Glossary of Lasik Laser Eye Surgery Related Terms D-E
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
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.
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.
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
Diabetes Type II
Non-insulin dependent, resulting from tissue resistance to insulin.
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
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.
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.
Tiny yellow or white deposits in the retina or optic nerve head.
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
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
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.
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
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.
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
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
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.
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.
Looking For Best Lasik Surgeon?
If you are ready to choose a doctor to be evaluated for conventional
or custom wavefront Lasik, Bladeless Lasik, PRK, or any refractive surgery procedure, we recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization.
Locate a USAEyes Evaluated & Certified Lasik Doctor.
If this article did not fully answer your questions, use our
free Ask Lasik Expert patient forum.