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Glossary
Topography, pachymetry, capsulorhexis, EDOF: an eye consultation comes with its own vocabulary, and none of it is obvious. Here, in plain English, are definitions of the 62 terms used on this site, and of the ones you will hear during a consultation.
A
- Aberrometry
- A test that measures the optical imperfections of the eye, beyond the simple correction in dioptres. It helps explain night-time visual discomfort, or disappointing quality of vision despite a good acuity score.
- Add-on lens
- A thin second lens placed in front of the one already implanted during earlier cataract surgery. It corrects a residual error or adds near vision, and it has the advantage of being removable.
- AMD (age-related macular degeneration)
- Damage to the central area of the retina, which affects fine vision and face recognition while sparing peripheral vision.
- Ametropia
- The general term for any vision defect caused by the way the eye focuses: myopia, hyperopia, astigmatism and presbyopia. An eye without ametropia is called emmetropic.
- Angle (iridocorneal)
- The space between the iris and the cornea, through which the fluid filling the front of the eye drains away. How open it is determines the risk of glaucoma and whether a phakic lens can be implanted. It is examined by gonioscopy.
- Aqueous humour
- A clear fluid produced continuously behind the iris, in the ciliary body. It passes through the pupil, fills the space between the cornea and the natural lens, then drains through a filter in the angle of the eye. The balance between how much is produced and how much drains away sets the intraocular pressure, and slower drainage is what causes glaucoma. It has nothing to do with tears, which bathe the surface of the eye.
- Astigmatism
- A defect caused by a cornea that is not perfectly spherical: it is shaped more like a rugby ball than a football. The image is distorted at all distances.
B
- Biometry
- A set of measurements of the eye (length, curvature, depth) used to calculate the power of the lens to be implanted during lens surgery. This is the test that determines how precise the result will be.
C
- Capsule
- A very thin, transparent envelope that holds the natural lens. During cataract surgery the lens is removed but the capsule is kept: it is the capsule that holds the implant.
- Capsulorhexis
- A circular opening made in the front of the capsule to reach the natural lens. How regular it is determines how well the implant stays in place.
- Capsulotomy (YAG)
- A laser opening of the capsule when it has become cloudy after cataract surgery. It is done during a consultation, takes a few minutes and needs no incision. It is the treatment for secondary cataract.
- Cataract
- Gradual clouding of the natural lens, which sits behind the pupil. It mainly comes with age and can only be treated with surgery.
- Choroid
- The layer of blood vessels under the retina, which nourishes it. This is where the abnormal vessels of wet AMD grow from.
- CIRCLE
- A technique for an enhancement after SMILE. The femtosecond laser turns the old corneal cap into a full LASIK flap, which can then be lifted to complete the correction.
- Cornea
- The transparent, curved membrane at the front of the eye, like a porthole. It provides two thirds of the eye's focusing power, and it is the part the laser reshapes.
- Corneal flap
- A thin layer of cornea cut and lifted during LASIK, then laid back at the end of the procedure. It adheres on its own, without stitches. SMILE and Trans-PRK do not create one.
- Corneal topography
- A relief map of the cornea that shows its shape and irregularities. It is the key test of the pre-operative assessment, and the one that detects keratoconus.
- Crystalline lens
- The natural lens behind the pupil, which fine-tunes focusing. Flexible in youth, it stiffens with age (that is presbyopia) and then becomes cloudy (that is cataract).
- Cycloplegia
- Putting in eye drops that temporarily block accommodation, so that the eye's true correction can be measured without it compensating. Near vision is blurred for a few hours.
D
- Dilated eye examination (fundus examination)
- Examination of the retina, the optic nerve and the blood vessels, carried out after the pupil has been dilated. Vision stays blurred for a few hours afterwards: it is best not to drive.
- Dioptre
- The unit used to measure a vision defect. Myopia of −3 dioptres is moderate; beyond −8 it is considered high. It is the figure on your glasses prescription.
E
- Ectasia
- Progressive, irreversible deformation of the cornea, which bulges abnormally. It is the complication the pre-operative assessment is above all designed to prevent, by ruling out corneas that are too thin or irregular.
- EDOF
- Short for extended depth of focus. A family of lens implants that give clear distance and intermediate vision, with fewer night-time halos than multifocal lenses.
- Emmetropia
- The state of an eye that needs no correction: the image forms exactly on the retina.
- Endothelium
- The deepest layer of the cornea, whose cells keep it transparent. They do not regenerate, which is why they are counted regularly in people with a phakic lens.
- Epithelium
- The outermost layer of the cornea, which regenerates after an injury. Trans-PRK removes it; the three to five days it takes to grow back explain the recovery after this technique.
- Excimer laser
- A laser that vaporises corneal tissue to the micron, without contact and without heat, to change the curvature of the cornea. It is the laser that performs the correction itself.
F
- Femtosecond laser
- A laser that cuts tissue inside the cornea itself, without heat. It creates the LASIK flap and the SMILE lenticule. It is different from the excimer laser, which reshapes.
G
- Glaucoma
- Progressive damage to the optic nerve, most often linked to excessive pressure inside the eye. It destroys peripheral vision first, without pain or warning signs, which is why screening matters.
