Cataract Glossary

Glossary

Terms and Definitions

Medical terms such as “refractive power” make information about cataract surgery difficult to follow and understand. This glossary defines the terms of cataract surgery from A to Z so that you can be a knowledgeable, active participant in your eye treatment discussion.

  • All
    • 20/20

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

    • Accommodation

      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. This is a special function of the eye. Intraocular lenses help improve vision, but they cannot adopt this function.

    • Aspheric intraocular lens

      Patients with impaired vision quality and contrast sharpness, particularly in poor lighting conditions (at dusk or at night) can chose to let their natural lens be replaced by an intraocular lens with an aspheric shape (i.e. not round) in cataract surgery. This way, the light rays can be optimally focused onto the retina.

    • Astigmatism

      Astigmatism is a condition in which vision is skewed, distorted and blurry due to an unevenly distributed refractive power. The severity can be classified in low (from 0.25 to 0.75 dpt), mild (1.00 to 2.50 dpt), severe (2.75 to 4.75 dpt) and extreme (≤ 5.00 dpt) astigmatism.

    • Bifocal intraocular lens

      The cloudy natural lens can be replaced by a bifocal intraocular lens in cataract surgery. Such lenses have two focal points, providing clear vision for far and close distances. However, patients may still need to wear eyeglasses for certain intermediate-range tasks (approx. 80 cm) after surgery.

    • Cataracts

      The condition appears as a cloud over the natural lens, which can develop in one or both eyes. It blurs vision and might end in blindness. Cataracts (nuclear sclerosis) usually develop with age, but can be treated with surgery, which removes the natural lens and replaces it with a small artificial lens.

    • 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 come from the cornea.

    • Contact lens

      A thin and lightweight lens placed directly on the cornea (surface of the eye). Contact lenses are considered medical devices requiring a prescription by a qualified eye-care practitioner. They are worn to correct vision, or for cosmetic or therapeutic reasons.

    • Cylindrical lens

      A lens, which focuses light into a line. The curved surfaces are sections of a cylinder, and focus the image passing through it into a line parallel to the intersection of the surface of the lens, and a plane tangent to it.

    • Dioptre (dpt)

      A unit used to measure the refractive power of the lens based on the curvature of the surface, the natural lens and the length of the eye.

    • EDoF (Extended Depth of Focus)

      These lenses use an advanced optical technology that allows to increase the range of vision from far through intermediate distances.

    • Emmetropia

      The medical term for the state of normal vision where an object is in sharp focus at all distances with the eye lens in a relaxed state, and without making an effort. In sharp vision, the eye focuses images that are near and far directly onto the retina with a single focal point.

    • Epithelium

      The top, outermost layer of the cornea is made up by lens epithelial cells.

    • Extraocular muscles

      Six muscles attached to the eye that control its movement: the four rectus muscles (superior, inferior, medial, and lateral) and two oblique muscles (superior and inferior).

    • Eye exam

      A series of tests performed by an ophthalmologist or optometrist to assess vision, the ability to focus on and discern distant objects, and general eye health. Periodic and thorough eye examinations as part of routine examinations are generally recommended.

    • Eye strain

      An eye condition often occurring after tedious visual tasks. Symptoms can be fatigue, pain in or around the eyes, blurred vision, headaches and occasionally double vision.

    • Farsightedness

      With farsightedness, also called hyperopia, close objects appear blurry and distant objects are sharply focused. A hyperopic eye refracts light to a focal point that lies behind the retina. Blurred vision occurs because the light is not focused on the retina, where the optic nerve transmits the image to the brain.

    • 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.

    • Fovea

      In the eye, a tiny pit located in the macula of the retina that provides the clearest vision of all. Only in the fovea are the layers of the retina spread aside to let light fall directly on the cones, the cells that give the sharpest image. Also called the central fovea or fovea centralis.

    • Glaucoma

      A disease where blocked tubes cause a higher intraocular pressure than normal within the eye, preventing the eye fluid from draining properly, and damaging the optic nerves. This hinders the field of vision and results in blindness if not treated.

