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Cryogenic therapy of herpes keratitis
326
AMERICAN JOURNAL OF OPHTHALMOLOGY
100 91TJ personnel each year will be re quired to maintain the needs. A training manual has been prepared for these technicians. Lectures given cover basic subjects in ophthalmology and otolaryngology. The OJT portion of the eye course stresses vision testing, visual field perfor mance, tonometry, neutralization of lenses, fitting and ordering of spectacles, and as sisting the doctor with patient care in the clinic. The students are trained to remove conjunctival foreign bodies, instill medica tions, and to accomplish other similar proce dures. These personnel then work in this field during their service duty and are especially valuable assistants at Army Eye and E N T clinics. At retirement, or after completion of their service obligation, many of these tech nicians would be ideal candidates for posi tions as ophthalmic assistants to civilian ophthalmologists. Some agency is needed that can gather and provide information on both ophthalmic assistant opportunities and on available applicants. Possibly civilian ophthalmology can provide this agency. Once provided, the Armed Services un doubtedly can furnish this information to the applicable personnel leaving the service for civilian life. Jack W. Passmore Washington, D.C. CRYOGENIC THERAPY OF HERPES KERATITIS
Editor, American Journal of Ophthalmology : In the March issue (Am. J. Ophth. 63:399, 1967) M. E. Corwin, R. L. Copeland and S. Birnbaum reported their results in experimentally produced herpetic kerati tis treated with cryogenic technique. In this carefully controlled experiment, the authors obtained a negative result with the ap plication of a cryostylet at a temperature of —20°C. This negative result could have been predicted because (1) the optimal temper ature for inactivating virus is —40°C, and
AUGUST, 1967
(2) the instrument was apparently not thawed before it was removed from the cornea. Since the instrument temperature used by Corwin was — 20° C, it must then be assumed that the actual temperature at the point of contact with the warm cornea was consider ably higher, so that instead of — 20°C, he was actually using a temperature of —5° to — 10°C. When the solid carbon dioxide in strument is used, with a temperature of — 79°C, the temperature at the point of con tact is - 4 0 ° C . Greiff (Cryobiology, Merryman, editor, 1966, pages 697-728) has demonstrated that there is a marked reduction in virus concen tration following rapid freezing at — 40°C and equally rapid thawing, in a quick succession of repeated applications. For ex ample, if the initial concentration of virus is 1,000,000 it would be reduced to 400,000 after the first application of freezing, and to perhaps 10,000 after the second cycle of freezing and thawing. Only a few viruses survive the third freezing process. If the instrument is not thawed before lifting it from the cornea, it removes the ep ithelium adhering to the instrument. In doing this, the valuable antiviral interferon formed in the epithelial cells is lost. In stead, by thawing the instrument before re moving it, the ophthalmologist leaves the in fected cells (that have been disrupted by freezing) on the cornea. This allows the interferon to enter the uninfected epithelial cells, where it prevents the replication of the few surviving viruses that may enter these cells. Another factor that may not have been considered is the anatomic difference be tween the rabbit and human cornea. The ab sence of Bowman's membrane in the rabbit would lead to a more rapid scarring of the animal's cornea. Finally, Krwawicz (Brit. J. Ophth. 49:37, 1965) and others (Society for Cryo-Ophthalmology meeting, January, 1967) reported on low-temperature treatment in several hun-
VOL. 64, NO. 2
CORRESPONDENCE
dred cases of herpetic keratitis. Rapid recov ery occurred in four to five days. In 20% of the cases, a second application was required on the sixth day. I wish to commend the authors on these experiments. It is heartening to see an in creasing interest in ocular cryogenics. It is only with more research that the usefulness of low-temperature therapy will be estab lished. John G. Bellows Chicago, Illinois
327 ECLIPSE BLINDNESS
Editor, American Journal of Ophthalmology : Do you not have an editor in charge of physical units and factors? I have in mind occasional lapses of rigor in presentation which go somewhat beyond acceptable lim its. There are two examples on the same subject in the June, 1966, issue of the AMER ICAN JOURNAL OF OPHTHALMOLOGY.
