EYE TERMINOLOGY

Fraser Valley Cataract and Laser emphasizes technology, experience, and safety. To learn more about your visual diagnosis and/or upcoming procedure, please review the terms below.

Ablation
In laser vision correction surgery, ablation refers to the removal of corneal tissue to correct a refractive error like nearsightedness, farsightedness or astigmatism.

Ablation Zone
The area of corneal tissue that is treated/removed during laser surgery.

Accommodation
The ability of the eye to change focus while looking at objects at varying distances. For example, looking at the TV then looking at your phone or book.

Astigmatism
A condition in which one of the eyes’ refractive surfaces has an irregular shape (not spherical), causing visual distortion.

Cataract
Clouding of the lens in the eye which leads to a decrease in vision. Symptoms may include blurry vision, faded colors, halos around lights, and difficulty seeing at night. Cataracts can occur in one or both eyes and are most commonly due to aging but may be congenital or the result of trauma.

CK (Conductive Keratoplasty)
Refractive surgery procedure that reshapes the cornea using radio waves. CK is used to treat hyperopia and presbyopia.

Cornea
The transparent outer covering of the eye that allows light to enter and helps the eye focus.

Corneal Flap
The thin flap that is created during LASIK surgery.

Corneal Haze
Clouding of the cornea which creates the sensation of hazy vision.

Diopter
The unit of measurement for refractive errors. Myopic (nearsighted) patients will have a negative diopter value and hyperopic (farsighted) patients will have a positive diopter value.

Dry Eye Syndrome
Dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance and tear film instability.  Potential damage to the ocular surface can occur with dry eye and it may be accompanied by increased osmolarity of the tear film and inflammation of the ocular surface. Common symptoms of dry eye include foreign body sensation, stinging, burning, discomfort, scratchiness, and intermittently blurry vision.

Endothelium
The single layer of cells on the inner surface of the cornea.

Epithelium
The single layer of cells on the outermost surface of the cornea.

Excimer laser
Surgical equipment that produces a thin, powerful beam of ultraviolet light. An excimer laser is used to remove microscopic layers of tissue from the cornea to enhance vision.

Ghost Image
A visual distortion that causes the object you are viewing to have a fainter second image.

Glare
Difficulty seeing in the presence of bright light (such as direct or reflected sunlight) or artificial light (such as car headlamps at night).

Halos
Halos are bright circles that appear to surround a source of light, such as an oncoming car’s headlights.

Higher-order Aberration
Visual imperfections other than refractive errors (farsightedness, nearsightedness, and astigmatism).

Hyperopia ‐ (Farsightedness)
A visual defect that causes difficulty viewing near objects, while distant objects are easily focused on.

Intraocular Collamer Lenses (ICL)
Thin clear lenses that are surgically implanted into the eye in front of your natural lens and behind your iris. The ICL procedure is often recommended for patients with high myopic or hyperopic prescriptions as the cornea is often not thick enough to be treated safely with LASIK/PRK.

Iris
The flat, coloured, ring-shaped tissue behind the cornea with an adjustable circular opening (pupil) in the center. This controls the amount of light entering into the eye (similar to an aperture on a camera).

Keratitis
Inflammation or dryness of the cornea.

Keratoconus 
A condition characterized by progressive irregularity and thinning of the cornea resulting in blurred and distorted images. It can affect one or both eyes and can be treated with corneal cross-linking. Early diagnosis and treatment are recommended.

LASEK (Laser Epithelial Keratomileusis)
Vision correction procedure that uses a laser to reshape the cornea’s inner layers. LASEK laser eye surgery may be appropriate for individuals who are not candidates for LASIK due to thin corneas.

LASIK (Laser-Assisted In-Situ Keratomileusis)
Vision correction procedure that uses a laser to reshape the cornea’s inner layers, improving nearsightedness, farsightedness, astigmatism, and other visual imperfections.

Lens
The part of the eye that has focusing ability. It changes shape to allow the eye to focus on objects at various distances.

Microkeratome
A surgical instrument with a blade designed for creating corneal flaps in LASIK.

Monovision
Adjusting one's dominant eye for distance and the other eye for near (for patients with presbyopia). This surgical option is available for both PRK and LASIK.

Myopia (Nearsightedness) 
The ability to see near objects while distant objects are blurry. 

Ophthalmologist
A medical doctor that specializes in the study and treatment of disorders and diseases of the eye.

Optometrist
A primary health care provider, who diagnoses, manages and treats refractive errors and eye disorders.

Overcorrection
An unexpected outcome of PRK/LASIK surgery when the correction achieved is more than desired.

Pachymetry
Measurement of corneal thickness using an ultrasound device called a pachymeter.

Presbyopia
A condition which makes focusing on near objects difficult. It is caused when the lens loses its elasticity. This typically occurs around the age of 45 years.

PRK (Photorefractive Keratectomy) 
A procedure involving the gentle removal of the surface layer of the cornea (epithelium) and then the use of a computer-controlled excimer laser to reshape the stroma. It can treat nearsightedness, farsightedness, and astigmatism.

Pupil
The opening in the centre is the iris. It changes shape based on the amount of surrounding light‐ it increases in size in dim light and decreases in size in bright light. 

Radial Keratotomy (RK)
A refractive surgical procedure that involves radial cuts to the cornea and is performed to treat myopia.

Refraction
An examination that tests the refractive power (e.g. nearsighted, farsighted and/or astigmatism) of the eye.

Refractive Errors
Occurs when the shape of one’s eye does not bend light correctly, resulting in a blurred image. The main types are hyperopia, myopia, and astigmatism.

Refractive Lens Exchange (RLE)
Also called lens replacement surgery or clear lens extraction. The procedure replaces the eye’s natural lens with an artificial intraocular lens (IOL) to correct a refractive error.  It is recommended for patients with presbyopia and/or with a high degree of refractive error. 

Retina
A light-sensitive membrane that lines the inside wall of the eye; this membrane receives images and sends signals to the brain via the optic nerve. The retina captures images much like the film of a camera.

Sclera
The protective white, fibrous outer layer of the eye containing collagen and elastic fiber.

Stroma
The middle layer of the cornea. This is the corneal tissue that is reshaped by an excimer laser during LASIK/PRK procedures.

Topography
A non-invasive medical imaging technique used to map the surface curvature of the cornea.

Undercorrection
An unexpected outcome of PRK/LASIK surgery when the correction achieved is less than desired.

Visual Acuity 
The clarity of vision measured by the ability to discern letters or numbers at a given distance on a Snellen visual acuity chart.

Vitreous Humour 
Transparent jelly-like tissue that fills the space between the lens and the retina.

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