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of the vitreous face, occurring in more than 10% of his cases. Should he not have used another agent, for example, Diamox, for comparison? Furthermore, what steps were taken to exclude the possibility that in those cases in which bulging occurred after glyc-erol other contributory factors were not present ?

d. As for the duration of the osmotic effect of glycerol, it is common knowledge that a single dose of oral glycerol or other osmotic agent usually results in a recession of the anterior hyaloid membrane followed by a return to its former position after ap­proximately six hours (Weiss and co-work­ers, Arch. Ophth. 68:341, 1962; Virno and co-workers, Am. J. Ophth. 55:1133, 1963; Kornblueth and Gombos, Am. J. Ophth. 54: 753, 1962 and many others). It is during this period that critical changes, at present ill understood, could be occurring which might well be related to the operation itself. For example, the injection of trypsin and sa­line into the open eye may have less effect on the hyaloid membrane itself because we are dealing with a more concentrated vitre­ous. This subject is currently under investi­gation in our department.

e. Regarding his comment on the postop­erative integrity of the anterior hyaloid membrane, I should mention that, in the published series, no cases of ruptured ante­rior hyaloid membrane were recorded either during the operation or during he first nine or 10 postoperative days. I should point out that no mention whatsoever of this aspect was made in our paper.

G. Gombos Jerusalem, Israel

V M A AND H V A IN RETINOBLASTOMA

Editor, American Journal of Ophthalmology:

The article by D. H. Brown on "Excretion of VMA and HVA in retinoblastoma" (Am. J. Ophth. 62:239 [Aug.] 1966) is of con­

siderable interest. It is a pity that in this im­portant study so few controls were used. Four controls done in a distant laboratory hardly constitute a sound baseline, particularly in children (whether expressed in μg/mg creati-nine or not).

The author states: " . . . a positive test (one that is greater by 3 S.D. than the nor­mal for that particular laboratory) would be confirmatory." This is an interesting conclu­sion considering the facts that, (1) on the previous page he has told us that statistical evaluation shows his data to be not significant and (2) he does not have any data for determining the normal for his par­ticular laboratory.

The VMA or HVA levels will not influence the decision of whether to remove an eye in my patients until a controlled se­ries is presented.

John Retzlaff Rochester, Minnesota

* * * DR. BROWN'S REPLY Editor, American Journal of Ophthalmology :

I agree completely that "four controls . . . hardly constitute a sound baseline" and also that "statistical evaluation shows his data to be not significant." I have no laboratory and all the procedures were done by Dr. Leon­ard. This includes both the normals and ab-normals. However, Dr. Retzlaff's arguments are basically correct.

This paper was a preliminary attempt to see if further work should be done. It was intended to interest others in applying the knowledge of clinical chemistry to the field of ophthalmic surgery. By Dr. Retzlaff's question, I believe it has succeeded.

David Henderson Brown Honolulu, Hawaii

CORRECTION

In the paper by Virno et al, 62:824 (Nov.) 1966, paragraph 4, the word rexin should read rhexis.