Image of an eye with flap removal

Glossary

Terms and definitions

Medical terms such as “refractive power” make information about laser eye surgery difficult to follow and understand. This glossary clearly defines these terms from A to Z. This way, you can be a knowledgeable, active participant in your eye treatment.

  • All
    • 20/20

      20/20 denotes visual acuity. If the result of an eye exam is 20/20, it means that a person has typical vision. 20/20 specifically refers to a person who is able to see the same detail from 20 feet away as an average person from 20 feet away. It is possible to have visual acuity better than 20/20; the best known is 20/10.

    • Ablation

      Ablation is the precise removal of corneal tissue with a special laser, called an excimer laser. Both PRK and LASIK use this laser to sculpt the cornea and correct the refractive error.

    • Accomodation

      Refers to the ability of the eye to alter the focusing power of the natural lens (also referred to as the optical or refractive power) to see images sharply at varying distances. Accommodation decreases with age because the natural lens gradually loses its flexibility.

    • Astigmatism

      Astigmatism is a condition in which vision is blurred, skewed and/or distorted due to an unevenly distributed refractive power. Severity can be classified in low (from 0.25 to 0.75 diopters), mild (1.00 to 2.50 diopters), severe (2.75 to 4.75 diopters) and extreme (≥ 5.00 diopters) astigmatism.

    • Bandage contact lens

      A thin and soft contact lens without refractive power that is usually placed on the eye to protect it and improve healing after laser eye surgery with PRK/LASEK or occasionally after flap creation.

    • Cap

      Corneal tissue above the created and extracted lenticule during SMILE surgery.

    • Cataract

      A cataract is a clouding of the natural lens in the eye, which can lead to a decrease in vision in one or both eyes. It blurs vision and might end in blindness. Cataracts usually develop with age, but can be successfully treated with surgery that removes the natural lens and replaces it with a small artificial lens (intraocular lens).

    • Clear lens exchange

      During a clear lens exchange, a tiny incision is made in the eye where the clear natural lens is removed. The affected natural lens is then replaced by a small artificial lens (intraocular lens). This procedure can be performed to correct the refractive error and several other eye conditions without the indication of cataract in the eye.

    • Conjunctiva

      The thin membrane covering the inner part of the eyelid and the white part of the eyeball (the sclera), keeping the eye moist and protected.

    • Cornea

      The transparent front part of the eye that refracts light rays coming into the eye through the iris and pupil. Two-thirds of the eye’s refractive power comes from the cornea.

    • Cornea Transplant

      A donated, healthy cornea from a donor is transplanted via surgery to replace the damaged cornea of the receiver.

    • Diopter (dpt)

      A unit used to measure the refractive power of an optical system such as the eye or a part of it. Diopters are used to describe the level of visual error, where 0 dpt describes no refractive error.

    • Diplopia (double vision)

      The simultaneous perception of seeing two images of a single object displaced around the actual object.

    • Dry eye syndrome

      A condition in which the eye does not produce tears properly, or that the tears evaporate too quickly because they are not of the correct consistency. Dry eye can cause discomfort and blurry vision. This syndrome is relatively common in the early postoperative time period after laser eye surgery but can also be caused by extended wear of contact lenses.

    • Ectasia (corneal ectasia)

      A thinning and thus weakening of the cornea may lead to progressive steepening or bulging (ectasia) of the cornea. This condition could occur naturally (called keratoconus) or after laser eye surgery.

    • Emmetropia

      The medical term when there is no refractive error with the eye in a relaxed state and without effort (no accommodation). The eye focuses distant images onto the retina with a single focal point (i.e. no need to wear glasses for distant vision).

    • Epithelium

      The top, outermost layer of the cornea.

    • Excimer laser

      An ultraviolet laser used in laser eye surgery to remove corneal tissue by ablation.

    • Femtosecond laser

      An extremely short-pulsed, near infrared laser used to create a LASIK flap and for all SMILE operations. The laser’s high peak intensity over a very short pulse duration (within a few femtoseconds of time) allows the laser to create micro-precision single cuts or planes in the corneal tissue without affecting the surrounding tissue.

    • Flap

      A thin, hinged layer of the upper corneal tissue that is folded back during LASIK in order to access the underlying corneal tissue for tissue ablation with an excimer laser. After the ablation, it is put back.

    • Focal point

      The point at which light rays meet after refraction within the eye. In normal eyesight, the focal point is on the retina. If a refractive error is present, the focal point lies in front of or behind the retina.

