Glossary
As with all medical specialties, the field of vision correction has its own language. Designed to help patients navigate information about the various refractive procedures available today, the following is a list of frequently used terms and their definitions.
20/20 Vision: Eye care practitioners consider this “normal” vision. Seeing an object clearly that is 20 feet away. However, some people naturally see as well as 20/15 or even 20/10. People with 20/40 vision can see clearly at 20 feet what people with 20/20 vision can see clearly at 40 feet. In most of the United States, people with 20/40 vision can get a driver’s license without needing to wear corrective lenses.
A
Aberrometer: A computerized instrument that measures vision. Light waves are projected into the eye, and the aberrometer analyzes the aberrations – or distortions – that occur as the light waves travel through the cornea and the lens eye. Those distortions represent specific vision problems.
Ablate, ablation: To remove tissue during surgery, often with a laser.
Accommodation: The ability of the eye’s natural lens to change shape so it can focus on objects at various distances.
Accommodative lens: A type of intraocular lens (artificial lens implanted in the eye in place of or in front of the natural lens to improve focus and correct vision problems). Has a fixed focal point, but physically changes shape inside the eye in response to eye muscle movements to adjust for clear vision at near, intermediate, or far distances.
Anesthetic: Medicine that causes a loss of sensation, including loss of pain. Local anesthetic causes numbness and pain relief in a specific area, such as the eye, without affecting the senses in the rest of the body.
Astigmatism: A common vision problem and type of refractive error. Caused by either irregularity in the curvature of the cornea or the lens of the eye. People with astigmatism have blurry vision and generally have difficulty seeing fine details at all distances. Astigmatism is measured in degrees of cylinder and is treated with corrective lenses, laser vision correction, or toric IOLs
B
Best Corrected Visual Acuity (BCVA): The best vision you can achieve with correction, such as glasses, as measured on the standard Snellen eye chart. For example, if your uncorrected eyesight is 20/200, but you can see 20/20 with glasses, your BCVA is 20/20.
Best Uncorrected Visual Acuity (BUCVA): The best vision you can achieve without correction, such as glasses, as measured on the standard Snellen eye chart. For example, if your uncorrected eyesight is 20/200 without your glasses, then your BUCVA is 20/200.
C
Cataract: Clouding of the eye’s lens that blocks light to the retina, resulting in impaired vision. Often a result of normal aging, cataracts form when protein clumps cloud areas of the eye’s lens. As the cataract progresses, vision worsens and often requires surgical replacement of the damaged lens with an artificial one.
Cornea: Clear, curved surface at the front of the eye. Light first enters the eye through the cornea, making it the first line of focus. During many types of laser vision correction surgery, such as LASIK, SMILE, and PRK, the cornea is reshaped to reduce or eliminate most of the common vision problems, including nearsightedness, farsightedness, and astigmatism.
Corneal flap: A thin layer of tissue in the surface of the cornea created at the beginning of LASIK surgery. Made with either a microkeratome or a femtosecond laser. The flap is folded back before the LASIK reshapes the inner layers of the cornea.
D
Dilated or Dilation: During an eye examination and in preparation for types of eye surgery, drops will be used to dilate or open the pupil, giving the eye doctor the ability to examine the entire eye.
Diopters: A measurement of vision problems, also known as refractive errors. Hyperopia, or farsightedness, is measured in terms of positive diopters (+1, +2). Myopia, or nearsightedness, is measured in terms of negative diopters (-1, -2).
Dry eye: Burning, grittiness, irritation, and tearing are all symptoms of dry eye. It can be a temporary or chronic condition and can be caused by a wide variety of issues. Often, dry eye is related to allergies, hormonal changes, wind, or lack of humidity in the air, and problems with the eye itself. Approximately 42 million Americans experience dry eye. Severe dry eye can become chronic, also known as Dry Eye Syndrome, and can lead to a condition known as Ocular Surface Disease. All forms of dry eye should be discussed with an eye care professional.
E
Ectasia: Progressive thinning and bulging of the cornea.
Endothelium: The cornea’s inner layer of cells.
Epithelium or epithelial layer: Cellular tissue that covers the surface of the body, including the outside of the cornea.
Excimer laser: A type of “cold” laser that emits precise beams of ultraviolet light. Used in refractive surgery to remove microscopic pieces of corneal tissue and reshape the corneal surface.
Extended Depth of Focus: Extended Depth of Focus (EDOF or EDF), or Extended Range of Vision, is a new IOL technology for the treatment of presbyopia. In contrast to multifocal intraocular lenses (IOLs) used in the treatment of presbyopia, EDOF lenses work by creating a single elongated focal point to enhance “range of vision” or “depth of focus”.
