Measuring accommodation at 33 cm reduces the effects of spectacle minification compared with testing at 40 cm.

Measuring accommodation at 33 cm reduces the effects of spectacle minification compared with testing at 40 cm.

• A. False
• B. True
• C. Not applicable
• D. Depends on pupil size

Answer: (B)

When you test accommodation with spectacles, the optics of the lenses can change how large the target appears to the eye. This alteration in perceived image size, or spectacle minification, can bias the measured accommodative response because the eye can respond differently to a smaller or larger image than reality. Testing closer, at 33 cm, increases the eye’s accommodative demand (about 3.0 diopters) and makes the target subtend a larger visual angle. The larger angular size and stronger blur cues at this nearer distance make the measured accommodation more driven by the actual focusing ability of the eye rather than by the relative size change induced by the lenses. In other words, the optical distortion from the spectacles has a smaller impact on the accommodation measurement at 33 cm than at 40 cm, where the target is smaller and the same minification would sway the response more. So measuring at a closer near distance reduces the influence of spectacle minification on the accommodation measurement compared with testing at a farther near distance.

When you test accommodation with spectacles, the optics of the lenses can change how large the target appears to the eye. This alteration in perceived image size, or spectacle minification, can bias the measured accommodative response because the eye can respond differently to a smaller or larger image than reality.

Testing closer, at 33 cm, increases the eye’s accommodative demand (about 3.0 diopters) and makes the target subtend a larger visual angle. The larger angular size and stronger blur cues at this nearer distance make the measured accommodation more driven by the actual focusing ability of the eye rather than by the relative size change induced by the lenses. In other words, the optical distortion from the spectacles has a smaller impact on the accommodation measurement at 33 cm than at 40 cm, where the target is smaller and the same minification would sway the response more.

So measuring at a closer near distance reduces the influence of spectacle minification on the accommodation measurement compared with testing at a farther near distance.