VISUALLY IMPAIRED CHILDREN: Measure for Measure – what do the eye measurements really mean?

Saturday 3 December 2011

Measure for Measure – what do the eye measurements really mean?

We all need to understand what a child’s eyesight measurement means. I am frequently asked what the fractions or figures describing a child’s eyesight actually mean. For example I can say little Enid is 6/24 or Frank is 6/60 or Mabel is maybe 6/250. But what does all this really mean?

It is further complicated there is a new system of measuring eyesight called LogMAR. The standard eye test was invented by Mr Snellen and consists of increasingly smaller letters on a chart. The biggest at the top has one letter (this is 6/60 or 20/200), while at the bottom are eight small letters (6/6 – 20/20). However with the LogMar test your child can have a visual acuity measurement of zero and that might sound scary but it means they have perfect vision or an equivalent of 6/6 in Snellen metric measurement (metres) or 20/20 in feet (USA).

The conversion chart shows that 6/18 is LogMAR 0.48 and Snellen 6/60 is LogMAR 1. But zero vision does not sound quite the same as 20/20 or 6/6 vision and LogMAR 1 meaning severely visually impaired really needs to be unpacked. I am sure that LogMAR is more precise or accurate but I think it is confusing to the layman. And that is perhaps why many teaching professionals who are vision specialists are slow to convert over to LogMAR. At least that is my experience. It is still easier to explain that 6/60 (20/200ft) means that the person sees at six metres (20ft) what a person with ‘standard vision’ can see at 60 metres (200ft) even if technically it all refers to an angle. Or I might explain it by saying the person can just about see the top line of the eye chart, which is even easier to follow. Registered blind vision is 3/60 which is in LogMAR a value of 1.3.

LogMAR /	Snellen
0	6/6
0.18	6/9
0.30	6/12
0.48	6/18
0.60	6/24
0.78	6/36
1.00	6/60

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One of the great inspirations to me must be Helen Keller. Helen Keller was not born blind and deaf; it was not until she was 19 months old that she contracted an illness described by doctors as "an acute congestion of the stomach and the brain", which might have been scarlet fever or meningitis. The illness left her deaf and blind. At that time, she was able to communicate somewhat with Martha Washington, the six-year-old daughter of the family cook, who understood her signs; by the age of seven, she had over 60 home signs to communicate with her family.

In 1886, her mother, inspired by an account in Charles Dickens' American Notes of the successful education of another deaf and blind woman, Laura Bridgman, dispatched young Helen, accompanied by her father, to seek out Dr. J. Julian Chisolm, an eye, ear, nose, and throat specialist in Baltimore, for advice.^[11] He subsequently put them in touch with Alexander Graham Bell, who was working with deaf children at the time. Bell advised the couple to contact the Perkins Institute for the Blind, the school where Bridgman had been educated, which was then located in South Boston. Michael Anaganos, the school's director, asked former student Anne Sullivan, herself visually impaired and only 20 years old, to become Keller's instructor. It was the beginning of a 49-year-long relationship, Sullivan evolving into governess and then eventual companion.

Anne Sullivan arrived at Keller's house in March 1887, and immediately began to teach Helen to communicate by spelling words into her hand, beginning with "d-o-l-l" for the doll that she had brought Keller as a present. Keller was frustrated, at first, because she did not understand that every object had a word uniquely identifying it. In fact, when Sullivan was trying to teach Keller the word for "mug", Keller became so frustrated she broke the doll.

Keller's big breakthrough in communication came the next month, when she realized that the motions her teacher was making on the palm of her hand, while running cool water over her other hand, symbolized the idea of "water"; she then nearly exhausted Sullivan demanding the names of all the other familiar objects in her world.

Due to a protruding left eye, Keller was usually photographed in profile. Both her eyes were replaced in adulthood with glass replicas for "medical and cosmetic reasons". Wikipedia

Ophthalmology and opthalmologists

Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems. The ophthalmologist is the eye doctor. Since ophthalmologists perform operations on eyes, they are considered to be both surgical and medical specialists.

