Grading of Angle Width
Grading of Angle Width
The grading of angle width is an essential part of the ocular examination.
The main aims are to evaluate the functional status of the angle, the
degree of closure, and the risk of further closure. It is important to
determine:
1. the geometrical angle width in degrees
2. the shape and contour of the peripheral iris
3. the most posterior structure seen
4. the presence of peripheral anterior synechiae
5. the amount of trabecular pigmentation.
Shaffer Grading System
The Shaffer system (Fig. 13.13) records the angle in degrees of arc
subtended by two imaginary tangential lines drawn to the inner surface
of the trabecula and the anterior surface of the iris about one-third of the
distance from its periphery. 10 In practice, the angle is graded
according to the visibility of various angle structures. The
system assigns a numerical grade (4–0) to each angle with associated
anatomical description, angle width in degrees, and implied clinical
interpretation.
1. Grade 4 (35–45°) is the widest angle characteristic of myopia and
aphakia in which the ciliary body can be visualized with ease; it is
incapable of closure.
2. Grade 3 (25–35°) is an open angle in which at least the scleral spur can
be identified; it is also incapable of closure.
3. Grade 2 (20°) is a moderately narrow angle in which only the trabecula
can be identified; angle closure is possible but unlikely.
4. Grade 1 (10°) is a very narrow angle in which only Schwalbe’s line, and
perhaps also the top of the trabecula, can be identified; angle closure is
not inevitable but the risk is high.
5. Slit angle is one in which there is no obvious iridocorneal contact but no
angle structures can be identified; this angle has the greatest danger of
imminent closure.
6. Grade 0 (0°) is a closed angle due to iridocorneal contact and is
recognized by the inability to identify the apex of the corneal wedge.
Indentation gonioscopy with a Zeiss goniolens is necessary to
differentiate ‘appositional’ from ‘synechial’ angle closure.
FIGURE13.13
Shaffer grading system (see text).
Reproduced from Salmon JF, Kanski JJ, eds
In real life the degree measurement of the angle eg 20 degrees, 30 degrees, 40 degrees might not always exactly correspond to the structures seen. For example, you might be able to see as far as scleral spur, thus designating the angle grade 3, but the actual “walls” of the angle (if you think of it like a valley between the cornea and iris or TM tangent and iris) might be quite steep and deep, so it could be 20 degrees rather than the 30 degrees you would expect with a grade
3. This scenario is uncommon, and usually the angle between the “valley walls” corresponds to the structures seen, but of course, patients don’t read the textbook. The important message about angle grading with Shaffer is to grade according to the structures seen, from Grades 0 to
4. You will notice in the attached Word excerpt from Glaucoma by Shaaraway et al., that the degree measurement is in brackets as a secondary notation. Important when recording to note not just the Shaffer number, but also the structures seen, the degree measurement, and the
presence or absence of other features such as PAS, pigment, vessels, masses.