    • Halo

      This phenomenon occurs at night time around bright lights. When it is dark, the pupil may dilate to a bigger size.

    • Hyperopia

      The medical term for farsightedness. A condition in which light rays are refracted by the cornea through the natural lens in such a way that the focal point lies behind the retina. This causes objects that are close to appear blurry. Low hyperopia is considered to be below +2.00 dpt, mild hyperopia ranges from +2.25 to +5.00 dpt and severe hyperopia higher than +5.00 dpt.

    • Intraocular Pressure (IOP)

      The fluid pressure inside the eye, based on the balance between production and drainage of liquids. A balanced IOP keeps the eye in shape, provides nutrients to intraocular structures and maintains the function of these structures. IOP is an important aspect in the evaluation of patients at risk for glaucoma.

    • Iris

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

    • Keratoconus

      A rare disease of the eye, characterised by a cone-like protruding deformation of the cornea that usually affects both eyes. It is caused by a thinning of the corneal stroma. Keratoconus causes nearsightedness, astigmatism and double vision.

    • Keratoplasty

      Surgical modification of the cornea; the removal of a portion of the cornea containing an opacity, and transplanting corneal material of the same size and shape.

    • Lens (Natural lens)

      A transparent part of the eye that with the help of the cornea bends light onto the retina to create a sharp image. The lens changes its shape so that the eye can focus on objects at different distances, which is called accommodation.

    • Macula

      A part of the retina appearing as a yellow spot with a high density of photoreceptors. The macula is important for acuity of vision and colour perception.

    • Meridian

      An imaginary line on the surface of the eye’s spherical body, marking the intersection with the surface of a plane passing through its axis.

    • Monovision

      The Monovision method corrects vision in one eye (non-dominant) purposely for farsightedness, while correcting the other eye (dominant) for nearsightedness. This results in the non-dominant eye seeing clearly at short distances, and the dominant eye seeing clearly at every possible distance. This procedure is only applicable to a certain amount of patients.

    • Multifocal intraocular lens
      These lenses have two or three focal points and restore vision at more than one distance, giving the patient a chance of being more independent of visual aids.
    • Myopia

      The medical term for nearsightedness. A condition in which 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 < -0.25 dpt, mild -0.25 to -4 dpt and severe > -4 dpt.

    • Nearsightedness

      For people with myopia, known commonly as nearsightedness, far away objects appear blurry whereas close objects are sharply focused. As the eye has too much refractive power in relation to its length, the focal point of incoming light lies at a point before the retina, where the optic nerve transmits the image to the brain.

    • Ophthalmic Viscosurgical Device (OVD)

      During cataract surgery, a jelly-like substance called ‘Ophthalmic Viscosurgical Device’ (OVD) is injected into the eye in order to protect the eye and support intraocular structures.

    • 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 the blind spot.

    • Optometrist

      Optometrists are healthcare professionals who provide primary vision care ranging from sight testing and correction to the diagnosis, treatment, and management of vision changes. Their prescriptions may be used by opticians; technicians trained to design, verify and fit devices to correct eyesight. Opticians are not permitted to diagnose or treat eye diseases.

    • Phacoemulsification

      During cataract surgery, the cataractous lens is softened and broken apart using a small ultrasound device called a ‘phaco tip’. The lens is then removed from the eye by the phaco tip, using gentle suction.

    • Posterior capsule opacity (PCO)

      During cataract surgery recovery, the posterior portion of the lens capsule becomes hazy. PCO occurs because lens epithelial cells remain after the surgery and grow on the capsule.

    • 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 affected persons to use reading glasses. Low hyperopia is considered to be below +2.00 dpt, mild hyperopia ranges from +2.25 to +5.00 dpt and severe hyperopia higher than +5.00 dpt.

    • Pupil

      This part of the eye is a hole in the centre of the iris (coloured region). The pupil changes size to control how much light enters the eye. It appears black as it absorbs all incoming light rays – with one exception: flashlights make the pupil look red.

