Ophthalmology – Radiation Keratopathy

Basics

Description

Radiation keratopathy refers to corneal injury caused by electromagnetic radiation and encompasses two clinically different entities:

• Ultraviolet photokeratitis — an acute epithelial injury after excessive UV exposure
• Ionizing radiation keratopathy — acute or delayed corneal and ocular-surface damage following therapeutic radiation such as external-beam radiotherapy or ocular brachytherapy

Radiation injury may affect:

• Epithelium
• Limbal stem cells
• Stroma
• Corneal nerves
• Endothelium
• Conjunctiva
• Lacrimal and meibomian glands

The result can range from transient punctate epithelial keratitis to:

• Persistent epithelial defects
• Neurotrophic keratopathy
• Limbal stem-cell deficiency
• Stromal ulceration
• Corneal vascularization
• Scarring
• Thinning
• Perforation

Key Clinical Distinction

UV Photokeratitis

Usually:

• Acute
• Bilateral
• Very painful
• Delayed several hours after exposure
• Self-limited

Typical examples:

• Welding arc injury
• Snow blindness
• Tanning-bed exposure
• High-altitude reflected sunlight

Therapeutic Radiation Keratopathy

Usually:

• Delayed
• Chronic or progressive
• Related to radiation dose and field
• Frequently accompanied by dry eye, neurotrophic disease, or limbal damage

The long-term prognosis is therefore very different between the two.

Radiation Types

Ultraviolet Radiation

The cornea absorbs much of the shorter-wavelength UV reaching the eye, particularly:

• UV-B
• UV-C

Excess exposure causes epithelial phototoxicity.

Ionizing Radiation

Therapeutic radiation includes:

• External-beam radiotherapy
• Intensity-modulated radiotherapy
• Proton-beam therapy
• Stereotactic techniques
• Plaque brachytherapy

Corneal injury depends on:

• Total dose
• Dose per fraction
• Volume irradiated
• Location of treatment field
• Degree of ocular shielding
• Preexisting ocular-surface disease

Epidemiology

Radiation keratopathy is uncommon overall.

Photokeratitis is seen particularly in:

• Welders
• Outdoor workers
• High-altitude exposure
• Snow or water reflection
• Unprotected artificial UV exposure

Chronic radiation keratopathy is mainly encountered after treatment for:

• Orbital tumors
• Eyelid tumors
• Sinonasal tumors
• Head and neck malignancies
• Intracranial tumors near the orbit
• Intraocular tumors

Risk Factors

Important risk factors include:

• High cumulative corneal or limbal radiation dose
• Large fraction size
• Direct exposure of anterior segment
• Inadequate shielding
• Preexisting dry eye
• Reduced corneal sensation
• Exposure keratopathy
• Prior ocular surgery
• Diabetes
• Poor eyelid closure
• Cranial nerve V dysfunction
• Cranial nerve VII dysfunction
• Previous ocular surface disease

UV-Specific Risk Factors

These include:

• Welding without protective shield
• High-altitude sunlight
• Snow reflection
• Water reflection
• Tanning lamps
• Germicidal UV lamps
• Arc lamps

Prevention

UV Injury

Preventive measures include:

• UV-blocking protective eyewear
• Welding masks with appropriate filters
• Wraparound sunglasses
• Snow goggles
• Avoiding direct viewing of UV sources

Radiation Therapy Planning

Prevention of chronic radiation keratopathy should begin before treatment.

Important strategies include:

• Corneal shielding where technically feasible
• Lacrimal-gland sparing
• Limbal sparing
• Modern conformal treatment planning
• Reduction of unnecessary anterior-segment radiation dose
• Multidisciplinary planning with radiation oncology

Pathophysiology

Ionizing radiation produces:

DNA damage + reactive oxygen species + impaired cellular replication

Rapidly dividing tissues are particularly vulnerable.

The corneal epithelium depends on continuous renewal from:

Limbal epithelial stem cells

Therefore significant radiation injury to the limbus can lead to:

Limbal stem-cell deficiency

and chronic failure of epithelial regeneration.

Epithelial Injury

Radiation may cause:

• Reduced epithelial mitosis
• Abnormal epithelial adhesion
• Increased apoptosis
• Delayed wound healing

Clinical consequences include:

• Superficial punctate keratitis
• Recurrent epithelial breakdown
• Persistent epithelial defect

Limbal Stem-Cell Injury

Damage to limbal stem cells can cause:

• Persistent epithelial defects
• Conjunctivalization of cornea
• Superficial neovascularization
• Recurrent epithelial breakdown
• Chronic inflammation

Severe cases progress to:

Limbal stem-cell deficiency (LSCD).

