Laser Safety in Ophthalmology

Key points at a glance

Key points of this condition

• Laser light is monochromatic, collimated, and coherent, and it is especially dangerous because it can be focused on the eye.
• The FDA class system (I to IV) defines hazard levels, and medical lasers fall into Class IV.
• The main symptoms of laser injury are flashes of light, reduced vision, dark spots, distorted vision, and color vision changes.
• There is no standardized treatment protocol for laser-induced retinal injury.
• Reflected light is the most common cause of accidental exposure, and the blink reflex is greatly reduced under anesthesia.
• Proper settings of wavelength, spot size, exposure time, and power are essential to prevent complications from medical lasers.
• Safer new technologies, such as pattern scan lasers and micropulse methods, are already in practical use.

1. What is laser safety in ophthalmology

LASER is short for Light Amplification by Stimulated Emission of Radiation. It began with the medical use of sunlight in ancient civilizations and developed into modern precise laser treatment.

Laser light has the following three characteristics.

• Monochromatic (monochromatic): made up only of light with a single wavelength.
• Collimated (collimated): the beam does not spread and travels in parallel.
• Coherent (coherent): the light waves are in step and reinforce each other.

Because of these properties, lasers have a radiance millions of times greater than the sun. Since the eye focuses laser light onto a small area of the retina and amplifies it more than 100 times, safety management is especially important in ophthalmology¹.

The biological effects of lasers are broadly divided into five types: disruption, photoablation, coagulation, hyperthermia, and photochemical reaction.

Pigments (chromophores) in the eye that absorb laser light include the following.

• Melanin in the retinal pigment epithelium (RPE)
• Oxyhemoglobin and deoxyhemoglobin in blood vessels
• Melanin in the uvea
• Xanthophyll in macular pigment
• Water

Laser is used in almost every field of medicine. As it becomes more widely used, complacency can easily set in, and it is always important to remember that laser surgery is also a medical procedure that carries risks.

The lasers mainly used in ophthalmology are shown by wavelength range.

Wavelength range	Representative laser	Main uses
Ultraviolet range (193 nm)	Excimer (ArF)	Refractive correction (LASIK), treatment of corneal opacity
Near ultraviolet to near infrared	Femtosecond	LASIK flap, cataract surgery assistance
Visible light (green to red)	Argon, krypton, diode	Retinal photocoagulation, iridotomy, trabeculoplasty
Near infrared (810 nm)	Semiconductor (diode)	Transscleral cyclophotocoagulation, transscleral retinal photocoagulation
Infrared (1,064 nm)	Nd:YAG	Posterior capsulotomy, transscleral cyclophotocoagulation
Far infrared (10.3 μm)	Carbon dioxide (CO₂)	Eyelid skin incision

Q How is laser light different from ordinary light?

A

Ordinary light contains many wavelengths and spreads in all directions, but laser light has three properties: a single wavelength, parallelism, and coherence. Because of this, it does not scatter and can travel far while maintaining high brightness; when focused into the eye, it delivers concentrated energy to the retina.

2. Main symptoms and clinical findings

Subjective symptoms

In acute exposure to a high-density laser, a bright flash is seen first, followed by decreased vision due to phototoxicity. The main subjective symptoms are listed below.

• Flash: A strong light is seen immediately after exposure.
• Decreased vision: Due to phototoxicity or retinal damage.
• Scotoma: A visual field defect corresponding to the injured area.
• Photophobia: Sensitivity to light.
• Metamorphopsia: Objects appear distorted.
• Dyschromatopsia: Abnormal color vision.
• Temporary eye pain and headache: Seen in the acute phase.

Symptoms are often present in one eye only, or in both eyes with uneven severity. Chronic pain, redness, and irritation are not caused by laser injury and suggest another cause.

Clinical findings (findings confirmed by the doctor during examination)

With a dilated fundus examination, confirm tissue bleeding, perforation, and scarring. Imaging includes AOSLO, FA, fundus autofluorescence, and OCT. Injury sites and findings differ by wavelength band.

