PAM stands for "potential acuity meter." It is an instrument used to examine the eyes. Your doctor can use this tool to predict how well you may see after eye surgery. People who have reduced vision due to cataracts may also have other reasons for poor vision. The PAM will help predict what the vision will be after the cataracts are removed. If cataracts are severe, the PAM may not give useful information.
Potential acuity meter
Datiles MB III, Ansari RR. Clinical Evaluation of Cataracts. In: Tasman W, Jaeger EA, eds. Duane's Ophthalmology. 2013 ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2013: vol 1, chap 73B.