How to Understand the Eye Test
An eye exam is a series of tests concerning the functionality of your vision. Distance and near visual acuity, astigmatism, internal eye pressure for glaucoma, retinal detachment and diabetic retinopathy are among the disorders screened in these exams. There generally is no prior preparation for these exams.
Snellen Eye Chart
The Snellen eye chart is used to test distance and near visual acuity. The Snellen eye chart is a series of letters or pictures as a certain size at a certain distance. A person is expected to be able to read a size font from a designated number of feet from the chart. Perfect vision is 20/20, while 20/200 with visual correction is considered legally blind. The Snellen eye chart is often placed within a device called a phoropter. The phoropter is an instrument used to determine the strength of prescription glasses needed for the patient to see clearly.
Ability to Focus
The ability to focus is called "diopter". A diopter reading of one means you can focus at the length of one meter or 39 inches. Many people over 50 have a diopter reading of one and are diagnosed with presbyopia. In another words, they need reading glasses. A child or young adult may have a diopter reading of 40.
Physical Examination
Physical examination of the eye involves the optometrist looking at the eye structures using a light. He may ask you to look away while he closely examines the retina and circulation of the viscous of the eye. Ask concerning the venous system, inform him if you have "floaters" and "dark spots" as this may be indication of retinal detachment. He will also examine the corona, sclara and iris, and he will look for discharge or irritation of the mucous membranes. PERRLA is an acronym for "pupils equal, round, and reactive to light and accommodation".
Glaucoma Test
Dilation of the pupil is often part of the eye exam to test for glaucoma. The optometrist puts a small amount of solution into your eye to increase or dilate the pupil. He then asks you to place your chin on a rest in front of a Tonometry. The machine will blow a small burst of air into your eye and measure pressure of the aqueous humor.