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Optical performance of the penguin eye in air and water
419
CURRENTOPHTHALMOLOGY
Effects of Megavolt Therapy of Cancer on the Eye, by E. Nordman, L.E.O. Nordman and A. Voutilainen. Strahientherapie 152:254-259, 1976 Twenty-two patients treated by megavoltage therapy between 1968 and 1972 for malignant tumours adjacent to the eye are presented. Among these patients, there were nine epidermal carcinomas, five lymphomas, one basal cell, one adenoid cystic, three other carcinomas and one metastasis. There was one tibrosarcoma and one hemangiopericytoma. Eight of the tumors were situated in the maxilla, five in the nasal cavity, four in orbit, three in ethmoidal sinuses, and two in the buccal region. The total dosage varied from 1400 to 6300 rad to the globe in three to eight weeks. The followup time was 12 to 60 months. In five cases the patient died or the eye was enucleated in connection with extirpation of the tumor within seven months. Four of the patients had no complications caused by radiotherapy, their doses having ranged from 1400 to 5 100 rad. Cataract was verified in seven cases after doses of 3400 to 6000 rad. Radiation keratitis was documented in fifteen cases after a dose of 3000 to 6300 rad. In three cases a cornea1 ulcer developed with doses of 4900 to 6ooO rad. Glaucoma developed in three cases after doses of 3600 to 6000 rad; two of these patients had an accompanying iritis. These complications seemed to have correlation to the total dose. Radiation retinopathy developed in two cases after doses of 4000 and 5700 rad. The latency time for cataract, glaucoma and radiation retinopathy was 3 to 60 months. Keratitis appeared usually during the last part of radiation treatment. This complication had no correlation to the total dose administered. The visual acuity was established in fifteen eyes during radiotherapy and during the followup time; in spite of quite high dose therapy to the eye, the visual acuity was preserved in ten eyes as 0.5 or better. Only in one case did the eye have to be enucleated because of irradiation sequelae (glaucoma, iritis, cornea1 ulcer), following a dose of 6000 rad. In the other cases the distressing symptoms were relieved with appropriate therapy. It would seem that enucleation of the irradiated eye is rarely indicated as long the dose delivered to the globe remains below 6000 rad. As the prognosis for malignant tumors in this area usually is not favorable, radiation sequelae to the eye on the affected side is to be accepted as a calculated risk to achieve a more effective cancer control. A cataract can be operated and a painful globe with glaucoma can be enucleated later on, if necessary. Even if the irradiated eye is blind, the patient prefers his own eye to an artificial one. (abstract by E. Nordman)
Comment This article helps fill a gap in the literature. Only on rare occasions do we read of a study with a 12-60 month followup period after cobalt-60-unit or linear acceleration megavoltage radiation therapy to the globe. In only 2 of the 22 cases could the eye be shielded. The results are in general gratifying. Only one eye had to be enucleated due to the sequelae of irradiation. This is in contrast to the results following radiation therapy to an unshielded globe during the era prior to split dose megavoltage therapy. In such instances, perforation of the globe and enucleation were not uncommon. The authors state that they undertook “appropriate” therapy for each complication of irradiation in several instances; details of this therapy were not discussed. I have found that the application of a soft lens reduces the severity of keratitis following irradiation. In many instances, the keratitis is exacerbated by the sandpaper effect of the keratinized palpebral conjunctiva which occurs following radiation. After some months, the keratinization resolves. I believe that soft lens therapy had decreased our incidence of perforation. Following the above report, it seems likely the mode of radiation itself has improved the prognosis, It is difficult to calculate the median followup period as the symbol that denotes “greater than” was used to denote the observation period in 13 of the 22 cases. Median observation time was approximately 26 months when “greater than” was discounted. JULES L. BAUM
Optical Performance of the Penguin Eye in Air and Water, by J.G. Sivak and M. Millodot. J. Comp. Physiol. 129:241-247, 1977 On land, the penguin reminds us of a laughable little man in a tuxedo, waddling amongst its neighbors as if slightly tipsy at a formal bail. Yet in the water, it becomes a sleek mariner, efficiently overtaking its prey, or eluding its enemies. The authors of this paper became curious about the eyes of this fascinating
