The complex shape of the cornea can mean there are many different factors that can cause distortion or blurring of the viewed image. It is possible to derive the individual contributing factors that cause these distortions. These are called aberrations. Lower order aberrations (such as ‘Sphere’ or ‘Cylinder’) are corrected by glasses or contact lenses or standard laser procedures such as LASIK laser eye surgery. Higher order aberrations (such as ‘Coma’ or ‘Trefoil’) can only be corrected by the latest Wavefront laser eye surgery treatments.


Measuring the extent of a person’s optical aberrations using a diagnostic instrument known as an aberrometer.


In laser eye surgery, to remove.


The vaporization of tissue with the
excimerExcimerEXCited diMER – The type of laser used in laser eye surgery. laser. Further reading

Ablation zone

The area of tissue that is removed during laser eye surgery. Further reading


See corneal abrasion.


The ability of the eye to change its focus from distant objects to near objects.


See visual acuity.


Calculations that have taken into account various factors. When applied to laser eye surgery software this means the calculations should allow for the factors and correctly predict the change that is made in the patient’s prescription.

Ambient Illumination

Brightness of surrounding level of light.


Clinical name for a lazy eye, blind or low-functioning eye. Many patients with amblyopia can still be treated with laser eye surgery, although the underlying difference in vision between the two eyes will still remain. Further reading


Anaesthetic eye drops are used during laser eye surgery to numb the eye for about an hour, with no injections required. Further reading


A difference in image size between the two eyes. Further reading


A significant difference in refractive power between the two eyes, usually where the variance is at least one dioptre. Further reading

Anterior chamber

The fluid-filled area between the cornea and the lens. Further reading

Anterior uvetitis

Inflammation at the front of the eye. Further reading


Drugs taken in the form of drops or ointments which reduce the inflammation and aid in pain relief. Further reading

Aqueous humor

The fluid in the anterior chamber. Further reading

Artificial Lens Implant (ALI)

This vision correction treatment involves the implant of a soft, synthetic lens into the eye. This will act in the same way as a standard contact lens, staying in place to help the eye to focus clearly.


A refractive error caused by an irregular shape of the cornea (much like a rugby ball). Astigmatism is measured in terms of dioptres, and axis. Uncorrected astigmatism may produce ghosting or double images. Further reading


In ophthalmology, a line that is the symmetrical centre of a curved optical surface. Measure of astigmatism.


Bandage contact lens

This is a soft contact lens which the surgeon inserts in the eye directly after LASEK laser eye surgery treatment to reduce discomfort. The lens is removed after 4-7 days.

Best corrected visual acuity (BCVA)

The best possible vision a person can achieve with corrective lenses.


Glasses or contact lenses with a different power for distance vision at the top and a prescription for reading at the bottom of the lenses (sometimes you can see the dividing line on the glasses if you look closely). Patients with bifocal lenses will need reading glasses if fully corrected by laser eye surgery, unless monovision treatment is opted for.


Referring to both eyes. Laser eye surgery is usually bilateral.


Inflammation of the eyelids, usually with redness, swelling, and itching. This needs to be controlled before the eye can be treated with laser eye surgery. Further reading

Bowman’s membrane

The non-regenerative layer of tissue between the epithelium and the stroma (5-10 microns thick). Further reading

Broad beam laser

A medical instrument that produces a powerful beam of light that is focused at close range to remove corneal tissue. A broad beam laser uses a relatively large beam diameter (from 6.0 to 8.0 millimeters), which can be manipulated to ablate the cornea.

Broad spectrum

The description of an antibiotic that is designed to kill most strains of bacteria. Further reading

Buttonhole flap

A flap complication where the flap that is created has a central hole. This complication only occurs with mechanical methods, and is eliminated by laser flap creation. Treatment is abandoned and the flap is put back to heal. The cornea is allowed to heal (normally 3 months) and laser eye surgery treatment can be redone.


Cataract removal

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


The brownish membrane of the eyeball between the sclera (outer) and the retina (inner). Further reading

Ciliary body

The part of the eye that connects the choroid with the iris. Further reading


During the healing process after laser eye surgery, patients may experience pain on waking up, 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.

Conductive Keratoplasty (CK)

CK is designed to treat your near vision using the controlled release of radio frequency energy to strengthen the cornea – this eye surgery procedure does not use a laser or any cutting, therefore is minimally invasive, safe and convenient alternative to reading glasses.