In the excellent article "Eclipse blind ness" by Penner and McNair, Figure 2 * * * =κ presents a "portion of continuous recording of radiant energy level measured on Febru DR. CORWIN'S REPLY ary 4, 1962, on the island of Oahu. The Editor, abscissa measures energy in gm cal/cm/ American Journal of Ophthalmology: min." In fact the abscissa represents time ( from Thank you for the opportunity of reading right to left) and it is the ordinate which Dr. Bellows' comments on our paper. As stated in his letter, the temperature represents energy (actually power density), used in our study differed from that de but the dimensions are faulty in that centi scribed in the clinical treatment of herpes meters must be squared to create the dimen simplex keratitis. We mentioned, however, sions of area. These are small points of error in which that the duration and intensity of cold tem perature was not varied and, therefore, fur these authors stand in good company, for in one of the major source articles of all times ther investigation might be warranted. on effects of radiant energy upon the eye, Since this article was submitted, we have re Verhoeff and Bell use the words erg-sec/cm 2 , peated parts of the experiment using — 79°C temperature. Our results were consistently which has no meaning, except possibly poor. Several factors may account for this. under conventions no longer used. These First, we produced — 79°C by applying a words persist in the literature to this day, Krwawicz type instrument in methyl alcohol however, as you will note in Duke-Elder's and dry ice. It is conceivable that the alcohol Textbook of Ophthalmology, Vol. VI, pp. might have had some effect on the cornea 6495,6507. although an attempt was made to remove the Somewhat more alarming is the possible alcohol by wiping the tip of the instrument. misconstruction of the diagram already re Second, the instrument was removed from the ferred to, for, while it is true that the total cornea without thawing. power flux falling upon the surface of the We hope to repeat this study using a earth is reduced, the power per unit area closed type cryogenic instrument and to try (power density) of the retinal image is in deed enhanced by the increased pupil size. to thaw between applications. Despite the rabbit having no Bowman's Since we live daily so near the borderline of membrane, IDU appears to be effective in hazard from retinal solar effects, the im the rabbit cornea in spite of this anatomic portance of this enhancement during eclipses should not be overlooked. Certainly difference. the reader should not be left with any Martin E. Corwin suggestion or hint that the transient reducLivingston, New Jersey
AMERICAN JOURNAL OF OPHTHALMOLOGY
100 91TJ personnel each year will be re quired to maintain the needs. A training manual has been prepared for these technicians. Lectures given cover basic subjects in ophthalmology and otolaryngology. The OJT portion of the eye course stresses vision testing, visual field perfor mance, tonometry, neutralization of lenses, fitting and ordering of spectacles, and as sisting the doctor with patient care in the clinic. The students are trained to remove conjunctival foreign bodies, instill medica tions, and to accomplish other similar proce dures. These personnel then work in this field during their service duty and are especially valuable assistants at Army Eye and E N T clinics. At retirement, or after completion of their service obligation, many of these tech nicians would be ideal candidates for posi tions as ophthalmic assistants to civilian ophthalmologists. Some agency is needed that can gather and provide information on both ophthalmic assistant opportunities and on available applicants. Possibly civilian ophthalmology can provide this agency. Once provided, the Armed Services un doubtedly can furnish this information to the applicable personnel leaving the service for civilian life. Jack W. Passmore Washington, D.C. CRYOGENIC THERAPY OF HERPES KERATITIS
Editor, American Journal of Ophthalmology : In the March issue (Am. J. Ophth. 63:399, 1967) M. E. Corwin, R. L. Copeland and S. Birnbaum reported their results in experimentally produced herpetic kerati tis treated with cryogenic technique. In this carefully controlled experiment, the authors obtained a negative result with the ap plication of a cryostylet at a temperature of —20°C. This negative result could have been predicted because (1) the optimal temper ature for inactivating virus is —40°C, and
AUGUST, 1967
