Glossary of Laser Eye Surgery Terms

laser eye surgery glossary


Surgical excision of the cornea using a laser during treatment. Tiny amounts of corneal tissue are evaporated by the cold energy of the laser.


Imperfections in the optical system of the eye that can affect quality of vision. This is measured by Advanced Wavefront laser technology.


Increase in optical power by the eye in order to maintain a clear image (focus) as objects are moved closer; occurs through a process of ciliary muscle contraction and zonular relaxation that causes the elastic-like lens to ’round up’ and increase its optical power. Natural loss of accommodation with age is called presbyopia.


Advanced Vision Care monitors the health of the eye and vision at a series of appointments following laser eye surgery. In most cases, the aftercare schedule lasts for one year and is structured as follows:

1-4 days after treatment (post-op)
1-2 weeks post-op
6 weeks post-op
3 months post-op
6 months post-op
12 months post-op


A condition in which vision does not develop adequately in early childhood because the eye and the brain are not working together correctly. Amblyopia, which usually affects only one eye, is also known as a ‘lazy eye’. A person with amblyopia experiences blurred vision in the affected eye. Treatment for amblyopia can only take place before the age of 8 years for it to be successful and often involves patching the good eye, wearing glasses and/or surgery. Amblyopia cannot be treated in adulthood.


Topical anaesthetic is used to numb the cornea before laser eye surgery and before performing particular diagnostic tests. Once applied, the anaesthetic numbs the cornea within 10-20 seconds, although the duration of effect can last up to one hour in some cases. It is advised not to rub the eyes for one hour after instillation in case excessive force is used.


These ointments or drops are administered regularly for the first few days/weeks after treatment to prevent infection. Oftaquix is commonly used by AVC.


These are lubricating eye drops designed to relieve the symptoms of dry eyes. After laser treatment the eyes may feel dry as they heal. As part of Advanced Vision Care’s post-operative care, each patient receives lubricating eye drops and is regularly reviewed to ensure that the drops are meeting the needs of the healing eye.


Common vision condition caused by an irregularly curved cornea or crystalline lens. People with uncorrected astigmatism may experience blurred vision, eyestrain or headaches. Astigmatism can be corrected with glasses, contact lenses or surgery. Laser eye correction can treat up to 6.00 dioptres of astigmatism.


A contact lens which the surgeon places on the eye directly after treatment to protect the eye and reduce post-treatment discomfort. The lens is removed 24 to 48 hours after having LASIK treatment and 4 to 5 days after LASEK.


Referring to both eyes. AVC’s founder and lead surgeon Mr Pillai was one of the first surgeons to carry out bilateral laser treatment in the UK.


Prior to IntraLase, the first step of the LASIK surgical procedure was done manually using a hand-held device with an oscillating metal razor blade called a microkeratome. IntraLase replaces the hand-held blade with a computer-guided laser, delivering micron-level accuracy more than 100 times greater than a microkeratome.


Inflammation of the eyelids, usually with redness, swelling and itching. This needs to be controlled before the eye can be treated with any correction or treatment. Blepharitis treatment usually involves drops, lid hygiene and compresses.


A minor complication where the flap that is created has a central hole. Treatment is abandoned and the flap is put back to heal. The cornea is given time to heal (normally 2 months) and treatment can be successfully re-done.


A condition in which the crystalline lens of the eye, which is normally clear, becomes cloudy or opaque. Cataracts are painless and form slowly and can affect one or both eyes. Over time, a cataract may interfere with vision, causing images to appear blurred or fuzzy and colours to seem faded. Most cataracts are related to ageing and affect more than 50 per cent of all adults by the age of 80. They are the primary cause of vision loss in people aged 55 and older. Those in the early stages of this condition may benefit from new glasses, better lighting and sunglasses. Cataract surgery, which is common, involves removal of the cloudy lens and replacement with an artificial lens. [Search for more]


Removal of the cloudy crystalline lens from the eye. Surgical removal of cataracts and replacement with an artificial lens (called an intraocular lens) is the most successful surgical procedure in the country. This is performed as an out-patient procedure under local anaesthesia.


The Clear Lens Exchange procedure is very similar to a cataract operation and involves replacing the human lens with an artificial intraocular lens implant (IOL). The lens is bespoke and calculated to the patient’s exact prescription to provide optimum vision. In presbyopic lens exchange, the surgeon implants a specialist multifocal lens. This type of surgery is ideal for patients aged 45 and over who require a different prescription for both their reading and distance vision.


