Here is some information I found on the code from a 2001 article. Note when you read the section on the 99172 code that it says it was requested by Occupational Medicine and should only be used when screening pilots and other occupations where good vision is critical.
Tom Cheezum, O.D., CPC
The most appropriate code to use for vision screening in primary care pediatrics is 99173 (screening test of visual acuity, quantitative, bilateral [The screening test used must employ graduated visual acuity stimuli that allow a quantitative estimate of visual acuity (e.g., Snellen chart). Other identifiable services unrelated to this screening test provided at the same time may be reported separately (e.g., preventive medicine services). When acuity is measured as part of a general ophthalmological service or of an E/M service of the eye, it is a diagnostic examination and not a screening test.]). The correct ICD-9 code for 99173 is V72.0 (examination of eyes and vision).
Avoid 99172
CPT 2001 has added a second visual screening code, 99172 (visual function screening, automated or semi-automated bilateral quantitative determination of visual acuity, ocular alignment, color vision by pseudoisochromatic plates, and field of vision [may include all or some screening of the determination(s) for contrast sensitivity, vision under glare] ... [This service must employ graduated visual acuity stimuli that allow a quantitative determination of visual acuity (e.g., Snellen chart). This service may not be used in addition to a general ophthalmological service or an E/M service]). This code is for visual function screening, but it is not for use by pediatricians in screening children for developmental visual problems. The code was requested by occupational medicine practitioners, and is for use only in screening pilots and other professionals whose vision abilities are imperative to job requirements.