Conjunctivitis is redness and soreness (inflammation) of the clear covering (the conjunctiva) which coats the white of the eye and lines the 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 from your doctor. This condition needs to have cleared up before you can have laser eye surgery. Further reading

Consultant ophthalmic surgeon/Ophthalmologist

In order to become a consultant in the UK a doctor must be on the Specialist Register of the General Medical Council (GMC). Entry to the Specialist Register is with the CCST (Certificate of Completion of Specialist Training) or through equivalent qualifications under the European Union Law.


A free appointment with Ultralase where we assess your suitability for laser eye surgery.

Contrast sensitivity

A measurement of how well a person can distinguish objects against a background – usually more difficult in dim light. Further reading


The outer part of the eye that provides 70% of the eye’s refractive power. The cornea is approximately 500 microns thick and consists of 5 layers epithelium, Bowman’s membrane, stroma, Descemet’s membrane and endothelium. Further reading

Corneal abrasion

The temporary loss of some of the cells of epithelium, usually by the surface being rubbed. Further reading

Crystalline Lens

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

Custom Ablation

This refers to Wavefront guided laser eye surgery treatment. When the laser has been programmed specifically for the patient’s irregularities of cornea based on their topography or on Wavefront scans.


A type of lower order aberration associated with astigmatism. See Aberrations.



Abbreviation for dioptre sphere – the measurement of short/long sight.


In this context this is the removal by the surgeon of tissue by gentle scraping of the eye’s surface using a blunted hand-held instrument. Debrided epithelium regrows in 24-72 hours. Further reading

Descemet’s membrane

The layer of the cornea between the
stroma and endothelium. Five microns thick, this membrane provides an adhesion layer for the endothelium. Further reading

Diabetic retinopathy

Diabetic retinopathy is caused by changes in the blood vessels of the retina, which can lead to vision loss. People with diabetes should have routine eye examinations so that diabetes-related problems can be diagnosed and treated as soon as possible. Surgical and laser treatments can help many people affected with this condition but this is a different type of treatment to laser eye surgery. Further reading


A process by which the pupil is enlarged, in order to see the back of the eye. Further reading


A measurement of refractive error. Hyperopia is measured in terms of positive diopters. Myopia is measured in terms of negative dioptres. Further reading

Dominant eye

Usually the eye used to focus a camera. During laser eye surgery, this eye is 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 sitting. Further reading

Double vision

Seeing two or more images, often shown with a prism reading on the prescription. Laser eye surgery can only treat the distance vision problem. If you are happy with the vision from contact lenses, then you should be suitable for laser eye surgery. Further reading

Dry eye

A syndrome characterised by corneal dryness due to deficient tear production. Further reading



A progressive corneal thinning and bulging.


People who have no refractive error.


The ophthalmic term for a perfect refractive state – no nearsightedness, farsightedness or astigmatism. Further reading


The innermost layer of the cornea. The endothelium is one cell layer thick (5-10 microns) and provides hydration balance to maintain the cornea’s transparency. The endothelium serves three main purposes it regulates the stroma’s water content, provides a barrier to ingress of several constituents of the aqueous humor, and actively transports glucose. Further reading


A secondary laser eye surgery procedure performed after the initial one in an attempt to achieve better visual acuity.

Epithelial ingrowth

A complication of LASIK laser eye surgery wherein epithelial cells grow underneath the corneal flap.


The outermost layer of cells of the cornea. Six cells thick (20 microns), the epithelium is the eye’s first defense against infection. Further reading


EXCited diMER – The type of laser used in laser eye surgery. Further reading

Eye drops

Drugs administered to the eye in drop form. Further reading

Eye-pressure test

A standard eye test that determines the fluid pressure inside the eye. The test is called tonometry. Increased pressure within the eye is a possible sign of glaucoma and must be treated to avoid blindness.



Or long-sightedness. See Hyperopia. Further reading


The abbreviation for the Food and Drug Administration. It is the United States governmental agency responsible for the evaluation and approval of medical devices. Further reading


The femtosecond laser for ophthalmology is used to create a LASIK flap in a laser eye surgery procedure commonly called Intralase or ‘blade-free LASIK laser eye surgery’. It is a silent, bladeless, computer-guided laser used in Step One of LASIK laser eye surgery to safely create corneal flaps of exact size, shape, and depth. The lasers uses femtosecond technology to pass through the cornea at 15,000 pulses per second.


In this context the ‘flap’ is the thin layer of corneal tissue that is temporarily lifted aside during laser eye surgery, whilst the laser is applied to the inner layers of the cornea.


