There are several practical consequences of discarding intraocular pressure (IOP) as central to the definition of glaucoma.1,2 One is that the clinician must become proficient at examining the optic nerve head (ONH) to appreciate the often subtle signs of glaucomatous optic atrophy; neither tonometry nor perimetry alone can be relied on to determine the presence of the disease. In fact, there is increasing evidence that alterations in the ONH are the earliest

signs of primary open-angle glaucoma (POAG), and that visual field studies are more useful later in the disease process.3–6,6b

Similarly, instead of using the IOP for classification into ‘normal-tension’ or ‘high-pressure’ glaucoma, various subtypes of glaucomatous disease are postulated based on various appearances of the glaucomatous ONH, with specific disc changes often seen in constellation with associated clinical findings.7–13 Although technological advances have been made in imaging and quantifying the three-dimensional features of the ONH, the fact remains that the clinician’s mastery of discriminating ophthalmoscopy is indispensable for the appropriate management of the glaucoma patient.

Clinical techniques of evaluation

The observer’s ability to stereoscopically evaluate the ONH with sufficient magnification is the essence of optic nerve surveillance in glaucoma.This can effectively be done at the slit lamp, using a variety of contact and non-contact lenses. It can also be performed using stereoscopically obtained disc photographs. Comparable information can be obtained from a variety of commercial imaging devices (see Ch. 14).

Slit-lamp funduscopy provides a good stereoscopic, direct view of the ONH when the pupil is at least 4 mm in diameter.14 Direct visualization of an upright image can be performed with a noncontact lens such as the Hruby or high-diopter (78D or 90D) ­fundus lens, or with contact devices such as the Zeiss four-mirror or Goldmann macular lens. With proper calibration and attention to detail, reliable measures of the optic disc diameter and disc area can be generated with such techniques, whose data are comparable to laborious planimetric measurements.15–18 For smaller pupils, a contact lens is often required for stereopsis. Indirect and inverted disc visualization with the 60D, 78D, or 90D fundus lenses can best be obtained when the pupil is dilated.The consistent advantage of high-magnification stereoscopic viewing is that many subtle alterations in the ONH can be detected, such as discrepancies between the cup size based on color criteria and contour criteria. Similarly, the shallow cupping of myopia is more obvious with a narrowed slit-lamp beam, and the disc often can be better seen this way in patients with early cataracts.

Monocular examination of the ONH is done with a hand-held, direct ophthalmoscope. The ease of this method makes it suitable for glaucoma screening and for interval evaluations that seek information on specific disc findings, such as the presence or resolution of a disc hemorrhage. Direct ophthalmoscopy is best thought of as an adjunct to the stereoscopic evaluation, the latter providing the specific three-dimensional details that are then monitored monocularly by parallax viewing and creation of shadows.19 The halogen bulb in the direct ophthalmoscope provides a brighter view than standard bulbs; when used with a red-free green filter, the nerve fiber layer can be visualized effectively.

If the pupil is small, if the cornea is irregular, or if the eye moves (as in children or patients with nystagmus), the patient can be placed supine, and a smooth-domed Koeppe lens can be applied. This will hold the lids open and help steady the globe, both allowing gonioscopy and providing a clear (but minified) view of the posterior fundus and ONH with the direct ophthalmoscope.

Photographs of the ONH continue to remain an extremely useful technique for documenting change in the disc over time (Fig. 13-1A, B).20–23 Precisely because photographic slides are portable, durable and independent of constantly changing technological platforms, they conserve invaluable information for long-term care. For example, they are useful to obtain as a baseline before refractive corneal surgery in young myopes at risk for glaucoma, since the images of their discs allow future comparisons decades hence. Baseline photographs should be taken in glaucoma suspects and glaucoma patients at the time of the initial visit, and then at intervals of every 6–18 months, depending on the patient’s stage of disease and clinical stability.1 Careful stereo evaluation of these pictures, using commercial viewers or 10 lenses, allows for the appreciation of subtle changes in the contour of the cup and shape of the neuroretinal rim (NRR), changes in the pathway of vessels, subtle disc hemorrhages not clinically appreciated 23bor alterations in the peripapillary choroid (Figs. 13-2 and 13-3).

The clinician’s disc drawings are a useful adjunct to disc photographs and should be performed regularly on all patients (see Fig. 13-1C, D).They are valuable for two reasons: they require the clinician to pay attention to subtle details in the ONH, and they are an incentive to regularly review previous drawings and photographs to assess disc stability. Likewise, they can potentially be as valuable as disc photographs in determining progression.24,25 Various drawing routines have been devised,26 but attention to stereoscopic details

– such as the vertical and horizontal demarcation of the cup; the integrity and regularity of the NRR; the configuration of vessels at the disc margins; the appearance of laminar pores or disc hemorrhages; and peripapillary disc changes – can be methodically delineated when attention is given to their diagrammatic rendering.

Fig. 13-2  Optic disc pit. The inferior pole of this optic disc has a horizontally elliptical greyish defect into which the inferior vein falls. This is a dramatic optic pit. This eye had a corresponding dense superior visual field defect.

Spaeth and co-workers have proposed an elaborate but reproducible clinical scheme for diagramming and staging the extent of glaucomatous disc damage, using slit-lamp and direct ophthalmoscopic technology.27–30 The Disc Damage Likelihood Scale (DDLS) distinguishes 10 stages of progressive glaucomatous changes of the disc, whose clinical significance is discriminated based on whether the disc size is small, average or large. Classification is abetted by a standardized chart with examples (Fig. 13-4).30 First, either a 60D, 66D or 90D lens is used at the slit lamp to estimate the disc size in millimeters with a reticule, and the value multiplied by lens-power-dependent constants: this determines a small, average or large optic nerve size. Next, the neuroretinal rim is assessed at its narrowest point (i.e., the cup axis is discriminated at its largest extent) by direct ophthalmosocopic exam, and notated; the disc is drawn, with careful attention to the NRR. Lastly the DDLS is invoked by integrating