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The Pulfrich Effect in Anisometropic Amblyopia and Strabismus: Reply
370
March, 1985
AMERICAN JOURNAL OF OPHTHALMOLOGY
References 1. Evans, L. R., and Morgan, C. G.: Intensity distribution of focused laser beams in bio-medical studies. Phys. Med. BioI. 14:205, 1969. 2. Taboada, J., and Ebbers, W. R.: Ocular tissue damage due to ultrashort 1060 nm light pulses from a mode-locked Nd: glass laser. Appl. Opt. 14:1759, 1975. 3. Coster, H. G. 1., and Zimmerman, U.: The mechanism of electrical breakdown in the membranes of valonia utriculanis. J. Membr. BioI. 22:73, 1975.
Biofeedback Therapy of Essential Blepharospasm
was first imputed to him by Banister" in 1932. Pulfrich used a hand-driven reciprocating device and, with his son's help, produced a theoretical background to his observers' data, which, contrary to Banister's opinion, was soundly based on the physiologic ideas prevalent at the time, although the underlying algebra has since been modified.! The results observed by Tredici and von Noorden are noteworthy in that they demonstrated a Pulfrich effect when one might have expected it, that is, when foveal and nonfoveal stimuli are combined. I suspect that, as long as fusion takes place, for which function it is an unsurpassed test, it fulfills a useful diagnostic role. Moreover, the spontaneous Pulfrich effect is easily quantified, for example, in terms of the neutral density (in front of the leading eye) required to eliminate the phenomenon. PROFESSOR R. A. WEALE
EDITOR:
I read with interest the article, "Biofeedback therapy of essential blepharospasm" (Am. J. Ophthalmol. 98:28, July 1984), by R. S. Surwit and M. Rotberg. Being familiar with how almost any type of treatment gives transient relief of blepharospasm, I was disappointed that there was no discussion of careful follow-up for these patients. There is merely a statement that, "Informal followup visits have confirmed that these improvements are durable over a six-month period." This does not say how many patients were followed up and for what intervals, nor do I know what the authors mean by "informal follow-up." For any treatment of blepharospasm to be considered efficacious, data on proper follow-up are essential. I hope the authors can provide this so that the efficacy of their use of biofeedback can be assessed. BARTLEY R. FRUEH, M.D.
Ann Arbor, Michigan
The Pulfrich Effect In Anisometropic Amblyopia and Strabismus EDITOR:
The interesting article by T. D. Tredici and G. K. von Noorden (Am. J. Ophthalmol. 98:499, Oct. 1984) is introduced by what appears to be a historical error: I hope the authors will forgive me if I comment on it. They say "Pulfrich noted that a pendulum oscillating in a frontal plane and viewed binocularly with a filter over one eye appeared to move in an ellipse."! However, he cannot have noted anything of the sort, because he was oneeyed. Moreover, he did not mention any pendulum. As far as I have been able to discover, this
London, England
References 1. Pulfrich, c.: Die Stereoskopie im Dienste der isochromen und heterochromen Photometrie. Naturwissenschaften 10:553, 1922. 2. Banister, H.: Retinal traction time. In Report of a Joint Discussion on Vision. London, Physical Society, 1932, pp. 227-234. 3. Weale, R. A.: Theory of the Pulfrich effect. aphtha1mologica 128:380, 1954.
_ _ _ _ _ _ _ Reply
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EDITOR:
We were aware that Carl Pulfrich injured his left eye in childhood, 1 and therefore never actually observed the stereoscopic illusion that bears his name. It is of interest that the portrait of Pulfrich in the archives of the Carl Zeiss Company, for whom he worked for many years, shows him to have had an exotropia of the left eye. We wish to thank Professor Weale for informing us that Banister first suggested to Pulfrich that a pendulum could be used to illustrate his stereoscopic principle. Much of the literature on the Pulfrich effect is unclear on this historical point. TOMAS D. TREDIel, M.D. GUNTER K. VON NOORPEN, M.D.
Houston, Texas
Reference 1. Schneider, F.: Carl Pulfrich. Prof. Dr. Carl Pulfrich zu seinem 100. Geburstag am 24. September 1958. Jenaer Rundschau 3:127, 1958.