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 usually are 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 optician or ophthalmologist urgently. Only in very severe cases would they affect your suitability for laser eye surgery. Further reading


Point at which light rays meet. When these rays focus correctly on the retina (at the back of the eye) the image is clear. In short-sighted people the light rays meet just too short of the retina and images are blurred. In long-sighted people the light rays meet just behind the retina so near vision is not in focus. Further reading


Fellow of the Royal College of Ophthalmologists.


Fellow of the Royal College of Surgeons. Further reading


Fellow of the Royal College of Surgeons – Edinburgh.


Fellow of the Royal College of Surgeons in Ireland. Further reading


Gas permeable contact lenses

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


A distortion of image due to irregular healing of the corneal surface.


A complication of laser eye surgery in which the patient sees additional lustre around lights. Glare is a subjective experience that often decreases with time. Further reading


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 total blindness. Vision lost as a result of such damage cannot be restored. A person who has glaucoma may not realise it at first, because the disease often progresses with no symptoms or warning signs. Early detection through regular eye examination and prompt treatment is essential to prevent vision loss. Daily medication (usually eye drops), eye surgery, or a combination of both enables most people to control their intra-ocular pressure and retain their vision. Further reading


The eyeball.



A complication of laser eye surgery in which the patient sees additional rings around lights at night. Halos are subjective experiences that usually decrease with time. Further reading


Condition that can sometimes occur after LASEK laser eye surgery treatment where the transparent cornea becomes slightly hazy. This will usually resolve over time.

Healthcare commission

A government body responsible for regulating Laser Vision Correction establishments, such as Ultralase. Further reading

Higher order aberrations

Refractive errors, other than short-sightedness, long-sightedness, and astigmatism, that cannot be corrected with glasses or contacts.


People who are long-sighted.

Hyperopia (long-sightedness)

This common vision problem occurs when light rays entering the eye focus further than the retina, not directly on it. Hyperopia may cause eyestrain or headaches, especially with reading. Spectacles or contact lenses can correct hyperopia. For people who do not want to wear glasses or contact lenses, refractive surgery is available. Further reading



Naturally occurring. Further reading

In Situ

A Latin term meaning “in place” or not removed. Further reading

Informed Consent Form

A document disclosing the risks, benefits, and alternatives to a procedure. Ultralase will supply you with a copy of this prior to your laser eye surgery consultation, and you will be required to sign it before we can treat you.


Intrastromal Corneal Ring Segments used to treat kerataconus. An alternative laser eye surgery using two ring shaped implants, surgically inserted into the cornea. This has a flattening effect on the cornea caused by kerataconus and is potentially reversable. Further reading


LASIK laser eye surgery procedure where the flap is created by an Intralase laser and not with a microkeratome (surgical blade) as in standard LASIK. It eliminates the blade and associated flap complications.

Intra-ocular lens (IOL)

Intra-ocular lens eye surgery is used to treat severe cases of hyperopia, astigmatism and myopia. This procedure involves inserting an implant called an intra-ocular lens into the eyes. Further reading

Intra-ocular pressure

The pressure the fluid contained within the eye exerts on the globe. Further reading


The coloured ring of tissue behind the cornea and immediately in front of the lens. The Iris expands and contracts to alter the amount of light entering the eye. Further reading

Iris recognition

Like your fingerprints, no two irises are the same and this can be used to provide a unique identification. The Zyoptix z100 system can scan your irises during the Zywave measurement and maps the entire iris, generating a unique digital Zy-ID for each eye. This map of the iris forms the foundation from which the Multi-Dimensional Eyetracker operates. The Zy-ID is the unique digital file that contains the patient’s laser eye treatment information, including the map of the Iris. Further reading



The portion of the LASIK laser eye surgery procedure in which the surgeon raises a thin layer of the cornea – creating a corneal flap – with an instrument called a microkeratome (a surgical blade), to expose the layer of the cornea called the stroma. Ultralase have now replaced this process with Intralase – the blade-free alternative to flap creation in all our LASIK laser eye surgery procedures. Further reading


Inflammation of the cornea. Further reading


Prefix indicating relationship to the cornea.


A rare inherited condition of the cornea in which the cornea is steepened to the point of being cone-shaped.


Measurement of the curvature of the cornea. Can be obtained by using instruments such as the Oculus Keratometer or the Orbscan.


