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SUMMARY The electron microscopic appearances of the corneoscleral and iris tissue removed at operation from a child with Hurler disease and glaucoma showed distinctive swollen cells with intracellular inclusions similar to those which are observed in other tissues in these patients and which are due to abnormal lysosomal storage of mucopolysaccharides. Some recent observations on the possible relationship between mucopolysaccharides and the drainage of fluid from the anterior chamber are briefly reviewed and correlated with the present observations. The development of glaucoma in this patient is thought to be associated with the presence of the mucopolysaccharidecontaining cells in the region of the aqueous drainage channels.

BRITISH MEDICAL JOURNAL 8 JUNE 1974 533 between serum albumin and serum zinc in 27 T-hough these mechanisms-may to varying degrees influence the serum zinc concentration in leprosy the nost likely explanation for the decreased serum values is that they are a non-specific metabolic consequence of skin disease, since a sinilar lowering of serum or plasma zinc concentrations was found in pulmonary tuberculosis in the presen-t study and in psoriasis, venous leg ulceraition, and other dermatoses in an earlier investigation (Greaves and Boyde, 1967). Shuster and Marks (1970) highlighted the varied metabolic costs of skin disease, which include lowering of the serum iron, folate deficiency, and hypoalbuminaemia, and it seems probable that lowered serum zinc should be added to the list. The presumed non-specific nature of -the decreased serum zinc in trophic skin ulceration of leprosy does not, however, exclude the possibility that zinc may be a limiting factor in -the rate of healing of the ulcers, and it is of interest tat in leg ulceration from other causes also associated with decreased serum zinc concentratis a beneficial effect of systemic zinc treatment has been claimed (Husain, 1969;Serjeant et al., 1970;Hallbook and Lanner, 1972).

THE electroretinogram (ERG) is used as an objective test of retinal function. However, in normal clinical recording, the potential investigated is produced by the entire retina (Asher, 1951). Therefore, though diffuse retinal damage can be detected, normal responses are obtained if the lesion is small and localized, such as a macular degeneration.It has been shown in animal experiments that local ERGs can be obtained by using micro-electrodes (Brown and Wiesel, 1959). More recently local responses have been obtained in experimental subjects using corneal electrodes and averaging techniques (Brindley and Westheimer, 1965). It is the purpose of this communication to show that such techniques can be used to obtain true foveal ERGs and are practicable in clinical circumstances.Patients and normal subjects were fitted with standard contact lens electrodes (modified Karpe type) and no correction for refractive error was incorporated. The stimulus was a back-illuminated diffuser 1 5 cm. in diameter at 43 cm., subtending a visual angle of 20. Its retinal image covered either the fovea or the blind spot. The front face of the diffuser was surrounded by a large piece of white card, illuminated by a blue-green light. The stimulus flashes (150/min.) were provided by a Xenon stroboscope, covered by a red filter. Broadband filters made of sheets of "Cinemoid" were used.When the stimulus fell on the blind spot and there was no blue-green background, a "diffuse" ERG could be obtained. The background intensity was increased till this vanished (less than 0 5 jV of potential averaged from 150 responses, using a Mnemotron CAT). If the stimulus was now shifted to the fovea, well marked a and b waves of peak amplitude approx. 10 gV were recorded, using the same averaging technique. The responses were much smaller if the stimulus colour was green or blue, or if the stimuli fell on the retinal periphery. Thus the ERG was obtained from the photopic mechanism, and was generated by the neurones and receptors directly under the physical image of the stimulus.Patients have been tested using these stimulus parameters. In one case of unilateral macular degeneration, an extinguished foveal ERG was obtained from the affected side, and a normal response from the other eye. In other patients with bilateral involvement, abnormal ERGs of reduced amplitude were recorded. In all these patients, the disease was strictly limited to the fovea.It seems, therefore, that with standard contact lenses the foveal responses of unselected patients can be investigated in this way.

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