Glaucoma Terminology
Chat Highlights
May 10, 2006

On Wednesday, May 10, 2006, Dr. Elliot Werner, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Glaucoma Terminology."

Moderator:    Welcome back to chat, Dr. Werner.  Tonight our topic is glaucoma terminology. Will you please start by defining glaucoma?

Dr. Elliot Werner:    Glaucoma is not a disease.  It is a family of a large number of diseases that have in common the tendency to produce a particular type of optic nerve damage we call cupping.  Most, but not all, glaucomas are also associated with a tendency to have an elevated pressure inside the eye.

Glaucomas can be divided into several categories.  Primary glaucomas are those that result from some abnormality of the structures that control the eye pressure or the optic nerve, and there is no other underlying abnormality detectable.

Secondary glaucomas are those that result from some other underlying eye disease that can be seen to cause the abnormal eye pressure and/or optic nerve damage.

Primary open-angle glaucoma (POAG) is the most common type of glaucoma in the West.  It is usually associated with a modest elevation of eye pressure and cupping of the optic nerve.  A significant number of patients with POAG do not have a detectable elevation of the eye pressure outside the normal range, called normal-tension glaucoma (NTG). Fundamentally, NTG is the same disease.

P:    It seems to me that in ordinary English, “disease” is associated with infectious agents, and “disorder” is used more often for structural problems like glaucoma.  In medicine, are distinctions made between the use of words such as “disease,” “sickness,” “disorder,” etc.?

Dr. Elliot Werner:   Disease is a general term for any abnormality that results in some sort of tissue damage, abnormal function, or disability.  Not all diseases are infectious.  Trauma, for example, is a disease. Sickness and disorder are synonyms for disease.

P:   What is perioperative care and how does it relate to glaucoma?

Dr. Elliot Werner:   Perioperative refers to the time just before, during, and just after surgery. Perioperative care is just what you do for patients around the time of their surgery.

P:   When an eye is said to be “long,” is that front to back, or side to side, or up and down?  Are there any implications for glaucoma?

Dr. Elliot Werner:   Long usually refers to the diameter from front to back.  Long eyes are generally nearsighted and are at greater risk for glaucoma, as well as a number of other eye diseases.  Long eyes also have thinner sclera, which makes doing glaucoma surgery more risky.

P:   What does “pseudo” mean?  How is it used in glaucoma?

Dr. Elliot Werner:   Pseudo means false.  A couple of conditions with the prefix pseudo are related to glaucoma.  The best known is pseudoexfoliation.  That is a condition where an abnormal material is deposited on the structures of the eye.  When you look at it with the slit lamp, it looks like sheets of material are falling off the lens. “Hence, the term, pseudoexfoliation. True exfoliation is a condition that results from exposure to infrared radiation.

P:   How is “trauma” defined?

Dr. Elliot Werner:   Trauma means injury.  Eye trauma means an injury to the eye.  That is a frequent cause of secondary glaucoma.

P:   What is a “bleb”?

Dr. Elliot Werner:   A bleb is the blister-like structure that forms on the surface of the eye after certain types of glaucoma surgery.  The fluid in the eye leaks out into the bleb, which is why the pressure is lowered after glaucoma surgery.

P:   What adjectives describe good and bad blebs?

Dr. Elliot Werner:   Good is functioning.  Bad is failed.  Functioning blebs are usually diffuse, translucent, and avascular.  Vascularized, cystic, thick-walled, scarred, and flat describe failing blebs.

P:   I'm guessing that some medical terms with suffixes point to specific meanings.  Would you define some of them, such as “ectomy,” “plasty,” and “dotomy”?

Dr. Elliot Werner:   Ectomy refers to removing something, as in appendectomy, removing the appendix.  Otomy means cutting into something, like keratotomy, making a cut in the cornea.  Plasty means altering the shape of something, like rhinoplasty, a nose job.  Another term is ostomy, which means creating an opening, like colostomy, making an opening in the colon.

P:   What is an encapsulated bleb?

Dr. Elliot Werner:   Encapsulated bleb is a complication of glaucoma surgery usually occurring between two and eight weeks post-op (after surgery).  The bleb assumes a tense, dome-like appearance and does not function.  The pressure is high as a result of a fibrous capsule forming inside the bleb.  Hence, the term "encapsulated".

P:   So what is removed in trabeculectomy?

Dr. Elliot Werner:   In trabeculectomy, usually a portion of the peripheral cornea and trabecular meshwork is removed.  The operation as originally described called for removal of a piece of trabecular meshwork only.

P:   What does Mm Hg mean?

Dr. Elliot Werner:   Mm Hg means millimeters of mercury, the same measurement of pressure used in a barometer and on the weather report.

Moderator:   Isn't that the same measurement used to measure intraocular pressure in the eye? Is the eye inflated like a tire?

