Ocular abnormalities in the myopathic hamster (UM-X7.1 strain)

/. H. Thakar,9 D. H. Percy,90 and K. P. Strickland9

Eyes from cardiomyopathic hamsters (UM-X7.1 strain) were examined histologically for evi- dence of ocular defects. Changes observed included microphthalmia, scleral ectasia, scleral rupture, keratoconus, retinal detachment, retinal dysplasia, retinal fragmentation, retinal thinning, fibrosis of iris and ciliary body, ectopia lentis, and cataract formation. Lesions charac- teristic of cardiomyopathic hamsters were observed in the myocardium and skeletal muscle. This strain may be a suitable animal model to study the pathogenesis of ocular changes seen in certain congenital connective tissue disorders in man.

Key words: Cardiomyopathic hamster, animal model, microphthalmia, scleral ectasia, retinal dysplasia, ectopia lentis, cataract formation.

I n the strains BIO 14.6 and UM-X7.1 of cardiac muscle are present in virtually all 2 3 Syrian hamster, there is a hereditary poly- mature animals. - Death is usually due to 2 myopathy characterized by primary cardio- terminal congestive heart failure. In this myopathy and muscular dystrophy.13 Both animal model, abnormalities of membrane- 4 of these strains are considered to be ap- bound enzymes have been observed. Of propriate animal models of the Duchenne particular interest are the elevated calcium type of human muscular dystrophy.1"3 Mus- levels in serum, skeletal, and cardiac mus- 5 6 cular dystrophy in these polymyopathic cles. ' The purpose of this communication hamsters is transmitted by an autosomal is to describe concurrent ocular changes recessive gene, and histological evidence of observed in animals of the UM-X7.1 strain. skeletal muscle lesions may be observed in animals as young as 20 days old.2 In the Materials and methods UM-X7.1 strain, lesions in skeletal and Animals of the UM-X7.1 strain were obtained from Dr. G. Jasmin, University of Montreal, Mon- treal, P. Q., and then bred locally. Both animals with clinically detectable abnormal eyes and those with normal eyes were killed at various ages for From the "Departments of Biochemistry, and macroscopic and microscopic evaluation. Tissues 0 "Bacteriology and Immunology, The University from nonaffected BIO hamsters (Trenton Experi- of Western Ontario, London, Canada. mental Laboratory, Bar Harbor, Maine) were used Support in part by Medical Research Council of as controls. Animals were killed by chloroform Canada grant MT-617 and National Institutes inhalation, fixed by immersion in Bouin's fluid or of Health grant EY01833-01. 3 percent glutaraldehyde, embedded in paraffin, Submitted for publication: April 27, 1977. sectioned at 5 M, and stained with hematoxylin Reprint requests: Dr. J. H. Thakar, Health Sci- and eosin (H & E). Halved, meridional sections ences Centre, The University of Western On- of both eyes, quadriceps muscle, and heart were tario, London, Ontario, N6A 5C1 Canada. routinely examined. Lesions were graded accord- 1047

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Fig. 1. Hamster 3759 examined at 3 months of Fig. 2. Higher magnification of retina shown in age. There is marked microphthalmia with ir- Fig. 1. Although there are multiple undulations, regular contours of sclera and lens (L). Primordial most layers, including the inner and outer nuclear uveal tract (U) is thrown into folds and adherent layers, are clearly delineated. Identifiable lens to lens. Retina is at upper left. (H & E; x30.) epithelium and fibers are present at the left. (H & E; x82.5.) Table I. Incidence of ocular lesions in the UM-X7.1 hamster

A ge at exam- No. of animals affected/ Sclera Uveal ination (days) no. of animals examined & cornea* tract* Retina* Lens* Microphthalm ia * 1-34 4/11 4/22 2/22 4/22 Mil 2/22 35-56 0/5 0/10 0/10 0/10 0/10 0/10 70-112 4/9 5/18 4/18 6/18 2/13 1/18 180-245 7/8 11/16 5/16 8/16 6/12 1/16 •No, of eyes with lesions/no, of eyes examined. ing to the size, distribution, and intensity of the scleral contours were demonstrable on affected areas. gross examination, but frequently ocular abnormalities were only evident micro- Results scopically. Clinical and macroscopic findings. Some Microscopic findings. In general, abnor- clinically affected animals were reported to mal eyes were most numerous in. older exhibit intermittent ptosis with a tendency animals (Table I). Unilateral microphthal- to recur and regress over a period of mia was observed in four hamsters.. Scleral several weeks. Frequently, only one eye outlines were irregular and undulating, was involved. Macroscopically, a few af- with no evidence of normal globe forma- fected eyes were irregular in shape and tion (Fig. 1). The uveal tract was poorly markedly reduced in size. In some in- developed, with incomplete adherence to stances, irregularities in the corneal or the adjacent sclera. Portions interpreted to

