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The main discussion of these abbreviations in the context of drug prescriptions and other medical prescriptions is at List of abbreviations used in medical prescriptions. Some of these abbreviations are best not used, as marked and explained here.
No light perception is considered total visual impairment, or total blindness; see Visual impairment#Classification: NPC: Near point of convergence or no previous correction NRC Normal retinal correspondence NV Near vision NWT Normal wearing time o symptoms Zero symptoms Φ Horizontal orthophoria θ Vertical orthophoria ⊕
Nyctalopia (/ ˌ n ɪ k t ə ˈ l oʊ p i ə /; from Ancient Greek νύκτ-(núkt-) 'night' ἀλαός (alaós) 'blind, invisible' and ὄψ (óps) 'eye'), [1] also called night blindness, is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases.
Night vision is of lower quality than day vision because it is limited in resolution and colors cannot be discerned; only shades of gray are seen. [1] In order for humans to transition from day to night vision they must undergo a dark adaptation period of up to two hours [ 2 ] in which each eye adjusts from a high to a low luminescence "setting ...
Visual snow is a phenomenon where a person perceives visual disturbances, such as fine graininess or "static," in their field of vision. This can occur in low-light conditions, in the dark, or when the visual system amplifies light perception.
An epileptic aura is the consequence of the activation of functional cortex by abnormal neuronal discharge. [3] In addition to being a warning sign for an impending seizure, the nature of an aura can give insight into the localization and lateralization of the seizure or migraine.
A reference value above which visual acuity is considered normal is called 6/6 vision, the USC equivalent of which is 20/20 vision: At 6 metres or 20 feet, a human eye with that performance is able to separate contours that are approximately 1.75 mm apart. [9] Vision of 6/12 corresponds to lower performance, while vision of 6/3 to better ...
Mesopic vision occurs in intermediate lighting conditions (luminance level 10 −3 to 10 0.5 cd/m 2) [citation needed] and is effectively a combination of scotopic and photopic vision. This gives inaccurate visual acuity and color discrimination. In normal light (luminance level 10 to 10 8 cd/m 2), the vision of cone cells dominates and is ...