Clinical refraction may be viewed as a procedure for generating messages—prescriptions—each containing a certain definite amount of information acquired from the patient. As part of the development of an automatic refraction system, this information flow has been analyzed, using concepts and metrics introduced by Shannon. Results from a sample block of 650 consecutive patients entering a University optometric clinic indicate that the general use prescription for both eyes contains about 23 bits of information. Total information acquired on sex, age, visual acuity, static skiametry and subjective refraction was about 60 bits, indicating 62% redundancy. Detailed analysis showed that subjective refraction could alone supply 75% of the required information, and that the inclusion of either age or visual acuity data increased this to 85%. The missing 15% of the prescription may either be genuine information derived from unrecorded or multiple sources (“clinical judgment”) or spurious information (error or “noise”). Hence minimum criteria are established for the informational performance of an automatic refraction system.
*Submitted August 18, 1970, for publication in the May. 1971. issue of the American Journal of Optometry and Archives of American Academy of Optometry.
†Industrial Engineer, Ph.D.. Member of Faculty.
‡Research Engineer, M.S.
aOptometrist, PhD., Member of Faculty. Fellow, American Academy of Optometry.
© 1971 American Academy of Optometry