<prompt> A person came to eye OPD for routine eye check. On snellens cha he was found to read 66 in both eyes. What is the largest approximate distance at which he would be able to read the first topmost letter36 m24 m60 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 660 means that a normal patient should be seeing at 60 metre, but this patient has to be much closer that means 6 metre This also means that the letter written at 660 is big enough that 66 vision person can read it at even 60 metre 