    • Glaucoma

      Glaucoma is a disease that damages your eye’s optic nerve. It is associated with high pressure inside the eye. Glaucoma is a leading cause of blindness for people over 60 years old. However, blindness from glaucoma can often be prevented with early treatment.

    • Halo

      A ring-like phenomenon around lights, typically seen at night time.

    • Haze

      Haze can either refer to blurry/foggy vision or the slight opacity of the cornea, which can be observed after PRK/LASEK procedures. This is a healing response and typically resolves as healing completes. In rare severe cases a doctor may prescribe eye drops or additional procedures.

    • Hyperopia

      The medical term for farsightedness. A condition in which there is not enough optical power in the cornea or natural lens, so that light rays from a distant object are focussed behind the retina. Objects that are close by are especially blurry. Low hyperopia is typically considered to be below +2.00 diopters, mild hyperopia ranges from +2.25 to +5.00 diopters and severe hyperopia higher than +5.00 diopters.

    • Intraocular lens

      An artificial lens implanted in the eye, which is used as a treatment for cataracts as well as for specific refractive errors.

    • Iris

      The coloured ring of tissue between the cornea and the natural lens. People refer to their iris when referring to their eye colour. The iris regulates the amount of light entering the eye by changing the size of the pupil.

    • Keratoconus

      A disease of the eye, characterised by a cone-like protruding deformation of the cornea that usually affects both eyes. It is caused by an unknown weakening of the corneal stroma. Keratoconus can cause nearsightedness, astigmatism and double vision. Patients with keratoconus should not undergo Laser Vision Correction.

    • Laser

      A device that generates an intense beam of energy in the form of light. It is used in refractive eye surgery to cut or ablate tissue. In refractive surgery, the laser light can be infrared or ultraviolet, both invisible to the human eye.

    • Laser eye surgery

      A medical procedure that corrects refractive errors by sculpting the cornea to properly refract light onto the retina.

    • LASEK

      The acronym stands for Laser Sub-Epithelial Keratomileusis. The operation corrects refractive errors by temporarily removing the epithelium and shaping the cornea with an excimer laser. After surgery, the doctor replaces the epithelium and inserts a bandage contact lens to support healing. Today, it is used mainly to treat low to moderate myopia.

    • Lens (natural lens)

      The lens behind the iris that helps to focus light on the retina. It changes shape so that the eye can focus on objects at different distances.

    • Lenticule

      A small lens shaped corneal tissue created during SMILE while the cornea remains intact, using only a femtosecond laser system.

    • Macula

      The area on the retina where we have central vision. It has the highest density of photoreceptors and is critically important for excellent vision and color perception.

    • Microkeratome

      A precision surgical device with a mechanically oscillating blade used to cut the corneal flap during LASIK.

    • Myopia

      The medical term for nearsightedness. A condition in which the eye has too much optical power. Light rays are refracted by the cornea and the lens in such a way that the focal point is in front of the retina. This causes objects in the distance to appear blurry. The severity of Myopia is classified in diopters: Low < 3 dpt, mild -3 to -6 dpt and severe > -6 dpt.

    • Ophthalmologist

      A doctor who has completed medical school and many years of surgical training on diseases of the eye.

    • Optic nerve

      The optic nerve belongs to the central nervous system. It transfers visual information from the retina to the brain. The point where the optic nerve meets the eye is called a blind spot.

    • Overcorrection

      Overcorrection describes a refractive error remaining after surgery. This may occur due to variances in how a person's eyes heal after surgery or too much tissue was removed during the procedure. Sometimes the physician will deliberately aim for overcorrection because the healing process of the eye may lead to a regression of the correction. If still present after the healing process is completed, it may be correctable with enhancement surgery.

    • Presbyopia

      A condition in which the eye’s natural lens loses its flexibility, resulting in an impaired ability to see close objects sharply. Presbyopia comes with age and often requires the use of reading glasses.

    • PRK

      A type of eye laser surgery used to correct nearsightedness, farsightedness and astigmatism. The outermost layer of the cornea (epithelium) is removed from the top of the eye, typically using an alcoholic solution. Then an excimer laser reshapes the front of the eye (cornea) to properly focus light in the back of the eye for clearer vision.

    • Pupil

      This part of the eye is an aperture in the center of the iris (coloured region). The pupil appears black as it absorbs all incoming light rays – with one exception: Flashlights make the pupil look red. This is because light is reflected off the retina. A large burst of light reaches the retina, reflects back, and is captured on film. The eyes look red due to the rich blood supply of the retina. The pupil changes size to control how much light enters the eye and to change the depth of focus in order to see objects of interest clearly.

