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Glossary of Terms - Glaucoma

Don Minckler

While recognizing that clinical vision terminology is continually changing, based on new insights gained from ongoing research, it is nevertheless desirable to use standard terminology whenever possible in published manuscripts. Authors should use commonly understood terms with precision and consistently define any term in a written report where failure to do so may cause confusion to readers or researchers trying to replicate observations.

Use of the term glaucoma (i.e., angle-closure glaucoma or open-angle glaucoma) implies optic nerve damage or that damage to other ocular tissues (lens, iris, cornea) has occurred due to elevated IOP.

Angle-closure modifiers:

1. Acute (acute angle-closure typically is used to describe the initial attack, including high IOP, visual blur secondary to corneal edema, pain, lacrimation and lid swelling, nausea, and vomiting)
2. Subacute (sub-acute angle-closure implies recurring, longer duration attacks of less severe intensity)
3. Intermittent (intermittent angle-closure describes relatively mild repeated attacks with mild symptoms, spontaneous resolution, and normal visual function between attacks)
4. Chronic appositional (chronic appositional angle-closure is an appropriate descriptor for eyes that show focal gonioscopic pigment disruption but no PAS)
5. Chronic synechial

Aqueous misdirection (replaces malignant glaucoma): (elevation of IOP associated with angle-closure accompanied by forward displacement of the lens-iris diaphragm due to increased vitreous pressure):

1. Primary: pupillary block is usually not present, but aqueous percolates primarily posteriorly over-pressurizing the vitreous cavity (aqueous misdirection). Ultra biomicroscopy typically demonstrates anterior ciliary effusions.
2. Secondary: vitreous volume displacement (expansion of the choroid after PRP, uveal tumor, CRVO)

Appositional angle-closure: closure of the anterior chamber without peripheral anterior synechias, demonstrable by indentation (compression) gonioscopy.

Ciliary block: block to anterior aqueous circulation at the level of the ciliary body-lens equator, presumably due to abnormal vitreous.

Closed-angle: the scleral spur cannot be visualized on gonioscopy:

1. appositional closure (no peripheral anterior synechias demonstrable with compression gonioscopy)
2. synechial closure (peripheral anterior synechias)

Combined-mechanism glaucoma: glaucomas in which both open-angle and angle-closure components are present.

Cup-to-disc ratio: the ratio of the central depression in the optic nerve head defined at some plane (i.e., the edge of Bruch's membrane) to the diameter of the optic canal (usually at the central edge of the scleral canal - equivalent to the edge of Bruch's membrane).

(A vertical cup-to-disc ratio normally found in only 2.5% of the general population under study has been suggested as the 'ideal' definition of an abnormally large cup-to-disc ratio).

Glaucoma: a group of ocular disorders characterized by progressive damage to the optic nerve (structural damage) and visual field (functional damage) corresponding to injury to retinal nerve fiber layer axons.

Lens-induced angle-closure: angle-closure caused by forward movement of the lens-iris diaphragm creating or aggravating pupillary block with iris bombé (spherophakia, mircospherophakia, trauma, floppy lens syndrome)

Low-tension glaucoma (preferred to normal-tension glaucoma): progressive optic neuropathy, typical for that usually associated with elevated IOP (chronic open-angle glaucoma), occurring at normal levels of IOP.

Mixed-mechanism glaucoma: residual appositional angle-closure (by another mechanism) remaining after elimination of pupillary block with partial opening of the angle.

Narrow angle: an angle judged to be occludable by gonioscopy. (Grades I - II of the Shaffer scheme) (narrow angle-glaucoma should not be used). The scleral spur is visible.

Occludable angle: an angle that can close for 90 - 180^o in dark conditions, but which shows no evidence of pigment disruption or PAS, consistent with previous pathological closure.

Open-angle: an angle judged to be incapable of spontaneous occlusion (Graded III - IV of the Shaffer scheme). The scleral spur is visible.

Phacomorphic angle-closure: elevation of IOP caused by angle-closure induced by lens swelling with increased pupillary block.

Phacomorphic elevation of IOP: elevation of IOP secondary to angle-closure caused by lens enlargement and volume displacement (intumescence, age-related lens enlargement).

Plateau iris: an angle in which the iris root angulates forward, so that the body of the iris lies in a plane anterior to the iris root. The approach to the angle across the iris is flat until dropping steeply to the insertion.

1. Complete: capable of closure to Schwalbe's line (only recognized after iridectomy)
2. Incomplete: capable of closure only to a point between Schwalbe's line and the scleral spur (only recognized after iridectomy)

Plateau iris configuration: a plateau iris not capable of appositional closure (only recognizable after iridectomy).

Plateau iris syndrome: a plateau iris capable of appositional closure.

Pre-glaucoma: a condition in which IOP may be normal or elevated (ocular hypertension) in the absence of any functional or structural damage to the optic nerve.

