TERMS

these are commonly used terms related to glaucoma and the eye

Click on a term below to see the definition.

Aqueous Humor
The fluid produced within the front part of the eye.
Bleb
A bubble within the tissue overlying the new drainage opening created during surgery.
Central Vision
What is seen when you are looking straight ahead or reading.
Ciliary Tissues
Tissues located around the lens of the eye that supply nourishing fluid to the eye.
Conjunctiva
A thin, clear membrane that lines the inner surface of the eyelids and the outer surface of the eyeball, except for the cornea.
Cornea
The clear part of the eye located in front of the iris. Part of the eye’s protective covering.
Drainage Canals
Small openings around the outer edge of the iris, which provide the final pathway for fluid to leave the inside of the eye. Sometimes referred to as the trabecular meshwork or, Schlemm’s canal.
5-FU
A medication that stops the healing process. Sometimes used around the new drainage hole created during surgery (the bleb) to stop it from healing or scarring over.
Glaucoma Suspect
A person may be considered a glaucoma suspect on the basis of high intraocular pressure, a suspicious appearance of the optic disc or visual field, a family history of glaucoma, or narrow angles between the iris and cornea.
 
Gonioscopy
In this test, a contact lens that contains a mirror is gently placed on the eye. The mirror lets the doctor look sideways into the eye to check whether the angle where the iris meets the cornea is open or closed. This helps the doctor decide whether open-angle or angle-closure glaucoma is present.
Intraocular Pressure (IOP)
The internal pressure of the eye. Normal intraocular pressure usually ranges from 10-22 mm Hg, although people with relatively low pressures can still have glaucoma (see normal tension glaucoma.)
Iris
The colored part of the eye that can expand or contract to allow just the right amount of light to enter the eye.
Laser Surgery
A type of surgery in which a tiny, powerful beam of light is used to solve problems in the eye. There are three common forms of laser surgery for glaucoma:
  • Laser Peripheral Iridotomy - Creates a new drainage hole in the iris, allowing the iris to fall away from the outflow channel so fluid can drain out of the eye.
  • Laser Trabeculoplasty - In this procedure, the laser is aimed toward the normal drainage channels of the eye, in an attempt to open those channels so fluid can leave the eye more efficiently.
  • Laser Cyclophotocoagulation - This laser procedure is usually used in people who have severe glaucoma and are not responsive to standard glaucoma surgery. Laser energy is used to partially destroy the tissues that make the fluid within the eye.
Lens
Located behind the iris, helps light focus onto the retina.
Microsurgery
Surgery performed with a microscope in which and instrument is used to make a tiny, new opening in the sclera so that intraocular fluid can drain out of the inside of the eye.
Mm Hg
An abbreviation for “millimeters of mercury,” which is a scale for recording intraocular pressure.
Normal Tension Glaucoma
A rare form of glaucoma in which intraocular pressure stays within the normal range (10-22 mm Hg), but damage still occurs to the optic nerve and visual fields.
Ophthalmoscopy
A test designed to examine the inside of the eye, especially the optic nerve. An instrument with a small light on the end is held up to the inside of the eye in a darkened room. This instrument lights up and magnifies the eye, and lets the doctor look at the shape and color of the optic nerve.
 
Optic Nerve
The nerve in the back of the eye that carries visual images to the brain.
Perimetry
(Also known as the visual field test.) A test that produces a map of the complete field of vision, designed to determine whether there is damage to any area of vision.
Peripheral Vision
The top, sides, and bottom areas of vision, which are usually the first areas of vision affected by glaucoma.
Pupil
The opening that regulates how much light enters the inner part of the eye.
Retina
The part of the eye that carries light and images to the brain through the optic nerve.
Sclera
The tough, white, protective, outer coat of the eye.
Tonometry
The use of a device to measure the pressure within the eye. There are three types of tonometry:
  • Air Puff - This is the only type of tonometry that does not touch the surface of the eye. The patient sits upright at the instrument, and a warm puff of air is directed at the eye.
  • Applanation - The patient’s eye is first treated with numbing drops and a stain called fluorescein. The tonometer is then placed gently on the cornea, and a very small amount of pressure is applied to the cornea. The patient may sit in front of the tonometer or a hand-held tonometer may be used.
  • Schiotz - This type of tonometer was formerly used in the operating room or with people who are unable to sit upright (such as infants or small children). The patient is lying down or sitting back. After use of a numbing drop, the tonometer is placed gently on the front part of the eye. This type of tonometry is rarely used today.
Trabecular Meshwork
The formal name of the mesh-like drainage canals all around the iris.
 