420
SurvOphthalmol
22 (6) May-June
CURRENT
1978
OPHTHALMOLOGY
avian schizophrenic. So, they went off to the Edinburgh zoo, where they photokeratoscoped and retinoscoped (in air and under water) members from three penguin species. (There exist 17 species in all) The investigators learned that penguins are essentially emmetropic in air, and average about 10 diopters of hyperopia in water. This last figure compares very favorably to the 40 diopters of hyperopia that humans experience under water, when their corneas become surrounded by water. The authors conclude that this special combination of refractive events can only take place if the cornea is not a powerful refracting element. Indeed, photokeratoscopy confirms their hypothesis. The average penguin cornea has a refracting power of only 14 diopters. This leads the authors to suggest that while underwater, the animal must have a powerful accommodative mechanism. Finally, the authors report that the penguin’s eye has 2 diopters of chromatic aberration, about twice as much as the human eye. (Abstract by D. Miller)
Comment In order to appreciate the unique features of the penguin eye, one should be familiar with the double life that this animal leads. On land, he is a mild mannered suburbanite, living in communities as large as 30,000. As a good neighbor, he will huddle in large groups to conserve body heat. He and his mate will share the lengthy duties involved in incubating the eggs and rearing the young. His fidelity is expressed in a low divorce rate (15%) and his social responsibility is expressed in organization of communal nurseries, as well as caring for lost orphans, as if they were his very own. But in the sea, the penguin is able to race through icy water at speeds as high as 30 mph, dive to depths of 60 feet, spear shrimp-like animals as small as 8mm, and avoid the murderous advances of the leopard seal and the killer whale. How does he do it? Credit certainly must go to the powerful flippers, and the efficient oxygen extraction in both lung and muscle. However, Drs. Sivak and Millodot have pointed to another unique resource of the penguin. For example, in the rockhopper penguin, the relatively flat cornea, along with the emmetropia in air and the 8 diopter hyperopia underwater, suggest an eye with an axial length more than double that of the human. Such a large eye produces a retinal image more than twice as large as the human counterpart. Now if the penguin clearly sees those 8mm shrimp-like Euphausia, it must overcome its underwater hyperopia and accommodate another five to ten diopters, giving it a substantial accommodative amplitude. The increased chromatic aberration may also be a blessing, acting as a clue in deciding whether to increase or decrease accommodation. Certainly, the presence of a magnified retinal image, which focuses sharply and quickly, must play a major role in the antics of this aquatic superstar. DAVID MILLER
The Use of Freeze-Etching Technique in the Study of the Ultrastructure of the Cornea, by M. Hirsch, G. Renard, P. Montcourrier, J.P. Faure and Y. Pouliquen. Arch Uphtalmol (Paris) 36.663432, 1976 The freeze-fracture technique has been applied to the study of the fine structure of the cornea, and the data thus obtained have been compared with the now classical data of transmission and scanning electron microscopic observations. This technique allows observation, with the transmission electron microscope, of replicas of cells or tissues fractured in a vacuum at very low temperatures. It offers two major advantages over classical electron microscopic observation. First, most of the drastic treatments inflicted on cells or tissues in the preparation of ultra-thin sections are avoided; second, the cleavage plane tends to lie inside the membranes in their hydrophobic matrix. The freeze-fracture technique is especially useful for the study of membranes and their specializations, e.g. intercellular junctions, which have important functions in such phenomena as cell adhesivity, transcellular permeability and ionic and metabolic exchanges between the cells. The main ultrastructural characteristics of epithelium, stroma and endothelium of the rabbit’s cornea utilizing the freeze-fracture technique is described with special consideration of the intercellular junctions. I. Epithelium: In the un-fixed, cryopreserved tissue, desmosomes appear as an aggregate of particles on the fracture faces. [After cleavage of the membranes, two fracture-faces are defined: P-face (PF) corresponds to the surface of the half-membrane which remains related to intracellular material; its complementary E-face (EF) corresponds to the surface of the half-membrane which remains related to ex-
