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A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862 as a measurement tool for the acuity formula developed by his professor Franciscus Cornelius Donders .
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.
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 .
As a result of their towering height, giraffes spend most of their days grazing amongst the canopies of acacia trees. Our giraffe unit plan takes students on an All About Giraffes: A 5-Day Lesson Plan
The coat patterns of modern giraffes may also have coincided with these habitat changes. Asian giraffes are hypothesised to have had more okapi-like colourations. [6] The giraffe genome is around 2.9 billion base pairs in length, compared to the 3.3 billion base pairs of the okapi. Of the proteins in giraffe and okapi genes, 19.4% are identical.
Giraffes, just like humans, have seven cervical vertebrae. Unlike humans, giraffe cervical vertebrae are attached to each other with ball and socket joints, making them able to bend their necks in ...
Some giraffes will sleep even less than usual, and Africa Freak shared, "When giraffes move from one zoo to another, or lose a mate, they tend to sleep for fewer hours than normal. Or end up ...
Birds have acute eyesight—raptors (birds of prey) have vision eight times sharper than humans—thanks to higher densities of photoreceptors in the retina (up to 1,000,000 per square mm in Buteos, compared to 200,000 for humans), a high number of neurons in the optic nerves, a second set of eye muscles not found in other animals, and, in some ...