Spectacle correction for aphakia. The prismatic effect

Area of Science:

• Ophthalmology
• Optometry
• Visual Optics

Background:

• Spectacle lenses are fixed relative to the eyes, leading to prismatic effects during visual tasks like reading.
• The limited field of view through spectacle lenses (approx. 13mm wide for central vision) is a critical factor in visual performance.
• High plus corrections present unique challenges for comfortable binocular vision.

Purpose of the Study:

• To investigate the prismatic effect experienced by patients during reading with high plus spectacle corrections.
• To determine the maximal bifocal addition for comfortable binocular vision in high plus corrections.
• To assess the impact of decentered bifocal segments on prismatic effects.

Main Methods:

• Analysis of visual axes during convergence in relation to spectacle lens optical centers.
• Calculation of prismatic effect based on lens power and eye rotation.
• Evaluation of bifocal segment decentration in high plus corrections.

Main Results:

• The visual axes pass nasal to the optical centers during convergence, inducing a prismatic effect.
• A reading addition of +6.00 D is suggested as the maximal bifocal addition for comfortable binocular vision.
• A base-out prismatic effect of at least 4 prism diopters per eye occurs at reading distance, even with adequate bifocal decentration.

Conclusions:

• High plus spectacle corrections inherently create significant base-out prismatic effects during reading.
• Prescribers should consider the limitations of binocular vision with high plus bifocal additions.
• Further research may be needed to optimize bifocal design for high plus corrections to mitigate prismatic effects.