Eye Test – Must Try Harder


The words “test” and “exam” still make me shudder.  At their very utterance, I am transported back to fusty classrooms and the sound of chalk scraping on the blackboard while the clock above it relentlessly ticks away the minutes until the words “Time’s up! Pens down now!” are called out and I just know that the tricky questions – the ones I decided to leave until last – will remain unanswered resulting in a big fat zero in the margin. Will the other answers be enough?

A chilling memory indeed.

So perhaps it’s not too surprising that “test” and “exam” equate in my brain to: “must do better” or “should try harder”. By putting the word “eye” in front doesn’t seem to make much difference.

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When faced with the “Snellen Chart” (those charts of decreasing size letters used by eye care professionals to measure visual acuity – or the acuteness and clearness of vision) I revert to the competitiveness of my schooldays. Will I pass? How low can I go?

While researching this post I have discovered that Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862. Traditionally they are printed with eleven lines of block letters. The first line has one very large letter – usually an E, H or N and subsequent rows have increasing numbers of letters in decreasing size– through the 20/20 line of eight letters to the tiny bottom line of eleven miniscule letters. The single top letter should be 88 mm in height and the viewing distance for the chart is 6 meters or 20 feet.

I believe that people who are unable to read the large, top, single letter – even with the best possible glasses – are technically categorised as blind.

Apparently the traditional Snellen chart only used ten letters – C,D,E,F,L,N,O,P,T and Z but modern charts add other letters into the mix – despite the fact that some are considered harder to distinguish than others such as P versus F; and G,Q’s and O’s..

Over the years the technique has been criticised due to the fact that the number of letters increases while the size decreases which introduces two variables.  Also it is possible to cheat – take the driving test scenario – by memorising the sequence.  Although I’ve never understood how anyone could remember such a random sequence of letters – at least without making up some bizarre sentences to use as a memory aid.

Eye Test – Must Try Harder