    • Pupil dilation

      Dilating (widening) the pupil permits your eye to be examined for signs of disease. To do this, drops are placed into the eye - possibly causing blurred vision for several hours.

    • Receptor

      A protein molecule that receives chemical signals from outside a cell, being embedded in its plasma membrane. It is linked to a specific cellular biochemical pathway and can therefore respond to these outside signals, e.g. with a change in the cell’s electrical activity.

    • Refraction and refractive error

      Refraction is the change in the direction of a light beam because of changes in the refractive index in the medium of transmission. A refractive error occurs when there is an imbalance between the curvature 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.

    • 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.

    • Retinal examination

      In order to examine the retina at the back of your eye, your eye doctor will dilate your pupils by putting drops in your eyes. This way, your pupils will open wide and your eye can be easily examined.

    • Sclera

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

    • Slit lamp examination

      This examination allows your ophthalmologist to view your cornea, iris, lens and the space between your iris and cornea in small sections. This makes it easier to detect any abnormalities due to cataract or other diseases of the eye.

    • Spherical aberration

      This visual defect occurs when the light rays passing into the eye are not precisely focused at one single point on the retina. Spherical aberrations are a result of the aging process.

    • Tear film (pre-corneal layer)

      A liquid layer between the conjunctiva and the cornea that keeps tears from quickly evaporating. 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.

    • Toric intraocular lens

      This premium lens implant is adapted to the circumstances of astigmatism. The vision of people suffering from astigmatism can be corrected by replacing the natural lens with a toric lens during cataract surgery.

    • Vision

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

    • Visual acuity

      Clarity of vision is referred to as acuity. In a visual acuity test, your ophthalmologist will ask you to read an eye chart in order to determine if your vision shows signs of impairment.

    • Visual aid

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

    • Vitreous cavity
      A space inside the eye behind the lens that is filled with a clear, jelly-like substance – the vitreous body – that maintains the shape of the eyeball.
    • Vitreous body

      A clear, jelly-like substance that fills the vitreous cavity. It helps maintain the shape of the eye.

  • A-F
    • 20/20

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

    • Accommodation

      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. This is a special function of the eye. Intraocular lenses help improve vision, but they cannot adopt this function.

    • Aspheric intraocular lens

      Patients with impaired vision quality and contrast sharpness, particularly in poor lighting conditions (at dusk or at night) can chose to let their natural lens be replaced by intraocular lens with an aspheric shape (i.e. not round) in cataract surgery. This way, the light rays can be optimally focused onto the retina.

    • Astigmatism

      Astigmatism is a condition in which vision is skewed, distorted and blurry due to an unevenly distributed refractive power. The severity can be classified in low (from 0.25 to 0.75 dpt), mild (1.00 to 2.50 dpt), severe (2.75 to 4.75 dpt) and extreme (≤ 5.00 dpt) astigmatism.

    • Bifocal intraocular lens

      The cloudy natural lens can be replaced by a bifocal intraocular lens in cataract surgery. Such lenses have two focal points, providing clear vision for far and close distances. However, patients may still need to wear eyeglasses for certain intermediate-range tasks (approx. 80 cm) after surgery.

    • Cataracts

      The condition appears as a cloud over the natural lens, which can develop in one or both eyes. It blurs vision and might end in blindness. Cataracts (nuclear sclerosis) usually develop with age, but can be treated with surgery which removes the natural lens and replaces it with a small artificial lens.

    • 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 come from the cornea.

    • Contact lens

      A thin and lightweight lens placed directly on the cornea (surface of the eye). Contact lenses are considered medical devices requiring a prescription by a qualified eyecare practitioner.They are worn to correct vision, or for cosmetic or therapeutic reasons.

    • Cylindrical lens

      A lens which focuses light into a line. The curved surfaces are sections of a cylinder, and focus the image passing through it into a line parallel to the intersection of the surface of the lens and a plane tangent to it.