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*ig. 3. Animal 3715-3, age 6 months, with scleral Fig. 4. Eye from No. 3715-2 at 6 months of age. ectasia. Note marked reduction in width of sclera Rupture of sclera (upper left) with fibrosis and progressing from normal sclera (lower center) to pigment deposition in damaged tissue. Note distor- thin undulating areas. There is a corresponding tion and fragmentation of retina (R). Lens (L) reduction in width of the adjacent retina. (H & E; has a thickened capsule, with numerous bladder x82.5.) cells in subcapsular region. (H & E; x82.5.)

be primordial iris and ciliary body were Clefts between the retina and sclera ap- composed of a folded layer lined by peared to contain vitreous material. Degen- cuboidal epithelial cells present in close erative retinal changes observed in affected apposition to the lens (Fig. 1). In one eyes included retinal detachment, dysplasia, animal, the retina was located outside the infolding, thinning, cystoid degeneration, confines of the sclera (Figs. 1 and 2). The and separation of affected portions (Figs. lens was reduced in size and lined by a 4 to 6), Thinning and obliteration of the relatively normal layer of epithelial cells layers of the retina, when present, were and had contours that followed the out- always in association with obvious scleral lines of the adjacent sclera (Fig. 1). abnormalities. In a few eyes, there was Scleral ectasia was a frequent finding. concurrent proliferation of pigment epithe- The sclera was markedly reduced in width lial cells, with fibrosis and obliteration of in affected areas, with undulations and the normal achitecture. eversion of the scleral contours. Changes Keratoconus and irregularities in the fil- in the retina included thinning and oblit- tration angle were occasionally observed. eration of identifiable nuclear layers (Fig. Marked thickening of the iris stroma and 3). In a few eyes, there were apparent fibrosis and mineralization of the iris root focal scleral disruption and rupture, with and trabecular meshwork were especially retraction of the severed ends, collapse of striking in single eyes from two animals the globe, and herniation and degeneration examined at 6 months of age (Fig. 7). In of pigment epithelium and neural retina. these animals, there were also marked

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Fig. 6. Higher magnification of Fig. 5, illustrating Fig. 5. Animal 3737B examined at 6 months ot extensive retinal degeneration. Large clefts are age. Progressive reduction in width of retina with evident, with absence of normal retinal architec- loss of identifiable layers. Lens is at right. (H & E; ture. Sclera is at left. Note subcapsular cataractous x82.5.) change in adjacent lens. (H & E; x208.)

changes in other regions of the same eye. ing an entire segment of muscle. In reac- However, in some eyes with scleral de- tive myofibers, poles of the nuclei were formities, the iris, ciliary body, and filtra- frequently aligned in close proximity along tion angle appeared to be histologically the sarcolemmal sheath (Fig. 8). normal. In one animal (No. 3740) there was malformation of the iris, with pro- Discussion liferation of pigment cells suggestive of Knapp and Polivanov7 and Robinson8 melanoma of the iris. reported on anophthalmic hamsters, and The lens was sometimes displaced into Yoon9 described anophthalmia in progeny the vitreous cavity and separated from the resulting from the cross-mating of two ciliary process. Lenticular changes included inbred lines, BIO 72.79 and BIO 4.24. A spherophakia, thickening and irregularities variety of eye defects have been associated of the lens capsule, proliferation and migra- with certain connective tissue diseases. tion of epithelial cells with "bladder cell" Keratoconus and ectopia lentis have been formation, fragmentation of lens fibers, and observed in the myopathic hamsters in this liquefaction of lens material (Figs. 4 and study and also occur in Marfan's syndrome 6). in man.10' " Spherophakia and ectopia lentis Myocardial lesions similar to those previ- have been observed in the Weill-Mar- ously described3 were evident in virtually chesani syndrome,11 and defects observed all animals examined at 6 weeks of age or in the eye of patients with Ehlers-Danlos older. The degree of involvement of syndrome have included keratoconus and skeletal muscle varied from degeneration ectopic lens.11 Ocular tonometry was not of isolated myofibers to large areas involv- performed on our animals to determine

