Duration of Transient Myopia
Transient myopia typically lasts from 35 seconds to 2 minutes in most individuals, with longer durations of up to 3 minutes observed in early-onset myopes and progressive myopes. The duration varies significantly based on refractive error type and progression status.
Factors Affecting Duration of Transient Myopia
Refractive Error Type
- Early-onset myopes: Experience longer decay times, averaging 63 seconds 1
- Late-onset myopes: Show faster decay to baseline, averaging 35 seconds 2
- Emmetropes: Generally do not experience significant transient myopia effects 2
Myopia Progression Status
- Progressive myopes: Show prolonged decay times compared to stable myopes 1, 3
- Stable myopes: Experience shorter decay durations 1
Duration After Different Near Work Periods
- After 5 minutes of near work: Effects may persist for up to 3 minutes in predisposed individuals 4
- After 1 hour of reading: Initial effects typically begin to decay within 30 seconds 1
- After 2 hours of reading: Effects may persist longer, with up to 46% of myopes not returning to baseline within 120 seconds 1
Clinical Implications
Additivity Effect
- Prolonged near work can lead to accumulation of transient myopia effects
- After 2 hours of reading, early-onset and late-onset myopes show significantly greater transient myopia than after 1 hour 1
- This additivity effect is particularly pronounced in progressive myopes but not in stable myopes 1
Population Differences
- Hong Kong Chinese children (a population with high myopia prevalence) show sustained transient myopia effects for longer than previously reported in white adult populations 4
- Preadolescent children with myopia may experience more persistent effects than adults 4
Management Considerations
- Vision therapy focusing on accommodative facility has been shown to reduce symptoms and improve objective measures of abnormal nearwork-induced transient myopia 5
- Treatment typically requires 7-10 weeks (5-6 sessions) of accommodative facility exercises 5
- Patients experiencing persistent transient myopia symptoms may benefit from accommodative vision therapy to improve their visual function 5
Important Caveats
- Up to 46% of myopes may not experience complete decay to baseline within 2 minutes after prolonged near work 1
- The persistence of transient myopia may contribute to permanent myopia progression with repeated cycles of near work 1
- Individuals with myopia should be advised about potential temporary distance vision blur after prolonged near work, particularly when engaging in activities requiring clear distance vision (like driving)