Like any elective surgery, laser eye surgery is not 100% risk free. During and after treatment patients may feel uncomfortable, experience tenderness, grittiness, glare around lights at night (halos), droopy eye lids, slight double vision or loss of best visual sharpness. These effects reduce gradually and rarely persist in the long term. The quality and experience of the eye surgeons at AVC mean that the clinic has a very low complication rate.


Conjunctivitis is redness and soreness (inflammation) of the conjunctiva which is the clear covering of the white of the eye and inside of the eye lids. This comes on relatively quickly and lasts for a fairly short time. Conjunctivitis may clear on its own but often needs treatment (eye drops). Conjunctivitis needs to be resolved before surgery.


Contrast sensitivity is the ability to see differences in contrast between objects or parts of objects. Reduced contrast sensitivity is a possible side effect of laser vision correction and is particularly troublesome in poor light conditions. Wavefront laser eye surgery technology reduces the change in contrast sensitivity and in some cases can actually improve it.


The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of the eye’s optical power. Because there are no blood vessels in the cornea, it is clear and has a shiny surface.


During the LASIK laser eye surgery procedure the superficial layer of the cornea needs to be lifted to reveal the lower corneal layers which are then shaped by the laser. This is done by creating a thin corneal flap which is hinged at a pre-determined point on the cornea. Once the cornea has been treated with the laser the flap is then replaced and a contact lens placed on the eye to protect it whilst it heals. The corneal flap can be created either by a miniature blade called a microkeratome or a specialised femtosecond laser.


Corneal thickness is one of the main factors that the eye surgeon will take into account when determining a patient’s suitability for laser eye treatment. During laser surgery the cornea is slightly thinned so the surgeon needs to ensure that it is thick enough to withstand the procedure. The thickness of the cornea is measured prior to surgery at the initial assessment using a device known as a pachymeter.


Corneal collagen cross-linking is used to halt the progression of keratoconus or pellucid marginal degeneration cases by strengthening the cornea. The technique uses UV light and riboflavin (a form of vitamin B12) to strengthen chemical bonds in the cornea.


The lens or crystalline lens is a transparent, bi-convex structure in the eye that, along with the cornea, helps to refract light to focus on the retina. Its function is similar to a man-made spectacle lens.


Diabetic retinopathy is the most common diabetic eye disease and a leading cause of blindness in adults. It is caused by changes in the blood vessels of the retina. The longer someone has had diabetes, the greater their likelihood of developing diabetic retinopathy. Changes in the tiny blood vessels of the retina can lead to vision loss. People with diabetes should have routine eye examinations so that diabetes-related eye problems can be diagnosed and treated as soon as possible. Maintaining strict control of blood sugar levels helps to prevent diabetic retinopathy. Surgical and laser treatments can help many people affected with this condition but this is a different type of treatment than laser eye correction.


Dilating eye drops contain medication to dilate the pupil by either stimulating the contraction of the muscles that enlarge the pupil, or relaxing the muscles that make the pupil constrict. A large pupil is helpful for examining the interior of the eye and allows for more accurate measurement of the prescription prior to laser eye surgery treatment. In general, dilation of the pupil can last from 4 to 24 hours depending on the strength of the drops used.


Usually the eye used to focus a camera or fire a gun. This eye would usually be treated second if the patient is only having one eye treated at a time. Most of the time patients now have both eyes treated at the same appointment.


Persistent dryness of the eyes resulting from too little production or too rapid evaporation of tears. People with dry eye syndrome may experience such symptoms as itching, burning or stinging eyes. Some people feel as though something is caught in their eye, causing an irritation. Dry eye syndrome has many causes. An optometrist may recommend the application of special eye drops called artificial tears to moisten the eyes. Laser eye surgery is not suitable for patients with severe dry eye syndrome.


At AVC eye clinic on Harley Street we use the sophisticated multi-dimensional Eyetracking Technology. This monitors the position of the eyes at all times during the laser eye surgery procedure and detects even the slightest movement to ensure the laser treatment follows the eye exactly. If too much eye movement is detected the laser is stopped immediately. Our state-of-the-art laser, the Bausch and Lomb z100, and the Eyetracking Technology enables us to deliver the highest quality and most accurate laser eye treatment available today.


A form of ultraviolet chemical laser which is commonly used in laser eye surgery and semiconductor manufacturing. This removes tissue accurately without increasing the temperature of the tissue. AVC uses the latest Bausch and Lomb z100 Technolas excimer laser.


This is an infrared laser that delivers pulses of energy to create small bubbles at precise points within the cornea. The bubbles separate the top layer of cornea to form a flap to allow refractive laser eye treatment to be performed. This is called blade-free technology as originally the flap could only be made using a miniature steel blade.