The word ophthalmology comes from the Greek roots ophthalmos meaning eye and logos meaning word, thought, or discourse; ophthalmology literally means "the science of eyes". As a discipline, it applies to animal eyes also, since the differences from human practice are surprisingly minor and are related mainly to differences in anatomy or prevalence, not differences in disease processes. However, veterinary medicine is regulated separately in many countries and states/provinces resulting in few ophthalmologists treating both humans and animals.

History of Ophthalmology

Seventeenth and eighteenth centuries

The seventeenth and eighteenth century saw the use of hand lenses (by Malpighi), microscopes (van Leeuwenhoek), preparations for fixing the eye for study (Ruysch) and later the freezing of the eye (Petit). This allowed for detailed study of the eye and an advanced model. Some mistakes persisted such as: why the pupil changed size (seen to be vessels of the iris filling with blood), the existence of the posterior chamber, and of course the nature of the retina. In 1722 Leeuwenhoek noted the existence of rods and cones^,though they were not properly discovered until Gottfried Reinhold Treviranus in 1834 by use of a microscope.

Ophthalmic surgery in Great Britain

The first ophthalmic surgeon in Great Britain was John Freke, appointed to the position by the Governors of St Bartholomew's Hospital in 1727, but the establishment of the first dedicated ophthalmic hospital in 1805; now called Moorfields Eye Hospital in London, England was a transforming event in modern ophthalmology. Clinical developments at Moorfields and the founding of the Institute of Ophthalmology (now part of the University College London) by Sir Stewart Duke Elder established the site as the largest eye hospital in the world and a nexus for ophthalmic research.

Ophthalmology and ophthalmologists

Purkinje is a known to all ophthalmologists for Purkinje's cells, Purkinje's images. Jan Evangelista Purkinje was a versatile scholar with wide-ranging interests and an exceptional capacity for innovative thinking. He used the name “Purkinje” until 1850, from whence he used the correct spelling, Pyrkyně. We use Purkinje for the eponyms because that is the more common. Purkinje was a Czech nationalist and had a major influence on Czech cultural life in the middle of the 19th century. He was a friend of the famous German poet Johann Wolfgang von Goethe, who wrote about Purkinje: “and should you fail to understand, let Purkyně give you a hand!” Purkinje published a Czech translation of Friedrich Schiller's poems, and translated works of William Shakespeare into Czech.

Purkinje created the world’s first department of physiology at the University of Breslau, Prussia in 1839 and the first official physiological laboratory, known as the Physiological Institute, in 1842. Purkinje used to believe that that experiments in one's own body ("in corpore nobili") gave more practical results than those in animal experiment ("in corpore vili") or in fatally ill patients. And when he was a medical student, Purkinje used to investigate the physiology of sight by experimenting on himself with a variety of drugs, including Belladonna. His interest in the physiology of light led him to make animated cartoons, and thus he became one of the earliest motion picture pioneers.

He is best known for his discovery of Purkinje cells, large nerve cells with many branching extensions found in the cortex of the cerebral cortex. He is also known for his discovery of Purkinje fibers, the fibrous tissue that conducts the pacemaker stimulus along the inside walls of the ventricles to all parts of the heart. It was Purkinje, who introduced the scientific terms plasma. An early user of the improved compound microscope, he discovered the sweat glands of the skin, germinal vesicles. He recognized fingerprints as a means of identification and noted the protein-digesting power of pancreatic extracts. He died on July 25 of 1868.


6/6 (20/20) 6/12 (20/40)	0.0 0.3
6/18 (20/60)	0.5
6/24 (20/80)	0.6
6/36 (20/120)	0.8
6/48 (20/160)	0.9
6/60 (20/200)	1.0
6/72 (20/240)	1.1
6/90 (20/300)	1.2
6/120 (20/400)	1.3
6/150 (20/500)	1.4
6/180 (20/600)	1.5
6/240 (20/800)	1.6
6/360 (20/1200)	1.8
6/480 (20/1600)	1.9

Saturday 3 December 2011

Measure for Measure – what do the eye measurements really mean?

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