F
Farsighted, farsightedness (hyperopia): A Common vision problem and type of refractive error. Caused by too little curvature of the cornea or too little distance between the front of the eye and the retina at the back. The result is that light rays focus behind the retina rather than on it. People with hyperopia have blurred near vision. Additional symptoms include eyestrain and squinting. Farsightedness can be treated with corrective lenses, laser vision correction, or intraocular lenses.
Femtosecond laser: A precision ultrafast infrared laser used in laser vision correction procedures, including LASIK and SMILE. In the LASIK procedure, the femtosecond laser is used to create the flap in the first step of the procedure. In the SMILE procedure, the femtosecond laser creates a disc of tissue within the layers of the cornea to change its shape.
H
Halos: A higher-order aberration that typically occurs naturally. Halos give the appearance of rings around lights at night. It can occur as a side effect of laser vision correction and often decreases with healing and time. It may also be caused by cataracts or other eye conditions.
Higher-order aberrations: All eyes have at least some degree of higher-order aberrations, including difficulty seeing at night, glare, halos, blurring, starburst patterns, or double vision. These more complex irregularities of the eye can cause vision problems. Some small degree of higher-order aberrations is normal and does not usually cause noticeable vision problems. With the introduction of wavefront technology, higher-order aberrations can now be measured and addressed by vision correction options, including corrective lenses and laser vision correction procedures.
I
Implantable Collamer Lens (ICL): ICLs, or phakic intraocular lenses (IOLs), are clear lenses that work within the eye to focus vision, rather than on the surface of the eye like a contact lens. Patients who have been told they are not eligible for laser vision correction procedures such as LASIK and PRK because the prescription is too strong, or the condition of their cornea is too poor may otherwise be suitable candidates for ICLs.
Intraocular Lens (IOL): Artificial lens made of plastic, silicone, or acrylic. Designed to be implanted in the eye in place of or in front of the natural lens to improve focus and correct vision problems, such as cataracts and presbyopia.
Iris: The colored membrane in front of the eye’s lens that manipulates the size of the pupil to regulate the amount of light entering the eye.
K
Keratometer: An instrument that measures the curvature of the eye’s clear, front surface (cornea). Keratometers help eye doctors collect information for contact lens fittings and laser vision correction procedures. Keratometry also can help diagnose dry eyes.
Keratorefractive Lenticule Extraction (KLEx)L The general term for corneal lenticule extraction surgeries for refractive error correction. This includes the earliest terminologies of Femtosecond Lenticule Extraction (FLE or FLEx) and Refractive Lenticule Extraction (ReLEx) as well as the latest Small Incision Lenticular Extraction (SMILE) procedure.
L
Laser Vision Correction: A class of surgeries where a laser is used to reshape the cornea to correct vision problems. LASIK, SMILE, and PRK are types of laser vision correction.
LASIK (Laser In-Situ Keratomileusis): Generally considered the most common and popular type of laser vision correction procedure. First, a thin flap is created in the cornea and folded back, then an excimer laser is directed to the corneal surface exposed beneath the flap to reshape the cornea for corrected vision. Finally, the flap is gently replaced.
LASIK Side Effects: Some patients experience side effects from LASIK, which generally include night vision visual symptoms such as glare, halos, ghosting, and starbursts, as well as dry eye. Typically, glare, halos, ghosting, and starbursts resolve by themselves. Some people require additional courses of eye drops to help reduce inflammation and/or dry eye that can contribute to visual symptoms.
Light Adjustable Lens: Specialized lens technology is made of a special material that can be modified using UV light treatments after it’s implanted in your eye, allowing you to make decisions about your vision after surgery.
Lens: The transparent disc behind the pupil that focuses light onto the retina. As the eye ages, the lens often becomes cloudy, which is called a cataract.
Lower order (first order) aberrations: Lower, or first, order aberrations include farsightedness, nearsightedness, presbyopia, and astigmatism. These make up most vision problems. First-order aberrations are identified by vision tests, including refractive and wavefront measurement instruments.
M
Microkeratome: A precision surgical instrument sometimes used to create the corneal flap in the uppermost layer of the cornea during LASIK.
Monofocal (or “standard”) intraocular lens: A type of intraocular lens (artificial lens implanted in the eye in place of or in front of the natural lens to improve focus and correct vision problems) designed to provide clear vision at one fixed focal point, usually for clear distance vision.
