Glossary of Lasik Laser Eye Surgery Related Terms - P-R
An procedure used to measure the thickness of the cornea.
Non-inflammatory swelling/elevation of the optic nerve often due to increased
intracranial pressure or the presence of a tumor.
Pellucid Marginal Degeneration
Pellucid marginal degeneration (PMD) is a rare, non-ulcerative thinning disorder
involving the outer edge of the lower portion of the cornea. PMD causes a
portion of the cornea to bulge forward, often first presenting as astigmatism. In
contrast to keratoconus,
where the greatest corneal protrusion is in the area of maximal thinning, the greatest
corneal protrusion with PMD is above the area of maximal thinning.
Abbreviated as PK or PKP. A surgical procedure when a button-like full thickness
segment of the cornea is removed and replaced with a donor cornea from another person;
a corneal transplant.
The ability to see objects and movement outside of the direct line of vision.
Pertaining to the period extending from the time of hospitalization or admittance
for surgery to the time of discharge.
A multi-center study of radial keratotomy (RK) outcomes funded by the National
Eye Institute. Ten-year results of RK patients who had the surgery in 1983 were
published in Archives of Ophthalmology in October 1994.
The study found that seven out of ten patients who had the operation on both
eyes no longer wore or required corrective lenses ten years after surgery, and 85%
of patients saw 20/40 or better without glasses. It concluded that RK is a "reasonably
safe operation" that can "effectively reduce but not eliminate myopia" (nearsighted,
The study also found that 43% of patients experienced a hyperopic shift
following surgery over the ten-year period. These patients typically experienced
an improvement in their vision as their refractive error moved closer to 20/20.
It is for this reason that ophthalmic doctors will often intentionally undercorrect
their patients, then monitor the rate of healing before performing a follow-up enhancement
Patients whose vision had achieved full correction or near full correction through
surgery and who experience a hyperopic shift could become farsighted and need to
A cataract surgical procedure which uses an ultrasonic vibration to shatter
and break up a cataractous lens, making it easier to remove. The vibration is delivered by an irrigation-aspiration
instrument. In a survey of ASCRS members in 1994, 86% preferred the phacoemulsification cataract removal
technique over the extracapsular cataract extraction technique. The technique was invented by Charles D. Kelman,
MD, and was first published in 1967.
Meaning that the natural crystalline lens of the eye is present.
Phakic Intraocular Lens
Abbreviated as P-IOL. Also known as Intraocular Contact Lens and abbreviated
as P-IOL. This is a tiny plastic lens that is placed inside the eye in front of
the natural crystalline
lens to provide additional refractive change. A Phakic Intraocular Lens is placed
either immediately behind or in front of the iris. Detailed
Verisyse and Visian ICL Phakic Intraocular Lens (P-IOL) Information
Phi-motion angiography employs a scanning laser to capture rapid-sequence images
of blood vessels underlying the retina.
An optical instrument containing many lenses which is used to determine the
required power of glasses or refractive error.
Abbreviated as PTK. The use of an excimer laser
to remove surface tissue of the cornea for medical or optical treatment reasons.
Very similar to PRK,
but for therapeutic rather than refractive purposes. See Phototherapeutic Keratectomy
The "cold" process of tissue removal which occurs with excimer laser radiation
in the 200nm wavelength range. This far-ultraviolet wavelength possess light photons
so powerful that the molecular bonds of the target tissue both break down and have
sufficient extra kinetic energy to fly off the surface; hence ablation. Microscopic
pictures show incredibly precise cuts with no evidence of tissue burning in adjacent
The process of tissue destruction accomplished by visible light radiation. Tissue
is broken down by the light and "clots" as if it were cooked.
Sensitivity to light.
Abbreviated as PRK. A surgical procedure using an excimer laser to reshape the central cornea to a flattened shape for people who are myopic and a more curved
surface for people who are hyperopic. Photorefractive
Keratectomy techniques may also be used to correct astigmatism.
See Photorefractive Keratectomy
The process of tissue destruction as occurs with infra red light radiation.
Shrinking of eyeball following injury, infection, or disease.
A yellowish spot seen on the white of the eye at the junction of the clear cornea and white sclera of the
eye. These lesions are usually caused by ultraviolet radiation. The white surface
of the eye cannot "tan" and therefore cannot protect itself from sunburn.
Used in a diagnostic setting to differentiate whether reduced vision is secondary
to uncorrected refractive error or to disease/amblyopia.
By eliminating the peripheral light rays and concentrating the central bundles of
light, the vision can be "sharper". But they have no therapeutic value. Pinhole
glasses can't permanently improve one's vision.
See Penetrating Keratoplasty.
See Penetrating Keratoplasty.
error. Normal vision. A diopter of 0.
