Facts and history about the eye test chart. The most commonly used eye chart is known as the Snellen chart. It usually shows 11 rows of capital letters. This eye test can only be considered a screening test.
A variety of factors, such as lighting, glare, and monitor quality, can affect the results of this test. An eye chart, or chart, is a chart used to subjectively measure visual acuity. Health professionals, such as optometrists, doctors, or nurses, often use eye charts to evaluate people for vision problems. Ophthalmologists, doctors who specialize in the eye, also use eye charts to monitor their patients' visual acuity in response to various therapies, such as medications or surgery.
To assess your near vision, the ophthalmologist may use a small portable card called a Jaeger eye chart. The Jaeger graphic consists of short blocks of text in various font sizes. For this test, the child sits in a chair 10 feet away from the board, gently holding an eye mask over one eye. If you don't wear glasses or contact lenses, your ophthalmologist will use the results to see if you need them.
A thorough eye exam can often detect certain underlying diseases that may endanger vision and eye health, such as diabetes, high blood pressure, high cholesterol, tumors, autoimmune diseases, and thyroid disorders. For the first time, the Snellen eye chart allowed a person to provide a standardized prescription from any eye care provider who chose any eyeglass manufacturer, and obtain the same optical lenses to accurately correct their vision. Having so many different eye charts made it impossible to standardize the vision correction available to patients. However, because many ophthalmologists have offices that are less than 20 feet long, the eye chart can be hung behind the patient's chair and reflected in the mirrors to simulate a distance of 20 feet.
In the United States, the standard eye chart location is on a wall that is 20 feet away from the eyes. During an eye exam, the ophthalmologist will ask you to look for the smallest line of letters you can read, and then ask you to read it. Even Japanese ophthalmologist Ema Tenko, who studied with Snellen, created an eye chart that was used in Japan. Parents and caregivers can examine their child's eyesight from home to identify possible vision problems that require an eye professional.
Before this standardized ophthalmic chart was developed, each ophthalmologist had their own chart that they preferred to use. Eye professionals can use certain tables to measure distance vision and others to measure near vision. The font size on a modern Jaeger eye chart generally ranges from J10 (approximately 14 points in Times New Roman font) to J1 (approximately 3 points in Times New Roman). Optotype, another term that could define an eye chart, is still the most common test for evaluating standard vision.
Although eye chart tests identify refractive errors, they cannot detect signs of deficiencies in visual abilities or diseases such as glaucoma, cataracts, or macular degeneration. The classic example of an eye test is the Snellen eye chart, developed by Dutch ophthalmologist Hermann Snellen in the 1860s.