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Some clinics do not have 6-metre eye lanes available, and either a half-size chart subtending the same angles at 3 metres (9.8 ft), or a reversed chart projected and viewed by a mirror is used to achieve the correct sized letters. In the most familiar acuity test, a Snellen chart is placed at a standard distance: 6 metres.
An eye chart is a chart used to measure visual acuity comprising lines of optotypes in ranges of sizes. Optotypes are the letters or symbols shown on an eye chart. [ 1 ] Eye charts are often used by health care professionals, such as optometrists , physicians and nurses , to screen persons for vision impairment .
Visual acuity with Near chart without correctors Visual acuity with eye chart at Near 15.7 inches (400 mm) and without (sc: Latin sine correctore) correctors (spectacles); Ncc is with (cc: Latin cum correctore) correctors. See Visual_acuity#Legal_definitions: VA OS Left visual acuity VA OD Right visual acuity VDU Visual display unit VF Visual field
The pupil of the human eye can range in size from 2 mm to over 8 mm to adapt to the environment. The human eye can detect a luminance from 10 −6 cd/m 2, or one millionth (0.000001) of a candela per square meter to 10 8 cd/m 2 or one hundred million (100,000,000) candelas per square meter.
Near visual acuity or near vision is a measure of how clearly a person can see nearby small objects or letters.Visual acuity in general usually refers clarity of distance vision, and is measured using eye charts like Snellen chart, LogMAR chart etc. Near vision is usually measured and recorded using a printed hand-held card containing different sized paragraphs, words, letters or symbols.
When printed out at this size, the E on line one will be 88.7 mm tall and when viewed at a distance of 20 ft, you can estimate your eyesight based on the smallest line you can read.}} |Source=Own work by uploader, Based
1:posterior segment 2:ora serrata 3:ciliary muscle 4:ciliary zonules 5:Schlemm's canal 6:pupil 7:anterior chamber 8:cornea 9:iris 10:lens cortex 11:lens nucleus 12:ciliary process 13:conjunctiva 14:inferior oblique muscule 15:inferior rectus muscule 16:medial rectus muscle 17:retinal arteries and veins 18:optic disc 19:dura mater 20:central ...
In a healthy eye, the cornea presents as a clear, domed, glossy covering over the iris and pupil. Corneal endothelium: a simple squamous or low cuboidal monolayer, approx 5 μm thick, of mitochondria-rich cells. These cells are responsible for regulating fluid and solute transport between the aqueous and corneal stromal compartments. [14]