Stromal Injury

Radiation can damage:

• Keratocytes
• Stromal collagen
• Limbal vasculature

leading to:

• Stromal haze
• Scarring
• Sterile ulceration
• Stromal thinning
• Rare perforation

Endothelial Injury

At sufficiently high doses, the corneal endothelium may be affected.

Consequences include:

• Endothelial cell loss
• Stromal edema
• Epithelial edema
• Chronic corneal decompensation

Ocular Surface Injury

Radiation may also damage:

• Lacrimal gland
• Meibomian glands
• Conjunctival goblet cells

This produces severe:

Aqueous-deficient and evaporative dry eye

which substantially worsens corneal healing.

Neurotrophic Keratopathy

Damage to:

• Trigeminal sensory innervation
• Corneal nerves

may reduce corneal sensation.

The result can be:

Neurotrophic keratopathy

with surprisingly little pain despite severe epithelial disease.

Exposure Keratopathy

Radiation involving:

• Facial nerve
• Eyelids
• Orbital tissues

may cause poor lid closure and exposure.

Thus many patients develop combined:

Radiation + neurotrophic + exposure keratopathy

rather than isolated direct corneal toxicity.

UV Photokeratitis Pathophysiology

Excess UV radiation damages corneal epithelial DNA and generates reactive oxygen species.

Because epithelial injury develops after a latent period, symptoms often begin:

6–12 hours after exposure

rather than immediately.

Clinical Presentation – Photokeratitis

Typical symptoms are:

• Severe bilateral eye pain
• Foreign-body sensation
• Photophobia
• Tearing
• Blepharospasm
• Redness
• Blurred vision

The delayed onset after welding is classic.

Slit-Lamp Findings – Photokeratitis

Typical findings include:

• Diffuse punctate epithelial erosions
• Confluent fluorescein staining
• Conjunctival injection
• Mild lid edema
• Occasionally mild anterior chamber inflammation

The pattern is usually:

Bilateral and symmetric

if both eyes were exposed.

Clinical Presentation – Therapeutic Radiation Keratopathy

Symptoms may begin:

• During treatment
• Weeks afterward
• Months or years later

Possible symptoms include:

• Dryness
• Foreign-body sensation
• Burning
• Photophobia
• Redness
• Fluctuating vision
• Persistent blurred vision
• Recurrent epithelial pain

Severe neurotrophic disease may produce surprisingly little pain.

Examination

Assess:

• Visual acuity
• Eyelid closure
• Blink
• Tear film
• Corneal sensation
• Fluorescein staining
• Corneal thickness
• Corneal vascularization
• Limbal integrity
• Anterior chamber inflammation

Corneal Sensation

Testing corneal sensation is particularly important when there is:

• Persistent epithelial defect
• Previous orbital radiation
• Trigeminal dysfunction

Reduced sensation suggests:

Neurotrophic keratopathy

and significantly changes management.

Early Corneal Findings

Early radiation injury may include:

• Superficial punctate keratitis
• Epithelial irregularity
• Filamentary keratitis
• Mild stromal edema

Persistent Epithelial Defect

A nonhealing epithelial defect is concerning for:

• Neurotrophic keratopathy
• Severe dry eye
• Limbal stem-cell deficiency
• Infection
• Exposure

It requires more aggressive treatment than uncomplicated photokeratitis.

Advanced Findings

Severe chronic radiation injury may produce:

• Corneal neovascularization
• Conjunctivalization
• Stromal scarring
• Lipid deposition
• Stromal thinning
• Keratinization
• Corneal ulceration
• Perforation

Limbal Stem-Cell Deficiency

Clinical findings include:

• Loss of normal limbal palisades
• Persistent epithelial irregularity
• Whorl-like epitheliopathy
• Conjunctival epithelial migration over cornea
• Superficial vascularization
• Recurrent epithelial defects

Diagnostic Testing

Radiation keratopathy is primarily a:

Clinical diagnosis

based on:

• Exposure history
• Timing
• Characteristic ocular surface findings

History

Important questions include:

• Type of radiation exposure
• Total radiation dose
• Fractionation schedule
• Treatment field
• Use of ocular shielding
• Timing of symptoms
• Previous ocular surface disease
• Prior surgery
• Cranial nerve dysfunction

For UV injury, ask specifically about:

• Welding
• Snow
• High altitude
• Tanning bed
• UV lamp exposure

Fluorescein Staining

Fluorescein is essential for detecting:

• Punctate epithelial erosions
• Epithelial defects
• Corneal ulceration

The size of any persistent defect should be documented serially.