This is an orange dye that is instilled in the eye in order to assess the health of the cornea. When a cobalt blue light is shone onto the eye, any problem on the surface of the cornea appears bright green. This enables the eye care professional to easily detect any problems that can affect the cornea, for example, dryness or a scratch from a foreign body.


Specks or strands that seem to float across the field of vision. Floaters and spots are actually shadows on the retina cast by tiny bits of gel or cells inside the clear fluid that fills the eye. Floaters and spots are usually normal and harmless. However, in some cases they may warn of serious conditions such as retinal detachment, diabetic retinopathy or infection. Someone who experiences a sudden decline in vision accompanied by flashes and floaters or a sudden increase in the number of floaters should consult an optometrist or ophthalmologist urgently. Only in very severe cases would they affect laser eye surgery.


A rigid type of contact lens that allows oxygen to permeate through it. Gas permeable lenses (also known as RGP) need to be removed about one month (sometimes more) prior to the consultation and laser eye treatment as they can warp the corneal shape.


Starburst and flaring effect when looking at bright lights, particularly noticeable at night with car headlights. Halos and haze is a common side effect of laser eye treatment. Wavefront technology reduces the incidence of halo and glare, enabling patients with larger pupils to now have successful treatment.


Disease in which the pressure of the fluid inside the eye is too high, resulting in a loss of peripheral vision. If the condition is not diagnosed and treated, the increased pressure can damage the optic nerve and eventually lead to irreversible total blindness. A person who has glaucoma will not experience any symptoms in the early stages of the disease. Early detection through regular eye examinations and prompt treatment is essential to prevent vision loss. Daily medication (usually eye drops), surgery or a combination of both enables most people to control their intraocular pressure and retain their vision. Glaucoma is generally a contra-indication for laser correction but it depends on how it is controlled.


Halos used to be experienced by patients with large pupils as the treated area of the cornea was smaller than pupil size. Wavefront laser eye technology can treat a larger optical zone and can now treat pupils measuring up to 8.5mm.


This common vision problem occurs when light rays entering the eye focus behind the retina, not directly on it. Hyperopia may cause eyestrain or headaches, especially with reading. Glasses or contact lenses can correct hyperopia. Laser eye surgery or ICL (Implantable Contact Lenses) can treat hypermetropia.


Implantable Contact Lenses are miniature contact lenses that are implanted inside the eye to correct vision instead of lying on the surface. They are made from a biocompatible material that will not be rejected by the body and so can be left in the eye permanently.

The lens is inserted through a small, self-sealing incision at the edge of the cornea and sits behind the iris, the coloured part of the eye. If required, the lens can be removed from the eye by a surgeon and it will return to its original state prior to the operation.


IntraLase is blade-free laser eye technology that creates the corneal flap at the beginning of the LASIK laser eye surgery procedure. Prior to IntraLase, the flap was created manually using a small steel blade called a microkeratome. IntraLase uses tiny, rapid pulses of laser to form a microscopic bubble at a specific depth and position that is determined by the surgeon. This separates the top layers from the rest of the cornea to create a very thin, precise flap.

Advantages of the IntraLASIK method over conventional LASIK laser eye surgery include:

  • Superior vision quality (e.g. minimal glare at night)
  • quicker recovery time and faster healing
  • Significantly reduced complication risk
  • Increased predictability and enhanced safety
  • Thinner, more precise, but stronger corneal flaps


This is the measurement of the fluid pressure inside the eye. The fluid in the eye (the aqueous humour) is made within the eye but drained continuously through a structure called the trabecular meshwork. If too much fluid is made, or if there is a blockage in the trabecular meshwork, the pressure within the eye will build up and cause damage to the optic nerve.


Like your fingerprints, no two irises are the same and this can be used to provide a unique identification. The Zyoptix z100 laser eye surgery system can scan your irises during the Zywave measurement and map the entire iris, generating a unique digital Zy-ID for each eye.


Keratoconus is a rare condition, often inherited, in which the cornea becomes progressively thinner and gradually bulges outward, causing blurred or distorted vision. The condition usually affects both eyes. Corneal cross-linking and INTACS eye surgery can stabilise the progression of the disease.


Acronym: Light Amplification by Stimulated Emission of Radiation. It is a high energy light source that uses light emitted by the natural vibrations of atoms (of a gas or solid material) to cut, burn or dissolve tissues for various clinical purposes: in the retina to treat diabetic retinopathy and macular degeneration to destroy leaking and new blood vessels (neovascularization); on the iris or trabecular meshwork to decrease pressure in glaucoma; after extracapsular cataract extraction to open the posterior lens capsule.