Dr. Elliot Werner:   Millimeters of mercury is a measure of pressure, any kind of pressure: air pressure, water pressure, etc.  The same units are used to measure blood pressure and atmospheric pressure.  Another unit of pressure is pounds per square inch (psi), which is usually used for tires.  The eye ball is not a terribly rigid structure. It's a bit like a basketball.  The fluid pressure in the eye keeps it inflated and maintains the normal shape.  Like a basketball with no air, the eye with no pressure will partially collapse.

P:   What is the difference between "aphakia" and "phakia"?

Dr. Elliot Werner:   Phakos is a Greek word meaning lens.  Phakia means the lens is in place. Aphakia means the eye has no lens.  Pseudophakia means there is a false lens in the eye, that is, an intraocular lens implant.

P:   When I'm researching a topic that pertains to my ICE syndrome or glaucoma in general, the articles sometimes assume the reader understands all the terms.  Could you recommend a site on the Internet that provides definitions of medical terms in plain English?

Moderator:   Taber's, a medical dictionary, is online at http://www.tabers.com/ .  Here's the URL for another medical dictionary: http://www.nlm.nih.gov/medlineplus/mplusdictionary.html

P:   What is 5-FU?

Dr. Elliot Werner:   5-FU (fluorouracil) is a drug used mainly for cancer chemotherapy.  It inhibits cell division. It is useful in glaucoma surgery because it will inhibit growth of the cells that cause scarring, which is the usual cause of failed glaucoma procedures.

P:   What is "PVD"?

Dr. Elliot Werner:   PVD, as far as I know, stands for posterior vitreous detachment, generally a benign and harmless aging change that causes annoying floaters.

P:   If PVD's are caused from aging, in what decade are they generally seen?

Dr. Elliot Werner:   That varies.  Typically, they occur between ages 40 and 70, but can occur earlier in nearsighted people.

P:   What are ciliary tissues?

Dr. Elliot Werner:   The ciliary body is a structure located just behind the iris and is responsible for two things: accommodation, that is, focusing the eye for near work, and production of the fluids that fill up the inside of the eyeball.

P:   What and where is the angle of eye?  What role does it play in diagnosing glaucoma?

Dr. Elliot Werner:   The angle of the eye is located where the iris and cornea meet. It is just where the white and colored part of the eye come together as you look at your eye in the mirror.  The angle is responsible for controlling the flow of the fluid in the eye and maintaining the normal eye pressure.  Most forms of glaucoma result from some abnormality of the structures in the angle.

P:   What is Schlemm's canal?

Dr. Elliot Werner:   Schlemm's canal is a vein located in the angle of the eye that is responsible for draining the circulating fluid in the eye out of the eye, and back into the blood stream.

P:   What is hypotony?

Dr. Elliot Werner:   Hypotony is a too-low eye pressure, usually less than 6 mm Hg.

P:   What is aqueous?

Dr. Elliot Werner:   Aqueous is the clear, watery fluid that fills and circulates in the front part of the eye, between the cornea and the lens.

P:   What is Tenon’s capsule?

Dr. Elliot Werner:   Tenon’s capsule is the layer of tissue that surrounds the white of the eye between the conjunctiva on the outside surface and the sclera.  It acts sort of like a lubricant to allow the eye to move in all directions.

P:   Where is the trabecular meshwork and what is its role in eye function?

Dr. Elliot Werner:   The trabecular meshwork also is located in the angle.  It functions like a strainer.  The aqueous fluid has to go through the meshwork to get into Schlemm's canal and ultimately out of the eye.

P:   Where are the zonules and what are they?

Dr. Elliot Werner:   The zonules are thin filament-like structures that hold the lens in place.  They arise from the ciliary body and attach to the outside of the bag holding the lens. If the zonules are broken, the lens will dislocate and fall, either back onto the retina or forward against the cornea.

P:   What happens to the zonules when a patient has cataract surgery?

Dr. Elliot Werner:   They remain in place and hold the lens implant in place.

P:  Would you please explain the difference between a limbus- and fornix- based conjunctival flap?

Dr. Elliot Werner:   In order to do a glaucoma operation, you have to get the conjunctiva out of the way temporarily until the end of the operation when you put it back.  That requires cutting into the conjunctiva. If you make your cut right at the limbus, near the cornea, you push the flap of cornea backwards.  The conjunctiva is still attached at the back in the fornix. That is a fornix-based flap. If you make your cut in the fornix, you push the conjunctiva forward and it is still attached at the limbus. That is a limbus-based flap.

P:   Where is the conjunctiva located?

Dr. Elliot Werner:   The conjunctiva is the transparent skin on top of the white of the eye. It also lines the inside of the eyelids.

Moderator:   That is all for this evening, Dr. Werner.  Thank you for your time.

Dr. Elliot Werner:   The time just flew by.  Goodnight everyone.

On May 17, Dr. Wilson discussed "Pros & Cons of Available Pressure-reducing Medications" in the Chat room. Click here for highlights of that meeting.

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