Fig. 7-2  Slit-lamp estimation of angle width: example of a grade 2 angle. Angle width can be estimated with the slit lamp by comparing the anterior chamber depth to the corneal thickness.

(From van Herick W, Shaffer RN, Schwartz A: Estimation of width of angle of anterior chamber: incidence and significance of the narrow angle, Am J Ophthalmol 68:626, 1969.)

Table 7-3  van Herick estimate of angle width from anterior chamber depth at the periphery

Spaeth classification

In an attempt to reduce a great deal of gonioscopic observational data into a concise format, Spaeth elaborated a complex grading

system that captures detailed three-dimensional information in coded form.3,4,28 It was designed for indirect goniolenses (e.g., Zeiss

four mirror) that allow for indentation (compression) gonioscopy. Interobserver variability has been found to be minimal.25 Moreover, this gonioscopic assessment shows high correlation with information obtained during ultrasonic biomicroscopy (UBM) of the angle,5 as well as with ‘biometric gonioscopy’ using a reticule to facilitate interobserver consistency in clinically grading the angle.26 As such, (UBM) may be used to delineate gonioscopic findings when gonioscopy itself is difficult, as in cases of congenital glaucoma.27

The Spaeth grading system uses an intricate alphanumeric scale, attempting to provide three-dimensional specificity to gonioscopic description. It addresses each of the following items in sequential order: (1) the site of insertion of the iris root in the eyewall; (2) the

Fig. 7-3  Illumination from temporal side casts shadow on iris if there is considerable bombé.

width or geometric angle of the iris insertion; (3) the contour of the peripheral iris near the angle;28 (4) the intensity of the trabecular pigmentation, and (5) the presence or absence of abnormalities such as mid-iris bowing, peripheral synechiae, and so on. If there is a discrepancy between the apparent and the actual site of iris insertion, as determined by indentation gonioscopy, this is so noted. Usually the grading is made for the four cardinal points of the angle, but especially in the normal angle’s most narrow (superior) and open (inferior) aspects.

Step 1: Site of Iris Insertion (Fig. 7-5a)

The first grading decision assesses the site of the iris insertion, both as it appears functionally (without pressure on the cornea) and as it actually inserts anatomically (after indentation). The capital letters A through E have simple alphabetic correspondences for the site of iris insertion:

A Anterior to trabecular meshwork (i.e., Schwalbe’s line)

B Behind Schwalbe’s line (i.e., at level of trabecular meshwork) C Centered at the level of the scleral spur

D Deep to the scleral spur (i.e., anterior ciliary body) E Extremely deewp in the ciliary body.

When the iris appears to be cramping the angle, with or without appositional touch (grade A or B), indentation gonioscopy may reveal an actual posterior site of insertion – the apparent level is placed in parentheses preceding the actual site. For example, a ‘(B)D’ notation means the iris appeared to insert at the level of the upper trabecular meshwork, but on indentation the actual insertion was revealed to be posterior to the scleral spur.

clinical assessments tend to overestimate by 5° the actual angle, as measured by the ultrasonic biomicroscope.5

Step 3: Configuration Of Peripheral Iris (Fig. 7-5C)

Originally Spaeth discriminated three contour configurations of the peripheral iris,3,4 designated in reverse alphabetical order:

s ‘steep’ or convexly configured (e.g., plateau iris) r ‘regular’ or flat (the most common contour seen)

q   ‘quixotic’ or ‘queer’ for deeply concave (e.g., pigment dispersion syndrome).

The newer system describes four iris configurations, indicated by the first letter of their description:28

b   ‘bows 1 to 4 plus’ (usually indicative of optically-appearing closure, altering with indentation)

p   ‘plateau’ (comparable to older ‘s’ designation)

f   ‘f lat approach’: the commonest iris appearance (comparable to the older ‘r’ designation)

c   ‘concave’ as in posteriorly bowed iris (comparable to the older ‘q’ designation).

Step 4: Trabecular Meshwork Pigmentation

As with the Shaffer scheme, the degree of trabecular meshwork pigmentation (TMP) is labeled from 1 to 4: minimal or no pigment is graded 1, and dense pigment deposition is indicated as grade 4, with lesser degrees between.

Step 2: Angle Width (Fig. 7-5B)

Exactly as with the Shaffer system, the geometric angle is estimated at the perceived intersection of the imaginary tangents formed by the peripheral third of the iris and the inner wall of the corneoscleral junction.Though some examiners prefer increments of 10°, as with the Shaffer system, and others use increments of 15°, these

Examples

•E40c, 4 TMP An extremely deeply inserting iris root, in a 40° angle recess, with posterior bowing of the peripheral iris and extensive TMP (as might be seen in a myopic eye with pigment dispersion syndrome).