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tig. 7. Animal 3737-A examined at 6 months of Fig. 8. Quadriceps muscle from hamster 3759. age. Note marked thickening and fibrosis of iris There is marked degeneration of sarcoplasm, with and ciliary body. The abnormal ciliary body is hypercellularity and proliferation of sarcolemmal adherent to the lens capsule (L). (H & E; x82.5.) nuclei. (H & E; xl60.)

• whether intraocular pressures were nor- Our thanks to Dr. C. Jasmin of the Department mal, but changes in the sclera, cornea, and of Pathology, University of Montreal, Montreal, P. Q., for providing us with the breeders, and retina might be secondary to glaucoma. to Mrs. K. Fuller for technical assistance. Infantile glaucoma has occasionally been observed in patients with Marfan's syn- drome and Weill-Marchesani syndrome.12 REFERENCES At present, the exact nature of the ab- 1. Homburger, F., Nixon, C. W., Eppenberger, normalities and the sequence of events M., and Baker, J. R.: Hereditary myopathy have not been determined. However, with in the Syrian hamster: studies on pathogene- the exception of eyes with severe micro- sis, Ann. N. Y. Acad. Sci. 138:14, 1966. 2. Homburger, F.: Disease models in Syrian phthalmia, the retinal changes may be hamsters, Prog. Exp. Tumor Res. 16;69, secondary to events such as detachment 1972. from pigment epithelium, scleral ectasia, 3. Jasmin, G., and Bajusz, E.: Polymyopathic et and scleral rupture. The UM-X7.1 strain cardiomyopathie h£r£ditaire chez le hamster represents a possible animal model to study de Syrie, Ann. Anat. Pathol. 18.-49, 1973. the pathogenesis of ocular changes that 4. Dhalla, N. S., McNamara, D. B., Balasubra- manian, V,, Greenlaw, R., and Tucker, F. R.: may have application to certain congenital Alterations of adenosine triphosphatase ac- connective tissue disorders in man. Abnor- tivities in dystrophic muscle sarcolemma, Res. malities observed in the heart and skeletal Comraun. Chem. Pathol. Pharmacol, 6:643, muscle are attributed to a "membrane 1973. defect,"4's which may also play a role in 5. Thakar, J. H., Wrogemann, K., and Blanchaer, M. C.: Effect of ruthenium red on oxidative the ocular changes. Additional studies are phosphorylation and calcium and magnesium in progress. content of skeletal muscle mitochondria of

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normal and BIO 14.6 dystrophic hamsters, apparent anophthalmos of the Syrian hamster, Biochim. Biophys. Acta 314:8, 1973. INVEST. OPHTHALMOL. 14:321, 1975. 6. Lossnitzer, K., and Bajusz, E.: Water and 10. McKusick, V. A.: The Marfan syndrome. In electrolyte alteration during the life course Heritable Diseases of Connective Tissue, ed. of the BIO 14.6 Syrian golden hamster. A dis- 4, St. Louis, 1972, The C. V. Mosby Co., p. ease model of a hereditary cardiomyopathy, 61. J. Mol. Cell. Cardiol. 6:163, 1974. 11. Punnett, H. H., and Harley, R. D.: Genetics 7. Knapp, B. H., and Polivanov, S.: Anoph- in pediatric ophthalmology. In Harley, R. D., thalmic albino: a new mutation in the Syrian editor: Pediatric Ophthalmology, Philadelphia, hamster, Cricetus (mesocricetus) auratus, Am. 1975, W. B. Saunders Co., p. 10. Naturalist 92:317, 1958. 12. Harley, R. D., and Manley, D. R.: Glaucoma 8. Robinson, R.: Genetic studies of the Syrian in infants and children. In Harley, R. D., hamster. VI. Anophthalmic white, Genetica editor: Pediatric Ophthalmology, Philadelphia, 35:241, 1964. 1975, W. B. Saunders Co., p. 390. 9. Yoon, C. H.: Total retinal degeneration in

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