Multifocal intraocular lens: A type of intraocular lens (artificial lens implanted in the eye in place of or in front of the natural lens to improve focus and correct vision problems) designed to include corrections for near, intermediate and distance vision in the same lens.
N
Nearsighted, nearsightedness (myopia): A common vision problem and type of refractive error. Caused by either too much curvature of the cornea or too much distance between the front of the eye and the retina at the back. Both structural defects cause light entering the eye to focus incorrectly on the retina, resulting in blurred distance vision. Treated with corrective lenses, laser vision correction, or multifocal or accommodative IOLs.
O
Ophthalmologist: Doctor of medicine (M.D.) or doctor of osteopathy (D.O.) who is qualified to diagnose, manage, and treat all eye and visual system disorders. An ophthalmologist is trained to render total eye care, including vision services, contact lenses, eye examinations, and medical and surgical eye care.
Optometrist: Eye health professional trained to provide primary eye care services, such as basic eye health and vision examinations, diagnosis of vision problems and eye diseases, and prescriptions for eyeglasses, contact lenses, and medications.
P
PRK (Photorefractive Keratectomy): A form of laser vision correction using an excimer laser to remove microscopic amounts of tissue from the surface of the cornea to improve its ability to focus and provide clear vision.
Presbyopia: Also called age-related loss of near vision. Presbyopia is a common vision problem that develops naturally over time, reducing the eye’s ability to focus at close distances or on fine details. Treated with reading glasses, contact lenses, laser vision correction, or lens replacement surgery.
Pupil: The black, circular area in the center of the iris (the colored part of the eye) that allows light into the eye.
R
Refraction: The test performed during an eye exam to measure the focusing ability of the eye and determine the eyeglass lens prescription needed for clear vision. Automated refraction uses an instrument that does not require the patient to respond. A manifest refraction is a manual process that places various lenses in front of the patient’s eyes, and the operator asks, “Which is better, lens A or lens B?”
Refractive error: Irregularities in the cornea, lens, or shape of the eye that prevent correct focus at any distance.
Refractive Lenticule Extraction (ReLEx): Similar to SMILE, ReLEx is a laser vision correction option recommended to patients with nearsightedness and astigmatism. A femtosecond laser is used to create a thin disc of tissue within the layers of the cornea, which is then removed through a small incision to reshape the cornea and improve vision.
Refractive surgery: Any surgical procedure that attempts to improve vision by eliminating or reducing the patient’s refractive error (irregularities in the eye that prevent correct focus). Laser vision correction is a common type of refractive surgery, as is lens replacement.
Refractive surgeon: An ophthalmologist (MD or DO) with additional training in vision correction procedures. Refractive surgeons are specialists within the field of eye care.
Retina: The system of optic nerves at the back of the eye, responsible for sending images to the brain.
Retreatment (LASIK enhancement): Additional LASIK treatment performed as a follow-up procedure to address any residual refractive error.
S
Sclera: The white part of the eye. Provides external protection for the eye, along with the cornea.
SMILE (Small Incision Lenticule Extraction): A laser vision correction option recommended to patients with nearsightedness and astigmatism. SMILE uses a femtosecond laser to create a thin disc of tissue within the layers of the cornea, which is then removed through a small incision to reshape the cornea and improve vision. For those patients who are not good candidates for LASIK, SMILE may be an option.
Snellen chart: Standard chart with letters, numbers, or symbols printed in rows of decreasing size used by eye care professionals in distance visual acuity testing.
T
Tear film: A very thin film of water and lubricants responsible for keeping the surface of the eye moist.
Tear gland: Also called lacrimal glands. These almond-shaped glands, one for each eye, secrete the water and mucus components of the tear film. They are in the upper, outer portion of each eye cavity.
Topography: A corneal topographer shines light onto the surface of the eye and then measures the reflected light to create a map of the cornea’s curvature as well as any irregularities. The map is used for evaluations related to refractive surgery, contact lens fitting, and corneal disease management. It is especially useful for measuring astigmatism. The color map uses blue and green to represent flatter areas of the cornea, while red and orange represent steeper areas.
V
Visual acuity: Sharpness of vision; usually as measured with the use of a Snellen chart. 20/20 is considered normal visual acuity, though some people can see even better, such as 20/15 or 20/10.
W
Wavefront: Designed to precisely measure the visual capacity of the cornea, a wavefront device transmits a ray of light into the eye. The light is reflected off the retina, out through the pupil, and into the device, where the reflected wave of light is received and arranged into a unique pattern that captures the patient-specific refractive errors (lower- and higher-order aberrations). The patient’s visual irregularities are then displayed as a wavefront map.