Cones and cone pathways remain functional in advanced retinal degeneration.

Most defects causing retinal degeneration in retinitis pigmentosa (RP) are rod-specific mutations, but the subsequent degeneration of cones, which produces loss of daylight vision and high-acuity perception, is the most debilitating feature of the disease. To understand better why cones degenerate and how cone vision might be restored, we have made the first single-cell recordings of light responses from degenerating cones and retinal interneurons after most rods have died and cones have lost their outer-segment disk membranes and synaptic pedicles. We show that degenerating cones have functional cyclic-nucleotide-gated channels and can continue to give light responses, apparently produced by opsin localized either to small areas of organized membrane near the ciliary axoneme or distributed throughout the inner segment. Light responses of second-order horizontal and bipolar cells are less sensitive but otherwise resemble those of normal retina. Furthermore, retinal output as reflected in responses of ganglion cells is less sensitive but maintains spatiotemporal receptive fields at cone-mediated light levels. Together, these findings show that cones and their retinal pathways can remain functional even as degeneration is progressing, an encouraging result for future research aimed at enhancing the light sensitivity of residual cones to restore vision in patients with genetically inherited retinal degeneration.

Separate ON and OFF pathways in vertebrate vision first arose during the Cambrian.

Ellis et al. show that retinal ON and OFF bipolar cells, and the novel metabotropic glutamate receptors of ON bipolar-cell dendrites, are both present in lamprey. They conclude that the fundamental organizing principle of separate ON and OFF pathways first appeared in the vertebrate visual system over 500 million years ago in the late Cambrian.

Complication rates of resident-performed cataract surgery: Impact of early introduction of cataract surgery training.

PURPOSE: To determine the effect of the early introduction of cataract surgery training on the complication rates of resident-performed cataract surgery. SETTING: University of California San Diego, San Diego, California, USA. DESIGN: Retrospective case series. METHODS: Two classes of ophthalmology residents were examined, one class with a late introduction of cataract surgery and one with an early introduction of cataract surgery. All cataract cases in which residents acted as primary surgeon were included. Patient charts were reviewed to collect data on patient characteristics, surgical details, and intraoperative and postoperative complications. RESULTS: The late-introduction cohort comprised 3 residents who performed 540 cataract cases, all during their final year of residency. The early-introduction cohort comprised 4 residents who performed 780 cataract cases beginning in the first year of residency. The late-introduction cohort had higher rates of major intraoperative complications than the early-introduction cohort (8.5% versus 3.1%) and of anterior vitrectomy (7.6% versus 2.1%) (both P < .001). Examination of the anterior vitrectomy rate as a function of experience showed the early-introduction cohort had a stable anterior vitrectomy rate of 1% to 2% throughout training, while the late-introduction cohort had a peak anterior vitrectomy rate of 12% at approximately case 20. Multivariable regression analysis showed the early-introduction cohort was independently associated with a lower rate of anterior vitrectomy (hazard ratio, 0.49; 95% confidence interval, 0.36-0.66) after adjusting for differences in patient characteristics and surgical complexity. CONCLUSIONS: Early introduction of cataract surgery training significantly decreased the rate of major intraoperative complications, specifically anterior vitrectomy, in resident-performed cataract surgeries.

Pulled-in-two syndrome: a multicenter survey of risk factors, management and outcomes.

BACKGROUND: Pulled-in-two syndrome (PITS) is a serious complication of strabismus surgery that occurs when an extraocular muscle ruptures under tension. The purpose of this study was to establish a database of PITS patients to identify risk factors and management of PITS. METHODS: Strabismus surgeons from around the world contributed cases of PITS through an online survey. Risk factors, management, and outcomes were identified. RESULTS: A total of 40 cases of PITS from 29 physicians in 6 countries were collected. The most commonly involved muscles were the medial rectus (18/40 [45%]) and the inferior rectus (17/40 [43%]). The most commonly identified risk factors were previous ocular surgery (11/40 [28%]) and cranial nerve palsy (11/40 [28%]). Advanced age was also a significant risk factor, with 28/40 (70%) of reported patients being ≥50 years of age. In most cases the muscle was found and reattached to the globe (28/40 [70%]). The muscle was lost in 12 cases (30%). Half of these patients received a transposition surgery; the other half were followed by observation. CONCLUSIONS: Our data suggests that strabismus surgeons might encounter one case of PITS approximately every 10 years. Major risk factors for PITS appear to be changes in the extraocular muscle due to cranial nerve palsy, prior surgery, and advancing age. The preferred management for PITS is surgical recovery and reattachment of the muscle; however, if the muscle is lost, transposition surgery or observation are common forms of management.

Shared and distinct retinal input to the mouse superior colliculus and dorsal lateral geniculate nucleus.

The mammalian retina conveys the vast majority of information about visual stimuli to two brain regions: the dorsal lateral geniculate nucleus (dLGN) and the superior colliculus (SC). The degree to which retinal ganglion cells (RGCs) send similar or distinct information to the two areas remains unclear despite the important constraints that different patterns of RGC input place on downstream visual processing. To resolve this ambiguity, we injected a glycoprotein-deficient rabies virus coding for the expression of a fluorescent protein into the dLGN or SC; rabies virus labeled a smaller fraction of RGCs than lipophilic dyes such as DiI but, crucially, did not label RGC axons of passage. Approximately 80% of the RGCs infected by rabies virus injected into the dLGN were colabeled with DiI injected into the SC, suggesting that many dLGN-projecting RGCs also project to the SC. However, functional characterization of RGCs revealed that the SC receives input from several classes of RGCs that largely avoid the dLGN, in particular RGCs in which 1) sustained changes in light intensity elicit transient changes in firing rate and/or 2) a small range of stimulus sizes or temporal fluctuations in light intensity elicit robust activity. Taken together, our results illustrate several unexpected asymmetries in the information that the mouse retina conveys to two major downstream targets and suggest that differences in the output of dLGN and SC neurons reflect, at least in part, differences in the functional properties of RGCs that innervate the SC but not the dLGN.