Year : 1983 | Volume
: 31 | Issue : 5 | Page : 545--547
Retinotoxic effect of zinc, manganese and molybdenum on rabbit retina (An experimental study)
PK Khosla, DB Karki, DK Gahlot
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, A.I.I.M.S., New Delhi, India
P K Khosla
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, A.I.I.M.S., New Delhi
|How to cite this article:|
Khosla P K, Karki D B, Gahlot D K. Retinotoxic effect of zinc, manganese and molybdenum on rabbit retina (An experimental study).Indian J Ophthalmol 1983;31:545-547
|How to cite this URL:|
Khosla P K, Karki D B, Gahlot D K. Retinotoxic effect of zinc, manganese and molybdenum on rabbit retina (An experimental study). Indian J Ophthalmol [serial online] 1983 [cited 2020 Feb 21 ];31:545-547
Available from: http://www.ijo.in/text.asp?1983/31/5/545/36583
The study has been undertaken to study the retinotoxic effect of zinc, manganese and molybdenum on rabbit retina.
Materials and Methods
A total of 36 healthy adult albino rabbits weighing between 1.25 to 1.65 kg. were taken and kept in the same environment of temperature, illumination and diet. Before the start of the experiment each animal was examined clinically including a fundus examination ERG was done. Anaesthesia used as nembutol in the dosage of 33 mg/kg body weight given intravenously. 4% topical xylocaine drops were also used. The animals were divided into control group consisting of nine animals and test groups consisting of 27 animals (nine for each element). They were further divided into three subgroups, consisting of three animals each of which were sacrificed at 2 weeks, 4 weeks and 8 weeks.
Zinc as zinc sulphate 0.5%, manganese as manganese sulphate 0.2% and molybdenum as sodium molybdate 0.2%, were administered intraperitioneally in the doses of 1ml. on alternate days in the test animals. In the control groups, sodium chloride 0.9% was given by the same route.
At the end of two, four or eight weeks a detailed clinical examination and ERG was repeated with identical parameters. Eyes were enucleated for histopathology.
Clinically no abnormal ocular findings were observed in either control or test groups besides general signs of toxicity in test groups.
Control group: No changes were observed both in ERG and histopathology.
Test Group I (Zinc)
Highly significant decrease in `a' wave (PTest Group II (Manganese)
A significant decrease in `a' wave (PTest Group III (Molybdenum)
'Time related highly significant decrease in `a' wave, `b' wave and total ERG (P  has reported similar finding with iodoacetate. Other retino-toxic substances like sodium fluoride (Orzalisi, 1970), Urethan (Bellhorn)  , Fenthium (Miyata et al)  etc. have also been reported similar ERG and histological changes. There is, however, no common basis for the biochemical or toxic effect of these agents but the elements studied by us are dietary essentials and vital to all living things.
A high zinc content in chorio-retina in the rabbit eye (Weitzel, 1968) and relationship between zinc and retinal mechanisms is well known (Halstead and Smith)  . Reading (1970) shows that zinc was necessary for maintaining normal level of Vitamin A in the body and a decrease in retinal alcohol dehydrogenase activity is seen in association with zinc levels. Hughes and Coogan  explained lead induced retinopathy by the inhibitory action of lead on zinc dependent enzyme system. Role of zinc in the metabolism of retina is further strengthened by the report of a pigmentary degeneration of retina induced by Dithizone which is a zinc precipitating agent (Sorsby, 1958). The role of zinc in cellular metabolism particularly of DNA and RNA has been emphasized recently by Prasad et al  . In the present study also retino-toxicity of zinc is likely to be directly or indirectly related to the inhibition of enzymatic system involved in the metabolism of retina.
Similarly manganese toxicity may result either due to direct toxic effect on the retina or indirectely by its relationship with other trace elements as excessive manganese is known to result in decreased concentration of copper in plasma (Gubler, 1954).
Molybdenum is functionally related to copper. Dick (1956) and Bowen (1966) have emphasized the complexity of molybdenumcopper interrelationship. It has been observed that while high manganese intake can block the limiting effect of molybdenum on copper retention (Dick, 1956), molybdenum restricts copper utilisation (Mills, 1961) and Molybdenum toxicity results in copper deficiency  .
Zinc, manganese and molybdenum are all potentially retino-toxic elements having a selective effect on photoreceptors and ganglion cells. Of the three elements studied molybdenum is found to be the most toxic.
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