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LNCtips.com: Analysis of Visual Acuity

We all know that normal visual acuity is 20/20 (feet) in the United States or 6/6 (meters) in the rest of the world.  However, I didn't understand the nuances of visual acuity tests until I analyzed several optometry and ophthalmology medical malpractice cases.  After analyzing those cases, I learned that there's much more to the documentation of visual acuity than 20/20.

The physician or technician measures and reports each eye separately, with the right eye documented first.  Visual acuity is the eyes' ability to distinguish letters at a given distance.  The Snellen eye chart is one of the most common for measuring visual acuity.  The chart is composed of seven lines which represent 20/20, 20/25, 20/30, 20/40, 20/50, 20/70, 20/100 and 20/200 vision.  The Snellen eye chart also has several lines of smaller letters; these represent better than 20/20 visual acuity.  Some charts use shapes, such as the tumbling E. 

Vision measured as 20/20 is normal vision.  The first and second numbers refer to how well the patient sees at a distance of 20 feet.  (The actual distance in the doctor's office may be much less than 20 feet by using mirrors projected on a screen.)  A patient who can only see the top letter on the chart has 20/200 vision.  This means that the patient can see at 20 feet what a person with normal vision can see at 200 feet.  A patient with 20/10 vision has better than normal visual acuity, in that the patient can see at 20 feet what persons with normal vision can see at 10 feet.

The physician or technician also documents visual acuity with plus and minus signs.  The minus sign refers to missed letters on a line.  For example, the doctor may document 20/50-2.  This means that the patient missed two letters on the 20/50 line.  A plus sign refers to the patient's ability to discern some letters on the following line.  For example, 20/50+1 means that the patient read all the letters on the 20/50 line plus one letter on the next line.

Except for OD (right eye), OS (left eye), and OU (both eyes), visual acuity abbreviations are different from what most nurses encounter in their day-to-day work life.  Even the abbreviation OU is slightly different in that it means both eyes together when referring to visual acuity.  Some abbreviations are easy to figure out - CL for contact lenses and GL for glasses - but some are harder.  Visual acuity itself is abbreviated V or VA.  It may also be abbreviated as DVA, or VAd, with the "D" meaning "distance."  Near visual acuity (NV, NVA, or VAn) is tested by the patient reading from a card held 14 to 16 inches (35½ to 40 cm) from the face.  Other abbreviations frequently used in visual acuity testing:

CC refers to "with correction" while SC refers to "without correction."

PH refers to "pinhole."  A pinhole is similar to squinting in that it removes the effects of refractive errors.

CF and FC refer to "finger counting."  "How many fingers do you see?"

HM refers to "hand motion."  If the patient cannot distinguish fingers, then the examiner determines if the patient can discern hand motion.

LP refers to "light perception" while NLP refers to "no light perception."

What does visual acuity mean to legal nurse consultants?  If a physician or technician improperly performs visual acuity testing, it's a standard of care issue.  However, my experience with optometry and ophthalmology cases has been in determining damages.  Those damages included poor visual acuity, even blindness, due to allegations of failure to refer patients, failure to diagnose and treat eye conditions, and/or improper performance of eye procedures.  Analyzing the results of visual acuity tests prior to and after the incident provides the basis for the claim of damages and the extent of those damages.

Want to learn more about LNC skills for legal nurse consultants? Check out the Archives.

...Katy Jones