Peripheral Field Constriction Research Articles

A plausible explanation for superiority of adreno-cortico-trophic hormone (ACTH) over oral corticosteroids in management of infantile spasms (West syndrome)

West syndrome (WS), an age dependent epileptic encephalopathy is identified as a triad of infantile spasms (IS), psychomotor retardation and a specific EEG pattern known as hypsarrhythmia. The exact pathophysiology still remains unclear, although a majority of cases reveal history of exposure to stress, mainly hypoxic-ischemia. The management remains empirical with a poor prognosis. Adrenocorticotrophic hormone (ACTH) and oral steroids continue to remain gold standard treatment. Vigabatrin (VGB), a newer anti-epileptic drug has emerged as an effective alternative but recent observation of a serious visual defect (constriction of peripheral field of vision that is likely to exaggerate the disability status of the WS patient) associated with its administration is gradually limiting its therapeutic usage and popularity. A number of studies have shown superiority of ACTH over oral steroids in the management of West syndrome, but the explanation for this long-standing observation is missing; however, this clinical observation has led to a wide acceptance of the implication of corticotropin releasing hormone (CRH) in causing spasms and at the same time also explaining the relief in spasms obtained by the inhibition of CRH secretion by ACTH and oral steroids. This hypothesis-article compares the negative feedback influences of ACTH and oral steroids on CRH secretion and shows that ACTH exerts a dual significantly stronger inhibitory influence on CRH secretion that far exceeds the inhibition exerted by oral steroids. Thus, this difference in feedback mechanism may be the major factor responsible for the superior therapeutic efficacy of ACTH over oral steroids in the management of West syndrome.

Some observations on the macula of pesticide workers.

To study the retinal changes in occupationally exposed pesticide workers, 79 subjects exposed to an organophosphate, fenthion, and 18 exposed to an organochlorine pesticide DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane], were subjected to a detailed study, including history taking, physical examination and ophthalmic evaluation. Fluorescein angiography was performed in selected cases. Serum cholinesterase level in 22 workers and serum DDT residue in 17 workers of the respective groups were also estimated. Fifteen workers (19%), who were exposed to fenthion had macular changes (P less than 0.01). The macular lesions were characterized by perifoveal irregularity of pigmentation and areas of hypopigmentation of 1/8-1/3 disc diameter. Mean age of the subjects having macular involvement was 30.6 years and mean duration of exposure 7.9 years. The symptoms reported by them were diminution of vision (8), dislike for bright light, flash of light, black dots in front of the eyes (2 each) and visual blurring (1). Paracentral scotoma and constriction of peripheral field were present in three workers each. Fluorescein angiography suggested pigment epithelium defect. Other causes of macular involvement in these workers were excluded; a possible role of pesticides in the genesis of these macular changes is suggested.

Retinal Injury from a Welding ARC

An 18-year-old man stared at a welding arc for approximately ten minutes, sustaining moderate facial erythema, keratoconjunctivitis, marked visual loss, a pupillary abnormality, and a retinal injury accompanied by a dense central scotoma and peripheral field constriction. A residual, partially pigmented foveal lesion remained after 16 months, with normal visual acuity. Since the degree of keratoconjunctivitis and facial erythema was known, we substantiated the duration of exposure to the arc by weighting the known action spectrum of moderate ultraviolet erythema with the ultraviolet spectral irradiance measurements of the arc. From the radiometric measurements of the visible brightness and visible and near infrared spectrum of the arc and from knowledge of pupil size, we calculated the retinal exposure dose rate, which was less than normally considered necessary to produce a chorioretinal burn. This case may provide a clinical example of photic maculopathy recently reported in experimental investigations. (auth)