Do you expect a patient to have a slight lag or slight lead of accommodation on MEM?

Do you expect a patient to have a slight lag or slight lead of accommodation on MEM?

• A. Lag
• B. Lead
• C. No difference
• D. Cannot determine

Answer: (A)

MEM measures how well the eyes’ accommodation matches the near demand. In normal functioning, the accommodative system tends to fall just a bit short of the exact demand at near, producing a small lag. So when you test with MEM, you expect a slight lag rather than a lead. A lead would mean the eyes are over-accommodating for the demand, which is not typical in a healthy, unstrained observer. At 40 cm, the near demand is about 2.50 diopters, and the actual response is usually a touch less than that, giving a small lag. This is why the correct expectation is a slight lag.

MEM measures how well the eyes’ accommodation matches the near demand. In normal functioning, the accommodative system tends to fall just a bit short of the exact demand at near, producing a small lag. So when you test with MEM, you expect a slight lag rather than a lead. A lead would mean the eyes are over-accommodating for the demand, which is not typical in a healthy, unstrained observer. At 40 cm, the near demand is about 2.50 diopters, and the actual response is usually a touch less than that, giving a small lag. This is why the correct expectation is a slight lag.