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Glossary of Lasik Laser Eye Surgery Related Terms D-E

Numbers A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Day Blindness
Common term for Hemeralopia.
A complication of refractive surgery. In perfect centration, the center of the corneal ablation exactly coincides with the center of the visual axis and/or pupil. This is like looking through the very center of your spectacle lens. If you look through the periphery of your lens, you might end up seeing partly through the lens and partly through the edge of the lens-this is decentration. Decentration can cause various symptoms including edge glare or even monocular double vision. Other factors such as the normal size of the pupil, whether it is dark out (your pupil will enlarge), or the size of the ablation zone will affect the severity or presence of symptoms.
Deep Lamellar Endothelial Keratoplasty
An endothelial cell transplant technique wherein a disk of endothelial cell tissue is removed from a donor cornea and placed on the underside of the recipient cornea, replacing a disk of endothelial cell tissue of equal size that has been removed from the recipient. The disk can be created with a mechanical device, or with the femtosecond laser. Deep Lamellar Endothelial Keratoplasty is an alternative to Penetrating Keratoplasty, which requires the full thickness of the cornea to be replaced. Detailed Deep Lamellar Endothelial Keratoplasty Information
Descemet's Layer
Layer of cells in the cornea above the corneal endothelium.
Depth of Focus
The range of distance that objects are in focus. Depth of focus is directly affected by accommodation, the ability of the natural crystalline lens within the eye to change shape and thereby change focus. After around age 40 the ability to accommodate is reduced due to presbyopia and near depth of focus is limited. Depth of focus is also affected by pupil size. The smaller the pupil, the greater the depth of focus.
Depth Perception
The ability of the vision system to perceive the relative positions of objects in the visual field. This ability to determine the distance of an object is provided by the two eyes receiving slightly different images due to their wide positioning on the face. The two images are compared by the brain to calculate distance.
Diabetes Mellitus
A chronic metabolic disorder characterized by a lack of insulin secretion and/or increased cellular resistance to insulin, resulting in elevated blood levels of simple sugars (glucose) and including complications involving damage to the eyes, kidneys, nervous system and vascular system.
Diabetes Type I
Insulin dependent, resulting from destruction of the insulin producing pancreatic islet cells.
Diabetes Type II
Non-insulin dependent, resulting from tissue resistance to insulin.
Diabetic Retinopathy
Diabetic retinopathy damages the tiny blood vessels that supply the retina. In the early stages of this disease-called non-proliferative or "background" retinopathy, the retinal vessels weaken and develop bulges that may leak blood or fluid into the surrounding tissue. Detailed Diabetic Retinopathy and Lasik Information
Diffuse Lamellar Keratitis
Also called Sands of Sahara due to the appearance of dunes of sand in the cornea with advanced stages. DLK is an inflammation under the Lasik flap of the cornea which is believed to be caused by a response to the presence of sterile infiltrates in the flap interface.
The complication occurs in the early post-operative period, vision is hazy and the eye is painful and teary. There is also an intolerance of bright light. Detailed Lasik and Bladeless Lasik Related Diffuse Lamellar Keratitis (DLK) Information
A process by which the pupil is enlarged. Allows more light to the interior of the eye.
A unit of measure of the refractive power if a lens. A one-diopter lens will focus parallel light rays one meter from the lens and a two-diopter lens will focus one-half of a meter from the lens. A plus 1.0 diopter lens is convex and will converge the light rays so they focus as a visible image 1 meter past the lens. A minus 1.0 diopter lens is concave and will diverge or spread light. The minus lens will not actually focus as a visible image on an optics table. Its image is known as a virtual image and if the diverging rays were followed to their point of origin, they would focus one meter in front of the minus lens.
Also called ghosting. A condition in which a single object is perceived as two; also called double vision. If you look at a clock and some of the numbers have a lighter image just off to the side, this is a typical presentation of diplopia. Usually with both eyes open as in binocular diplopia, but can be with only one eye as in monocular diplopia. Detailed Double Image and Ghosting Information
Dispensing Optician
See optician.
See Diffuse Lamellar Keratitis.
See doctorate of osteopathy.
Doctorate of Osteopathy
A certificate affirming that the holder has achieved the training required to be a medical doctor through a school of osteopathy.
