The effect of prism on preferred retinal locus

Area of Science:

• Ophthalmology
• Visual Neuroscience
• Low Vision Rehabilitation

Background:

• The effect of prism, particularly base-up prism, on the retinal area used for fixation in central scotoma patients remains controversial.
• This pilot study investigates the impact of base-up prism on the preferred retinal locus (PRL) using microperimetry.

Purpose of the Study:

• To evaluate the effect of base-up prism on the fixation locus (PRL) in individuals with central scotoma.
• To determine if prism can predictably relocate the PRL for improved visual function.

Main Methods:

• Microperimetry was used to assess the PRL in 13 visually impaired subjects with central scotoma.
• Measurements were taken under four conditions: no lens, control lens, 6Δ base-up prism, and 10Δ base-up prism.
• PRL location was quantified in degrees relative to the optic disc.

Main Results:

• The preferred retinal locus (PRL) did not significantly differ with no lens versus a control lens.
• Base-up prisms (6Δ and 10Δ) induced a superior shift in the PRL in 84.6% of cases.
• The magnitude of the PRL shift was significantly less than the prism power, and vertical and horizontal movements were comparable.

Conclusions:

• Base-up prism generally shifts the PRL towards the prism base, but the relocation is not consistently predictable.
• The observed shift in PRL may not be clinically significant, warranting further investigation.
• Additional research is required to ascertain the functional impact of prism-induced PRL shifts in low vision patients.