H
- Halos
- Rings of light seen around light sources, especially at night. Common after refractive surgery and expected with a multifocal lens, they fade over time.
- Haze
- A scar-like veil that clouds the cornea after surface surgery. It is rare and made more likely by ultraviolet exposure, hence the strict advice on sun protection after Trans-PRK.
- Hyperopia (long-sightedness)
- The opposite defect to myopia: the eye is too short, or the cornea too flat. Near vision tires first; distance vision deteriorates later.
I
- Intraocular lens (IOL)
- An artificial lens placed inside the eye. It replaces the natural lens in cataract surgery and PreLex, or is added in front of it in the case of a phakic lens.
- Iris
- The coloured part of the eye, which adjusts the size of the pupil according to the light.
K
- Keratoconus
- A disease that gradually deforms and thins the cornea. It is a strict contraindication to corneal laser surgery, and detecting it is one of the main purposes of topography.
L
- LASIK
- A refractive surgery technique combining two lasers: the femtosecond laser cuts a corneal flap, the excimer laser reshapes the deeper layer, then the flap is laid back.
- Lenticule
- A thin disc of corneal tissue shaped inside the cornea by the femtosecond laser during SMILE, then removed through a tiny incision.
M
- Macula
- The central area of the retina, a few millimetres across, responsible for fine vision, reading and recognising faces.
- Macular oedema
- A build-up of fluid in the macula, causing a drop in central vision. It is a complication of diabetes, of retinal vein occlusions and sometimes of surgery.
- Monofocal
- A lens implant that gives clear vision at a single distance, usually far. Glasses are still needed for reading. It is the implant covered by French national health insurance (Assurance Maladie).
- Multifocal
- A lens implant that spreads light over several distances, so that glasses can be left off in most situations. The trade-off: night-time halos, and the brain takes several months to adapt.
- Myopia (short-sightedness)
- The eye is too long, or the cornea too curved: the image forms in front of the retina. Distance vision is blurred; near vision stays sharp.
N
- Neuroadaptation
- The period during which the brain learns to make use of the images provided by a multifocal lens. It lasts three to six months, which is why the initial discomfort fades gradually.
O
- OCT
- Optical coherence tomography: cross-sectional imaging of the retina and the optic nerve, painless and contact-free. It detects abnormalities that cannot be seen on a standard examination.
- Optic nerve
- The cable connecting the eye to the brain, which carries visual information. Damage to it, as in glaucoma, is irreversible.
P
- Pachymetry
- Measurement of the thickness of the cornea. It sets the limit of what the laser can remove without weakening the eye, and so the maximum correction that can be considered.
- Phakic lens
- A lens implanted in front of the natural lens, which stays in place. Hence its name, from the Greek phakos, the lens. The most widely used model is the ICL. It is removable.
- PreLex
- Replacement of the natural lens, still clear but stiffened, with a multifocal lens in order to correct presbyopia. The procedure is the same as cataract surgery, done earlier.
- Presbyopia
- The gradual loss of the ability to focus up close, from around 40 to 45, caused by the natural lens hardening. It affects everyone and is not a disease.
- PRK
- Photorefractive keratectomy: a correction made on the surface, without a flap. Trans-PRK is the version in which the laser itself removes the epithelium, without contact.
- Pseudophakic
- Describes an eye whose natural lens has been replaced by an implant. This is the case for every eye that has had cataract surgery.
R
- Refraction
- The way the eye bends light to form a sharp image on the retina. Measuring it means determining your prescription.
- Refractive surprise
- A difference between the intended correction and the one obtained after a lens implant. It comes from the limits of the calculation formulas, and can be corrected in a second step.
- Retina
- The membrane lining the back of the eye, which captures light and converts it into nerve signals. It is the film in the camera.
S
- Secondary cataract
- Clouding of the capsule that supports the implant, occurring months or years after the operation. It is not the cataract coming back: the natural lens has been removed for good. Also called posterior capsule opacification.
- SMILE
- Removal of a corneal lenticule through a tiny incision, without cutting a flap. Only one laser is used, and more of the cornea's structure is preserved.
- Stroma
- The thickest layer of the cornea, made of collagen fibres. It is the part the laser reshapes to correct vision.
- Sulcus
- The space behind the iris and in front of an implant placed in the capsular bag. This is where an add-on lens sits.
T
- Toric lens
- A lens implant whose power varies along a precise axis, so that it corrects astigmatism along with the rest of the prescription.
- Trabeculoplasty (SLT)
- Laser treatment of the drainage filter in the angle of the eye, to lower intraocular pressure in open-angle glaucoma.
V
- Visual acuity
- A measure of how sharp your vision is. In France it is expressed in tenths: 10/10 (the equivalent of 6/6 or 20/20) means normal vision, not perfect vision. Quality of vision (contrast, absence of halos) is a separate criterion.
- Vitreous
- The clear gel that fills the inside of the eye. As it becomes more liquid with age, it can come away from the retina and cause floaters and flashes of light.
A term missing?
This glossary grows with the questions asked in consultation. If something is unclear to you, it is probably unclear to others too: let us know.
Dr Emmanuel Halimi
Ophthalmic surgeon · RPPS 10100555084 · Medical Council of Hauts-de-Seine no. 92/23003
Page written and approved by the surgeon.
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