    • Dioptre (dpt)

      A unit used to measure the refractive power of the lens based on the curvature of the surface, the natural lens and the length of the eye.

    • EDoF (Extended Depth of Focus)

      These lenses use an advanced optical technology that allows to increase the range of vision from far through intermediate distances.

    • Emmetropia

      The medical term for the state of normal vision where an object is in sharp focus at all distances with the eye lens in a relaxed state, and without making an effort. In sharp vision, the eye focuses images that are near and far directly onto the retina with a single focal point.

    • Epithelium

      The top, outermost layer of the cornea is made up by lens epithelial cells.

    • Extraocular muscles

      Six muscles attached to the eye that control its movement: the four rectus muscles (superior, inferior, medial, and lateral) and two oblique muscles (superior and inferior).

    • Eye exam

      A series of tests performed by an ophthalmologist or optometrist to assess vision, the ability to focus on and discern distant objects, and general eye health. Periodic and thorough eye examinations as part of routine examinations are generally recommended.

    • Eye strain

      An eye condition often occurring after tedious visual tasks. Symptoms can be fatigue, pain in or around the eyes, blurred vision, headaches and occasionally double vision.

    • Farsightedness

      With farsightedness, also called hyperopia, close objects appear blurry and distant objects are sharply focused. A hyperopic eye refracts light to a focal point that lies behind the retina. Blurred vision occurs because the light is not focused on the retina, where the optic nerve transmits the image to the brain.

    • 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.

    • Fovea

      In the eye, a tiny pit located in the macula of the retina that provides the clearest vision of all. Only in the fovea are the layers of the retina spread aside to let light fall directly on the cones, the cells that give the sharpest image. Also called the central fovea or fovea centralis.

  • G-K
    • Glaucoma

      A disease where blocked tubes cause a higher intraocular pressure than normal within the eye, preventing the eye fluid from draining properly and damaging the optic nerves. This hinders the field of vision and results in blindness if not treated.

    • Halo

      This phenomenon occurs at night time around bright lights. When it is dark, the pupil may dilate to a bigger size.

    • Hyperopia

      The medical term for farsightedness. A condition in which light rays are refracted by the cornea through the natural lens in such a way that the focal point lies behind the retina. This causes objects that are close to appear blurry. Low hyperopia is considered to be below +2.00 dpt, mild hyperopia ranges from +2.25 to +5.00 dpt and severe hyperopia higher than +5.00 dpt.

    • Intraocular Pressure (IOP)

      The fluid pressure inside the eye, based on the balance between production and drainage of liquids. A balanced IOP keeps the eye in shape, provides nutrients to intraocular structures and maintains the function of these structures. IOP is an important aspect in the evaluation of patients at risk for glaucoma.

    • Iris

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

    • Keratoconus

      A rare disease of the eye, characterised by a cone-like protruding deformation of the cornea that usually affects both eyes. It is caused by a thinning of the corneal stroma. Keratoconus causes nearsightedness, astigmatism and double vision.

    • Keratoplasty

      Surgical modification of the cornea; the removal of a portion of the cornea containing an opacity, and transplanting corneal material of the same size and shape.

  • L-O
    • Lens (Natural lens)

      A transparent part of the eye that with the help of the cornea bends light onto the retina to create a sharp image. The lens changes its shape so that the eye can focus on objects at different distances, which is called accommodation.

    • Macula

      A part of the retina appearing as a yellow spot with a high density of photoreceptors. The macula is important for acuity of vision and colour perception.

    • Meridian

      An imaginary line on the surface of the eye’s spherical body, marking the intersection with the surface of a plane passing through its axis.

    • Monovision

      The Monovision method corrects vision in one eye (non-dominant) purposely for farsightedness, while correcting the other eye (dominant) for nearsightedness. This results in the non-dominant eye seeing clearly at short distances, and the dominant eye seeing clearly at every possible distance. This procedure is only applicable to a certain amount of patients.

