Introduction

Light therapy, also known as phototherapy, refers to the use of devices emitting specific wavelengths of light, recognised for producing potential therapeutic and aesthetic effects on the skin and various medical conditions. A novel therapeutic approach of utilising light therapy lies within ophthalmology, where it has demonstrated notable benefits for eye health.¹ The precise mechanisms through which different types of light therapy elicit an improvement in visual health are still under the microscope of scientific research. An increasing number of trials are exploring the potential use of different light therapies, such as red light, intense pulsed light, and low-level light therapy, as viable treatment options for addressing various eye conditions, including as dry eyes, myopia, and age-related macular degeneration.^2,3,4

Light therapy is being inspected for its anti-ageing, anti-inflammatory, and immune-boosting capacities.¹ Bright light therapy has been demonstrated effective in treating mood disorders and sleep disturbances.⁵ Furthermore, while lPL was initially used in dermatology, it quickly gained popularity and was introduced in ophthalmology around 15 years ago, showing promising results. However, further comprehensive studies are imperative for the extensive clinical application of this method, establishing its long-term safety and efficacy.⁶

Basics of light and light therapy

Light is a form of electromagnetic radiation that travels in different wavelengths at a constant speed in a vacuum.⁷ The spectrum of wavelengths comprises radio waves, microwaves, infrared, the visible spectrum, ultraviolet (UV), x-rays and gamma rays. The visible to humans spectrum of light ranges from 400 nanometers (nm) to 700 nm.⁸ Photons are designated as the quantum (the smallest discrete particle) of light. They are able to produce energy that multiple materials, including biological entities, may absorb may. This wave-particle duality of light has had scientists intrigued as to how they could exploit this energy in various medical applications.¹

Interestingly, light therapy has made significant progress in recent decades, steadily approaching its zenith, with novel treatment options being investigated regularly. Specifically, the most common types of light therapy impacting the eyes include:

• Red light therapy/photobiomodulation therapy: also known as low-level laser therapy (LLLT), it uses low-power light from the far red to near-infrared (NIR) (600-1000 nm). This therapy utilises non-ionising sources such as lasers and light-emitting diodes (LEDs)⁹
• Intense pulsed light (IPL): uses flashes of light mainly across the visible to infrared range (515-1200 nm) with varying intensities. It was initially employed in dermatological and cosmetic departments but has also been submitted in ophthalmology⁶
• Photodynamic therapy: it is a synergetic therapy involving the administration of a photosensitising agent activated by specific light wavelengths¹⁰

How can light affect the human eye?

The human eye’s response to light, particularly sunlight, has been the subject of extensive study. Sunlight, with its multiple wavelengths in the visible spectrum, acts on distinct receptors in the body’s cells and tissues. Similarly, light therapy influences the eyes through various biological processes, with varying outcomes among the different wavelengths of light. Pointedly, the light gets absorbed by different photoreceptor cells found in the eye’s retina, including rods and cones responsible for visual conduction. Opsins, the proteins involved in the visual system transduction, are key players in how light influences the eyes.¹

Red and NIR light are believed to penetrate tissues and stimulate cellular processes and mitochondrial activation, promoting cellular energy production and facilitating cell repair and regeneration. Evidence also suggests that this therapy enhances oxidative metabolism, exerts anti-inflammatory and protective effects on the retina, and promotes cell homeostasis. The expanding applications of NIR light are advancing our knowledge of the exact mechanisms underlying biomodulation.¹

Effects of light therapy on eye diseases

Light therapy for dry eye disease

Dry eye disease (DED) is a frequent condition with multifaceted causes and risk factors. One of the leading causes of DED includes meibomian gland dysfunction, characterised by alterations in tear film lipid composition, compromising the ocular surface and leading to increased tear evaporation. One of the latest therapeutic approaches incorporated in clinics involves IPL therapy. IPL, of different wavelengths, targets the eyelids and is absorbed while the eyes remain protected. This strategy has provided promising results, reinforcing tear film stability and prolonging the film’s break-up times.

The efficacy appears to be influenced by the age of individuals and the exact settings of IPL devices, which are needed to ensure more personalised refinements.⁶ Subsequent regular IPL treatment visits have demonstrated the ability to alleviate meibomian gland dysfunction-related symptoms with a high safety profile, albeit at a rather high cost. Official protocols for this approach are crucial for revolutionising ocular treatments.¹¹

LLLT using LEDs has also proven effective in relieving DED symptoms, whether used alone or in combination with IPL therapy. This phototherapy, with biomodulatory actions, may improve the ocular surface, exhibit anti-inflammatory properties, boost tear secretion, and positively affect the lacrimal and meibomian glands (especially of the upper eyelid).²

Light therapy for age-related macular degeneration (AMD)

Macular degeneration is a progressive eye disease which can lead to vision loss among elderly populations. Photomodulatory therapy with red to NIR light has undergone studies for its capacities to induce modulatory reactions. It is known to increase mitochondrial function by acting on the chromophore cytochrome c oxidase, which is believed to be responsible for elevating ATP production (the energy needed for cellular reactions). Moreover, this form of energy has demonstrated minimising effects on oxidative damage and inflammation.

