Comparative Neurology of Circadian Photoreception: The Retinohypothalamic Tract (RHT) in Sighted and Naturally Blind Mammals.
Hannibal Jens
Frontiers in neuroscience
The mammalian eye contains two systems for light perception: an image detecting system constituted primarily of the classical photoreceptors, rods and cones, and a non-image forming system (NIF) constituted of a small group of intrinsically photosensitive retinal ganglion cells driven by melanopsin (mRGCs). The mRGCs receive input from the outer retina and NIF mediates light entrainment of circadian rhythms, masking behavior, light induced inhibition of nocturnal melatonin secretion, pupillary reflex (PLR), and affect the sleep/wake cycle. This review focuses on the mammalian NIF and its anatomy in the eye as well as its neuronal projection to the brain. This pathway is known as the retinohypothalamic tract (RHT). The development and functions of the NIF as well as the knowledge gained from studying gene modified mice is highlighted. Furthermore, the similarities of the NIF between sighted (nocturnal and diurnal rodent species, monkeys, humans) and naturally blind mammals (blind mole rats and the Iberian mole, ) are discussed in relation to a changing world where increasing exposure to artificial light at night (ALAN) is becoming a challenge for humans and animals in the modern society.
10.3389/fnins.2021.640113
[Non-organic visual loss].
Jeanjean L,Dupeyron G
Journal francais d'ophtalmologie
Functional or non-organic visual loss is a common problem in neuro-ophthalmologic consultation. There is a mismatch between visual acuity and/or visual field and the relative normality of the clinical examination. It is important to identify these patients so as not to prescribe unnecessary ancillary testing and so as to refer patients for a treatment of a possible psychiatric disorder. Conversely, there are many organic eye pathologies with a normal or quasi-normal fundus. We have at our disposal a large number of clinical and ancillary tests to demonstrate the non-organic nature of the visual loss: clinical examination, orthoptic testing, visual field, electro-physiologic tests. A rigorous diagnostic approach is essential to diagnose non-organic visual loss while avoiding diagnostic pitfalls.
10.1016/j.jfo.2013.12.005
Progressive Cone Dystrophy and Cone-Rod Dystrophy (XL, AD, and AR).
Tsang Stephen H,Sharma Tarun
Advances in experimental medicine and biology
A heterogenous group of diseases, progressive cone dystrophy usually begins in the mid-teenage years or later in life. The estimated prevalence is 1 in 30,000-40,000 individuals. Patients usually present with decreased central vision and a color vision deficit; the visual loss is progressive and often accompanied by day blindness (hemeralopia) and light intolerance (photophobia). Over time, affected individuals develop night blindness and loss of peripheral field. Visual acuity deteriorates to 20/200 or even counting fingers. There is some association between X-linked cone-rod dystrophy (CORD) and high myopia.
10.1007/978-3-319-95046-4_12
Transient smartphone blindness.
Eriksen Erik,Jørstad Øystein Kalsnes
Tidsskrift for den Norske laegeforening : tidsskrift for praktisk medicin, ny raekke
BACKGROUND:The aetiology of transient monocular vision loss is not necessarily thromboembolic, and careful history-taking is crucial in making the correct diagnosis. CASE PRESENTATION:A previously healthy woman in her thirties was referred to our outpatient stroke clinic on suspicion of recurring amaurosis fugax in her right eye. The ophthalmic and neurologic examinations were normal. A review of the medical history revealed that her symptoms occurred in connection with using her smartphone in bed, typically while lying on her left side with the left eye covered by the pillow. When standing up from the bed again with the lights turned off in the bedroom, she noticed vision loss in her right eye. INTERPRETATION:We concluded that the patient had experienced transient smartphone blindness. This phenomenon can occur when monocularly using a smartphone under scotopic lighting conditions; only the occluded eye adapts to darkness, and the other eye is perceived to be blind if looking away from the bright smartphone screen.
10.4045/tidsskr.20.0972