DEFINITIONS

these glaucoma terms are described in more complete detail

Click on a term below to see the definition.

 

Glaucoma

The simplest definition of glaucoma is that condition of the eye where the intraocular pressure is elevated beyond the limit that will permit normal function of the optic nerve. However, there are two parts to the definition. First, it implies the presence of abnormal intraocular pressure, generally above 21 mm Hg, which is somehow due to an abnormality in aqueous drainage from the eye, or impediment to aqueous flow from the posterior to the anterior chamber of the eye; second is the suggestion that the intraocular pressure somehow embarrasses the nerve fibers ganglion cells, the final neural pathway from the eye to the brain. The fact that this definition is simplistic is easily demonstrated be the patient with the so-called "normal" intraocular pressure, generally below 21 mm Hg, who has typical glaucomatous cupping of the optic nerve head and characteristic visual field defects. Then there is the patient with the marked elevation in ocular pressure, usually from an inflammatory condition, who sustains no optic nerve alternations even after a protracted period of time. Thus, glaucoma defies a simple explanation.

Acute Angle-Closure Glaucoma

Acute angle-closure glaucoma is a dramatic disorder of sudden onset and represents a true ophthalmic emergency. If not properly diagnosed and treated, progressive, permanent ocular damage occurs in a matter of hours to days. The history is characterized by the quite sudden onset of pain, redness of the eye, and blurred vision. The pain is usually severe and generally centered over the brow. Nausea, vomiting, and profuse sweating are commonly associated symptoms which may lead to improper diagnosis and treatment in an emergency room setting.

terms-aacg

Figure: Oblique flashlight illumination showing shallow anterior chamber, corneal edema and mid-dilated pupil. Gonioscopic appearance (above) shows closed angle without any visible angle structures. Note how the corneal beam tapers towards the Schwalbe's line.

Acute Angle-Closure Sequellae

There are numerous sequellae of an acute angle-closure attack. Vision is often affected and visual recovery is variable. Following an attack the cornea frequently develops folds in Descemet’s membrane; recovery is usually complete, although some degree of endothelial cell loss may occur. Occasionally, chronic corneal edema develops despite normalized intraocular pressure. This most often occurs in patients with pre-existing Fuch’s dystrophy, or long-standing angle-closure prior to treatment.

During the acute attack, sector ischemia of the iris may occur due to closure of its stromal vessels, and if marked, causes an aseptic anterior uveitis occasionally severe enough to produce a hypopyon. Ischemic necrosis of the iris causes sectorial atrophy, usually in the horizontal meridian. Though iris hole formation is rare, detachment of the superficial iris stroma may occur and can mimic iridoschisis (figure 31). The pupil may remain permanently dilated and unresponsive to miotics or mydriatics because of sphincter damage. In many cases there may also be characteristic “spiraling” of the superficial iris stroma. In such instances, the iris fibers appear to originate at a point near the pupil margin and fan out, in an oblique fashion. Rarely, pupil dilation can be so wide that it makes lens-iris block impossible, thus breaking the attack spontaneously and making an iridectomy unnecessary. Due to the sudden sustained rise in intraocular pressure, lens opacities called glaukomflecken may appear. These opacities represent areas of lens epithelium necrosis. Clinically, they initially appear as small whitish cloudy areas beneath the anterior capsule in the pupillary zone. They are permanent, and become increasingly denser and, with time, move deeper into the anterior cortex.

terms-aacs

Figure: Frontal view showing shallow anterior chamber, diffuse iris stromal atrophy, spiraling of the iris stroma inferiorly, and glaukomflecken of the lens. Gonioscopy shows permanent synechial closure.