Primary angle-closure: appositional or synechial closure of the anterior-chamber angle caused by pupillary block in the absence of other causes of angle-closure. The closure may or may not be associated with elevated IOP. If glaucomatous optic neuropathy is present and secondary to elevated IOP, angle-closure glaucoma or closed-angle glaucoma are the preferred terms.

Primary angle-closure stages

1. Narrow, occludable drainage angle
2. Primary angle-closure: narrow angle with high IOP or PAS with a normal disc and visual field
3. Primary angle-closure glaucoma: narrow angle and glaucomatous optic neuropathy

Primary open-angle glaucoma: a multifactorial optic neuropathy in which there is a characteristic acquired loss of retinal ganglion cells and atrophy of the optic nerve. Elevation of IOP of more than two standard deviations from the mean, (15 mmHg or IOP > 21 mmHg - values varying across populations), is the major risk factor for progressive injury in chronic open-angle glaucoma.

Pupillary block: impedance of aqueous flow from the posterior to the anterior chamber through the pupil.

1. Relative (physiological due to iris-lens contact)
2. Absolute (sequestered pupil due to posterior synechias)

European Glaucoma Society¹:

Visual field defect: an abnormal Glaucoma Hemifield Test, confirmed on two consecutive tests; or three points confirmed on two consecutive tests, with p < 5% probability of being normal, one of which should have p < 1%, none being contiguous with the blind spot; or CPSD < 5% if the visual field is otherwise normal, confirmed on two consecutive tests.

Progression of visual field defect: a cluster of three or more non-edge points, each of which declines > 5 dB compared to baseline on two consecutive fields; or a single non-edge point that declines > 10 dB compared to baseline on two consecutive fields; or a cluster of three or more non-edge points, each of which declines at a p < 5% level compared to baseline on two consecutive fields.

International Working Group on Defining Glaucoma:3

Visual field defect compatible with glaucoma: the most suitable standard currently available is white-on-white perimetry threshold testing using the Humphrey (HFA) I or II machines running the 24-2 program. (Gold Standard)

1. Glaucoma visual field abnormalities should include the following features:
2. Asymmetry across the horizontal midline (early and moderate stages)
3. Areas of abnormal function should show clustering
4. abnormalities should be reproducible on at least two consecutive tests
5. Testing results should be reliable
6. Lack of an alternative explanation (retinal disease, etc.)

Option 1:
Glaucoma hemifield test 'outside normal limits' and a cluster of three points on the pattern deviation matrix abnormal at the 5% level.

Option 2:
Corrected pattern standard deviation significant at the 5% level.

Option 3:
Corrected pattern standard deviation

Reliability indices:
HFA Standard
Fixation losses < 20%; False positives < 33%; False negative - no specification

Alternative visual field instruments (other than the HFA) should have sensitivity and specificity of 80% and 95%, respectively.

Glaucoma (structural disc criteria) for diagnosis:

1. Vertical C/D ratio* > 95th percentile ( > 0.7 )
2. Asymmetry of vertical C/D ratio > 97.5th percentile ( > 0.2)

*Not due to congenital disc asymmetry or other anomalies

Glaucoma (functional criteria) for diagnosis:

1. A psychophysical abnormality (visual field defect) measured with a validated methodology that is reproducible, and for which there is no alternative explanation.

Synechial angle-closure: closure of the anterior chamber angle by peripheral anterior synechias.

References to randomized controlled trial-tested visual field analyses:

1. The Advanced Glaucoma Intervention Study Investigators: 2. Visual field test scoring and reliability. Ophthalmology 1994; 101: 1445-1455
2. Musch DC, Lichter PR, Guire KE, Standardi CL: The Collaborative Initial Glaucoma Treatment Study: study design, methods, and baseline characteristics of enrolled patients. Ophthalmology 1999 106: 653-662
3. Keltner JL, Johnson CA, Beck RW, Cleary PA, Spurr JO: Quality control functions of the Visual Field Reading Center (VFRC) for the Optic Neuritis Treatment Trial (ONTT). Control Clin Trials 1993; 14(2): 143-159

General References:

1. 1998 Terminology and Guidelines for Glaucoma, European Glaucoma Society, Editrice DOGMA® S.rnl., Via Dei Cassari, 11R, 17100, Savona, Italy
2. American Academy of Ophthalmology Preferred Practice Patterns: Primary Open-Angle Glaucoma; Primary Open-Angle Glaucoma Suspect; Primary Angle-Closure. 2000
3. Meeting Notes: First Meeting of the International Working Group on Defining Glaucoma in Eye Examination Surveys, Leeuwenhorst, the Netherlands, June 27th and 28th, 1998
4. Johnson CA: Standardizing the measurement of visual fields for clinical research. Ophthalmology 1996
5. Ferris FL: Standardizing the measurement of visual acuity for clinical research studies. Ophthalmology
6. Kass MA: Standardizing the measurement of intraocular pressure for clinical research. Ophthalmology