LASEK is an abbreviation of Laser Epithelial Keratomilieusis and is also sometimes known as ‘Epi-Flap’. The LASEK laser eye surgery procedure is essentially the same as LASIK apart from the preparation of the cornea at the beginning of the procedure. In LASEK, the epithelium or outer layer of the cornea is placed aside with the help of a diluted alcohol solution instead of a corneal flap being created. Once the epithelial layer has been displaced, an excimer laser is then used to reshape the cornea, similar to LASIK laser eye surgery.


LASIK laser eye surgery is a highly successful and popular procedure for vision correction that has been available for over 20 years. The process creates a thin-hinged flap on the cornea (front of the eye) using IntraLase (blade-free treatment).


This eye condition is noted by the reduced vision that is not correctable by glasses or contact lenses and is not due to any eye disease. This is usually a contra-indication to laser treatment. Mild forms can sometimes be helped by laser treatment but if the vision is poor in the lazy eye then laser correction cannot help. Also see AMBLYOPIA.


Clear Lens Exchange can correct an unlimited range of prescriptions, including up to 5.00 dioptres of astigmatism. To correct an astigmatic prescription, the eye surgeon uses a specialist astigmatic lens, either fixed focus for distance or multifocal, to give good reading and distance vision.


Disease that causes dysfunction of the macula, the area of the retina responsible for central vision needed for such everyday activities as reading, driving, recognising faces and colours. The condition is commonly known as age-related macular degeneration (ARMD), and is the leading cause of visual impairment among older people. Macular degeneration causes blurred/distorted vision or a blind spot in the centre of the visual field. Peripheral vision is generally not affected. There is drug therapy available to treat certain forms of the disease but unfortunately not for all. Laser reye surgery is not a cure for ARMD.


Vision using one eye for distance and the other eye for clear reading vision. Presbyopic patients may find monovision a distinct advantage in that they do not need glasses at all. We recommend patients try this first in the form of contact lenses or glasses to ensure adaptation.


This condition occurs when light rays entering the eye focus in front of the retina, not directly on it. People with myopia are usually able to see close objects well, but objects in the distance appear blurred. Glasses or contact lenses can correct myopia. Laser eye surgery or ICL (Implantable Contact Lenses) treatment is another alternative.


A specialist lens implanted during the Clear Lens Exchange procedure that provides good distance and reading vision. If the intraocular lens used during the procedure is not multifocal, the patient will still achieve excellent distance vision but will require reading glasses to focus less than an arm’s length away.


Multifocal or progressive contact lenses allow you to see clearly for both near and far distances and are designed to remove the need for reading glasses for presbyopic patients. In general, one eye is slightly more biased towards seeing clearly for the distance than the other.


Abnormal formation of new blood vessels, usually in or under the retina or on the iris surface; can develop in diabetic retinopathy, central retinal vein occlusion or macular degeneration. Corneal neovascularisation develops in patients who overwear their contact lenses.


Condition that involves involuntary, rapid, repetitive movements of one or both eyes from side to side, up and down or in a circular motion. Nystagmus may be present at birth or, less commonly, may result from disease or injury. A full assessment would be needed to establish if the nystagmus is a contra-indication to laser eye surgery.


A doctor who specialises in the eye and its diseases. AVC’s Medical Director Mr CT Pillai is fully qualified with over 20 years of ophthalmic experience. As well as being a fellow of the Royal College of Surgeons (FRCS) and Royal College of Ophthalmologists (FRCOphth), Mr Pillai is currently Chairman of the UK’s Refractive Surgeons Association (RSA).


AVC eye clinic in London has established a network of clinical partners (all of whom are experienced and accredited optometrists) in the UK and Ireland to act as a referral base for initial consultation and aftercare. Our partners are well-trained, experienced professionals in refractive surgery. They are able to carry out both initial assessments and post-operative checks. All of AVC’s partners receive continued training and support to ensure that the best possible care is received by all patients who live outside the London area and who require local initial assessments and aftercare.


The Orbscan IIz topographer analyses the physical shape and contours of the corneas and allows our laser eye surgeon to decide if it has a suitable shape and is healthy and thick enough for treatment. It is the only topographer currently available that measures the shape of both the front and back surface of the entire cornea and can therefore provide a complete picture of the dimensions of the cornea.