March, 1985
AMERICAN JOURNAL OF OPHTHALMOLOGY
References 1. Evans, L. R., and Morgan, C. G.: Intensity distribution of focused laser beams in bio-medical studies. Phys. Med. BioI. 14:205, 1969. 2. Taboada, J., and Ebbers, W. R.: Ocular tissue damage due to ultrashort 1060 nm light pulses from a mode-locked Nd: glass laser. Appl. Opt. 14:1759, 1975. 3. Coster, H. G. 1., and Zimmerman, U.: The mechanism of electrical breakdown in the membranes of valonia utriculanis. J. Membr. BioI. 22:73, 1975.
Biofeedback Therapy of Essential Blepharospasm
was first imputed to him by Banister" in 1932. Pulfrich used a hand-driven reciprocating device and, with his son's help, produced a theoretical background to his observers' data, which, contrary to Banister's opinion, was soundly based on the physiologic ideas prevalent at the time, although the underlying algebra has since been modified.! The results observed by Tredici and von Noorden are noteworthy in that they demonstrated a Pulfrich effect when one might have expected it, that is, when foveal and nonfoveal stimuli are combined. I suspect that, as long as fusion takes place, for which function it is an unsurpassed test, it fulfills a useful diagnostic role. Moreover, the spontaneous Pulfrich effect is easily quantified, for example, in terms of the neutral density (in front of the leading eye) required to eliminate the phenomenon. PROFESSOR R. A. WEALE
EDITOR:
I read with interest the article, "Biofeedback therapy of essential blepharospasm" (Am. J. Ophthalmol. 98:28, July 1984), by R. S. Surwit and M. Rotberg. Being familiar with how almost any type of treatment gives transient relief of blepharospasm, I was disappointed that there was no discussion of careful follow-up for these patients. There is merely a statement that, "Informal followup visits have confirmed that these improvements are durable over a six-month period." This does not say how many patients were followed up and for what intervals, nor do I know what the authors mean by "informal follow-up." For any treatment of blepharospasm to be considered efficacious, data on proper follow-up are essential. I hope the authors can provide this so that the efficacy of their use of biofeedback can be assessed. BARTLEY R. FRUEH, M.D.
Ann Arbor, Michigan
The Pulfrich Effect In Anisometropic Amblyopia and Strabismus EDITOR:
The interesting article by T. D. Tredici and G. K. von Noorden (Am. J. Ophthalmol. 98:499, Oct. 1984) is introduced by what appears to be a historical error: I hope the authors will forgive me if I comment on it. They say "Pulfrich noted that a pendulum oscillating in a frontal plane and viewed binocularly with a filter over one eye appeared to move in an ellipse."! However, he cannot have noted anything of the sort, because he was oneeyed. Moreover, he did not mention any pendulum. As far as I have been able to discover, this
London, England
References 1. Pulfrich, c.: Die Stereoskopie im Dienste der isochromen und heterochromen Photometrie. Naturwissenschaften 10:553, 1922. 2. Banister, H.: Retinal traction time. In Report of a Joint Discussion on Vision. London, Physical Society, 1932, pp. 227-234. 3. Weale, R. A.: Theory of the Pulfrich effect. aphtha1mologica 128:380, 1954.
_ _ _ _ _ _ _ Reply
_
EDITOR:
We were aware that Carl Pulfrich injured his left eye in childhood, 1 and therefore never actually observed the stereoscopic illusion that bears his name. It is of interest that the portrait of Pulfrich in the archives of the Carl Zeiss Company, for whom he worked for many years, shows him to have had an exotropia of the left eye. We wish to thank Professor Weale for informing us that Banister first suggested to Pulfrich that a pendulum could be used to illustrate his stereoscopic principle. Much of the literature on the Pulfrich effect is unclear on this historical point. TOMAS D. TREDIel, M.D. GUNTER K. VON NOORPEN, M.D.
Houston, Texas
Reference 1. Schneider, F.: Carl Pulfrich. Prof. Dr. Carl Pulfrich zu seinem 100. Geburstag am 24. September 1958. Jenaer Rundschau 3:127, 1958.