The cutting of the cornea formerly done with a blade, now done with an excimer laser. Further reading


Lacrimal gland

Organ in the eye responsible for tear formation. Further reading

LASEK laser eye surgery

Laser ASsisted Epithelial Keratomileusis. An adaptation of the PRK procedure where the epithelium is first softened by diluted alcohol before moving it aside as an ‘epithelial flap’, prior to the use of the laser. Unlike PRK, the aim is to keep this epithelium flap intact and replace it in position once the laser eye surgery treatment is complete. This should mean the first 24-72 hours after treatment are more comfortable (less pain) than in the case of PRK. Further reading


An acronym for Light Amplification by Stimulated Emission of Radiation. A medical instrument that produces a powerful beam of light and can produce intense heat or cool vaporization when focused at close range. Lasers are often used in surgery to remove tissue. Further reading

Laser eye surgery

Laser eye surgery is any surgical procedure that attempts to decrease the patient’s refractive error using a laser. Typically the surgeon alters the shape of the cornea in order to change the angle at which an image is projected onto the retina. Further reading

Laser Keratome

A laser device used to create a corneal flap.

LASIK laser eye surgery

Laser Assisted In-Situ Keratomileusis. The most common laser eye surgery procedure in the world. A flap of corneal tissue is raised and the laser is applied to remove some of the tissue of the exposed layers of cornea, before the flap is replaced in position. The removal of the tissue makes the refractive change designed to improve vision without the need for glasses or contact lenses. Further reading

Lazy eye

See Amblyopia. Further reading


A transparent material used to bend light and form images correctly onto the back of the retina. Lenses placed in a frame and worn as glasses, or placed directly onto the surface of the eye as contact lenses, or surgically placed inside the eye. The natural lens inside the eye bends the light as it passes through can change shape (accommodate) in order to see objects at different distances. In older age this lens can become stiff which results in the need for reading glasses and is called presbyopia. In old age this lens can become cloudy and is called a cataract which then requires removal and replacement by a new lens. Further reading


The visual borderline between the clear window (cornea) and the white globe (sclera) of the eye. The conjunctival layer which covers the globe also joins at the limbus.



The small highly sensitive area of the central retina which provides vision for reading and fine detailed vision directly into the line of sight. Further reading

Macular Degeneration

Disease that causes dysfunction of the macula, the area in the middle of the retina that makes possible the sharp central vision needed for such everyday activities as reading, driving, and recognizing faces and colors. The condition is commonly known as age-related macular degeneration (ARMD) and is the leading cause of visual impairment among older people. Further reading

Macular oedema

The collection of fluid in and under the macular portion of the retina causing swelling. Further reading


Bachelor of Medicine. Further reading


Bachelor of Medicine and Surgery. Further reading


Bachelor of Medicine and Surgery. Further reading


Member of the British College of Optometrists (Ophthalmic Opticians).


Doctorate in Medicine. Further reading

Meibomian secretions

Oily secretions from the eyelid glands that supply the outer portion of tear film, prevent rapid tear evaporation and tear overflow.


The instrument a surgeon uses to create the corneal flap in the uppermost layer of the cornea during the LASIK laser eye surgery procedure. Ultralase have now replaced this process with Intralase – the blade-free alternative to flap creation in all our LASIK laser eye surgery procedures. Further reading


One thousandth of a millimetre.


The purposeful adjustment of one eye for near vision and the other for distance vision accomplished with either corrective lenses or laser eye surgery.


Member of the Royal College of Ophthalmologists.


Master of Science in Ophthalmology.


People who are short-sighted.


The medical term for short-sightedness. Eye is too steep, too long, image is focused in front of the retina. Further reading



Abbreviation for non-steroidal anti-inflammatory drugs.


Or short-sightedness. See Myopia. Further reading

Negative power lens

The shape of the lens used in glasses or contact lenses for people suffering from short-sightedness. The lens is thinner in the middle than the outside. A negative lens, diverges (bends outwards) light to compensate for the over-bending by the eye’s natural lens, inside the eye. A minus sign in front of your prescription indicates a negative lens if you are short-sighted.


A surgeon’s adjustment to the laser’s computer calculation to further refine his or her own results. Further reading

Non-dominant eye

The non-dominant eye is the eye which is left short-sighted when Monovision eye surgery is chosen. The dominant eye is the one most used for distance, i.e. the one used to focus a camera.