The specific wavelengths, energy levels, and time intervals appear to interact with this treatment’s efficacy, necessitating further studies. However, its ability to halt AMD progression, specifically in intermediate stages, is substantially proposed.¹² Consequently, another specific combination therapy, using photoresponsive drug carriers and green light (505 nm) for targeted drug delivery to eye sites, holds promise for numerous retinal and choroidal diseases.¹³

Light therapy for myopia

Myopia is one of the leading causes of visual impairment, with increasing prevalence. Beyond conventional laser treatments, which involve precise tissue removal and reshaping to address myopia, light therapy has recently gained traction as a treatment modality. Different light therapeutic approaches, including red light therapy, have exhibited positive outcomes in reducing myopia, ceasing its progression, and promoting hyperopia. Its mechanisms revolve around its protective effects on the cornea and retina, opposing the potential damage of blue light to the eyes.

This indicates that red light therapy could potentially be used as a preventive method for myopia. While these results are promising, further studies are pivotal to investigate the exact wavelengths, mechanisms, age groups, and adverse effects of red light therapy, including the presence of an afterimage.^2,14

Furthermore, exposure to bright light, such as sunlight, has also proven effective in preventing myopia. Scientists have found a correlation between spending time outdoors and increased dopamine levels, which attenuate myopia development.¹⁵ 

Light therapy for glaucoma

The increasing incidence of glaucoma, characterised by deterioration of the optic nerve, which may gradually lead to blindness, has become a problematic challenge. Among the different ways to manipulate light, scientists have explored its potential effects on glaucoma through photobiomodulation or red light treatment.

In particular, red light’s ability to penetrate tissues deeply has demonstrated its anti-inflammatory and oxidative stress-reducing actions with minimal adverse effects on the retina while also augmenting optic nerve resilience. As a result, this treatment may present potential therapeutic effects, especially when incorporated into combination therapies for glaucoma. Further studies for the establishment of protocols regarding the exact wavelength, treatment duration, and contact surface could promote the safe and effective use of this innovative approach.^9,16

Safety and considerations

From regulating circadian rhythm and mood disorders⁵ to cosmetic applications and photodynamic therapy against cancer cells,¹⁰ light therapies are applied across a broad range of medical topics. Despite its versatility, potential risks may be associated with light exposure. 

While sunlight and increased outdoor time are beneficial for preventing myopia,¹⁵ UV radiation may cause damage to the eyes. Hence, protection from bright light sources, including natural light and tanning beds, is crucial. Prolonged exposure to blue lights deriving from digital devices, may also harm the human eye, damaging the retina and causing vision problems.⁹ Therefore, it is important to prioritise eye protection measures. Even while using light devices for cosmetic purposes at home, seek certified manufacturers that comply with regulations.

Since light therapy has only recently gained such popularity, specific guidelines on suitable indications and device settings are still debated. The energy, frequency, type and duration of light therapy can yield different effects on the eyes. Additionally, certain patients may not be suitable candidates for specific light treatments.¹¹ Therefore, following a healthcare professional’s advice and discussing potential side effects is vital for safe light therapy implementation.

Summary

Light's capabilities to generate biological impacts are unquestionable and extend beyond its fundamental role in plant photosynthesis. It emerges as a remarkable tool with diverse biological modulatory functions in the medical community. From harnessing it to target cancer cells to using it as bioluminescent probes that highlight internal cells and genes for optical imaging, light holds immense potential as an innovative tool with multiple applications. 

Different frequencies of light, spanning UV, the visual range, and infrared, are associated with specific actions on the human eye. Extensive exposure to UV and blue light may be deleterious for the eye’s health. However, balanced use - such as spending time outside - could be beneficial. Similarly, controlled utilisation of NIF, IPL and red light, particularly under professional guidance, could assist eye health by preventing or alleviating symptoms of myopia, dry eyes, glaucoma, or AMD.

Following your doctor’s advice, thoroughly reviewing your medical history, analysing potential side effects, and selecting the most suitable treatment are crucial factors to a successful personalised therapy journey with optimal results in maintaining eye health.