Long-term effects of hyperbaric oxygen therapy on visual acuity and retinopathy.

Hyperbaric oxygen (HBO2) therapy is an adjunct treatment for diabetic foot ulcers. Since plausible mechanisms of action for this treatment include increased angiogenesis and high tissue oxygen concentrations, concerns about deterioration of retinopathy have been raised. The aim of this study was to evaluate the effects of HBO2 on visual acuity (VA) and retinopathy in patients with chronic diabetic foot ulcers during a two-year follow-up period. This is a randomized, single-center, double-blinded and placebo-controlled clinical trial evaluating the effects of HBO2 in patients with diabetes mellitus and chronic foot ulcers. All study participants underwent an ophthalmological examination before the first study treatment and then at three, six, 12 and 24 months. Fifty patients with a median age of 67 years were included. Visual acuity was similar between groups and did not change during the two-year observation period. No differences in retinopathy were seen between groups; neither were any differences found in numbers or areas of bleedings, hard exudates, microaneurysms or edemas, nor between groups or visits. New clinically significant macular edema was identified in four eyes in the HBO2 group and in three eyes in the placebo group. In this population of diabetic foot ulcer patients HBO2 seems to be neutral in an ophthalmological perspective. From a retinal point of view, we could not identify any indication of harmful effects of HBO2 on the microvascular bed in the placebo group.

Mutated alleles of the rod and cone Na-Ca+K-exchanger genes in patients with retinal diseases.

PURPOSE: To study the possible involvement of the rod (SLC24A1) and cone (SLC24A2) Na-Ca+K exchanger (NCKX) genes in retinal diseases. METHODS: DNA was collected from unrelated patients with retinal disease, mainly from North America. A human genomic library was screened with the cone NCKX cDNA, and hybridizing clones were sequenced to determine the genomic organization of the SLC24A2 gene. The single-strand conformation polymorphism (SSCP) technique and direct sequencing were used to screen the patients' DNA for mutations in SLC24A1 and SLC24A2. The effect of selected missense changes on protein function was tested by measuring potassium-dependent Na-Ca exchange of the mutant proteins expressed in insect cells. RESULTS: Twenty-seven novel sequence changes were found in the rod NCKX gene, 21 of which are unlikely to be pathogenic, because they did not cosegregate with the disease or did not affect conserved regions of the protein. Of the remaining six, two were frameshift mutations found in one patient each. If translated, these alleles would encode nonfunctional proteins. Three of the six possibly pathogenic mutations were missense changes located in conserved regions, and their protein functions were assayed. Only one (Ile992Thr) had a significantly low level of exchanger function, but it was found in two unrelated patients who were heterozygotes with different retinal diseases, and this mutation could not be unequivocally associated with either disease. The last of the six changes is likely to create a new splice acceptor site. The genomic organization of the cone NCKX gene was determined, and it contained 11 exons with a few splice variants. Fifteen novel sequence changes were identified in the cone exchanger gene in patients with a cone dysfunction or degeneration. Only three of these sequence changes, all missense changes found in heterozygous patients, were considered possibly pathogenic. Functional analysis showed only a slight reduction in the activity of the corresponding mutant proteins. CONCLUSIONS: Although variant alleles of the rod and cone NCKX genes were found, none could be definitively associated with a specific retinal disease. The human phenotype associated with mutant exchanger alleles remains unknown.