Conserved visual capacity of rats under red light

Recent studies examine the behavioral capacities of rats and mice with and without visual input, and the neuronal mechanisms underlying such capacities. These animals are assumed to be functionally blind under red light, an assumption that might originate in the fact that they are dichromats who possess ultraviolet and green but not red cones. But the inability to see red as a color does not necessarily rule out form vision based on red light absorption. We measured Long-Evans rats' capacity for visual form discrimination under red light of various wavelength bands. Upon viewing a black and white grating, they had to distinguish between two categories of orientation, horizontal and vertical. Psychometric curves plotting judged orientation versus angle demonstrate the conserved visual capacity of rats under red light. Investigations aiming to explore rodent physiological and behavioral functions in the absence of visual input should not assume red-light blindness.

Outcomes and surgical management of persistent fetal vasculature

ObjectiveTo analyse outcomes in different forms of persistent fetal vasculature (PFV).Methods and analysisRetrospective cohort study at a university-based practice of children presenting with PFV between 2011 and 2020. Exclusion criteria was surgical management outside of our institution and follow-up less than 1 month. Wilcoxon and Student’s t-tests were used for statistical analysis.ResultsForty-six eyes of 45 patients presented with PFV at 16.7±31.3 (median 2.8) months old with 32.6±29.8 (median 22.5) months of follow-up. Types of PFV included: mild combined anterior-posterior (23 eyes, 50%), severe combined anterior-posterior (18 eyes, 39%), severe anterior (3 eyes, 7%), mild anterior (1 eye, 2%) and posterior (1 eye, 2%). Thirty-two eyes (70%) underwent PFV surgical correction; lensectomy (13 mild combined), vitrectomy (3 mild combined), sequential lensectomy then vitrectomy (3 severe combined), combined lensectomy-vitrectomy (11 severe anterior or severe combined), laser retinopexy (1 mild combined). Five eyes required additional vitrectomy surgery for retinal detachment, fold or cyclitic membrane. Nine eyes developed glaucoma, six requiring Intraocular pressure (IOP)-lowering surgery. At final follow-up, 32 eyes had at least form vision and 6 eyes were aversive to light. Eight eyes, all which were severe combined, and four that did not undergo PFV surgery, were unable to detect light due to phthisis bulbi (7) and optic nerve hypoplasia (1).ConclusionsClassification of PFV is important in determining surgical approach with severe cases often requiring both lensectomy and vitrectomy for optimal anatomic and functional outcomes.

The associations between vision level and early hand use in children aged 6–36 months with visual impairment: A cross-sectional, historical case note review

Vision level varies within the population of children born with visual impairment (VI). Children with profound visual impairment (PVI – with light awareness at best) are more developmentally vulnerable than peers born with typical sight or those with severe visual impairment (SVI – basic form vision). Many children with VI are dependent on their hand skills to support their development. However, the impact of vision level on the development of hand use is poorly understood. The aim of the study was to describe the associations between vision level and early hand use in children between 6 and 36 months of age with SVI and PVI. A historical case note review, including video footage of 19 children with SVI ([Formula: see text] = 19 months) and 12 children with PVI ([Formula: see text] = 16 months), was completed. Hand use was observed while the children completed the Reynell-Zinkin Scales. Observations were recorded using a data collection tool designed for the study. The tool included a checklist of developmentally appropriate hand skills expected to emerge in the first 3 years of life. The observer marked each skill as present, absent or emerging in the video clips. Children with SVI used 80.2% (95% confidence interval [CI] = [75.0, 87.5]) of the hand skills under observation. Those with PVI used 57.1% (95% CI = [46.4, 67.9]) of these skills. Vision level and hand use were positively correlated: rs = .564 (95% CI = [.263, .765]), p < .01. This correlation was stronger than the association between developmental level and hand use: r = .364 (95% CI = [.012, .636]), p < .05. Furthermore, 15.8% (95% CI = [0.0, 31.6]) of the children with SVI and 66.7% (95% CI = [41.7, 91.7]) with PVI showed some reluctance to touch objects ( p < .05) by withdrawing their hands actively from items offered to them. Vision level and developmental level influenced hand use; however, vision level appeared to have the greater impact. Interventions that are tailored to promote hand use according to vision level have the potential to improve functional participation.

Conserved visual capacity of rats under red light

SummaryRecent studies examine the behavioral capacities of rats and mice with and without visual input, and the neuronal mechanisms underlying such capacities. These animals are assumed to be functionally blind under red light, perhaps originating in the fact that they are dichromats who possess ultraviolet and green but not red cones. But the inability to see red as a color does not necessarily rule out form vision based on red light absorption through their rod-dominated retina. We measured Long-Evans rats’ capacity for visual form discrimination under red light of various wavelength bands. Upon viewing a black and white grating, they had to distinguish between two categories of orientation, horizontal and vertical. Psychometric curves plotting judged orientation versus angle demonstrate the conserved visual capacity of rats under red light. Investigations aiming to explore rodent physiological and behavioral functions in the absence of visual input should not assume red-light blindness.

Can We See with Melanopsin?

A small fraction of mammalian retinal ganglion cells are directly photoreceptive thanks to their expression of the photopigment melanopsin. These intrinsically photosensitive retinal ganglion cells (ipRGCs) have well-established roles in a variety of reflex responses to changes in ambient light intensity, including circadian photoentrainment. In this article, we review the growing evidence, obtained primarily from laboratory mice and humans, that the ability to sense light via melanopsin is also an important component of perceptual and form vision. Melanopsin photoreception has low temporal resolution, making it fundamentally biased toward detecting changes in ambient light and coarse patterns rather than fine details. Nevertheless, melanopsin can indirectly impact high-acuity vision by driving aspects of light adaptation ranging from pupil constriction to changes in visual circuit performance. Melanopsin also contributes directly to perceptions of brightness, and recent data suggest that this influences the appearance not only of overall scene brightness, but also of low-frequency patterns.

Dynamic Electrical Stimulation of Sites in Visual Cortex Produces Form Vision in Sighted and Blind Humans

Visual cortical prosthetics (VCPs) offer the promise of restoring sight to blind patients. Electrical stimulation of a single site in visual cortex can reliably produce a percept of a spot of light in a fixed visual field location, known as a phosphene. Researchers developing VCPs have assumed that multiple phosphenes produced by concurrent stimulation of multiple sites in visual cortex can combine to form a coherent form, like pixels in a visual display. However, existing data do not support this assumption. Therefore, we developed a novel stimulation paradigm for VCPs termed dynamic current steering in which the visual form to be conveyed is traced on the surface of visual cortex by electrically stimulating electrodes in a dynamic sequence. When tested in sighted and blind subjects, this method of stimulating visual cortex allowed for the immediate recognition of a variety of letter shapes without training and with high accuracy.One Sentence SummaryStimulating human visual cortex using dynamic patterns of activity allows both blind and sighted patients to perceive visual percepts of useful forms.