Of, or relating to the eye. Further reading


A medical doctor specialising in the diagnosis and medical or surgical treatment of visual disorders and eye diseases. Further reading


The diagnosis and medical or surgical treatment of visual disorders and eye diseases. Further reading

Optic nerve

The millions of optical nerve fibers connecting to the eye and terminating in the brain where images are created and processed. Further reading


Relating to the eye or to the passage of light through lenses. Further reading


A primary eye care provider who diagnoses, manages, and treats disorders of the visual system and eye diseases. Further reading


The Orbscan IIz topographer analyses the physical shape and contours of your cornea and allows our surgeon to decide if it has a suitable shape and is healthy and thick enough for laser eye surgery. 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.



The process of measuring corneal thickness, usually using an ultrasonic probe. Further reading

Peripheral vision

The ability to see or be aware of objects and movement outside one’s direct line of vision. Peripheral vision can be damaged by prolonged raised internal eye pressure (glaucoma). Further reading


The cold process of tissue removal which occurs with laser radiation. Ultraviolet light is so powerful that the molecular bonds of the target tissue are broken apart causing ablation. Microscopic pictures show incredibly precise cuts with no evidence of tissue burning in adjacent cells.


Light sensitivity. Further reading


No refractive error.


The eye’s gradually decreasing ability to focus on nearby objects. Presbyopia is a normal part of ageing and affects virtually everyone, usually becoming noticeable after age 40. People with presbyopia typically hold reading materials at arm’s length in order to bring the words into focus. They may experience headaches or eyestrain while reading, viewing a computer screen, or doing close work. Presbyopia has been traditionally treated with reading glasses, bifocals, or contact lenses. PATIENTS WHO HAVE HAD LASER EYE SURGERY WILL STILL NOTICE THE EFFECTS OF PRESBYOPIA IN LAETR LIFE. But now there is CK (Conductive Keratoplasty), a minimally invasive eye surgery procedure developed specifically for presbyopic patients who only need near vision improvement. Further reading


The acronym for photorefractive keratotomy. A procedure involving the removal of the surface layer of the cornea (epithelium) by gentle scraping and use of a computer-controlled excimer laser to reshape the stroma. Further reading

PTK (Phototherapeutic Keratectomy)

The use of the Excimer laser to treat eye problems such as pronounced haze. Not laser eye surgery for short-sightedness. Further reading


The medical name for droopy eyelid. It can be a temporary side effect after laser eye surgery treatment. It is thought to be due to the ‘eye clamp’ pulling the eyelid muscles to hold the eye open. Is rarely permanent but can be surgically corrected if necessary. Further reading

Punctal occlusion

The punctum is the small hole on the lower eye-lid surface down which the tears drain away from the eye. In the case of quite severe eye dryness it is possible to block this hole with a small plug. This procedure is known as punctual occlusion.


Tear drains located in the upper and lower eyelids in the corners of the eye lids towards the nose.


The opening in the iris through which light passes so it may reach the retina. The pupil enlarges in dim light and closes in bright light. Further reading



The bending of light wave as they pass from one medium to another. Further reading

Refractive correction

This is the process of correcting refractive errors. There are many different forms of refractive correction, such as spectacles, contact lenses, surgical and non surgical laser eye procedures and also non-laser vision correction procedures such as CK.

Refractive Errors

Imperfections in the focusing power of the eye, for example, hyperopia, myopia, and astigmatism. Further reading

Refractive surgery

Any surgical procedure that attempts to decrease the patient’s refractive error. Leser eye surgery, Intra-Ocular Lens impolants, and CK are all forms of refractive surgery. Further reading

Refractive Lens Exchange (RLE)

Standing for Refractive Lens Exchange, this vision correction treatment uses a kind of Intra-ocular lens to replace the eye’s natural lens via an artificial equivalent. This will be customised to compensate for the eye’s imperfection and will reduce or eradicate the need for glasses and contact lenses. This vision correction treatment is generally effective for the over-50’s.


The precise doses and frequencies of medications.

Registered nurse

Nurse who is registered with the government to perform certain levels of care. Further reading


A backwards shift from the initial visual outcome of laser eye surgery.


The film at the back of the eye on to which the viewed image must be focused to ensure a sharp picture is communicated to the brain. Further reading

Retinal detachment

Damage to this thin membrane can occur as a result of an eye or head injury, but there can also be a genetic link to retinal disease. Very high short-sightedness (myopia) can occasionally ‘stretch’ the retina and lead to detachment. This is a separation of the retina from the outer layers of the eye. It can occasionally cause symptoms such as floaters (though these are not necessarily an indication of detachment) or bright flashes of light in the peripheral vision. This can usually be successfully treated if detected early. Further reading

Royal College of Ophthalmologists (RCO)

Official body that authorises Ophthalmologists to practice.