Angle-Closure Secondary

Primary cysts of the iris and ciliary body are uncommon, and only rarely cause glaucoma. Recently, however, Vela and colleagues reported three families in whom angle- closure glaucoma occurred in 4 of 11 patients with such cysts. It was suggested that in some instances of such cysts there may be autosomal dominant inheritance. There are no known systemically related disorders.

Slit-lamp evaluation may reveal a smooth irregularity to one or several areas of the iris with little alteration of normal surface markings. 1.) Peripheral anterior synechiae may form in the region where the cyst presses the iris forward to touch the angle structures. 2.) In affected individuals, gonioscopy shows partially closed angles in the region of peripheral mounds. 3.) Following pupillary dilation one may directly see the pigmented peripheral iris cyst(s) and gonioscopy may reveal smaller nonpigmented ciliary body cysts.

In instances where the intraocular pressure suddenly rises, pilocarpine can normalize the pressure. Peripheral and sector iridectomies have been relatively unsuccessful in managing these patients. Pigmented iris cysts can be treated by puncturing their walls with argon laser photocoagulative surgery. However, the cysts may redevelop and again close the angle. The nonpigmented ciliary body cysts do not respond to argon laser treatment. In time, the affected patients may have to undergo standard filtering surgery to control their secondary synechial angle closure glaucoma.

Patients with angle-closure glaucoma secondary to iris and ciliary body cysts should be carefully followed and their family members examined and appropriately counseled.

terms-acs

Figure: Multiple pigment cysts of the iris can be seen through the dilated pupil. The angle is irregularly narrowed and a broad peripheral anterior synechiae has formed.

Chronic Angle-Closure Glaucoma

The primary angle-closure glaucomas are conditions which by definition result in functional or organic obstruction of aqueous outflow at the trabecular meshwork by iris tissue. Gonioscopy is the key to their recognition and classification. A thorough knowledge of the normal angle is imperative before the subtle changes of peripheral anterior synechiae formation can be discovered and quantitated. Such knowledge is dependent on the ability to visualize all aspects of the angle recess no matter how narrow it appears.

Primary angle-closure glaucoma caused by a pupillary block mechanism can be divided into either acute or sub-acute angle-closure or chronic angle-closure. The initiating event is a functional block between the anterior lens surface and the posterior pupillary portion of the iris. This results in trapping of aqueous in the posterior chamber thus pushing the peripheral iris forward and closing of the angle. Outflow resistance increases, intraocular pressure rises, and with time permanent synechial closure ensues.

terms-cacg

Figure: Oblique flashlight illumination showing shallow anterior chamber, corneal edema and mid-dilated pupil. Gonioscopic appearance (above) shows closed angle without any visible angle structures. Note how the corneal beam tapers towards the Schwalbe's line.

Plateau Iris Syndrome

It has been recognized for about three decades that there is a small group of patients with primary angle-closure glaucoma in the absence of classic pupillary block. These patients are typically discovered when an angle-closure attack occurs in the presence of a patent iridectomy. The mechanism appears to be an abnormality of the peripheral iris which allows occlusion of the trabecular meshwork on dilation of the pupil. The classic picture is a normal appearing central chamber depth and a convexity of the peripheral iris. To fully understand this condition it should be divided into plateau iris configuration and plateau iris syndrome.

The plateau iris configuration refers to an anterior chamber of normal depth axially with a flat iris plane on direct examination but a narrow angle on gonioscopic examination. The plateau iris syndrome refers to the clinical picture either of spontaneous or mydriatic-induced angle-closure despite a patent iridectomy. In the majority of cases of angle-closure glaucoma associated with the plateau iris configuration, iridectomy is curative. The widening of the angle is not as dramatic and may not only be limited to the iris periphery. If iridectomy fails, the plateau iris syndrome should be considered. The plateau iris syndrome must not be confused with other conditions such as imperforate iridectomy associated with angle closure, elevated intraocular pressure from residual peripheral anterior synechiae, angle closure due to multiple cysts of the ciliary body, and mydriatic-induced intraocular pressure rise without angle closure. Once the diagnosis of plateau iris syndrome is made, the treatment is by continuous use of miotics. If miotics cannot be tolerated, laser iridoplasty(gonioplasty) has been reported to be curative.