Point Spread Function
Often used in wavefront diagnostic analysis. A single round spot of light becomes diffused when it passes
through an aberrated element such as a human eye. Aberrations cause some of the
light to spread beyond the boundaries of the light source, causing the dot of light
to appear fuzzy. Analysis of the diffusion of light (spread) helps doctors determine
what changes may be made to remove aberrations causing the diffusion.
Two or more images. Monocular polyopia
would be when a person sees multiple images in one eye. Monocular polyopia
is commonly described as ghosting or providing a ghost image. Binocular polyopia
is multiple images only when both eyes are used, indicating strabismus,
a misalignment of the eyes. Polyopia may be caused by neurological dysfunction,
disease, or medication.
Back surface or behind.
Posterior Capsular Opacification
Opacification of the posterior lens capsule. Sometimes called a "secondary cataract". Often a
consequence of modern cataract surgery. It occurs when a thin membrane of tissue
grows over the remaining capsule following cataract surgery, and can develop in
as many as half of all cases between several months and several years after surgery.
Most often treated using the YAG laser to ablate a hole in the capsule.
The space between the back of the iris and the front face
of the vitreous;
filled with aqueous fluid.
Posterior Optical Segment
The part of the eye behind to the crystalline lens,
including the vitreous, choroid, retina, and optic nerve.
Posterior Vitreous Detachment
The separation of the vitreous body from the retinal surface due to shrinkage from degenerative or inflammatory conditions or trauma.
Often an age-related condition.
See Preferred Provider Organization
Preferred Provider Organization
A medical or vision insurance plan that entices beneficiaries to use only the
facilities and physicians who have contracted with the plan to provide services
to beneficiaries by creating a financial disincentive if the beneficiary seeks care
outside the plan's panel of providers. Care provided to a patient by a facility
or physician that is not contracted by the Preferred Provider Organization is normally
a covered benefit of the plan, however at a significantly lower rate than the same
care provided by a facility or physician who is a contracted provider. The exception
is in some emergency situations or with prior authorization from the plan.
Pertaining to the period of time before surgery.
Part of the normal process of aging. As a person becomes older, we begin to
lose the flexibility of the natural crystalline lens of the eye and weakness of the ciliary muscle.
Presbyopia actually starts at about age ten. Most people do not begin to experience
the effects of presbyopia until their forties. This loss of flexibility limits the
ability of the eye to change its point of focus from distance to near. Because of
this normal process, people begin to wear bifocals or other
reading correction. The one advantage of mild myopia (nearsighted,
shortsighted vision)is the ability to remove your glasses after the onset of presbyopia
and continue to read. Mild myopia (nearsighted, shortsighted vision)effectively
counteracts presbyopia. Refractive
surgery does not change effects of presbyopia.
Presbyopic Lens Exchange
The term Presbyopic Lens Exchange (PRELEX) was created to describe a Refractive
Lens Exchange with an intraocular
lens designed to accommodate presbyopia.
Medical prescription terms were originally all written in Latin. Many of the
Latin terms continue to be used today. Eyeglass prescriptions are somewhat different,
and you can learn about them at Read Your Eyeglass and Contact Prescription. Common medical prescription terms
Surgical treatment for presbyopia owned by Refocus Group, Inc., and partnered
with CIBA Vision for distribution. PresVIEW has received European CE Mark approval
for the PresVIEW Scleral Incision System in August 2003. The company has re-engineered
the system for its PresVIEW Scleral Spacing Procedure, which surgically treats presbyopia,
primary open angle glaucoma and ocular hypertension. The updated procedure incorporates
automated components to simplify and enhance placement of Refocus Group's PresVIEW
scleral implants, resulting in greater reproducibility of the procedure by clinicians.
Refocus Group's strategic partner, CIBA Vision, plans a commercial launch of the
PresVIEW Scleral Spacing Procedure in selected European markets by the end of 2003.
Refocus Group also aims to begin FDA Phase II clinical trials of the procedure for
presbyopia in late 2003, subject to FDA approval.
A prism is a lens that will bends light towards its base. Prisms are used to
measure the angle of deviation in strabismus to correcting binocular polyopia when the
eyes become misaligned in adulthood. A prism may be included in spectacle correction
to help align images.
See Point Spread Function
When the natural crystalline lens of the eye has been replaced with an artificial lens during cataract surgery or Refractive
A growth of scar tissue on the cornea. These lesions
like pinguecula are caused by an ultraviolet burn to the surface layer or epithelium.
Closing off the punctum,
either with plugs, cauterization, or other natural or artificial methods
Small silicone or plastic plugs that are inserted into any or all of the punctum.
Tear drains around the eye. There are two in the upper lid and two in the lower
Appears as a small black dot in the center of the iris. The pupil changes
its diameter in response to changes in ambient lighting. The pupil varies the amount
of light reaching the retina and the depth of focus of the eye.
