Eye Examination Techniques

Optometrists and ophthalmologists use several techniques when determining the comprehensive vision of a patient. These range from color blindness testing to visual acuity tests which gauge the sharpness of your vision. A comprehensive vision examination typically lasts an hour or more and includes several variations of eye tests tailored to your needs and vision problems (if applicable).

Visual Acuity Test

• Visual acuity tests gauge the sharpness and scope of a person's vision. The doctor projects an image of a chart filled with letters of all sizes onto a screen 20 feet in front of the patient. The letters start out large and, for most, easy to read but become smaller as they go down the page. Patients must read each letter of each row from top to bottom, left to right. The vision "score" is based on what a "normal" human can read from 20 feet away from the chart. Therefore if the patient has 20/20 vision, he can read the chart's letters while standing 20 feet away. This is considered normal human vision. A person with 20/10 vision, however, sees better than a patient with 20/20 vision, since he can see letters on the chart when standing only 10 feet away from the chart. A person with below average vision who scored a 20/40 sees letters from 20 feet that those with normal vision can see from 40 feet away and so on. A vision score of 20/200 meets the requirements for blindness by United States standards.

Color Vision Testing

• Issues with color vision are common, particularly for men. Most individuals struggle to differentiate between reds and greens; however, some also have problems with blue-yellow colors. Color vision is usually tested by Pseudoisochromatic plates. The Pseudoisochromatic test is contained in a book and shows a variety of "plates" with varying colors and color combinations. Each of these plates varies in hue and possesses backgrounds and patterns in completely different colors. A person with average or "normal" color vision can easily spot a pattern in the plates, while a person with poor color vision see no pattern in the plates. This condition is referred to as being "dichromatic", meaning that two unlike colors appear to be the same.

Motility Test

• A motility test essentially tests the eye's ability to move and follow a specific target. The patient focuses on and follows a specific target such as the doctor's finger tracing a large letter. The patient must follow each movement of the finger while the doctor watches closely for the eyes' response. This test reveals any problems with both the eye muscles and the muscles' nerve supply.