Anterior Segment Photography

Photography is useful for documenting:

• Epithelial defect size
• Vascularization
• Scarring
• Thinning
• Limbal disease

Pachymetry

Pachymetry can be useful when monitoring:

• Corneal edema
• Progressive stromal thinning

Serial measurements may help identify impending melt.

Anterior Segment OCT

AS-OCT may help quantify:

• Stromal thinning
• Epithelial defects
• Corneal scarring
• Descemet/endothelial changes

especially when structural progression is suspected.

Corneal Cultures

Culture is not required for uncomplicated radiation injury.

Perform corneal scraping/culture when there is concern for:

Infectious keratitis

such as:

• Stromal infiltrate
• Suppuration
• Rapid progression
• Significant anterior chamber reaction
• Contact lens-associated epithelial defect

Differential Diagnosis

Important differentials include:

• Exposure keratopathy
• Neurotrophic keratopathy
• Severe dry eye disease
• Toxic keratopathy
• Infectious keratitis
• Herpes simplex keratitis
• Recurrent corneal erosion
• Limbal stem-cell deficiency from another cause
• Chemical injury
• Contact lens overwear
• Graft-versus-host disease

Photokeratitis vs Infectious Keratitis

Photokeratitis

Usually:

• Bilateral
• Diffuse punctate epithelial disease
• Clear exposure history
• No focal stromal infiltrate
• Rapid spontaneous recovery

Infectious Keratitis

More often:

• Unilateral
• Focal epithelial defect
• Stromal infiltrate
• Purulent discharge or anterior chamber reaction

Infection must be excluded before assuming severe focal disease is purely radiation-related.

Treatment – UV Photokeratitis

Most uncomplicated cases heal rapidly.

Management includes:

• Preservative-free artificial tears
• Lubricating ointment
• Oral analgesics
• Cold compresses
• Cycloplegic in selected patients with severe photophobia

Topical Antibiotics in Photokeratitis

Routine prophylactic antibiotics are not mandatory for every mild photokeratitis case.

An antibiotic ointment may be considered when there is:

• Large epithelial defect
• Significant epithelial breakdown
• Concern for secondary infection

Topical Anesthetic Warning

Topical anesthetic drops may be useful during examination but should generally:

Not be prescribed for unsupervised repeated home use

because prolonged use can cause:

• Severe epithelial toxicity
• Delayed healing
• Corneal ulceration
• Melt

Eye Patching

Routine pressure patching is:

Not generally recommended

for uncomplicated photokeratitis or corneal epithelial defects.

It may:

• Impair monitoring
• Increase microbial risk
• Provide little benefit

Bandage Contact Lens

A bandage contact lens may be considered in selected cases with:

• Significant epithelial defect
• Severe pain
• Recurrent epithelial breakdown

but requires:

• Infection surveillance
• Appropriate antimicrobial coverage in higher-risk cases
• Close follow-up

Prognosis of Photokeratitis

The prognosis is usually:

Excellent

Symptoms often improve markedly within:

24–48 hours

and epithelial healing is usually complete within approximately:

24–72 hours

if exposure does not recur.

Treatment – Chronic Radiation Keratopathy

Management depends on the dominant mechanism:

• Tear deficiency
• Exposure
• Neurotrophic disease
• LSCD
• Stromal ulceration
• Endothelial dysfunction

Lubrication

The foundation of therapy is:

Frequent preservative-free lubrication

using:

• Artificial tears
• Gel
• Ointment

Avoid chronic exposure to:

• Preservatives
• Toxic topical medications

when possible.

Tear Conservation

Consider:

• Punctal plugs
• Punctal cautery

when significant aqueous-deficient dry eye contributes and inflammation is controlled.

Meibomian Gland Dysfunction

If present, treat with:

• Warm compresses
• Lid hygiene
• Appropriate anti-inflammatory therapy

Radiation-related meibomian damage may be chronic and difficult to reverse.

Autologous Serum Tears

For persistent epithelial disease or severe ocular surface failure, consider:

Autologous serum tears

or other blood-derived tear products.

These provide:

• Growth factors
• Epitheliotrophic proteins
• Improved epithelial support

Neurotrophic Keratopathy Treatment

Management may include:

• Preservative-free lubrication
• Serum tears
• Bandage contact lens
• Scleral lens
• Amniotic membrane
• Temporary tarsorrhaphy

In appropriate cases:

Cenegermin

may be considered for neurotrophic keratitis.

