Visual fatigue, or asthenopia, occurs when visual demands exceed the capacity of the visual system, leading to various ocular discomfort and systemic symptoms. This condition can negatively affect personal activities, quality of life, and work productivity. Given the high prevalence of asthenopia in presbyopic population, finding effective methods to alleviate these symptoms is crucial. This study aims to evaluate the effects of repeated low-level red-light (RLRL) therapy on alleviating visual fatigue in individuals with presbyopia over a one-month period. Additionally, we will assess the potential benefits on accommodation function, cognition, and emotional effects of RLRL in this population.

Interested individuals will be invited to the PolyU Optometry Clinic to undergo an eligibility examination. An estimated sample size of 66 participants will be recruited. The inclusion criteria specify individuals aged 40 years or older who self-report visual fatigue symptoms and require near correction in daily life. Exclusion criteria include those with ocular disease, systemic diseases, illiteracy, or an afterimage duration longer than 6 minutes.

Eligible participants will be randomly assigned in a 1:1 ratio to either the intervention group or the control group. Each participant in the intervention group will be provided an RLRL therapy device, which they are required to use twice daily for 3 minutes per session, with a minimum interval of 4 hours between sessions, 7 days a week for one month. Participants in the control group will receive a sham device, following the same usage schedule. The study will evaluate changes in asthenopia questionnaire scores, CFF scores, other objective asthenopia indicators (i.e., eye movement, pupil parameters, and blink patterns), accommodation function, cognitive function, and emotional states at 2 weeks and 1 month compared to baseline. Statistical analysis will be conducted to explore evaluate within-subject changes over time and between-group differences in visual fatigue metrics, accommodation metrics, cognitive metrics, and emotional metrics.

The findings will contribute to evaluating the effectiveness of RLRL therapy in reducing asthenopia and presbyopia symptoms, as well as its impact on cognitive function and emotional well-being.

Inclusion Criteria:

• Individuals aged over 40 years old.
• Self-reported visual fatigue symptoms.
• Distance best-corrected visual acuity (BCVA) of 0.5 LogMAR or better, and near visual acuity worse than N8 (20/50) at 40 cm with the subject's habitual distance correction.
• Require near correction in daily life.
• No light therapy received in the past six months.
• Giving informed written consent.

Exclusion Criteria:

• Presence of diseases that can cause eye pain or headaches, such as strabismus, glaucoma, ocular trauma, conjunctivitis, migraines, keratitis, iridocyclitis, or other self-reported diseases.
• Systemic diseases (e.g., epilepsy, photosensitivity, seizure) or illiteracy.
• Afterimage time longer than 6 minutes.

According to the relevant agreement, all parties involved must keep study data confidential throughout the study process.