Minus lenses indirectly test which vergence function?

Minus lenses indirectly test which vergence function?

• A. NFV
• B. PFV
• C. Accommodation
• D. Proximal vergence

Answer: (A)

Minus lenses boost the eye’s accommodative effort. When you view a target through minus lenses, the eyes must accommodate more to keep the image clear, and that increased accommodation causes accommodative convergence. To keep the eyes aligned and single, the vergence system must provide enough divergence to offset that inward pull. That divergence capability is negative fusional vergence. So, by making the eyes accommodate more, minus lenses reveal how well the system can diverge, which is why they indirectly test NFV. This isn’t a direct test of NFV the way base-out prism would be; it’s an indirect readout driven by the accommodation–vergence link (AC/A). PFV would be tested with convergence demands (base-in prisms), not by minus lenses. Accommodation participates in the mechanism, but the focus is on the system’s ability to diverge to maintain single vision. Proximal vergence isn’t the primary factor here.

Minus lenses boost the eye’s accommodative effort. When you view a target through minus lenses, the eyes must accommodate more to keep the image clear, and that increased accommodation causes accommodative convergence. To keep the eyes aligned and single, the vergence system must provide enough divergence to offset that inward pull. That divergence capability is negative fusional vergence. So, by making the eyes accommodate more, minus lenses reveal how well the system can diverge, which is why they indirectly test NFV. This isn’t a direct test of NFV the way base-out prism would be; it’s an indirect readout driven by the accommodation–vergence link (AC/A). PFV would be tested with convergence demands (base-in prisms), not by minus lenses. Accommodation participates in the mechanism, but the focus is on the system’s ability to diverge to maintain single vision. Proximal vergence isn’t the primary factor here.