The tough, white, outer layer (coat) of the eyeball that, along with the cornea, protects the eyeball. Further reading


The distortion of sight because the eye is too long for its focusing power. The laser eye surgery corrects this by reducing the curvature of the cornea, which enables light to reach the retina at the back of the eye. The short-sighted eye bends light too much and focuses the image in front of the retina. To reduce this ‘over bending’ a negative lens distorts the light before it gets into the eye and so the light can be focused on to the retina. Further reading

Slit lamp

A microscope used to study the eye using a narrow beam of light. Used to rule out any significant corneal abnormalities such as scarring or the presence of a cataract. Further reading

Soft contact lenses

These should be removed before the laser eye surgery treatment and the consultation for a set amount of time depending on type of contact lens. Lenses can affect the surface of the eye. We require the most accurate refraction when the patient attends with a view to having laser eye surgery. If the lenses are not left out of the eye for long enough, treatment can be postponed.

Sphere (SPH)

A type of lower order aberration associated with myopia or hyperopia. See Aberrations.

Spot scanning laser

A medical instrument that produces a powerful beam of light that is focused at close range to remove corneal tissue. Spot scanning lasers use radar technology to track the eye’s movement.

Strabismus or Squint

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 eyeglasses, eye-muscle exercises, eye 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. Patients who are happy with their sight with contact lenses or specs can be considered for laser eye surgery. Further reading


Thickest part of the cornea (450-600 microns – approximately .5 millimeters). Between Bowman’s membrane and Descemet’s membrane.


This appears as a small lump on the inner or outer surface of the eyelid. Patients are advised to wait until the inflammation has cleared before undergoing laser eye surgery. Further reading


Twenty twenty vision (20/20 vision)

Normal visual acuity. Upper number is the standard distance (20 feet) between an eye being tested and the eye chart; lower number indicates that a tested eye can see the same small standard-sized letters or symbols as a normal eye at 20 feet. This is the American measurement; the UK version is 6/6.

Tear film

A very thin film of water and other chemicals riding on top of the epithelium that lubricates the front of the eye.

Tissue sparing treatment

Laser eye surgery treatments involve the removal of a small quantity of tissue from the front surface of the eye (the cornea). This will slightly alter the curvature of the cornea, thereby improving your vision. The higher the prescription then, the more tissue needs to be removed. Unfortunately this means that some patients are unable to have laser eye surgery, as it would leave them with a cornea thickness below the safety level. The Bausch and Lomb Zyoptix Tissue-Sparing system has been developed with these patients in mind because it is efficient in minimising the amount of corneal tissue to be removed in order to produce the desired prescription change. Tissue-sparing can remove up to 25% less tissue than standard laser eye surgery treatment. Instead of merely treating the prescription, the laser is guided in its treatment by the actual structure of the eye using the information collated from the scans taken at the initial consultation. This means that no two treatments are the same as each one takes into account the individual differences between each person’s eyes.


Equipment used to test the internal fluid pressure inside the eye (IOP). A puff Ionument is an instrument can be used without touching the eye by blowing a small puff of air into the eye. Further reading


Mapping a surface of the eye used to determine the corneal profile and it’s suitability for laser eye surgery. Further reading


A type of higher order aberration. See Aberrations.


Uncorrected visual acuity (UCVA)

A person’s vision without corrective lenses.



Glasses that incorporate an addition for reading as well as a distance prescription. People with varifocal lenses will require reading glasses after laser eye surgery unless they consider monovision.

Visual Acuity

The clearness of vision; the ability to distinguish details and shapes. Further reading

Vitreous humor

The gel-like fluid in the main cavity of the eye behind lens and pupil. Further reading



A detailed personalised description of the precise amounts and locations of an individual’s optical aberrations. This information is established using an aberrometer and then held on computer to be used to direct the laser for a bespoke laser eye surgery correction. Further reading



The very latest development in laser eye surgey technology from Bausch and Lomb is a system called Zyoptix. This is an advanced procedure that delivers a laser eye surgery unique to every individual. Zyoptix has many safety features that help to optimise the success of your laser eye surgery. It has a unique integrated diagnostic system – One set of data thoroughly evaluates the structure of your cornea to make sure you are a suitable candidate; The second measures your eyes’ anatomy to determine its unique optical characteristics using advanced wavefront technology. This process enables the surgeon to plan a personalised laser vision correction procedure completely individualised to you.

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