What MEM value range is considered a normal lag?

• A. 0.25-0.75
• B. 0.0-0.25
• C. 0.75-1.25
• D. 1.25-1.75

Answer: (A)

MEM assesses how accurately the eyes can accommodate at near by measuring the lens power needed to make a near target appear clear. The value you read is the amount of minus lens required to neutralize the target; a positive number means the eye is not fully meeting the near demand (an accommodative lag), while a negative value would indicate over-accommodation (a lead). The normal lag is about 0.25 to 0.75 diopters, reflecting a typical, age-appropriate response. For a near target at about 40 cm (demand ~2.50 D), a MEM of 0.25–0.75 D means the actual accommodation is roughly 1.75–2.25 D, which fits normal function. Larger lags suggest accommodative inefficiency, while values near zero or negative indicate little lag or excess accommodation.