    • Refraction and refractive error

      Refraction is the change in the direction of a light beam because of changes in the optical power in the medium of transmission . A refractive error occurs when there is an imbalance between the optical power of the eye (from both the cornea and natural lens) and the length of the eyecurvature of the surface, the natural lens, the length of the eye and the refractive power of the cornea and lens. It is a common eye condition that results in blurry vision. Examples are nearsightedness, farsightedness and astigmatism.

    • Refractive surgery

      A surgical procedure used to correct refractive errors. The cornea is reshaped, aiming for an improved focussing ability of the eye.

    • Retina

      A thin layer of sensory tissue that lines the back of the eye, which contains many photoreceptor cells. These cells are light-sensitive and trigger impulses to the optic nerve, which sends images to the brain.

    • Retinal detachment

      The detachment of the sensory retina and the retinal pigment of the cellular tissue. Needs immediate treatment to prevent vision loss and blindness.

    • Sclera

      The white area surrounding the iris acts as a protective outer layer to the eye.

    • SMILE

      The acronym stands for Small Incision Lenticule Extraction and describes the latest advancement of laser eye surgery to correct nearsightedness and astigmatism. This minimally invasive procedure creates a small lenticule in the cornea. This lenticule is extracted through a small incision to reshape and correct the refractive error. The outer corneal layer remains largely intact.

    • Stroma

      An inner sub-layer of tissue in the cornea.

    • Tear film (pre-corneal layer)

      A liquid layer on the cornea that keeps the cornea healthy and helps ensure good vision. Maintaining the eye’s lubrication reduces friction with blinking and eye movement. This layer also traps and flushes out foreign bodies and chemicals to prevent infections. In laser eye surgery, this layer is often affected, which can temporarily cause dry eye syndrome.

    • Undercorrection

      Undercorrection describes a residual refractive error remaining after surgery. This occurs due to differences in how a person's eyes heal after surgery. Under correction can often be corrected with enhancement surgery.

    • Vision

      The ability to transform incoming light into an image; the ability to see.

    • Visual acuity

      The clarity of vision is referred to as acuity. Visual acuity is a measure of the ability of the eye to distinguish shapes and details of objects at a given distance.

    • Visual aid

      A device to correct eyesight, like glasses or contact lenses, is considered a visual aid.

    • Vitreous cavity

      A space inside the eye behind the lens that is filled with a jelly-like substance that maintains the shape of the eyeball.

  • A-F
    • Ablation

      Ablation is the precise removal of corneal tissue with a special laser, called an excimer laser. Both PRK and LASIK use this laser to sculpt the cornea and correct the refractive error.

    • Accommodation

      Refers to the ability of the eye to alter the focusing power of the natural lens (also referred to as the optical or refractive power) to see images sharply at varying distances. Accommodation decreases with age because the natural lens gradually loses its flexibility.

    • Astigmatism

      Astigmatism is a condition in which vision is blurred, skewed and/or distorted due to an unevenly distributed refractive power. Severity can be classified in low (from 0.25 to 0.75 diopters), mild (1.00 to 2.50 diopters), severe (2.75 to 4.75 diopters) and extreme (≥ 5.00 diopters) astigmatism.

    • Bandage contact lens

      A thin and soft contact lens without refractive power that is usually placed on the eye to protect it and improve healing after laser eye surgery with PRK/LASEK or occasionally after flap creation.

    • Cap

      Corneal tissue above the created and extracted lenticule during SMILE surgery.

    • Cataract

      A cataract is a clouding of the natural lens in the eye, which can lead to a decrease in vision in one or both eyes. It blurs vision and might end in blindness. Cataracts usually develop with age, but can be successfully treated with surgery that removes the natural lens and replaces it with a small artificial lens (intraocular lens).

    • Clear lens exchange

      During a clear lens exchange, a tiny incision is made in the eye where the clear natural lens is removed. The affected natural lens is then replaced by a small artificial lens (intraocular lens). This procedure can be performed to correct the refractive error and several other eye conditions without the indication of cataract in the eye.

    • Conjunctiva

      The thin membrane covering the inner part of the eyelid and the white part of the eyeball (the sclera), keeping the eye moist and protected.

    • Cornea

      The transparent front part of the eye that refracts light rays coming into the eye through the iris and pupil. Two-thirds of the eye’s refractive power comes from the cornea.

