Snellen Chart

The Snellen Chart provides a measure of distant visual acuity. Visual acuity is the clarity of which we see objects, including the capability of identifying small visual details.

Set-up

Tape or velcro may be needed to attach to the wall
10 feet away from patient
Clear, non-cluttered wall with no visual distractions
Positioned at eye-level of patient, whether sitting or standing
Have cheat sheet accessible with Snellen chart and associated scores to ensure accuracy of patient’s letter reading and therapist’s scoring

(Gett & Romaniw, 2021)

Assessment

Patient can wear corrective lenses (glasses or contacts), but document if they are wearing them or not or if they don’t use corrective lenses at all
Assess patient’s performance with one eye covered, other eye covered, and then both eyes uncovered
Patient can start on the line furthest down that they can read
Continue until the patient misses over half of the letters on the line
Observe the following:
- sequencing errors
- letter reversals
DOCUMENTATION
- Record visual acuity measure for smallest line read correctly with more than half of the letters read
- 20/30 -2 if the patient misses 2 letters on the smallest line they can read
- Observations if they are struggling anywhere

(Gett & Romaniw, 2021)

Norms

Normal = 20/20
Minimum for driving in Pennsylvania = 20/40
Participation in daily occupations = 20/50
Legally blind = 20/200

(Gett & Romaniw, 2021)

Interpretation

Numerator = distance the patient is standing from the chart (in feet)
Denominator = distance from which a person with perfect eyesight can read the smallest line the patient can visualize
20/40 vision means that at 20 feet away, a patient with impaired vision can read what a person with perfect vision can read at 40 feet

(Pedretti et al., 2018)

References

Gett M. & Romaniw A. (2021, September 29). Vision [Lecture Notes]. Department of Health Sciences, Occupational Therapy, Chatham University. https://mylearning.chatham.edu/d2l/le/content/21252/Home

Pedretti, L. W., Pendleton, H. M. H., & Schultz-Krohn, W. (2018). Pedretti’s occupational therapy: Practice skills for physical dysfunction (8th ed.). Elsevier.

Schneider, J. (2002). Snellen chart. https://en.wikipedia.org/wiki/Snellen_chart