CURRENTOPHTHALMOLOGY
Effects of Megavolt Therapy of Cancer on the Eye, by E. Nordman, L.E.O. Nordman and A. Voutilainen. Strahientherapie 152:254-259, 1976 Twenty-two patients treated by megavoltage therapy between 1968 and 1972 for malignant tumours adjacent to the eye are presented. Among these patients, there were nine epidermal carcinomas, five lymphomas, one basal cell, one adenoid cystic, three other carcinomas and one metastasis. There was one tibrosarcoma and one hemangiopericytoma. Eight of the tumors were situated in the maxilla, five in the nasal cavity, four in orbit, three in ethmoidal sinuses, and two in the buccal region. The total dosage varied from 1400 to 6300 rad to the globe in three to eight weeks. The followup time was 12 to 60 months. In five cases the patient died or the eye was enucleated in connection with extirpation of the tumor within seven months. Four of the patients had no complications caused by radiotherapy, their doses having ranged from 1400 to 5 100 rad. Cataract was verified in seven cases after doses of 3400 to 6000 rad. Radiation keratitis was documented in fifteen cases after a dose of 3000 to 6300 rad. In three cases a cornea1 ulcer developed with doses of 4900 to 6ooO rad. Glaucoma developed in three cases after doses of 3600 to 6000 rad; two of these patients had an accompanying iritis. These complications seemed to have correlation to the total dose. Radiation retinopathy developed in two cases after doses of 4000 and 5700 rad. The latency time for cataract, glaucoma and radiation retinopathy was 3 to 60 months. Keratitis appeared usually during the last part of radiation treatment. This complication had no correlation to the total dose administered. The visual acuity was established in fifteen eyes during radiotherapy and during the followup time; in spite of quite high dose therapy to the eye, the visual acuity was preserved in ten eyes as 0.5 or better. Only in one case did the eye have to be enucleated because of irradiation sequelae (glaucoma, iritis, cornea1 ulcer), following a dose of 6000 rad. In the other cases the distressing symptoms were relieved with appropriate therapy. It would seem that enucleation of the irradiated eye is rarely indicated as long the dose delivered to the globe remains below 6000 rad. As the prognosis for malignant tumors in this area usually is not favorable, radiation sequelae to the eye on the affected side is to be accepted as a calculated risk to achieve a more effective cancer control. A cataract can be operated and a painful globe with glaucoma can be enucleated later on, if necessary. Even if the irradiated eye is blind, the patient prefers his own eye to an artificial one. (abstract by E. Nordman)
Comment This article helps fill a gap in the literature. Only on rare occasions do we read of a study with a 12-60 month followup period after cobalt-60-unit or linear acceleration megavoltage radiation therapy to the globe. In only 2 of the 22 cases could the eye be shielded. The results are in general gratifying. Only one eye had to be enucleated due to the sequelae of irradiation. This is in contrast to the results following radiation therapy to an unshielded globe during the era prior to split dose megavoltage therapy. In such instances, perforation of the globe and enucleation were not uncommon. The authors state that they undertook “appropriate” therapy for each complication of irradiation in several instances; details of this therapy were not discussed. I have found that the application of a soft lens reduces the severity of keratitis following irradiation. In many instances, the keratitis is exacerbated by the sandpaper effect of the keratinized palpebral conjunctiva which occurs following radiation. After some months, the keratinization resolves. I believe that soft lens therapy had decreased our incidence of perforation. Following the above report, it seems likely the mode of radiation itself has improved the prognosis, It is difficult to calculate the median followup period as the symbol that denotes “greater than” was used to denote the observation period in 13 of the 22 cases. Median observation time was approximately 26 months when “greater than” was discounted. JULES L. BAUM
Optical Performance of the Penguin Eye in Air and Water, by J.G. Sivak and M. Millodot. J. Comp. Physiol. 129:241-247, 1977 On land, the penguin reminds us of a laughable little man in a tuxedo, waddling amongst its neighbors as if slightly tipsy at a formal bail. Yet in the water, it becomes a sleek mariner, efficiently overtaking its prey, or eluding its enemies. The authors of this paper became curious about the eyes of this fascinating
