In the Lighthouse rule example, a near BCVA of 4M and a goal of reading 1M print at 25 cm yields which ADD?

In the Lighthouse rule example, a near BCVA of 4M and a goal of reading 1M print at 25 cm yields which ADD?

• A. +12.00 D
• B. +14.00 D
• C. +16.00 D
• D. +18.00 D

Answer: (C)

The Lighthouse rule estimates the near reading add by tying print size (in M) to the needed dioptric power for a close reading task. Reading 1M at 25 cm requires about 4.00 D of accommodative effort (since 1/0.25 m = 4 D). If the patient’s near vision is only 4M, this rule uses a simple relationship that translates that difficulty into the required near add, yielding 16.00 D in this case (4 × 4 = 16). So, the estimated ADD to achieve reading 1M at 25 cm is +16.00 diopters. In practice this is a rough teaching/example calculation to illustrate how poorer near acuity translates into a larger near add; real clinical determinations would be refined with further testing and practical considerations.

The Lighthouse rule estimates the near reading add by tying print size (in M) to the needed dioptric power for a close reading task. Reading 1M at 25 cm requires about 4.00 D of accommodative effort (since 1/0.25 m = 4 D). If the patient’s near vision is only 4M, this rule uses a simple relationship that translates that difficulty into the required near add, yielding 16.00 D in this case (4 × 4 = 16). So, the estimated ADD to achieve reading 1M at 25 cm is +16.00 diopters. In practice this is a rough teaching/example calculation to illustrate how poorer near acuity translates into a larger near add; real clinical determinations would be refined with further testing and practical considerations.