Wavelength band	Typical laser	Main eye findings
450–480 nm (blue)	Blue laser	Outer retinal defect, full-thickness macular hole, macular edema
520–536 nm (green)	Argon green	Outer retinal defects, RPE destruction and scarring
630–670 nm (red)	He-Ne, red diode	RPE lesions, destruction, and atrophy
1,064 nm (near-infrared)	Nd:YAG	Corneal epithelial injury, macular hemorrhage, full-thickness macular hole

Retinal injury from Nd:YAG lasers requires special caution. Because the 1,064 nm wavelength is invisible, accidents can easily occur, and accidental firing without protective goggles in the laboratory is common. It can cause foveal damage in the dominant eye, forming retinal opacity lesions, subretinal hemorrhage, and macular holes. In reported cases, even steroid treatment in the acute phase did not improve visual prognosis, and long-term follow-up has reported epiretinal membrane formation and residual vision of 20/100².

The features of various imaging studies are shown below.

• OCT: Detects abnormalities at the inner and outer retina, RPE, and choroid at the micron level. Confirms macular holes and increased reflectivity at the base.
• FA: Observe linear streak-like findings and the time course from hypofluorescence to hyperfluorescent RPE window defect.
• Amsler chart: Useful for detecting metamorphopsia and central and paracentral scotomas.
• Humphrey visual field 10-2: Highly sensitive for detecting focal central scotomas.

Q What visual abnormalities occur with laser injury?

A

With acute exposure to a high-density laser, a flash is followed by reduced vision. Afterwards, a scotoma, metamorphopsia, and color vision abnormality matching the injured area may persist. Chronic pain or redness suggests a cause other than laser injury, so a differential diagnosis is needed.

3. Causes and risk factors

Exposure from medical lasers

Medical lasers are controlled by the operator with a foot pedal and delivered through optical fibers. They may be equipped with an aiming beam (targeting laser). Delivery devices include slit lamps, surgical microscopes, intraocular probes, and indirect ophthalmoscopes. Delivery systems are classified into four types: transpupillary, transscleral, intraocular, and surface irradiation.

Exposure from non-medical lasers

• Community settings (laser pointers, scanners, projectors): Output is usually low and temporary, but high-power handheld lasers available through online shopping have been reported to cause photoreceptor damage, macular holes, and retinal hemorrhage³⁴.
• Laboratory and industrial settings (cutting, welding): High intensity. Occurs when equipment operating guidelines are not followed.
• Military lasers: Used for security, tactical, and communication applications. Laser weapons that cause blindness are prohibited by the Geneva Conventions and the 1995 U.N. Protocol.
• Laser illumination of aircraft: Illegal in the U.S. The main problems are distraction and temporary visual disturbance, and direct eye injury is uncommon.

Laser injuries may be underreported in all settings.

Hazard risk and FDA class classification

Reflected light is the most common cause of accidental exposure. Reflections from surgical instruments, contact lenses, and the cornea are a concern. Reflected light at ultraviolet and infrared wavelengths is invisible, which should be kept in mind. Also, under anesthesia, the blink reflex is greatly reduced or absent.

Class I

Non-hazardous: No eye hazard under normal use.

Laser printers, CD/DVD players, etc.

Class II

Low hazard: Visible light only. Protected by the blink reflex.

Barcode scanners, etc.

Class III

Caution: Direct viewing poses a serious hazard.

Laser pointers, etc.

Class IV

High risk: serious danger to the eyes and skin. Reflected light is also dangerous.

Research and medical lasers. There is also a fire risk.

An NHZ (Nominal Hazard Zone) is an area where the laser beam spread is limited, so the laser remains concentrated and dangerous even at long distances. Class IV lasers and their reflected light also carry a risk of igniting drapes.

The smaller the spot size and the shorter the exposure time, the more likely complications are.

Q Can over-the-counter laser pointers also damage the eyes?

A

Laser pointers correspond to FDA Class III, and looking directly at them is seriously dangerous. With normal use and short exposure, the severity is low, but high-output models above 5 mW available online have been reported to cause permanent retinal damage. In particular, children with behavioral, learning, or mental health problems have a higher risk of self-injury, and a UK survey reported that 85% of patients were male and 80% were under 20 years old⁴⁵.

4. Diagnosis and testing

If laser injury is suspected, take a detailed history of the laser’s wavelength, output, and emission mode. A dilated fundus examination is the basic test.

The main examinations are listed below.

