In Nott retinoscopy, how is the presence of a lag determined?

• A. Neutrality distance translating to more than 2.50 D
• B. Neutrality distance translating to exactly 2.50 D
• C. Neutrality distance translating to less than 2.50 D
• D. Neutrality distance translating to 0 D

Answer: (C)

Nott retinoscopy uses the neutrality distance to gauge how well the eye is accommodating to a near demand. The near task at which neutrality is achieved is tied to a typical near dioptric demand of about 2.50 D (40 cm). If the neutralization occurs at a distance that corresponds to less than 2.50 D (meaning the eye would need more distance to neutralize, i.e., the neutrality distance is farther than 40 cm), the eye isn’t accommodating enough for that near demand. That shortfall is a lag of accommodation.

So the presence of a lag is indicated when the neutrality distance translates to less than 2.50 D. If neutrality were exactly 2.50 D, accommodation matches the demand; more than 2.50 D would imply over-accommodation (lead). For a concrete example, neutrality at 50 cm corresponds to 2.0 D, signaling a lag of about 0.5 D.