    • Cornea transplant

      A donated, healthy cornea from a donor is transplanted via surgery to replace the damaged cornea of the receiver.

    • Diopter (dpt)

      A unit used to measure the refractive power of an optical system such as the eye or a part of it. Diopters are used to describe the level of visual error, where 0 dpt describes no refractive error.

    • Diplopia (double vision)

      The simultaneous perception of seeing two images of a single object displaced around the actual object.

    • Dry eye syndrome

      A condition in which the eye does not produce tears properly, or that the tears evaporate too quickly because they are not of the correct consistency. Dry eye can cause discomfort and blurry vision. This syndrome is relatively common in the early postoperative time period after laser eye surgery but can also be caused by extended wear of contact lenses.

    • Ectasia (corneal ectasia)

      A thinning and thus weakening of the cornea may lead to progressive steepening or bulging (ectasia) of the cornea. This condition could occur naturally (called keratoconus) or after laser eye surgery.

    • Emmetropia

      The medical term when there is no refractive error with the eye in a relaxed state and without effort (no accommodation). The eye focuses distant images onto the retina with a single focal point (i.e. no need to wear glasses for distant vision).

    • Epithelium

      The top, outermost layer of the cornea.

    • Excimer laser

      An ultraviolet laser used in laser eye surgery to remove corneal tissue by ablation.

    • Femtosecond laser

      An extremely short-pulsed, near infrared laser used to create a LASIK flap and for all SMILE operations. The laser’s high peak intensity over a very short pulse duration (within a few femtoseconds of time) allows the laser to create micro-precision single cuts or planes in the corneal tissue without affecting the surrounding tissue.

    • Flap

      A thin, hinged layer of the upper corneal tissue that is folded back during LASIK in order to access the underlying corneal tissue for tissue ablation with an excimer laser. After the ablation, it is put back.

    • Focal point

      The point at which light rays meet after refraction within the eye. In normal eyesight, the focal point is on the retina. If a refractive error is present, the focal point lies in front of or behind the retina.

  • G-K
    • Glaucoma

      Glaucoma is a disease that damages your eye’s optic nerve. It is associated with high pressure inside the eye. Glaucoma is a leading cause of blindness for people over 60 years old. However, blindness from glaucoma can often be prevented with early treatment.

    • Halo

      A ring-like phenomenon around lights, typically seen at night time.

    • Haze

      Haze can either refer to blurry/foggy vision or the slight opacity of the cornea, which can be observed after PRK/LASEK procedures. This is a healing response and typically resolves as healing completes. In rare severe cases a doctor may prescribe eye drops or additional procedures.

    • Hyperopia

      The medical term for farsightedness. A condition in which there is not enough optical power in the cornea or natural lens, so that light rays from a distant object are focussed behind the retina. Objects that are close by are especially blurry. Low hyperopia is typically considered to be below +2.00 diopters, mild hyperopia ranges from +2.25 to +5.00 diopters and severe hyperopia higher than +5.00 diopters.

    • Intraocular lens

      An artificial lens implanted in the eye, which is used as a treatment for cataracts as well as for specific refractive errors.

    • Iris

      The coloured ring of tissue between the cornea and the natural lens. People refer to their iris when referring to their eye colour. The iris regulates the amount of light entering the eye by changing the size of the pupil.

    • Keratoconus

      A disease of the eye, characterised by a cone-like protruding deformation of the cornea that usually affects both eyes. It is caused by an unknown weakening of the corneal stroma. Keratoconus can cause nearsightedness, astigmatism and double vision. Patients with keratoconus should not undergo Laser Vision Correction.

  • L-O
    • Laser

      A device that generates an intense beam of energy in the form of light. It is used in refractive eye surgery to cut or ablate tissue. In refractive surgery, the laser light can be infrared or ultraviolet, both invisible to the human eye.

    • Laser eye surgery

      A medical procedure that corrects refractive errors by sculpting the cornea to properly refract light onto the retina.

    • LASEK

      The acronym stands for Laser Sub-Epithelial Keratomileusis. The operation corrects refractive errors by temporarily removing the epithelium and shaping the cornea with an excimer laser. After surgery, the doctor replaces the epithelium and inserts a bandage contact lens to support healing. Today, it is used mainly to treat low to moderate myopia.

    • Lens (natural lens)

      The lens behind the iris that helps to focus light on the retina. It changes shape so that the eye can focus on objects at different distances.

    • Lenticule

      A small lens shaped corneal tissue created during SMILE while the cornea remains intact, using only a femtosecond laser system.