Corneal pachymetry is the process of measuring the thickness of the cornea. This measurement is essential prior to LASIK laser eye surgery for ensuring there is sufficient corneal thickness to prevent complications after treatment. At Advanced Vision Care, pachymetry is measured using three different devices to ensure accuracy; the ultrasound pachymeter, the pentacam and the orbscan.


The pentacam is the gold standard for evaluating the cornea. It takes measurements from 25,000 points on the cornea to generate a detailed three dimensional map which shows the thickness of the entire cornea. This is used by the laser eye surgeon to assess whether or not a patient is suitable for treatment.


AVC will not treat a woman who is pregnant or breast-feeding. They are advised to wait until three months after giving birth or breast feeding. This is because the eyes can change during this time.


The eye’s gradually decreasing ability to focus on nearby objects. Presbyopia is a normal part of aging and affects virtually everyone, usually becoming noticeable after the age of 40. Reading glasses or contact lenses are required to focus on near objects/reading material. There is a range of laser and non-laser eye surgery treatments available to correct this near vision deterioration.


Variable-sized black circular opening in the centre of the iris that regulates the amount of light that enters the eye.


Light sensitive nerve tissue in the eye that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain. The retina forms a thin membranous lining of the rear two-thirds of the globe.


Needed by virtually everyone after they reach their forties. This is because the muscles in the eye slowly become stiffer which affects the ability to focus clearly on objects very close up. The need for reading glasses is medically known as presbyopia. There are a range of laser and non-laser eye surgery treatments available for this.


Condition in which the eyes are not both directed toward the same point simultaneously. Strabismus occurs when eye muscles are not working together properly. It is most commonly an inherited condition, but may also be caused by disease or injury. If diagnosed early, strabismus can usually be corrected. The condition may be treated with corrective glasses, eye-muscle exercises, surgery or a combination of these approaches. Young children with this condition may need to wear an eye patch over their stronger eye to force their weaker eye to function correctly. Children whose strabismus is not corrected may develop amblyopia. It is usually a contra-indication to laser eye treatment. A full assessment would be required to confirm suitability.


A new laser eye treatment for treating presbyopia, where the reading prescription changes due to age. The procedure uses a different treatment profile to standard laser treatment in order to correct both eyes equally well for distance and near. At present, this laser eye surgery is only available for patients who are hyperopic (long-sighted).


Varifocal glasses combine three different prescriptions (near, intermediate and distance) in one pair of glasses. These are designed for patients who require different prescriptions due to age-related changes within the eye. Refractive surgery has now advanced to be able to treat these prescriptions, enabling patients to focus on close objects without the need for reading glasses.


Visian ICL is a popular brand of Implantable Contact Lens that is has been endorsed by the US Army due to its reliable high standard of vision. Since it was introduced in 2006, the US Military has implanted over 3,000 Visian Implantable Contact Lenses and recommends this as the treatment of choice for their recruits who are unsuitable for laser eye treatment.

20/20 VISION

‘Normal’ visual acuity in American terms. The UK version is 6/6. The upper number is the standard distance (20 feet/6 metres) between an eye being tested and the eye chart; the lower number indicates that a tested eye can see the same small standard-sized letters or symbols as a normal eye at 20 feet/6 metres. If a person does not have 20/20 vision with their glasses/contact lenses before surgery it is not possible to achieve it after laser eye surgery.


The measurement of visual clarity. Best corrected visual acuity (VA) is the measurement of the best vision achieved with glasses or contact lenses. Uncorrected VA is the sharpness of vision without spectacles and contact lenses.


Wavefront analysis is a precise way of measuring how perfectly the eye focuses light. Any imperfection of the eye’s focusing ability is known as an aberration. Most aberrations can be corrected by glasses or contact lenses; however, not even these methods can correct the higher order aberrations of the eye. In Wavefront guided laser eye treatment, the aberrations of the eye are measured using specialist equipment. These readings create a unique Wavefront map which is used to guide the laser during the laser eye surgery


The XP Microkeratome can be used to create the flap during the LASIK laser eye surgery procedure. This has now been preceded by a blade free option called IntraLase.


The very latest development in laser eye treatment from Bausch and Lomb is a system called Zyoptix. This is an advanced procedure that delivers a laser eye treatment unique to every individual. The laser has many safety features that help to optimise the success of the treatment. It has a unique integrated diagnostic system; one set of data thoroughly evaluates the structure of the cornea to confirm suitability. The second measures the eye’s anatomy to determine its unique optical characteristics using advanced Wavefront technology. This process enables the eye surgeon to plan a bespoke laser vision correction procedure completely personalised to each patient.


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