|
|
Glossary of Lasik Laser Eye Surgery Related Terms - S-Z
By Glenn Hagele
S
Saline Solution
A sterile salt solution used in cleaning, rinsing, and sometimes storing of
contact lenses.
Sands of Sahara
See Diffuse Lamellar Keratitis.
Schlemm's Canal
The passageway for the aqueous
fluid to leave the eye.
Sclera
The tough, white, outer layer (coat) of the eyeball. With the
cornea, it protects the entire eyeball.
Scleral Shell
Flush fitting thin artificial eye usually fit over
phthisis bulbi.
Scotopic Pupil Size
The size of a pupil under low light conditions
similar to light in a theater or during night driving.
Scotoma
An area of partial or complete loss of vision surrounded by an area of normal
vision.
Secondary Implant
If no lens was placed in the eye at the time of
cataract removal surgery, then a secondary procedure to implant an
intraocular lens may be completed later.
SEE
See
Society for Excellence in Eyecare.
Shirmer Test
Tiny strips of filter paper are placed in the patient's eyes just under the
lids. After five minutes the distance the tears have stained the paper is
measured. The greater the distance, the higher the natural tear production.
Side Vision
See
peripheral vision.
Slit Lamp
A microscope using various magnifications combined with a strong light that
can be focused into a slit for examining the eye.
Snellen Visual Acuity Test
The white chart with the big black E at the top and lines of letters that
become increasingly smaller. The Snellen Test is one of many tests used to
determine visual acuity. The term 20/20 means that the patient can see an
item 20 feet away with the same clarity that a normally sighted person can
see an item 20 feet away. 20/40 means that the patient can see an item 20
feet away with the clarity that a normally sighted person can see an item 40
feet away. This is worse than normal vision. 20/10 means that the patient
can see an item 20 feet away with the same clarity that a normally sighted
person can see an item 10 feet away. 20/10 is better than normal vision.
Society for Excellence in Eyecare
Ophthalmologist membership organization.
SOS
See
Sands of Sahara.
Sphere
Term
meaning spherical refractive error of
hyperopia or myopia.
Split-Beam
A split-beam excimer laser is a broad-beam laser with an adjustable iris to control the amount and location of the energy that is applied to the cornea. See also flying-spot laser.
SRP
See
Surgical Reversal of Presbyopia
Strabismus
More commonly known as crossed-eyes, is a vision condition in which a person
cannot align both eyes simultaneously under normal conditions. One or both
of the eyes may turn in, out, up or down. An eye turn may be constant; when
the eye turns all of the time. Strabismus may be intermittent; turning only
some of the time, such as, under stressful situations or when ill. See
Strabismus Details.
Starbursts
A known complication of refractive
surgery that causes images from light sources to blur with spikes
radiating out from the center. Starbursts also occur naturally without
refractive surgery.
Stereopsis
The ability to perceive three-dimensional depth due to the distance between
a person's two eyes.
Steroid
A large class of pharmaceutical agents that chemically resemble cholesterol.
Two better known types are anabolic steroids often used in athletics, and
glucocorticoid steroids that are used to reduce inflammation.
Stiles-Crawford Effect
The Stiles-Crawford effect (discovered in 1933) describes angular dependence
of retinal sensitivity. Rays which enter the pupil near its center, which
are parallel to retinal receptors, are more effective than oblique rays
which enter the pupil near its margins. So, the light passing through the
periphery of the pupil is less efficient at stimulating vision than the
light passing near the center of the pupil. It is believed that
photoreceptors act as light pipes, and more light gets down if it enters
straight down (through the center of the cornea), rather than at a large
angle (through the periphery of cornea).
Striae
Wrinkles in the corneal flap created for
Lasik. There are two kinds, macro striae and micro striae. See
Striae Flap Wrinkle Details
Stroma
Thickest and central layer of cells in the cornea.
Seborrheic Dermatitis
Seborrheic Dermatitis may involve the presence of somewhat greasy flaking
involving the area around the eyes, nose, presenting with crusts, scales,
itching and occasionally burning, and may also be found on the scalp, ears
and torso. Although closely related, it does not usually involve red bumps
as in Rosacea. See
Seborrheic Dermatitis Details.
Surgical Reversal of Presbyopia
A general term used for many different techniques that attempt to cure
presbyopia. To date, none of these techniques have been proven to be
safe, effective, and predictable. There are, however, surgical techniques
that offer a "work around" the symptoms of presbyopia, including
monovision.