The constriction and dilation of the pupil due to stimulation
by light or accommodation.
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Spectacles that induce a small amount of myopia (nearsighted,
shortsighted vision), also called plus lenses. Reading glasses, often called readers,
are used temporarily by individuals who are presbyopic to assist
with near vision. See also bifocals, trifocals,
Pertaining to the radius or line from a circle center to the circumference of
Abbreviated as RK. A surgical procedure that permanently alters the shape of
the cornea by placing
microscopically thin relaxing incisions in the peripheral cornea. The incisions
cause the central portion of the cornea to flatten, thereby reducing the power of
Manufacturer of ophthalmic equipment for Conductive
(1) A test to determine the best eyeglasses or contact lenses to correct a refractive error including myopia (nearsighted,
shortsighted vision), hyperopia (farsighted,
longsighted vision), or astigmatism (irregular cornea).
- AC (ante cibum) means "before meals"
- BID (bis in die) means "twice a day"
- GT (gutta) means "drop"
- HS (hora somni) means "at bedtime"
- OD (oculus dexter) means "right eye"
- OS (oculus sinister) means "left eye"
- PO (per os) means "by mouth"
- PC (post cibum) means "after meals"
- PRN (pro re nata) means "as needed"
- Q3H (quaque 3 hora) means "every 3 hours"
- QD (quaque die) means "every day"
- QID (quater in die) means "4 times a day"
- Sig (signa) means "write"
- TID (ter in die) means "3 times a day"
(2) The bending of light by the use of lens or other material.
See also Manifest
Refraction and Cycloplegic
The degree to which images received by the eyes are not focused on the retina
(myopia, hyperopia, or astigmatism)
measured in diopters.
Refractive error is commonly presented in an prescription for spectacles or
Refractive Lens Exchange
Refractive Lens Exchange (RLE), also known as Clear Lens Exchange (CLE), is
essentially cataract surgery without the cataract. The crystalline lens is removed from the eye and replaced with a clear plastic intraocular
lens (IOL). The new IOL will be of a power to correct refractive error.
Cataract surgery is performed when the crystalline lens has become cloudy. RLE is
performed for purely refractive purposes. Refractive Lens
Exchange (RLE) Details
Any surgical procedure which permanently alters the focusing power of the eye
in order to change refractive errors. Refractive surgery may include corneal surgery
such as Lasik, LASEK, PRK, Intacs, or lens surgery such as RLE or P-IOL
A return by the cornea toward the original refractive state. See Regression Details
An prescription eye drop with diluted cyclosporine anti-inflammatory used for
the treatment of dry eye and other ocular conditions.
The brand name for the AcrySof ReSTOR apodized multifocal intraocular lens.
The ReSTOR lens is used with cataract surgery and Refractive
Lens Exchange (RLE). The potential advantage of any multifocal lens is the ability
to see clearly objects both near and distant. ReSTOR attempts to resolve presbyopia. Details about RLE Details about
The light sensitive layer of cells (rods and cones) on the
inner back surface of the eye that converts light images into nervous impulses sent
along the optic nerve for transmission to the brain.
The nerve fiber extensions of the retinal photoreceptors that form the nerve
bundle called the optic nerve.
A separation of the neural tissue of the retina from the pigmented epithelium
layer and therefore the blood supply. Results in loss of vision in the detached
area. Repairable with fair to good prognosis for vision if diagnosed in the early
stages. See Retinal Detachment Details
Retinal Pigment Epithelium
The pigment cell layer that nourishes the retinal cells; located just outside
the retina and attached to the choroid.
The name given to a group of disorders of the Retina, all of which
result in a progressive reduction in vision. See Retinitis
The brand name for the ReZoom multifocal intraocular lens.
The ReZoom lens is used with cataract surgery and Refractive
Lens Exchange (RLE). The potential advantage of any multifocal lens is the ability
to see clearly objects both near and distant. ReZoom attempts to resolve presbyopia. Details about RLE Details about
Gas Permeable Contact Lens.
Rigid Gas Permeable Contact Lens
A hard contact lens that allows significant amount of air to pass through. This
type of lens often provides superior refractive correction to a soft contact lens.
Rods, Rod Cells
One type of specialized light sensitive cells (photoreceptors) in the retina that provide
side vision and the ability to see objects in dim light (night vision). Also, see cones.
Root Mean Square
Actually means the root of the mean of the squares and is an evaluative measurement
of a wavefront diagnostic. It describes the smoothness of the surface in terms of deviation from
the ideal spherical wavefront and is calculated using the same technique that is
used to derive standard deviation. As a general rule of thumb, a Root Mean Square
value of .30 microns or greater is an indication that a wavefront-guided
ablation is necessary to provide a patient a good refractive
Looking For Best Lasik Surgeon?
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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.
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