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Background/aims: Toxoplasmic retinochoroiditis is the commonest known cause of posterior uveitis worldwide and reactivation is unpredictable. Based on results from one study, the authors proposed that antitoxoplasmic therapy should be initiated as prophylaxis for intraocular surgery in patients with toxoplasmic scars. The aim of this study is to analyse the risk of toxoplasmic retinochoroiditis reactivation following intraocular procedures., Methods: Retrospective analysis of the medical records of a total of 69 patients who underwent intraocular surgery and presented with toxoplasmic retinochoroiditis scars., Results: No patient received prophylactic antitoxoplasmic therapy. Reactivation following the surgical procedure occurred in four cases, with one at 3 months and the others respectively at 13, 14 and 17 months., Conclusions: Our study shows that intraocular surgery did not result in a significant reactivation rate of toxoplasmic retinochoroiditis in the absence of preoperative prophylactic antitoxoplasmic therapy., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

We describe the first two cases of diffuse unilateral subacute neuroretinitis (DUSN) in the UK successfully treated with albendazole. Two patients are described who presented with unilateral reduction in vision, with clusters of yellow-white retinal lesions fading and reappearing in new locations of the fundus over a period of weeks. Based on the clinical picture, the diagnosis of DUSN was made, even though no subretinal worm could be found. Both patients were treated with albendazole 400 mg daily for 30 days. After 4 weeks the vision in the affected eye improved to 6/9 in each patient and the retinal lesions resolved completely. Over a follow-up period of 28 months and 13 months respectively, there was no recurrence of any lesion and the vision was maintained. DUSN is a sight-threatening disease and the preservation of vision relies on early diagnosis and treatment. Laser photocoagulation of the worm is the treatment of choice, but this was not possible in either case, as no worm could be found; however, oral albendazole proved to be a safe and effective alternative treatment.

Simulations of artificial vision were performed to assess "minimum requirements for useful artificial vision". Retinal prostheses will be implanted at a fixed (and probably eccentric) location of the retina. To mimic this condition on normal observers, we projected stimuli of various sizes and content on a defined stabilised area of the visual field. In experiment 1, we asked subjects to read isolated 4-letter words presented at various degrees of pixelisation and at various eccentricities. Reading performance dropped abruptly when the number of pixels was reduced below a certain threshold. For central reading, a viewing area containing about 300 pixels was necessary for close to perfect reading (>90% correctly read words). At eccentricities beyond 10 degrees, close to perfect reading was never achieved even if more than 300 pixels were used. A control experiment using isolated letter recognition in the same conditions suggested that lower reading performance at high eccentricity was in part due to the "crowding effect". In experiment 2, we investigated whether the task of eccentric reading under such specific conditions could be improved by training. Two subjects, naive to this task, were trained to read pixelised 4-letter words presented at 15 degrees eccentricity. Reading performance of both subjects increased impressively throughout the experiment. Low initial reading scores (range 6%-23% correct) improved impressively (range 64%-85% correct) after about one month of training (about 1 h/day). Control tests demonstrated that the learning process consisted essentially in an adaptation to use an eccentric area of the retina for reading. These results indicate that functional retinal implants consisting of more than 300 stimulation contacts will be needed. They might successfully restore some reading abilities in blind patients, even if they have to be placed outside the foveal area. Reaching optimal performance may, however, require a significant adaptation process.