- Email: [email protected]
Color Defective Individuals
722
AMERICAN JOURNAL OF OPHTHALMOLOGY
nomenon 1 (exacerbation of symptoms with exercise) for multiple sclerosis is unknown. How can heating the surface of the body uncover central neurologic de fects ? Nelson and McDowell 2 studied a group of patients by immersing them up to the nipple line in a hot bath with a temperature from 40.6 to 43.3° C. Core body temperature was measured with a thermocouple inserted into the rectum 6 inches or more. Thirteen of 14 patients developed neurologic signs when the body temperature was increased by 17.1 ± 17.4° C. In at least two patients only a 17.6° C increase was needed. The authors demonstrated that temper ature change and not stress of the test was the more likely cause. They kept one person with an increased temperature of 16.8° C in a bath for over two hours; the subject showed no neurologic signs. When the temperature was increased an other 17.7° C, signs appeared. When the temperature was decreased 17.7° C, signs disappeared. In another study, 3 unmyelinated nerves were placed in a temperature-controlled bath. A lesion was made in the axon by gently pinching and stretching it; the action potential changed from being biphasic to monophasic. Varying the tem perature between 25.0 and 25.5° C alter nately restored and removed the biphasic mode. This demonstrated the exquisite temperature sensitivity of an injured axon. Similarly, this temperature sensitiv ity has been demonstrated in myelinated nerves. 4 In a model, Tasaki 5 applied cocaine to a small portion of an axon. The drug de prived the nodes of Ranvier of the ability to produce an action current. The altered portion of the nerve simulated a plaque, as in multiple sclerosis. He found a sud den cessation of transmission along a nerve when the narcotized portion was large enough that the action current was
MAY, 1978
from one fifth to one seventh of the origi nal value. From this he defined the safety factor as the ratio of the action current generated by the nerve impulse to the minimum amount of current needed to maintain conduction. Thus the safety fac tor in a normal nerve is from 5 to 7. He suggested that if the safety factor is de creased by injury, cocaine, or disease to near unity, then a small additional insult could prevent conduction. Increased temperature increases the threshold for excitation for a nerve. 6 It also decreases the duration of the action potential. Both of these would tend to decrease the safety factor. All of the ef fects of temperature on conduction are not completely understood and need fur ther investigation. 4 D O N A L D D. B O D E ,
Denver,
M.D.
Colorado
REFERENCES 1. Uhthoff, W. P.: Untersuchungen iiber der mul tiple Herdsklerose vorkommenden Augenstorungen. Arch. Psychiatr. Nervenkr. 21:303, 1889. 2. Nelson, D. A., and McDowell, F.: Effects of induced hyperthermia on patients with multiple sclerosis. J. Neurol. Neurosurg. Psychiatry 22:113, 1959. 3. Davis, F. A.: Axonal conduction studies based on some considerations of temperature effects in multiple sclerosis. Electroencephalog. Clin. Neurophysiol. 28:281, 1970. 4. Davis, F. A.: Pathophysiology of multiple scle rosis and related clinical implications. Mod. Treat. 7:890, 1970. 5. Tasaki, I.: Nervous Transmission. Springfield, Illinois, Charles C Thomas, 1953, pp. 37-50. 6. Tasaki, I.: Nerve Excitation. Springfield, Illi nois, Charles C Thomas, 1967, p. 124.