terms-pis

Figure: Axial portion of the anterior chamber is of normal depth and an iridectomy is present at at 11 o'clock. The plane of the iris is vertical, and the iris root undergoes a knee-shaped bend (insert lower right) in the extreme periphery, causing sudden narrowing of the angle in the presence of a patent iridectomy. Insert upper right shows a closed angle in spite of a deep central anterior chamber.

Primary Open-Angle Glaucoma

Primary Open Angle Glaucoma (POAG), also known as chronic open angle glaucoma, is the most frequent type of human glaucoma. It is characterized by elevated intraocular pressure (IOP), cupping and atrophy of the optic nerve head, and typical visual field defects. There are no obvious ocular abnormalities, nor any specific systemic diseases related to POAG, though there is a higher incidence of the disorder in patients with diabetes mellitus and perhaps in hyperthyroidism. Both eyes tend to be involved at the same time and to a similar degree. All races have been noted to have the disorder and there is no sexual predilection. The prevalence of POAG in the Western world has been estimated to be about 0.5% and the incidence increases with age. Most cases are first detected after age 40.

The cause of POAG is unknown, but it has been suggested that there are multifactorial heritable factors; in many cases there is a strong family history of the disorder. To date, no specific histopathological abnormality has been noted.

terms-poag

Figure: The anterior segment including the angle appears to be within normal limits.

The Normal Angle

The anterior chamber angle is normally invisible by direct viewing of the anterior segment of the eye. Trantas, in 1907, was the first ophthalmologist to report visualization of the angle; this in a case of keratoglobus in which he intended the limbus. Trantas coined the term, gonioscopy, but the first goniolens was the introduced by Salzmann in about 1914. Indeed, Salzmann personally mane many angle paintings but these were never published. Koeppe, Barkan, Troncoso, and Goldmann were other early contributors to the instrumentation of gonioscopy and the description of the angle in health and disease. Various types of goniolenses are now available and all are used in conjunction with the slit-lamp biomicroscope or another magnification-illumination system. Most gonioscopy is done by an indirect method in which a mirrored contact lens is used at the slit-lamp to observe the angle opposite to the mirror. In contrast, direct gonioscopy uses a dome-shaped contact lens which eliminates internally reflected light and allows direct visualization of the angle with a gonioscope.

terms-tna

Figure:

Composite drawing of the normal angle seen in normal eyes.

Various widths of the normal angle seen in consecutive inserts. Note that the corneal optical wedge narrows as it approaches Schwalbe's line and seems to end there in the situation of a narrow angle.

a) Schwalbe's line b) Trabecular meshwork c) Scleral spur d) Ciliary body band e) Peripheral

The Optic Nerve

Damage to the nerve fibers of retinal ganglion cells is the most important sequellae of glaucomatous disease and is manifest clinically by alterations in the appearance of the optic disc. the pathogenic mechanism(s) by which an abnormality of intraocular pressure eventually results in retinal nerve fiber degeneration is a matter of intense debate. Histopathologic examination of the damaged optic nerve head reveals not only axonal degeneration of retinal ganglion cells but also loss of astroglial support tissue, reduction in disc vascularity, and collapse of the lamina cribrosa. Primary vascular, mechanical, and glial theories have all been suggested. Regardless of its etiology, there is a rather typical sequence of change that occurs to the optic disc in uncontrolled glaucoma.

terms-ton

Figure: Optic Nerve Head (a. - d., left to right)

  • Normal optic nerve head with small central physiologic cup, C/D ratio about 0.2
  • Concentric enlargement of the central cup, C/D ratio about 0.5
  • Irregular enlargement of the cup, especially inferiorly due to loss of inferior neural rim tissue
  • Marked glaucoma cupping with high degree of central atrophy, C/D ratio 0.7 to 0.8