    • Macula

      The area on the retina where we have central vision. It has the highest density of photoreceptors and is critically important for excellent vision and color perception.

    • Microkeratome

      A precision surgical device with a mechanically oscillating blade used to create the corneal flap during LASIK.

    • Myopia

      The medical term for nearsightedness. A condition in which the eye has too much optical power. Light rays are refracted by the cornea and the lens in such a way that the focal point is in front of the retina. This causes objects in the distance to appear blurry. The severity of Myopia is classified in diopters: Low < 3 dpt, mild -3 to -6 dpt and severe > -6 dpt.

    • Ophthalmologist

      A doctor who has completed medical school and many years of surgical training on diseases of the eye.

    • Optic nerve

      The optic nerve belongs to the central nervous system. It transfers visual information from the retina to the brain. The point where the optic nerve meets the eye is called a blind spot.

    • Overcorrection

      Overcorrection describes a refractive error remaining after surgery. This may occur due to variances in how a person's eyes heal after surgery or too much tissue was removed during the procedure. Sometimes the physician will deliberately aim for overcorrection because the healing process of the eye may lead to a regression of the correction. If still present after the healing process is completed, it may be correctable with enhancement surgery.

  • P-T
    • Presbyopia

      A condition in which the eye’s natural lens loses its flexibility, resulting in an impaired ability to see close objects sharply. Presbyopia comes with age and often requires the use of reading glasses.

    • PRK

      A type of eye laser surgery used to correct nearsightedness, farsightedness and astigmatism. The outermost layer of the cornea (epithelium) is removed from the top of the eye, typically using an alcoholic solution. Then an excimer laser reshapes the front of the eye (cornea) to properly focus light in the back of the eye for clearer vision.

    • Pupil

      This part of the eye is an aperture in the center of the iris (coloured region). The pupil appears black as it absorbs all incoming light rays – with one exception: Flashlights make the pupil look red. This is because light is reflected off the retina. A large burst of light reaches the retina, reflects back, and is captured on film. The eyes look red due to the rich blood supply of the retina. The pupil changes size to control how much light enters the eye and to change the depth of focus in order to see objects of interest clearly.

    • Refraction and refractive error

      Refraction is the change in the direction of a light beam because of changes in the optical power in the medium of transmission. A refractive error occurs when there is an imbalance between the optical power of the eye (from both the cornea and natural lens) and the length of the eye. It is a common eye condition that results in blurry vision. Examples are nearsightedness, farsightedness and astigmatism.

    • Refractive surgery

      A surgical procedure used to correct refractive errors. The cornea is reshaped, aiming for an improved focussing ability of the eye.

    • Retina

      A thin layer of sensory tissue that lines the back of the eye, which contains many photoreceptor cells. These cells are light-sensitive and trigger impulses to the optic nerve, which sends images to the brain.

    • Retinal detachment

      The detachment of the sensory retina and the retinal pigment of the cellular tissue. Needs immediate treatment to prevent vision loss and blindness.

    • Sclera

      The white area surrounding the iris acts as a protective outer layer to the eye.

    • SMILE

      The acronym stands for Small Incision Lenticule Extraction and describes the latest advancement of laser eye surgery to correct nearsightedness and astigmatism. This minimally invasive procedure creates a small lenticule in the cornea. This lenticule is extracted through a small incision to reshape and correct the refractive error. The outer corneal layer remains largely intact.

    • Stroma

      An inner sub-layer of tissue in the cornea.

    • Tear film (pre-corneal layer)

      A liquid layer on the cornea that keeps the cornea healthy and helps ensure good vision. Maintaining the eye’s lubrication reduces friction with blinking and eye movement. This layer also traps and flushes out foreign bodies and chemicals to prevent infections. In laser eye surgery, this layer is often affected, which can temporarily cause dry eye syndrome.

  • U-Z
    • Undercorrection

      Undercorrection describes a residual refractive error remaining after surgery. This occurs due to differences in how a person's eyes heal after surgery. Under correction can often be corrected with enhancement surgery.

    • Vision

      The ability to transform incoming light into an image; the ability to see.

    • Visual acuity

      The clarity of vision is referred to as acuity. Visual acuity is a measure of the ability of the eye to distinguish shapes and details of objects at a given distance.

    • Visual aid

      A device to correct eyesight, like glasses or contact lenses, is considered a visual aid.

    • Vitreous cavity

      A space inside the eye behind the lens that is filled with a jelly-like substance that maintains the shape of the eyeball.

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