Color Defective Individuals Editor: As a proctologist, I recently encoun tered a meticulous red color blind patient with advanced midrectal carcinoma; at resection there were numerous regional positive nodes. Alteration in bowel function for two weeks triggered his request for inspection
723
CORRESPONDENCE
VOL. 85, NO. 5
of the bowel movement by his spouse, who noted the blood. He then realized in retrospect that there had been "a peculiar color change" in the accustomed brown color with which he was familiar. Upon inquiry among ophthalmologists here, I discovered that is had never oc curred to them to alert this type of patient to the potential danger of bleeding from any body orifice, and that if this were suspected another person should be re quested to inspect. Further, apparently it is unusual to test for color blindness in the routine ophthalmologic examination. I believe early awareness may salvage many red color blind individuals. SYDNEY S. P E A R L
Elizabeth,
New Jersey
Reply Editor: In our years of studying color defect we have heard many cautionary tales of the problems and difficulties experienced by color defective observers, but this partic ular problem is a new one to us. Dr. Pearl refers to the color defect protanopia, which occurs in 1% of the Ameri can white male population. Another 1% of male whites have the color defect deuteranopia and may experience a similar difficulty. We do not know the incidence of disorders accompanied by rectal bleed ing but there are undoubtedly protanopic and deuteranopic individuals at risk. We would agree with Dr. Pearl's point that such individuals should be identified and informed that they may not recognize one of the important symptoms of rectal carci noma. Color screening is not performed rou tinely in the United States. Many of the individuals we test learned of their defect during screening for military duties. We were amused recently when an ophthal mologist stated in a popular consumer magazine that color screening is a "com
plete waste of time." On the other hand, color defect can be a genuine visual han dicap. Color defective individuals are re stricted in many occupations. Many color defectives have memories of being teased or punished for not recognizing a color difference obvious to the normal eye. Many are frustrated because so few clini cians are willing to explain the defect to them. We feel strongly that color defec tive individuals should be identified at an early age for their own information and for career counseling. Certainly, we agree with Dr. Pearl that any protanopic or deuteranopic individual at risk for rectal bleeding should be informed of the need for extra caution and attention to changes in bowel function. J O E L POKORNY, P H . D. VIVIANNE C. S M I T H , P H . D.
Chicago,
Illinois
E q u i p m e n t Needs in Bangladesh Editor: I am working as a consultant with the World Health Organization in the field of prevention of blindness in this country. In the course of my work here I have witnessed several cataract operations being performed in eye camps under dif ficult, and what one may call, "primitive" conditions. One of the prime reasons for this is the lack of suitable equipment such as operating tables, lamps, sterilizers, au toclaves, and surgical instruments. Many of these camps are organized by voluntary agencies whose resources are sufficient only to buy drugs and items of food for 20,000 to 30,000 patients each year. There are also base eye hospitals set up in rural areas to deal with the curable blind, but these too have meagre equipment. I am not certain what American and other foreign colleagues do with their outdated equipment and instruments. If any of the latter are available it would go a long way to help the ophthalmologists
AMERICAN JOURNAL OF OPHTHALMOLOGY
nomenon 1 (exacerbation of symptoms with exercise) for multiple sclerosis is unknown. How can heating the surface of the body uncover central neurologic de fects ? Nelson and McDowell 2 studied a group of patients by immersing them up to the nipple line in a hot bath with a temperature from 40.6 to 43.3° C. Core body temperature was measured with a thermocouple inserted into the rectum 6 inches or more. Thirteen of 14 patients developed neurologic signs when the body temperature was increased by 17.1 ± 17.4° C. In at least two patients only a 17.6° C increase was needed. The authors demonstrated that temper ature change and not stress of the test was the more likely cause. They kept one person with an increased temperature of 16.8° C in a bath for over two hours; the subject showed no neurologic signs. When the temperature was increased an other 17.7° C, signs appeared. When the temperature was decreased 17.7° C, signs disappeared. In another study, 3 unmyelinated nerves were placed in a temperature-controlled bath. A lesion was made in the axon by gently pinching and stretching it; the action potential changed from being biphasic to monophasic. Varying the tem perature between 25.0 and 25.5° C alter nately restored and removed the biphasic mode. This demonstrated the exquisite temperature sensitivity of an injured axon. Similarly, this temperature sensitiv ity has been demonstrated in myelinated nerves. 4 In a model, Tasaki 5 applied cocaine to a small portion of an axon. The drug de prived the nodes of Ranvier of the ability to produce an action current. The altered portion of the nerve simulated a plaque, as in multiple sclerosis. He found a sud den cessation of transmission along a nerve when the narcotized portion was large enough that the action current was
MAY, 1978
from one fifth to one seventh of the origi nal value. From this he defined the safety factor as the ratio of the action current generated by the nerve impulse to the minimum amount of current needed to maintain conduction. Thus the safety fac tor in a normal nerve is from 5 to 7. He suggested that if the safety factor is de creased by injury, cocaine, or disease to near unity, then a small additional insult could prevent conduction. Increased temperature increases the threshold for excitation for a nerve. 6 It also decreases the duration of the action potential. Both of these would tend to decrease the safety factor. All of the ef fects of temperature on conduction are not completely understood and need fur ther investigation. 4 D O N A L D D. B O D E ,
Denver,
M.D.