• OCT: Detects abnormalities in the inner and outer retina, RPE, and choroid at the micron level. Evaluates macular holes, elevation, and increased reflectivity at the base.
• Fundus fluorescein angiography (FA): observe linear, streak-like findings and the time-course changes from hypofluorescence to hyperfluorescent RPE window defects.
• Fundus autofluorescence (FAF): assesses RPE dysfunction.
• AOSLO (adaptive optics scanning laser ophthalmoscopy): used for high-resolution visualization and recording of tissue damage.
• OCT angiography: noninvasively evaluates the retinal and choroidal circulation. It can also be performed in patients with contrast allergy.
• Amsler chart: used to detect metamorphopsia and paracentral scotoma.
• Humphrey visual field 10-2: highly sensitive for detecting localized central scotoma.

5. Standard treatment methods

There is no standardized treatment protocol for laser-induced retinal injury.

• Steroids (intravenous or oral): Proposed to reduce harmful inflammatory cellular responses (such as macular edema). There are reports of improved vision with oral prednisolone 0.5 mg/kg/day combined with lutein⁶, but they have side effects, and their effectiveness for Nd:YAG laser injury is unclear².
• VEGF inhibitors: used to treat choroidal neovascularization associated with laser injury.
• Photodynamic therapy (PDT): may be used for choroidal neovascularization.
• Surgical treatment: usually not indicated. For unresolved complications (macular hole, epiretinal membrane), surgical removal of scar tissue or hemorrhage may be performed.

Because no effective treatment has been established, prevention—such as strict use of protective eyewear—is most important.

Prevention of complications when using medical lasers

Overcoagulation is the main cause of complications. In photocoagulation, the coagulation settings should be adjusted in the order of wavelength → spot diameter → exposure time → power.

• Spot diameter setting: As a rule, 50–200 μm near the fovea and within the vascular arcade, and 200–500 μm in the peripheral retina.
• Exposure time setting: Near the fovea, 0.02–0.1 seconds; in the periphery, 0.2 seconds as standard; for abnormal vessels, up to 0.5 seconds.
• Power setting: If an appropriate coagulation spot cannot be obtained, do not simply increase the power; consider surgical treatment.

The main complications of photocoagulation are as follows.

• Nerve fiber layer damage → visual field defects
• Retinal, subretinal, and sub-RPE hemorrhage; choroidal hemorrhage
• Epiretinal membrane formation → tractional retinal detachment
• Vitreous contraction → vitreous hemorrhage and worsening of tractional retinal detachment
• Choroidal circulatory insufficiency → macular edema, ciliochoroidal detachment, and exudative retinal detachment
• Choroidal neovascularization, cataract
• Accidental irradiation of the fovea and iris → iris atrophy
• Accommodation disorder with mydriasis

Corneal opacity, anterior chamber hemorrhage, iris atrophy, posterior synechiae of the iris, and cataract have also been reported as complications of photocoagulation.

Precautions in treatment

The smaller the irradiation diameter and the shorter the irradiation time, the narrower the treatment area and the higher the risk of complications. Blue wavelengths (450–480 nm) are strongly absorbed by macular pigment xanthophyll, so they are unsuitable for treatment of the macula. In laser treatment, the goal is always to achieve the desired effect with the minimum necessary energy.

Q Is there a treatment if the eye is injured by a laser?

A

There is no standardized treatment protocol. Steroids, VEGF inhibitors, PDT, and surgery may be considered depending on the situation, but an effective treatment is not always established. In particular, the effect of steroid therapy for Nd:YAG laser injury is unclear. Prevention is most important, and wearing protective eyewear is essential.

6. Pathophysiology and detailed pathogenesis

Laser light is highly directional, high-power, monochromatic coherent light, and in living tissue it acts through wavelength-specific mechanisms.

Destruction (Disruption)

Nd:YAG laser (pulsed wave) is a representative example. It mechanically cuts tissue by plasma formation. It is used for posterior capsulotomy and skin incision.

Photoablation

Excimer laser (ArF 193 nm) is a representative example. It emits pulses that break molecular bonds and destroys tissue without scarring. Used for LASIK corneal ablation.

Coagulation

Visible-light lasers (green, yellow, red) are typical examples. They are absorbed by melanin and hemoglobin, causing thermal coagulation. Used for retinal photocoagulation and iridotomy.

