${Mean}_{pre}$	Mean RNFL thickness before the ethambutol administration;
${Mean}_{post}$	Mean RNFL thickness after the ethambutol administration;
${SD}_{pre}$	The standard deviation of RNFL thickness before the ethambutol administration;
${SD}_{post}$	The standard deviation of RNFL thickness after the ethambutol administration;
$N$	The number of eyes.