Colorado
REFERENCES 1. Uhthoff, W. P.: Untersuchungen iiber der mul tiple Herdsklerose vorkommenden Augenstorungen. Arch. Psychiatr. Nervenkr. 21:303, 1889. 2. Nelson, D. A., and McDowell, F.: Effects of induced hyperthermia on patients with multiple sclerosis. J. Neurol. Neurosurg. Psychiatry 22:113, 1959. 3. Davis, F. A.: Axonal conduction studies based on some considerations of temperature effects in multiple sclerosis. Electroencephalog. Clin. Neurophysiol. 28:281, 1970. 4. Davis, F. A.: Pathophysiology of multiple scle rosis and related clinical implications. Mod. Treat. 7:890, 1970. 5. Tasaki, I.: Nervous Transmission. Springfield, Illinois, Charles C Thomas, 1953, pp. 37-50. 6. Tasaki, I.: Nerve Excitation. Springfield, Illi nois, Charles C Thomas, 1967, p. 124.
Color Defective Individuals Editor: As a proctologist, I recently encoun tered a meticulous red color blind patient with advanced midrectal carcinoma; at resection there were numerous regional positive nodes. Alteration in bowel function for two weeks triggered his request for inspection
723
CORRESPONDENCE
VOL. 85, NO. 5
of the bowel movement by his spouse, who noted the blood. He then realized in retrospect that there had been "a peculiar color change" in the accustomed brown color with which he was familiar. Upon inquiry among ophthalmologists here, I discovered that is had never oc curred to them to alert this type of patient to the potential danger of bleeding from any body orifice, and that if this were suspected another person should be re quested to inspect. Further, apparently it is unusual to test for color blindness in the routine ophthalmologic examination. I believe early awareness may salvage many red color blind individuals. SYDNEY S. P E A R L
Elizabeth,
New Jersey
Reply Editor: In our years of studying color defect we have heard many cautionary tales of the problems and difficulties experienced by color defective observers, but this partic ular problem is a new one to us. Dr. Pearl refers to the color defect protanopia, which occurs in 1% of the Ameri can white male population. Another 1% of male whites have the color defect deuteranopia and may experience a similar difficulty. We do not know the incidence of disorders accompanied by rectal bleed ing but there are undoubtedly protanopic and deuteranopic individuals at risk. We would agree with Dr. Pearl's point that such individuals should be identified and informed that they may not recognize one of the important symptoms of rectal carci noma. Color screening is not performed rou tinely in the United States. Many of the individuals we test learned of their defect during screening for military duties. We were amused recently when an ophthal mologist stated in a popular consumer magazine that color screening is a "com
plete waste of time." On the other hand, color defect can be a genuine visual han dicap. Color defective individuals are re stricted in many occupations. Many color defectives have memories of being teased or punished for not recognizing a color difference obvious to the normal eye. Many are frustrated because so few clini cians are willing to explain the defect to them. We feel strongly that color defec tive individuals should be identified at an early age for their own information and for career counseling. Certainly, we agree with Dr. Pearl that any protanopic or deuteranopic individual at risk for rectal bleeding should be informed of the need for extra caution and attention to changes in bowel function. J O E L POKORNY, P H . D. VIVIANNE C. S M I T H , P H . D.
Chicago,
Illinois
E q u i p m e n t Needs in Bangladesh Editor: I am working as a consultant with the World Health Organization in the field of prevention of blindness in this country. In the course of my work here I have witnessed several cataract operations being performed in eye camps under dif ficult, and what one may call, "primitive" conditions. One of the prime reasons for this is the lack of suitable equipment such as operating tables, lamps, sterilizers, au toclaves, and surgical instruments. Many of these camps are organized by voluntary agencies whose resources are sufficient only to buy drugs and items of food for 20,000 to 30,000 patients each year. There are also base eye hospitals set up in rural areas to deal with the curable blind, but these too have meagre equipment. I am not certain what American and other foreign colleagues do with their outdated equipment and instruments. If any of the latter are available it would go a long way to help the ophthalmologists