Ophthalmic survey of Bhopal victims 104 days after the tragedy.
Studies carried out at the time of MIC leak at Bhopal had revealed the nature and extent of the immediate ophthalmic problem. In a study involving 261 people in the exposed group and 99 people residing 10 km or farther away, Anderson et al had named the lesions as "Bhopal Eye" 2 weeks after the disaster and had described widespread conjunctivitis, chemosis, keratitis, photophobia and occasionally iritis. In addition, local ophthalmologists had also reported occasional cases of intra-ocular haemorrhages, mainly intra-retinal. However, no systematic study had been carried out to assess the residual ocular morbidity 3 months after the gas tragedy, and hence the present study was undertaken as a part of the survey described elsewhere in this issue.
The clinical survey was carried out as described earlier in two groups of subjects. The individuals having eye complaints in both the groups were referred to ophthalmology O.P.D. of the survey camp. Totally 367 patients were examined; out of them, 261 belonged to Group I and 106 belonged to Group II.
All patients were from the same socioeconomic group with incomes varying from 3,600 to 10,000 rupees per annum. At the time of examining the patients, the ophthalmologist was not informed whether the patient belonged to Group I or Group II. All the patients were examined by the author. The following studies were done: detailed interrogation for current eye complaint, distant vision by Snellen's chart; colour vision by Ishihara's colour plates; ocular movement in 6 cardinal positions of gaize; external eye examination by a powerful ophthalmic torch; pupillary reactions; ocular tension by Schiotz's tonometer in all patients above the age of 40 and fundus examination by direct ophthalmoscopy through undilated pupils in patients with clear media and after dilatation of pupils with 10% phenylephrine in those with opacities in the media.
In the age-group of less than 10 years, vision test findings were not reliable due to lack of co-operation. All the cases of corneal opacity and conjunctivitis were stained with sterile filter strips of fluorescein.
Impact of distance from the site of the accident on the occurrence of ophthalmic symptoms was studied by comparing the prevalence of complaints in 95 people in Group I staying at half kilometer distance from the factory, 95 people in Group I staying at 2 km distance from the factory and all 106 subjects in Group II residing 8 km away from the factory.
Both the groups were demographically and socio-economically similar in composition. There were 127 males and 134 females in Group I compared to 51 males and 55 females in Group II.
[Table - 1] shows the frequency of eye symptoms in Group I and Group II subjects. No patient from either group, complained of disturbance of colour vision. Colour vision as objectively tested on Ishihara's colour charts also revealed no abnormality. No patient complained of any gaze restriction. Ocular movements were normal in all the subjects.
[Table - 2] shows the findings of distant vision testing in both the groups. Those with vision between 6/12 and 6/60 were considered moderately affected while those with vision less than 6/60 in the more severely affected eye were considered severely affected.
The results of eye examination are given in [Table - 3]. The diagnosis of cataract was made if the fundus examination with dilated pupils revealed any lenticular opacity. Six out of II Group I subjects having cataract were in the age group of 21-50 years and 5 were in the age group above 50 years, whereas all the 3 Group II patients having cataract were in the age group above 50 years. None of the patients subjected to fluorescein staining had corneal staining positive. Out of 127 males and 134 females in Group I, 109 males and 81 females had no eye involvement. This difference was statistically significant.
Comparison of frequency of ophthalmic symptoms in subjects staying at different distances from the factory showed that complaints were present in 80% of subjects residing half kilometer away from the factory, in 60% of the individuals staying 2 km away and in 40% of the people residing 8 km away from the factory.
Significance of night blindness observed in Group I patients is difficult to judge date to non-availability of measurement of dark adaptation. Whether MIC has a subclinical effect on retinal sensitivity is a moot point. Charting of visual fields during subsequent studies would prove useful, especially in view of the fact that a statistically significant number of patients in Group I had their visual acuity moderately affected with normal fundi. Cyanide is known to exist in a dynamic equillibrium with thiocyanate in vivo and to inhibit the enzyme cytochrome oxidase over prolonged periods. This may be the cause of impaired retinal metabolism and hence impaired function.
The higher prevalence of cataract in Group I as well as its occurrence in the younger age group as compared to Group II suggests that MIC has some cataractogenic effect or hastens the onset of senile cataract. This is confirmed by Dr. Harding (personal communication) who demonstrated the cataractogenic effect of MIC in vitro. Smokers, who have increased thiocyanate levels have also been shown to have an increased risk of cataract.
Corneal opacities were of varying density, usually nebulomacular, usually one or two, discrete, non-vascularised, with no predilection for any particular quadrant but seldom involving more than one quadrant and never involving the whole cornea. Sixty per cent were uniocular. The drop in vision in these cases as compared to the non-affected eye was seldom greater than two lines of the E chart. All these cases were carefully interrogated; those that gave history of the opacities being present before the MIC leak and doubtful cases were excluded. These findings are to be expected, as those workers who have studied the patients during the acute episode have reported mainly superficial keratitis, in the interpalpebral area of the cornea, which healed fairly, easily, without leaving dense opacities.
Hyperemia of the conjunctiva was found to involve mainly the lower fornix, with the vessels congested and the fornix slightly sticky, though there was little or no discharge.
The difference in the overall prevalence of eye involvement between males and females was probably due to the fact that at the first sign of trouble, the males left the households to run for safety, leaving the females behind to fend for themselves. Ironically, this made the males more vulnerable to the MIC in the atmosphere.