Sulcus
Upper eyelid depression.
Summit
Ophthalmic equipment company.
Sunrise Technologies
Ophthalmic equipment company.
Superior
Upper, as in upper eyelid.
Suppression
The inability to perceive all of part of objects in the field of vision of
one eye.
Surface Ablation
Any surgical procedure that ablates
tissue at the surface of the cornea, rather than
under a Lasik
or Bladeless Lasik
stromal flap. PRK,
LASEK, and Epi-Lasik are all surface
ablation techniques. Several studies have shown that surface ablation
techniques provide better refractive
surgery outcomes than Lasik or Bladeless Lasik, for patients who are
appropriate candidates for both types of surgery.
T
TBUT
See
Tear Break Up Test
Tear Break Up Test
A test that determines the quality of the tears on the eye. The doctor
observes the tear film under the microscope while the patient avoids
blinking until tiny dry spots develop. The longer the amount of time that
passes before the tear film breaks up, the more stable the tear film. A good
value is more than 10 seconds.
Temporal
Toward the ear.
Tonometry
A procedure for the measurement of the fluid pressure inside the eye (intraocular
pressure). One of the tests for glaucoma.
Topcon
Ophthalmic equipment company.
Topographic Supported Customized Ablation
Abbreviated as TOSCA, a system to use a
topographical mapping system to guide the laser during
refractive surgery.
Topography
To measure the high and low areas of a plane. See
corneal topography.
Toric
A contact lens that is designed to correct
sphere and astigmatism. A toric
lens is weighted on the bottom so it will maintain the same axis position of
the astigmatic correction.
TOSCA
Is the acronym for
Topographic Supported Customized Ablation. This means using a
topographical mapping system to guide the excimer laser ablation.
Trabecular Meshwork
The spongy, mesh-like tissue near the front of the eye that allows the
aqueous fluid to flow to Schlemm's canal then out of the eye through
ocular veins.
Transition Zone
The area of laser ablation that changes
for the full correction of the central ablation zone
optical ablation zone to the original surface depth of the
cornea.
Trifocals
Corrective lenses that have three powers of correction. Typically the
majority of the lens is corrected for distance vision while a small area is
corrected for near vision and another small area is corrected for middle
vision. Trifocals and bifocals are normally
prescribed for individuals with presbyopia.
U
UCVA
See
Uncorrected Visual Acuity.
Ultrasound
Procedures using sound waves to measure certain portions or detect
abnormalities within the eye. See A Scan
and B Scan.
Ultraviolet Radiation
Radiant energy with a wavelength just below that of the visible light. UV-c
is the shortest wavelength at 200-280nm and is absorbed by the atmosphere
before reaching the surface. Extremely damaging to living tissue. UV-b, at
280-315nm is "burning rays" of the sun and is damaging to most living
tissue. UV-a, at 315-400nm is "tanning rays" of the sun and is somewhat
damaging to certain tissues. UV radiation has been described as a
contributing factor to the processes that results in
ARMD, cataracts, and causes exposure keratitis.
um
Abbreviation meaning 10 to the -6 power meter.
Uncorrected Visual Acuity
The best vision measurement taken without the use of glasses or contact
lenses.
Undercorrection
A complication of refractive surgery
where the expected amount of correction is less than desired.
Undercorrection often occurs where healing
regresses more vigorously than predicted.
Uvea, Uveal Tract
The middle coat of the eyeball, consisting of the
choroid in the back of the eye and the
ciliary body and iris in the front of the
eye.
V
Variable Spot
This is a method of applying excimer laser energy. Rather than applying all
excimer energy in a broad-beam across the
entire ablation area, or with a very small
flying spot of excimer energy applied in rapid succession at different
locations across the ablation area, the energy is applied in variable spot
sizes across the ablation area.
Visian ICL
P-IOL manufactured by STAAR Surgical. See
Visian ICL Details.
Vector Vision
Ophthalmic equipment company.
Vision Therapy
A treatment process for the improvement of visual perception and/or
coordination of the two eyes for efficient and comfortable binocular vision
(orthopedics, vision training, and eye exercises).
Visual Acuity
Clearness of vision. The ability to distinguish details and shapes of
objects; also called central vision.
Visual Axis
The central area of the cornea,
pupil, and lens that light passes
through to reach the retina and be "seen".
Visual Field
The area or extent of space visible to an eye in a given position of gaze.
The central visual field is directly in front and the target at which we are
looking. The peripheral visual field is that which we perceive in our "side
vision". The fields of each eye partly overlap.