420
SurvOphthalmol
22 (6) May-June
CURRENT
1978
OPHTHALMOLOGY
avian schizophrenic. So, they went off to the Edinburgh zoo, where they photokeratoscoped and retinoscoped (in air and under water) members from three penguin species. (There exist 17 species in all) The investigators learned that penguins are essentially emmetropic in air, and average about 10 diopters of hyperopia in water. This last figure compares very favorably to the 40 diopters of hyperopia that humans experience under water, when their corneas become surrounded by water. The authors conclude that this special combination of refractive events can only take place if the cornea is not a powerful refracting element. Indeed, photokeratoscopy confirms their hypothesis. The average penguin cornea has a refracting power of only 14 diopters. This leads the authors to suggest that while underwater, the animal must have a powerful accommodative mechanism. Finally, the authors report that the penguin’s eye has 2 diopters of chromatic aberration, about twice as much as the human eye. (Abstract by D. Miller)
Comment In order to appreciate the unique features of the penguin eye, one should be familiar with the double life that this animal leads. On land, he is a mild mannered suburbanite, living in communities as large as 30,000. As a good neighbor, he will huddle in large groups to conserve body heat. He and his mate will share the lengthy duties involved in incubating the eggs and rearing the young. His fidelity is expressed in a low divorce rate (15%) and his social responsibility is expressed in organization of communal nurseries, as well as caring for lost orphans, as if they were his very own. But in the sea, the penguin is able to race through icy water at speeds as high as 30 mph, dive to depths of 60 feet, spear shrimp-like animals as small as 8mm, and avoid the murderous advances of the leopard seal and the killer whale. How does he do it? Credit certainly must go to the powerful flippers, and the efficient oxygen extraction in both lung and muscle. However, Drs. Sivak and Millodot have pointed to another unique resource of the penguin. For example, in the rockhopper penguin, the relatively flat cornea, along with the emmetropia in air and the 8 diopter hyperopia underwater, suggest an eye with an axial length more than double that of the human. Such a large eye produces a retinal image more than twice as large as the human counterpart. Now if the penguin clearly sees those 8mm shrimp-like Euphausia, it must overcome its underwater hyperopia and accommodate another five to ten diopters, giving it a substantial accommodative amplitude. The increased chromatic aberration may also be a blessing, acting as a clue in deciding whether to increase or decrease accommodation. Certainly, the presence of a magnified retinal image, which focuses sharply and quickly, must play a major role in the antics of this aquatic superstar. DAVID MILLER
The Use of Freeze-Etching Technique in the Study of the Ultrastructure of the Cornea, by M. Hirsch, G. Renard, P. Montcourrier, J.P. Faure and Y. Pouliquen. Arch Uphtalmol (Paris) 36.663432, 1976 The freeze-fracture technique has been applied to the study of the fine structure of the cornea, and the data thus obtained have been compared with the now classical data of transmission and scanning electron microscopic observations. This technique allows observation, with the transmission electron microscope, of replicas of cells or tissues fractured in a vacuum at very low temperatures. It offers two major advantages over classical electron microscopic observation. First, most of the drastic treatments inflicted on cells or tissues in the preparation of ultra-thin sections are avoided; second, the cleavage plane tends to lie inside the membranes in their hydrophobic matrix. The freeze-fracture technique is especially useful for the study of membranes and their specializations, e.g. intercellular junctions, which have important functions in such phenomena as cell adhesivity, transcellular permeability and ionic and metabolic exchanges between the cells. The main ultrastructural characteristics of epithelium, stroma and endothelium of the rabbit’s cornea utilizing the freeze-fracture technique is described with special consideration of the intercellular junctions. I. Epithelium: In the un-fixed, cryopreserved tissue, desmosomes appear as an aggregate of particles on the fracture faces. [After cleavage of the membranes, two fracture-faces are defined: P-face (PF) corresponds to the surface of the half-membrane which remains related to intracellular material; its complementary E-face (EF) corresponds to the surface of the half-membrane which remains related to ex-