Optical compensation for night myopia based on dark focus and CA/C ratio

Area of Science:

• Ophthalmology
• Optometry
• Vision Science

Background:

• Night myopia, a condition affecting visual acuity in low light, presents challenges for optical correction.
• Individual variations in ocular responses, such as dark focus and accommodation, are known to influence refractive error.
• Understanding these individual differences is crucial for personalized vision correction strategies.

Purpose of the Study:

• To investigate if dark focus and the convergence accommodation to convergence (CA/C) ratio can guide the prescription of optimal optical corrections for night myopia.
• To determine the relationship between these individual factors and the required lens power for best visual acuity under dim lighting conditions.

Main Methods:

• Visual acuity and contrast sensitivity were measured across various lens powers and luminance levels to determine optimal correction for night myopia.
• Dark focus was assessed using an infrared optometer.
• Convergence accommodation to convergence (CA/C) ratio was measured using an infrared optometer and an eyetracker in young subjects (mean age 25.4 years).

Main Results:

• Optimal lens power for night myopia showed a significant correlation with dark focus, irrespective of the CA/C ratio.
• A steeper regression slope between lens power and dark focus was observed in subjects with lower CA/C ratios (<0.4 D/MA) compared to those with higher ratios (>0.4 D/MA).
• Mean optimal lens power and dark focus differed between low and high CA/C groups, indicating distinct refractive responses.

Conclusions:

• Intersubject variability in dark focus and CA/C ratio are significant factors in optimizing visual performance for night myopia.
• For individuals with low CA/C ratios, prescribing a lens power approximating their full dark focus yielded the best visual outcomes.
• For individuals with high CA/C ratios, a lens power of half their dark focus was found to be optimal.