Visx
Ophthalmic equipment company.
Vitreoretinal
Involving the vitreous humor,
retina, or both.
Vitreous Humor
The transparent, colorless mass of gel that lies behind
lens and in front of retina.
W
WASCA
See
Wavefront Supported Corneal Ablation
Wave Length
The distance between the top of one wave and the top of the next wave. The
length of one complete wave of the argon fluoride excimer laser is 193 nm.
This wavelength is in the far ultraviolet end of the electromagnetic
spectrum.
Wavefront
A technology used in optics that is able to determine and measure high order
aberrations. These aberrations directly relate to an individual's quality of
vision. Conventional
eye examinations can detect two types of error on the
cornea - spherical (myopia and
hyperopia) and cylindrical (astigmatism).
Wavefront diagnostic can detect an infinite set of ocular aberrations called
The Zernike polynomials, but
in ophthalmology discussion has generally been limited to the first 15 or
so. The wavefront
sensor system includes a fixation target, an input laser beam that generates
a point light source, a wavefront sensor that measures the slope of the
exiting wavefront, and software that will determine the characteristics of
the excimer ablation.
The visual fixation target assists the patient in maintaining view,
direction and accommodation during the wavefront measurement. While the
patient fixates, a laser beam is shined into the eye. The light is reflected
from the retina back through the pupil, and the wavefront of the light
leaving the pupil is relayed to the wavefront sensor. The wavefront gets
distorted by the refractive properties in the human eye.
When the laser beam enters the eye, it has a flat wavefront. In theory, a
perfect human eye would reflect back a beam with its wavefront still flat.
But in a normal human eye — after the beam of light has traveled through an
imperfect crystalline lens, an irregular cornea and the other ocular media —
the flat wavefront has become irregular. Think of a square grid being
projected in and a wavy grid reflecting out.
Detailed Custom Wavefront Lasik Information.
Wavefront Supported Corneal Ablation
Trade name of the Carl Zeiss Meditec
WASCA aberrometer and the MEL 70 or MEL 80
excimer laser system when used for
wavefront guided excimer laser ablation
for Lasik,
Bladeless Lasik, PRK,
LASEK, and Epi-Lasik.
WaveLight
Ophthalmic equipment company.
Welch Allyn
Ophthalmic equipment company.
With-the-rule Astigmatism
"With the rule" astigmatism has an
axis of about 180 degrees (when Rx is written in minus cylinder form).
"Against the rule" astigmatism has the axis at about 90 degrees.
Both
forms are common. Nevertheless, when looking at population norms, "with the
rule" is more common in young adults while "against the rule" is more common
in older adults.
X
Y
YAG Laser
YAG is an abbreviation for neodymium yttrium-aluminum-garnet, the material
used generate a short pulsed, high-energy light beam in the infra red
wavelength of 1064 nm. The YAG laser is a surgical instrument that can be
precisely focused by computer to cut, photovaporize, or fragment tissue. The
YAG laser is used to treat posterior capsular opacification; a clouding of
the remaining capsular tissue that develops postoperatively in as many as
75% of cataract removal operations. The tissue is vaporized with carefully
controlled pulses of the YAG laser, and the surgery is performed on an
outpatient basis. The common misconception that "lasers" are used to remove
cataracts occurs because post-cataract patients eventually require YAG laser
capsulotomy.
Z
Zernike
See
Zernike Polynomial.
Zernike Polynomial
Zernike polynomials are mathematical blueprints of ocular aberrations
measured with wavefront technology.
Each Zernike polynomial, called a mode, describes a certain type of
geometric shape, a certain three-dimensional surface. The second-order
Zernike terms represent the conventional aberrations defocus (spherical
correction) and astigmatism. Zernike aberrations above the second order are
called higher order aberrations. The third-order Zernike terms are coma (a
wavefront shape with twofold symmetry) and trefoil (a wavefront shape with
threefold symmetry). The fourth order Zernike terms include spherical
aberration and four other terms, and so on. The Zernike polynomials are an
infinite set, but in ophthalmology discussion has generally been limited to
the first ten or so.
Zyoptix
The brand name for wavefront guided
custom ablation on the Bausch & Lomb Technolas excimer laser.
Zonules
The fibers that hold the lens
suspended in position and enable it to change shape during
accommodation.
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.
Personalized Answers
If this article did not fully answer your questions, use our
free Ask Lasik Expert patient forum.
|
Last updated
|
|