Visual Acuity

• Optometrists tests patients' eyes to detect vision problems and ensure that a patient has normal depth and color perception. A person's ability to see is called visual acuity. Visual acuity is classified as a fraction, with normal vision being 20/20. This means that a person with 20/20 vision is able to see letters or symbols clearly on an optometrist's reading chart from a distance of twenty feet without having to move closer to or further away from the chart. A person with myopia, or short sightedness, might be classified as 12/20, meaning that she has to move within twelve feet of a reading chart that should be seen clearly at twenty feet. Once the optometrist has determined that eye glasses will help her patient attain better vision, she uses a special machine called a phoropter to find the best prescription for her patient.
  
  

Phoropters

• A phoropter is a machine that is fitted around a patient's head and over his eyes. The optometrist is able to test with a series of lenses which prescription will be the best for the patient's needs. While using the phoropter to try different lenses, the optometrist will test how well the patient focuses on light using another instrument called a retinoscope, which is lighted. Some optometrists use an automated machine that measures how well the eyes focus. Once the optometrist has determined which lens prescription helps the patient to see as clearly as possible, she will write him a prescription for eye glasses. The optometrist will sometimes use eye drops for patients who cannot speak for themselves or who need more extensive tests. The eye drops prevents the patient's eyes from changing focus and allows the optometrist to use an automated machine to test focusing ability.
  
  

Conditions Requiring Eye Glasses

• There are a number of conditions that can be diagnosed by an optometrist and require the use of eye glasses. One, previously mentioned, is nearsightedness or myopia. This happens when a person cannot easily focus on objects at a distance, but can more easily see nearby objects. The opposite of this condition is called hyperopia, more commonly known as farsightedness. A farsighted person needs glasses for nearby objects and activities, such as reading or writing. A condition that can accompany both nearsightedness and farsightedness is called astigmatism. Astigmatism is an abnormal curvature of the cornea or lens inside the eye. This abnormal curvature does not reflect light properly on the retina and often requires the use of eyeglasses to provide clear vision. An optometrist will use the phoropter to prescribe eye glasses that correct both astigmatism and myopia or hyperopia.