<prompt> A person came to eye OPD for routine eye check u. On snellens cha he was found to read 66. At what distance he should be able to read 62436 m24 m6 m1 m  <response>: What does 66 mean in Snellens cha It means that the patient with or without glasses can see the letter at a distance of 6 m which a person normally should have been seeing at 6 m Now you would understand it by next example 612 means a letter which a normal patient should be seeing at 12 metre , this patient can see only when he is nearer, that means 6 metre from Target 624 means that a normal patient should be seeing at 24 metre, but this patient has to be much closer that means 6 metre This also means that the letter written at 624 is big enough that 66 vision person can read it at even 24 metre 