Ablation – the removal of material by a laser. The excimer laser ablates tissue and reshapes the cornea during laser vision correction.
Astigmatism – the condition where the light rays entering the eye come into focus at two or more different points. This causes blurry vision both at near and at far.
Cataract – the clouding of the crystalline lens in the eye. As the eye ages, the lens can lose its clarity. When this interferes with vision, cataract surgery may be performed; removing the cloudy lens and replacing it with a clear implant, usually made of acrylic, silicone, or other biocompatible substance.
Contrast Sensitivity – the ability of the eye to resolve a given object against background illumination. As the levels of the target lighting and background lighting approach each other, the more difficult it becomes to resolve the target. Certain centers can measure contrast sensitivity by a variety of means. Decreased sensitivity can occur in certain corneal conditions, cataracts, and retinal diseases.
Cornea – the clear dome on the front of the eye. It is the part of the eye through which you can visualize the iris, or colored (brown, blue, hazel, etc.) part of the eye. Contact lenses are placed on the cornea. The cornea is also reshaped by a laser in laser vision correction procedures.
Hyperopia – (farsightedness) the condition where the eye does not have enough focusing power and so the light rays entering the eye only come to a focus behind the retina. This causes the eye to strain to see up close and often causes blurry vision both at near and even at a distance.
LASIK – “laser in-situ keratomileusis” – a procedure whereby an eye surgeon creates a thin, superficial flap of the cornea using a microkeratome or laser to expose the underlying tissue (stromal bed or body of the cornea). The excimer laser is then applied to reshape this deeper layer effecting a permanent change in the shape of the cornea and resultant permanent correction to the vision.
LASEK – a modification of the PRK procedure wherein the superficial layer of the cornea (epithelium) is preserved and then replaced after the laser treatment is completed.
Monovision – describes the planned correction of one eye to make it somewhat nearsighted in order for a presbyopic patient to see up close. The other eye (usually the dominant eye) is corrected for distance. Monovision allows the person to see both at near and at far, reducing the need for reading glasses.
Myopia – (nearsightedness) the condition where light rays entering the eye are focused in front of the retina (which is the back of the eye) causing blurry vision at distance. This means the focal point of the eye is at near making objects within a close distance clear but distant objects blurry.
Presbyopia – the natural ageing of the eye and lens in which focusing on near objects becomes harder. A person usually starts experiencing presbyopia sometime in their forties. It is related to the decreased ability of the lens to change shape, which is required to focus up close.
PRK – “photorefractive keratectomy” – laser vision correction of the cornea without the creation of a flap. The laser treatment is started at or near the surface of the cornea. The visual results are the same as for LASIK, but the healing time may be longer.
RK – “radial keratotomy” – an older form of refractive surgery, wherein the surgeon would place radial incisions into the cornea to flatten it and correct nearsightedness. It has been largely replaced by the new laser vision procedures.
Refraction – the procedure wherein the refractive error of the eye (nearsightedness, farsightedness, and/or astigmatism) is measured. This may be given to the patient as a prescription for glasses or contact lenses, or may be used to program a laser to correct in laser vision correction procedures.
- Myopia – (nearsightedness) the condition where light rays entering the eye are focused in front of the retina (which is the back of the eye) causing blurry vision at distance. This means the focal point of the eye is at near making objects within a close distance clear but distant objects blurry.
- Hyperopia – (farsightedness) the condition where the eye does not have enough focusing power and so the light rays entering the eye only come to a focus behind the retina. This causes the eye to strain to see up close and often to cause blurry vision both at near and even at a distance sometimes.
- Astigmatism – when the light rays entering the eye come into focus at two or more different points. This causes blurry vision both at near and at far.
Retina – the light sensitive ‘back’ of the eye where the photoreceptors (rods and cones) are located and at which point light rays entering the eye should be focused for proper, clear vision.
Visual Acuity – the capacity of the eye to discern detail. An individual who can resolve letters approximately one inch high at 20 feet is said to have 20/20 visual acuity. This is considered “normal” acuity. An individual with 20/40 vision requires the object to be at 20 feet in order to visualize it with the same resolution as an individual with 20/20 vision standing 40 feet from the object. Likewise, a person with 20/200 vision needs to be 20 feet from the chart to see the same letter that someone with 20/20 vision can see standing 200 feet away. And so, 20/15 or 20/16 vision is better than 20/20.