How does red light affect vision?

Effects of Red Light on Vision

Red light has significant effects on vision, including potential retinal hazards with high-intensity exposure, circadian rhythm disruption when used in the evening, and therapeutic applications in specific clinical contexts such as photodynamic therapy and myopia control. 1

Physiological Effects of Red Light on Vision

Retinal Impact

• Red light (600-700nm wavelength) poses less risk to the retina compared to blue light (400-450nm), which can potentially cause irreversible damage to photosensitive neurotransmitters in the macula 2, 1
• However, high-intensity red light can still pose hazards to the eye, particularly when used in therapeutic settings like photodynamic therapy 2, 1
• Unlike blue light, red light does not typically cause photochemical damage to the retina at normal exposure levels 3

Circadian Effects

• Red light has less impact on circadian rhythms compared to blue light, which strongly suppresses melatonin 2
• Evening exposure to red light is less likely to delay circadian phase and disrupt sleep patterns compared to blue-enriched light 2
• The timing of light exposure is critical - light administered before core body temperature minimum typically delays circadian phase, while light after advances circadian phase 2

Clinical Applications of Red Light

Photodynamic Therapy (PDT)

• Red light is used in photodynamic therapy in combination with photosensitizing agents (not as standalone therapy) for treating:
  • Actinic keratosis
  • Bowen's disease
  • Superficial basal cell carcinoma 2, 1
• Most PDT is conducted at longer red bandwidths rather than blue light to minimize retinal hazards 2
• Safety precautions include wearing suitable filter spectacles during treatments to limit transmission of high-intensity light 2, 1

Myopia Control

• Recent clinical trials suggest that brief periods of exposure to red light (repeated low-level red light therapy) may produce anti-myopia effects 4, 5
• Studies in tree shrews and macaque monkeys have shown that daily exposure to long-wavelength (red or amber) light promotes slower eye growth and hyperopia development 5
• Several randomized controlled trials in Chinese children demonstrated that exposure to red light for 3 minutes twice a day significantly reduces myopia progression and axial elongation 5

Potential Risks and Side Effects

Ocular Hazards

• High-intensity red light can cause pain described as "burning," "stinging," or "prickling" during PDT treatments 1
• Potential for hyperpigmentation or hypopigmentation in treated areas, usually resolving within 6 months 2, 1
• Long-term cumulative exposure effects are currently unknown 3

Wavelength-Specific Considerations

• Red light with longer wavelengths tends to form images behind the retina and may potentially induce myopia more easily in some species 6
• However, different species respond differently to lights of different wavelengths 6
• Chronic exposure to bright visible light can cause permanent retinal damage, with thresholds within one or two log units of light levels encountered in normal visual environments 7

Clinical Recommendations

• For therapeutic applications of red light:

  • Use appropriate eye protection (filter spectacles) for both patients and staff 2, 1
  • Monitor for potential side effects including pain, hyperpigmentation, and skin reactions 1
  • Avoid high-intensity exposure without proper medical supervision 1

• For general exposure:

  • Red light in the evening may be preferable to blue-enriched light to minimize circadian disruption 2
  • Consider red light as a potential alternative to blue light for evening illumination to reduce sleep disruption 2

Emerging Research

• The potential of red light therapy for myopia control is promising but requires further investigation regarding optimal parameters (intensity, duration, wavelength) 4, 5
• The mechanisms by which red light affects refractive development and potentially controls myopia are still being explored 5

Red light's effects on vision are complex and context-dependent, with both potential benefits in specific therapeutic applications and possible risks with improper or excessive exposure.