Amblyopia is an acquired defect in vision due to an abnormal visual experience during a sensitive period of visual development. The neuronal basis of amblyopia is the study of the effects of "abnormal" environmental influences on the genetically programmed development of the visual processing system. Visual pathway development commences with ganglion cells forming the optic nerve. The process that guides these neurones initially to the lateral geniculate nucleus (LGN) and then onto the visual cortex is genetically programmed. Initially this process is influenced by spontaneously generated impulses and neurotrophic factors. Following birth, visual stimuli modify and refine the genetically programmed process. Exposure to the visual environment includes the risk of abnormal inputs. Abnormal stimuli disrupt the formation of patterned inputs allowing alteration of visual cortical wiring with reduction in ocular dominance columns driven by the abnormal eye. Correction of the abnormal visual input and penalisation of the "normal" input is the mainstay of therapy for amblyopia. Further understanding of the mechanisms involved in the development of a normal visual processing system will allow trialing therapies for amblyopia not responding to occlusion therapy. Levodopa is one agent providing insights into recovery of visual function for short periods in apparently mature visual systems.

A total of 151 retinitis pigmentosa (RP) patients from 83 families were screened and the frequencies of different genetic categories studied. One hundred and ten patients out of 151 had a positive inheritance pattern, and autosomal recessive (AR) emerged as the predominant (53 out of 151), genetic pattern followed by isolated or sporadic (41 out of 151) cases. Further study of autosomal recessive cases revealed consanguinity as the main characteristic (49 out of 53) in the Indian population studied. Early onset and severe progression of disease was seen in the consanguineous group.

The serum concentration of various acute phase reactants were studied in patients with non-insulin dependent diabetes mellitus with and without retinopathy and in control subjects. The serum levels of haptoglobin was elevated in diabetics with retinopathy and the levels were highest in those with proliferative diabetic retinopathy. The levels of serum albumin, alpha-1 acid glycoprotein, alpha-1 antitrypsin and caeruloplasmin were not significantly different between the patients with retinopathy and controls. Haptoglobin increases serum viscosity and this could be the mechanism by which it plays a role in pathogenesis of diabetic retinopathy. These preliminary observations need to be confirmed by studies based on larger number of patients. Longitudinal studies on acute phase reactants in various stages of development of diabetic retinopathy would also provide valuable information.

All the presently available antiglaucoma medications have either local or systemic adverse effects. Combinations of drugs are being used not only to increase the effectivity and compliance but also to decrease the incidence and magnitude of side effects. The single dose response of open angle glaucoma eyes to pilocarpine 1%, clonidine 0.125%, a combination of pilocarpine 1% and clonidine 0.125%, and timolol 0.5% was studied in a double blind, masked, cross over study. Over a period of twelve hours the effectivity of the combination of pilocarpine 1% and clonidine 0.125% was significantly more than that of either drug alone and was found to be similar to that of timolol 0.5%. No local or systemic adverse effects were seen.

To study the effect of 5-Fluorouracil (5-FU) in glaucoma filtration surgery, 13 eyes of 12 patients with glaucoma were subjected to trabeculectomy with intraoperative one minute exposure of 50 mg/ml 5-FU. The average age of patients was 36.42 ± 18.78 years. Two of the patients had developed hypotony in the fellow eye following the use of Mitomycin C with trabeculectomy. The mean follow-up period was 9.54 ± 5.17 weeks. Two patients developed a shallow anterior chamber with choroidals postoperatively which responded to conservative treatment. One patient developed an encysted bleb one month after surgery. Single one minute intraoperative exposure to 5-FU is a convenient and inexpensive method which appears to have no significant side effects. It may be a useful adjunctive treatment to optimise the results of glaucoma filtration surgery particularly in young and myopic patients. The long term effects, however, are not known.

The practising ophthalmologist is frequently confronted with treatment options shown to be "statistically significantly better" than those currently in use. Unfortunately what is statistically significant may not necessarily be clinically significant enough for the practitioner to change from the currently preferred method of treatment. In this article we use common ophthalmic examples to introduce the "number needed to treat" (NNT), as a simple clinical approach for the practising ophthalmologist wishing to assess the clinical significance of treatment options.