Dominant Eye
The dominant eye is the eye that looks directly at an object. The non-dominant eye is the eye that looks at an object from the side. Detailed Dominant Eye Information plus download the USAEyes Dominant Eye Test Card to check your eye dominance at home.
Double Image
See Diplopia.
Tiny yellow or white deposits in the retina or optic nerve head.
Dry Eye
The term dry eye is used to describe a variety of ocular disorders with diverse aetiopathogenesis but similar symptoms: discomfort, a feeling of dryness, burning or stinging, grittiness, foreign body sensation and photophobia. Detailed Dry Eye and Lasik Information
The term used to describe a wasting or weakening of biological material, such as corneal endothelial dystrophy (also known as Fuch's Dystrophy) being the wasting or weakening of the endothelium.
See Anterior Basement Membrane Dystrophy.
See Extracapsular Cataract Extraction.
An outward bulging of the cornea due to internal pressures and/or a cornea weakened by surgery.
Swelling, inflammation.
Refractive condition in which no refractive error is present and distant images are focused sharply on the retina with no need for corrective lenses. Perfect vision or 20/20.
A prefix meaning within or inside.
An inflammation within the eye. Inflammations may be caused by organisms such as bacteria or may be sterile as in immune disorders. Endophthalmitis usually indicates an infectious disease, but occasionally occurs as a complication of surgery.
The inner layer of cells on the inside surface of the cornea.
Endocrine System
The endocrine system is a collection of glands that secrete chemical messages we commonly call hormones.
Secondary refractive surgery treatments made to refine or improve the original visual result. Outcome predictability is reduced at higher corrections. Higher corrections and wider optical zones require deeper sculpting and consequently undercorrection and overcorrection are more common. Enhancement treatment by contrast is usually a small correction and usually has higher outcome predictability. Detailed Lasik Enhancement Information Detailed Lasik Enhancement Rate Information
Surgical removal of the eye.
A watering of the eyes due to excessive secretion of tears or to obstruction of the lacrimal passages.
A mechanical device similar to a microkeratome that uses a blunt separator rather than a sharp blade to produce an epithelial sheet for Epi-Lasik. Rather than a more destructive alcohol mixture to loosen the epithelial cells used in LASEK. The epithelial cells are moved over the treatment area after Excimer_Laser energy has been applied.
See Epithelial Laser in-situ Keratomileusis
Epithelial Ingrowth
A complication of refractive surgery when epithelial cells under the flap begin to grow and multiply causing visual abnormalities and if sever, loss of visual acuity. The most common treatment is lifting the flap, removing the cells, irrigation of the interface, and repositioning of the flap. Detailed Epithelial Ingrowth Information
Epithelial Laser in-situ Keratomileusis
Modified LASEK with the epithelial cells removed by a mechanical microkeratome using a blunt, rather than sharp, blade. Detailed Epi-Lasik Information
The outer surface layer of the cornea, like the epidermis or outer layer of the skin.
Epithelium Basement Membrane Dystrophy
See Anterior Basement Membrane Dystrophy
The position of the eyes in an over-converged position compensated by the external eye muscles so that the eyes do not appear turned inward.
The position of the eyes in an over-converged position so that the non-fixating eye is turned inward.
Excimer Laser
An argon-fluoride laser that emits ultraviolet light that is emitted in pulses at a wavelength of 193 nm. The term Excimer comes from the concept of an energized molecule with two identical components or excited dimer (contracted to one word exci-mer). Each pulse of this his "cool" laser removes 1/4000 millimeter of tissue from the targeted surface by breaking intra molecular bonds in collagen molecules. It would take about 200 pulses from an Excimer laser to cut a human hair in half. This laser was originally developed for use in the microprocessor industry and later found its application in vision correction.
The position of the eyes in an over diverged position compensated by the external eye muscles so that the eyes do not appear turned outward.
The position of the eyes in an over diverged position so that non-fixating eye is turned outward.
External Ocular Muscles
The six muscles that turn the eyes to position them for viewing.
Extracapsular Cataract Extraction
A surgical procedure that removes the cataractous lens of the eye but leaves the posterior lens capsule intact.

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