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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.
Intraocular pressure varies throughout the night and day. The diurnal variation for normal eyes is between 3 and 6 mmHg and the variation may increase in glaucomatous eyes. During the night, intraocular pressure may not decrease [ 17 ] despite the slower production of aqueous humour. [ 18 ]
Ocular hypertension is the presence of elevated fluid pressure inside the eye (intraocular pressure), usually with no optic nerve damage or visual field loss. [1] [2]For most individuals, the normal range of intraocular pressure is between 10 mmHg and 21 mmHg. [3]
Effect of night blindness. Left: good night vision. Right: nightblind. Insufficiency of adaptation most commonly presents as insufficient adaptation to dark environment, called night blindness or nyctalopia. [35] The opposite problem, known as hemeralopia, that is, inability to see clearly in bright light, is much rarer.
For eye pressures, a value of 28 hPa (21 mmHg) above atmospheric pressure 1,010 hPa (760 mmHg) is often used, with higher pressures leading to a greater risk. [2] [26] However, some may have high eye pressure for years and never develop damage. [2] Conversely, optic nerve damage may occur with normal pressure, known as normal-tension glaucoma. [27]
Xerophthalmia (from Ancient Greek xērós (ξηρός) meaning "dry" and ophthalmos (οφθαλμός) meaning "eye") is a medical condition in which the eye fails to produce tears. It may be caused by vitamin A deficiency, [1] which is sometimes used to describe that condition, although there may be other causes.
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Subconjunctival bleeding initially appears bright red underneath the transparent bulbar conjunctiva. Later, the bleeding may spread and become green or yellow as the hemoglobin is metabolized. It usually disappears within two weeks. [5] The affected eye may feel dry, rough, or scratchy, but the condition is not usually painful.