate the health of posterior eye structures such as the vitreous, retina, macula and optic nerve head.

Dilation: Drops are used to cause the iris to contract, resulting in a larger pupil. This allows for a better view of the internal eye structures, especially the peripheral retina.

Contact Lens Fitting: The process of determining what contact lenses are most appropriate based on a patient's eyeglass prescription, visual activities and eye shape and health. Thankfully we now have a plethora of contact lens options.

Laser Vision Correction: A surgical procedure in which an excimer laser is used to change the shape of the cornea to allow the eye to be focused at far distance (or sometimes reading distance for one eye in patients with presbyopia). Before the excimer laser is used a flap is made and lifted in the cases of LASIK or LASEK, or the top layer of corneal cells, the epithelium, is removed in the case of PRK.

Laser Eye Surgery: Another phrase usually synonymous with Laser Vision Correction.

LASIK: Laser-Assisted In Situ Keratomileusis. A stable flap is created on the top part of the cornea by either using a tool called a microkeratome that uses a blade, or a different laser device (IntraLase) that does not use a blade and is generally more precise. Once the flap is lifted the excimer laser is used to change the shape of the cornea and the flap is replaced.

LASEK: Laser Epithelial Keratomileusis. Similar to LASIK, but a very thin flap involving mainly just the epithelium is made. This procedure may be done when the cornea is relatively flat or thin.

PRK: Photorefractive Keratectomy. The top layer of corneal cells is removed prior to using the excimer laser to change the shape of the cornea. A bandage contact lens is then placed on the cornea to allow the epithelium to heal.

Cataract Surgery: Small tools are used to remove the old lens material in the eye (the cataract), and a new artificial lens is placed inside the eye. The new lens may be a monofocal design (focused at one distance) or a multifocal design (which provides a range of vision from far distance to intermediate and/or reading distance). There are several multifocal lens designs, with more being developed.


This list of eye-related terms and associated information is intended to be partial and user-friendly. It is not intended to be a complete list of eye-related terms, nor provide a complete definition of each term. Topics not covered in this website can be discussed with our eye doctor. This information is not a substitute for a thorough eye examination by an optometrist or ophthalmologist. If you need further information or would like to schedule an eye exam, please call our office at (707) 570-2418.