Photochemical reaction

PDT (photodynamic therapy) is a representative example. A photosensitizing substance absorbs light and produces reactive oxygen species that damage tissue. Used to treat choroidal neovascularization.

The absorption characteristics by wavelength in the visible light range are as follows.

• Melanin absorption: The longer the wavelength, the lower the absorption coefficient.
• Hemoglobin absorption: Highest at yellow wavelengths, decreases at red wavelengths.
• Tissue penetration: Higher at longer wavelengths. Yellow is widely used because it has high thermal conversion efficiency.
• Red wavelengths: Low hemoglobin absorption and excellent penetration. Suitable for lesions beneath hemorrhage and cases with opacity in the eye’s transparent media.
• Blue wavelengths (450–480 nm): Strongly absorbed by the macular pigment xanthophyll. Not suitable for macular treatment.
• Diode laser (810 nm): It has high tissue penetration and is used for transscleral cyclophotocoagulation and transscleral retinal photocoagulation. It also matches the peak absorption wavelength of ICG.
• Carbon dioxide laser (10.3 μm): It is absorbed by water and causes vaporization. It is used in pulsed mode for eyelid skin incisions.

A femtosecond laser (pulses on the order of 10^-15 seconds) uses tissue disruption from plasma generation. It is used in refractive surgery (LASIK flap creation) and cataract surgery (corneal incisions, anterior capsulotomy, nucleus fragmentation).

7. Latest research and future prospects (research-stage reports)

For patients: Please read carefully

The following content is currently at the research stage or in clinical trials, and is not standard treatment available at ordinary hospitals. It is reference information for specialists about future medical advances.

Pattern scan laser

This technique automatically delivers multiple coagulation spots in a pattern with a single exposure. The exposure time per spot is very short, about 0.02 seconds, so it limits damage to the inner retina and choroid and creates coagulation spots confined to the outer layer. It can greatly shorten treatment time.

Short-pulse photocoagulation

This treatment sets the exposure time to about one-tenth of the conventional time (0.01 to 0.02 seconds) and the output to about three times higher. It causes less damage to the inner retina and reduces pain during treatment. Long-term enlargement of the coagulation spots is also said to be less common.

Micropulse photocoagulation

This is a subthreshold treatment that selectively coagulates only the retinal pigment epithelium. It is expected to achieve treatment effects while minimizing damage to the retinal nerve fiber layer.

Navigation Laser

This is a fundus-camera-type delivery system with automatic irradiation and tracking functions. It can be overlaid with angiographic images to achieve highly accurate irradiation.

Use of OCT angiography

This is a noninvasive technique that can evaluate the retinal-choroidal circulation, and it can also be performed in patients with contrast-agent allergy. It is spreading as a new option for preoperative examination before laser photocoagulation.

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8. References

Footnotes

1. Bhavsar KV, Michel Z, Greenwald M, Cunningham ET Jr, Freund KB. Retinal injury from handheld lasers: a review. Surv Ophthalmol. 2021;66(2):231-260. PMID: 32628946. ↩

2. Park DH, Kim IT. A case of accidental macular injury by Nd:YAG laser and subsequent 6 year follow-up. Korean J Ophthalmol. 2009;23(3):207-209. PMID: 19794950. ↩ ↩²

3. Birtel J, Harmening WM, Krohne TU, Holz FG, Charbel Issa P, Herrmann P. Retinal Injury Following Laser Pointer Exposure. Dtsch Arztebl Int. 2017;114(49):831-837. PMID: 29271340. ↩

4. Linton E, Walkden A, Steeples LR, Bhargava A, Williams C, Bailey C, Quhill FM, Kelly SP. Retinal burns from laser pointers: a risk in children with behavioural problems. Eye (Lond). 2019;33(3):492-504. PMID: 30546136. ↩ ↩²

5. Farassat N, Boehringer D, Luebke J, Ness T, Agostini H, Reinhard T, Lagrèze WA, Reich M. Incidence and long-term outcome of laser pointer maculopathy in children. Int Ophthalmol. 2023;43(7):2397-2405. PMID: 36670265. ↩

6. Marinescu AI, Hall CM. Laser-Induced Maculopathy and Outcomes After Treatment With Corticosteroids and Lutein. Cureus. 2021;13(9):e18268. PMID: 34692258. ↩