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



16 comments:

  1. 6/20 how bad is this for my 6 year old son for eyesight

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  2. 6/20 is mild or borderline visual impairment. It implies that you son's vision is slightly blurry at distance. However the answer to your question depends on a. whether it can be corrected; b. what is the actual eye condition; c. whether there are other issues i.e. if its likely to get worse or if your son has specific leaning difficulties not related to vision. let me know if i can help further. best wishes, Maurice

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  3. what much difference is their between +3.00 and +3.50 in reading glasses?

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  4. my son has 6/20 in right eye and 6/38 in left eye. does this mean he is sight impaired? thanks

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  5. what do you make of the following. 7yr old son.

    Right Eye: sph +8.00, cyl 200, axis 180, VA 6/38

    Left Eye: sph +7.50, cyl 175, axis 165, VA 6/20

    High hyperopia, Binocular Amblyopia and right Esotropia. BCVA very poor.

    This is what it states on my sons report from Bsc(Hons) MCOptom that we visited a few days ago.

    Thanks

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  6. +1.25 is equal to? plz tell me as soon as possible

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  7. what does -0.03 mean for right eye and 1.37 left eye on logmar chart mean?

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  8. It's a great sight for solving eyesight problems. Their overnight vision correction provides the best vision correction method for children and adults with active lifestyles or progressive myopia and so on. Ortho-K Vision Correction

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  9. Whether 6/36 both eyes may get benefit of reservation in government jobs

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  10. This comment has been removed by the author.

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  11. This comment has been removed by the author.

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  12. Whether 6/36 both eyes may get benefit of reservation in government jobs

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  13. Can someone join us army as a pilot with 20/200 vision?

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  14. My 2.10yr old son has -0.75 spherical and -1.50 Cylinderical for both the eye..How bad it is?should he has to use glasses in this early age??can it be corrected through Diet??Will be grateful if u can answer

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  15. Hi, my son has 6/9 vision with glasses on he has been diagnosed with ocualtaneous albinism. I am aware until he can do letter tests the tests are an overestimate as he is only turning 4. Does he need a VI teacher? As I believe he is t the lesser end of the albinism spectrum.

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