Early detection of glaucomatous damage. II. Changes in the appearance of the optic disk.
Once we understand that an increase in the size of the optic disk cup is due to loss of optic nerve fibers combined with some physical tissue rearrangements, it is quite clear that cupping begins as soon as nerve loss begins. Methods to detect cupping are more sensitive to the earliest glaucoma damage than are present field testing methods. This conclusion is supported by large clinical studies and histological demonstration of nerve fiber loss prior to field loss in eyes with abnormal cups, asymmetric cupping, or nerve fiber layer abnormalities. While automated perimetry is likely to increase the sensitivity of detection, better test methodologies are needed to combine with the objectivity of computer-assisted machines. Disk hemorrhages, nerve fiber layer defects, and color vision abnormalities are early signs of damage, supporting the conclusion that damage is present before field loss. A number of other methods await further testing to determine their effectiveness. The idea that the disease glaucoma is defined by a certain visual field finding on the Goldmann perimeter is not valid if we define glaucoma as an eye with a history of elevated IOP and optic nerve damage. While such field loss is a convenient means of defining a particular stage of damage in glaucoma, there are clearly earlier stages of damage, whether we can always detect them or not. No patient should be told that he or she does not have glaucoma, but rather has ocular hypertension, based on a particular visual field finding. As testing and examination methods improve, so, hopefully, will our ability to determine whether damage is present. As this occurs, we will be better enabled to select most rationally those patients who will benefit from therapy. The idea that field testing is relatively insensitive to the earliest glaucoma damage might lead the skeptic to conclude that perimetry is not worth the trouble. This review has indicated that none of our present methods, ophthalmoscopic, psychophysical or otherwise, is perfect. But to omit using any of them (especially field testing) does a great disservice to the glaucoma patient. The greatest usefulness of the new automated instruments is that adequate field testing is now available in a cost-effective form to every ophthalmic office. We need to strive for better detection and follow-up of glaucoma damage to prevent needless blindness.
D003119:Color Perception Tests; D005128:Eye Diseases / Q000473:pathology; D005451:Fluorescein Angiography; D005901:Glaucoma / Q000175:diagnosis* / Q000473:pathology / Q000503:physiopathology; D006470:Hemorrhage / Q000473:pathology; D006801:Humans; D009798:Ocular Hypertension / Q000503:physiopathology; D009898:Optic Disk / Q000098:blood supply / Q000473:pathology*; D009900:Optic Nerve / Q000473:pathology; D010780:Photogrammetry; D011446:Prospective Studies; D011680:Pupil; D013997:Time Factors; D058609:Visual Field Tests; D014794:Visual Fields