In Brewster distance setting, which statement is true?

In Brewster distance setting, which statement is true?

• A. Contains +5.00 lenses whose optical centers are at 95 mm apart; due to proximal vergence the targets are actually 87 mm apart; targets less than 87 mm apart generate an Eso posture; more than 87 generate an Exo posture; In distance setting every 2 mm change in separation causes 1 prism diopter change in vergence.
• B. Contains +5.00 lenses whose optical centers are at 87 mm apart; actual 95 mm apart.
• C. Targets are 87 mm apart with no vergence effect.
• D. There is no relationship between target separation and vergence.

Answer: (A)

The concept being tested is how proximal vergence ties target separation to the eye’s vergence posture in a Brewster distance setting. In this setup, the instrument uses +5.00 lenses with optical centers 95 mm apart. Proximal vergence makes the targets seem closer together than they actually are, so the perceived separation is 87 mm. That 87 mm acts as the boundary: targets closer than 87 mm demand inward eye convergence (eso posture), while targets farther than 87 mm push the eyes outward (exo posture). The setting is calibrated so that, in distance mode, every 2 mm change in target separation changes vergence by 1 prism diopter. This combination of numbers and the 2 mm → 1 PD rule is what makes that statement correct. The other options either reverse the numerical arrangement, deny the vergence effect, or claim there’s no relationship between target separation and vergence, which contradicts how Brewster distance settings operate.

The concept being tested is how proximal vergence ties target separation to the eye’s vergence posture in a Brewster distance setting. In this setup, the instrument uses +5.00 lenses with optical centers 95 mm apart. Proximal vergence makes the targets seem closer together than they actually are, so the perceived separation is 87 mm. That 87 mm acts as the boundary: targets closer than 87 mm demand inward eye convergence (eso posture), while targets farther than 87 mm push the eyes outward (exo posture). The setting is calibrated so that, in distance mode, every 2 mm change in target separation changes vergence by 1 prism diopter. This combination of numbers and the 2 mm → 1 PD rule is what makes that statement correct. The other options either reverse the numerical arrangement, deny the vergence effect, or claim there’s no relationship between target separation and vergence, which contradicts how Brewster distance settings operate.