    • Multifocal intraocular lens
      These lenses have two or three focal points and restore vision at more than one distance, giving the patient a chance of being more independent of visual aids.
    • Myopia

      The medical term for nearsightedness. A condition in which 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 < -0.25 dpt, mild -0.25 to -4 dpt and severe > -4 dpt.

    • Nearsightedness

      For people with myopia, known commonly as nearsightedness, far away objects appear blurry whereas close objects are sharply focused. As the eye has too much refractive power in relation to its length, the focal point of incoming light lies at a point before the retina, where the optic nerve transmits the image to the brain.

    • Ophthalmic Viscosurgical Device (OVD)

      During cataract surgery, a jelly-like substance called ‘Ophthalmic Viscosurgical Device’ (OVD) is injected into the eye in order to protect the eye and support intraocular structures.

    • 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 the blind spot.

    • Optometrist

      Optometrists are healthcare professionals who provide primary vision care ranging from sight testing and correction to the diagnosis, treatment, and management of vision changes. Their prescriptions may be used by opticians; technicians trained to design, verify and fit devices to correct eyesight. Opticians are not permitted to diagnose or treat eye diseases.

  • P-T
    • Phacoemulsification

      During cataract surgery, the cataractous lens is softened and broken apart using a small ultrasound device called a ‘phaco tip’. The lens is then removed from the eye by the phaco tip, using gentle suction.

    • Posterior capsule opacity (PCO)

      During cataract surgery recovery, the posterior portion of the lens capsule becomes hazy. PCO occurs because lens epithelial cells remain after the surgery and grow on the capsule.

    • 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 affected persons to use reading glasses. Low hyperopia is considered to be below +2.00 dpt, mild hyperopia ranges from +2.25 to +5.00 dpt and severe hyperopia higher than +5.00 dpt.

    • Pupil

      This part of the eye is a hole in the centre of the iris (coloured region). The pupil changes size to control how much light enters the eye. It appears black as it absorbs all incoming light rays – with one exception: flashlights make the pupil look red. 

    • Pupil dilation

      Dilating (widening) the pupil permits your eye to be examined for signs of disease. To do this, drops are placed into the eye - possibly causing blurred vision for several hours.

    • Receptor

      A protein molecule that receives chemical signals from outside a cell, being embedded in its plasma membrane. It is linked to a specific cellular biochemical pathway and can therefore respond to these outside signals, e.g. with a change in the cell’s electrical activity.

    • Refraction and refractive error

      Refraction is the change in the direction of a light beam because of changes in the refractive index in the medium of transmission. A refractive error occurs when there is an imbalance between the curvature 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.

    • 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.

    • Retinal examination

      In order to examine the retina at the back of your eye, your eye doctor will dilate your pupils by putting drops in your eyes. This way, your pupils will open wide and your eye can be easily examined.

    • Sclera

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

    • Slit lamp examination

      This examination allows your ophthalmologist to view your cornea, iris, lens and the space between your iris and cornea in small sections. This makes it easier to detect any abnormalities due to cataracts or other diseases of the eye.

    • Spherical aberration

      This visual defect occurs when the light rays passing into the eye are not precisely focused at one single point on the retina. Spherical aberrations are a result of the aging process.

    • Tear film (pre-corneal layer)

      A liquid layer between the conjunctiva and the cornea that keeps tears from quickly evaporating. 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.

    • Trifocal intraocular lens

      The cloudy natural lens can be replaced by a trifocal intraocular lens in cataract surgery. Such lenses provide clear vision for close, intermediate and far distances. Many patients no longer need to wear eyeglasses at all after surgery.

  • U-Z
    • Vision

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

    • Visual acuity

      Clarity of vision is referred to as acuity. In a visual acuity test, your ophthalmologist will ask you to read an eye chart in order to determine if your vision shows signs of impairment.

    • Visual aid

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

    • Vitreous cavity
      A space inside the eye behind the lens that is filled with a clear, jelly-like substance – the vitreous body – that maintains the shape of the eyeball.
    • Vitreous body

      A clear, jelly-like substance that fills the vitreous cavity. It helps maintain the shape of the eye.

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