(2) the instrument was apparently not thawed before it was removed from the cornea. Since the instrument temperature used by Corwin was — 20° C, it must then be assumed that the actual temperature at the point of contact with the warm cornea was consider ably higher, so that instead of — 20°C, he was actually using a temperature of —5° to — 10°C. When the solid carbon dioxide in strument is used, with a temperature of — 79°C, the temperature at the point of con tact is - 4 0 ° C . Greiff (Cryobiology, Merryman, editor, 1966, pages 697-728) has demonstrated that there is a marked reduction in virus concen tration following rapid freezing at — 40°C and equally rapid thawing, in a quick succession of repeated applications. For ex ample, if the initial concentration of virus is 1,000,000 it would be reduced to 400,000 after the first application of freezing, and to perhaps 10,000 after the second cycle of freezing and thawing. Only a few viruses survive the third freezing process. If the instrument is not thawed before lifting it from the cornea, it removes the ep ithelium adhering to the instrument. In doing this, the valuable antiviral interferon formed in the epithelial cells is lost. In stead, by thawing the instrument before re moving it, the ophthalmologist leaves the in fected cells (that have been disrupted by freezing) on the cornea. This allows the interferon to enter the uninfected epithelial cells, where it prevents the replication of the few surviving viruses that may enter these cells. Another factor that may not have been considered is the anatomic difference be tween the rabbit and human cornea. The ab sence of Bowman's membrane in the rabbit would lead to a more rapid scarring of the animal's cornea. Finally, Krwawicz (Brit. J. Ophth. 49:37, 1965) and others (Society for Cryo-Ophthalmology meeting, January, 1967) reported on low-temperature treatment in several hun-
VOL. 64, NO. 2
CORRESPONDENCE
dred cases of herpetic keratitis. Rapid recov ery occurred in four to five days. In 20% of the cases, a second application was required on the sixth day. I wish to commend the authors on these experiments. It is heartening to see an in creasing interest in ocular cryogenics. It is only with more research that the usefulness of low-temperature therapy will be estab lished. John G. Bellows Chicago, Illinois
327 ECLIPSE BLINDNESS
Editor, American Journal of Ophthalmology : Do you not have an editor in charge of physical units and factors? I have in mind occasional lapses of rigor in presentation which go somewhat beyond acceptable lim its. There are two examples on the same subject in the June, 1966, issue of the AMER ICAN JOURNAL OF OPHTHALMOLOGY.
In the excellent article "Eclipse blind ness" by Penner and McNair, Figure 2 * * * =κ presents a "portion of continuous recording of radiant energy level measured on Febru DR. CORWIN'S REPLY ary 4, 1962, on the island of Oahu. The Editor, abscissa measures energy in gm cal/cm/ American Journal of Ophthalmology: min." In fact the abscissa represents time ( from Thank you for the opportunity of reading right to left) and it is the ordinate which Dr. Bellows' comments on our paper. As stated in his letter, the temperature represents energy (actually power density), used in our study differed from that de but the dimensions are faulty in that centi scribed in the clinical treatment of herpes meters must be squared to create the dimen simplex keratitis. We mentioned, however, sions of area. These are small points of error in which that the duration and intensity of cold tem perature was not varied and, therefore, fur these authors stand in good company, for in one of the major source articles of all times ther investigation might be warranted. on effects of radiant energy upon the eye, Since this article was submitted, we have re Verhoeff and Bell use the words erg-sec/cm 2 , peated parts of the experiment using — 79°C temperature. Our results were consistently which has no meaning, except possibly poor. Several factors may account for this. under conventions no longer used. These First, we produced — 79°C by applying a words persist in the literature to this day, Krwawicz type instrument in methyl alcohol however, as you will note in Duke-Elder's and dry ice. It is conceivable that the alcohol Textbook of Ophthalmology, Vol. VI, pp. might have had some effect on the cornea 6495,6507. although an attempt was made to remove the Somewhat more alarming is the possible alcohol by wiping the tip of the instrument. misconstruction of the diagram already re Second, the instrument was removed from the ferred to, for, while it is true that the total cornea without thawing. power flux falling upon the surface of the We hope to repeat this study using a earth is reduced, the power per unit area closed type cryogenic instrument and to try (power density) of the retinal image is in deed enhanced by the increased pupil size. to thaw between applications. Despite the rabbit having no Bowman's Since we live daily so near the borderline of membrane, IDU appears to be effective in hazard from retinal solar effects, the im the rabbit cornea in spite of this anatomic portance of this enhancement during eclipses should not be overlooked. Certainly difference. the reader should not be left with any Martin E. Corwin suggestion or hint that the transient reducLivingston, New Jersey