Applanation Tonometry without Fluorescein

VOL. 89, NO. 2

CORRESPONDE1'CE

human malignant melanomas. Semin. Oneol. 2:83, 1975.

Reply Editor: Dr. Rodriguez-Sains brings up an interesting point, one that was discussed even further by Professor Alfred W. Kopf in the Parker Heath Memorial Lecture at the recent meeting of the American Academy of Ophthalmology. Dr. Rodriguez-Sains points out that the premalignant (preinvasive) stage of many cutaneous melanomas lasts five to ten or more years but, in addition, according to the recent studies described by Dr. Kopf, long periods also elapse between invasion of the superficial dermis, invasion of the deep dermis, and invasion of the subcutis; thus, just as changes in our conception of uveal melanomas have taken place during recent years, so also are we beginning to appreciate that cutaneous malanomas are not as rapidly growing or as highly malignant as once thought. By comparison, however, there are still reasons for continuing to have greater concern about cutaneous than about uveal melanomas: (1) mitotic activity is typically much greater in cutaneous than in uveal melanomas, (2) low-grade spindle cell melanomas are common in the uvea but rare in the skin, and (3) metastatic disease is observed much more frequently at the time of initial manifestation among patients with cutaneous melanomas. Dr. Rodriguez-Sains has focused attention mainly on the long period of time that elapses between several premalignant conditions and the truly malignant, invasive stages of cutaneous melanomas, and suggests that perhaps there may be similar "growth patterns" that precede the development of uveal melanomas. Uveal melanomas are more likely to arise in congenital ocular melanocytosis, in the nevus of Ota, in neurofibromatosis, and in large

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nevi of the uveal tract than in completely normal eyes; but to date, we are not aware of any significant variations in clinical behavior or metastasizing potential that can be correlated with these histogenetically different types of uveal melanomas. LORENZ E. ZIMMERMAN, M. D. IAN W. McLEAN, M.D. Washington, D.C.

Applanation Tonometry Without Fluorescein Editor: I am writing to reply to the question raised by Raymond Smith regarding applanation tonometry without fluorescein in the Correspondence section (Am. J. Ophthalmol. 87:583, 1979). I wish to emphasize that applanation tonometry without fluorescein will result in marked underestimation of the intraocular pressure. This occurs because one is observing the edge of the meniscus of the tear film rather than the true edge of the applanation prism. As is pointed out in standard textbooks of ophthalmology, for the applanation principle to be correct one must apply force to an area of 3.06 mm! in size. On a series of 100 consecutive eyes I performed applanation tonometry without fluorescein and then with fluorescein and the blue exciting filter. In every case the true intraocular pressure was underestimated by a significant amount. The pressure was lower by a range of 3 to 10 mm Hg and this probably represents the amount of tearing the patient experienced after use of the topical anesthetic. The use of fluorescein is important so that serious errors in judgement will not be made in the management of patients with glaucoma. MICHAEL B. RUMELT, M.D. Creve Coeur, Missouri