Cenegermin

Cenegermin is recombinant human nerve growth factor.

It may improve healing in:

• Persistent neurotrophic epithelial defects
• Neurotrophic corneal ulcers

Its usefulness depends on whether the dominant mechanism is genuinely neurotrophic.

Scleral Lenses

A scleral lens may provide:

• Continuous fluid reservoir
• Mechanical protection
• Improved vision

in selected patients with:

• Severe dry eye
• Neurotrophic keratopathy
• Irregular corneal surface

It requires specialist fitting and infection surveillance.

Amniotic Membrane

Amniotic membrane transplantation can promote epithelial healing and reduce inflammation.

It is particularly useful for:

• Persistent epithelial defects
• Sterile ulceration
• Neurotrophic keratopathy
• Severe ocular surface inflammation

Tarsorrhaphy

Temporary or permanent tarsorrhaphy is highly effective when epithelial failure is driven by:

• Exposure
• Neurotrophic disease
• Severe tear deficiency

It reduces:

• Evaporation
• Mechanical trauma

and promotes healing.

Conjunctival Flap

A conjunctival flap may be considered in:

• Refractory nonhealing ulcer
• Severe neurotrophic cornea
• Impending perforation

particularly when visual rehabilitation is not the immediate priority.

Corneal Thinning

If stromal thinning develops, management may include:

• Intensive lubrication
• Discontinuation of toxic medications
• Antibiotics if infection suspected
• Doxycycline in selected sterile melts
• Vitamin C in selected cases
• Amniotic membrane

The exact approach depends on etiology.

Corneal Perforation

Urgent options include:

• Tissue adhesive
• Bandage contact lens
• Amniotic membrane
• Tectonic patch graft
• Lamellar or penetrating keratoplasty

depending on:

• Size
• Location
• Cause
• Ocular surface status

Limbal Stem-Cell Deficiency

Management may include:

• Aggressive ocular surface optimization
• Preservative avoidance
• Serum tears
• Scleral lenses
• Amniotic membrane

Definitive reconstruction may involve:

Limbal stem-cell transplantation

in selected severe cases.

Limbal Stem-Cell Transplantation

Options depend on laterality and available donor tissue and may include:

• Autologous limbal transplantation
• Living-related allogeneic tissue
• Cultivated epithelial transplantation

Allogeneic techniques require:

• Systemic immunosuppression

and should be performed in specialized ocular-surface centers.

Corneal Transplantation

Keratoplasty may be required for:

• Dense central scar
• Severe stromal thinning
• Perforation
• Endothelial decompensation

However:

Corneal transplantation performs poorly if severe dry eye, neurotrophic disease, exposure, or LSCD has not first been controlled.

Ocular surface rehabilitation comes first whenever possible.

Topical Corticosteroids

Topical corticosteroids may be useful for:

• Significant sterile inflammation
• Post-radiation inflammatory ocular surface disease

but should be used cautiously.

Do not use corticosteroid monotherapy when:

• Infection is possible
• Significant epithelial ulceration has not been adequately assessed

Monitor for:

• IOP elevation
• Delayed epithelial healing
• Infection

Referral

Urgent corneal specialist evaluation is warranted for:

• Persistent epithelial defect
• Corneal infiltrate
• Progressive stromal thinning
• Corneal perforation
• Significant LSCD
• Severe neurotrophic disease
• Progressive vascularization or scarring

Follow-Up

Acute UV Injury

Reassessment is appropriate within approximately:

24–48 hours

if:

• Symptoms are severe
• Defect is extensive
• Diagnosis is uncertain
• Healing is incomplete

Straightforward cases often resolve rapidly.

Chronic Radiation Injury

Patients who have received substantial periocular radiation require long-term surveillance for:

• Dry eye
• Neurotrophic keratopathy
• Persistent epithelial defects
• LSCD
• Corneal edema
• Stromal thinning
• Cataract
• Radiation retinopathy
• Radiation optic neuropathy

Late complications may appear:

Months to years after treatment.

Prognosis

Prognosis depends strongly on the type of radiation exposure.

Photokeratitis

Usually:

Excellent

with complete epithelial recovery.

Chronic Therapeutic Radiation Keratopathy

Variable and influenced by:

• Radiation dose
• Limbal involvement
• Lacrimal gland damage
• Corneal innervation
• Eyelid function
• Development of infection
• Presence of LSCD

Severe chronic disease may be:

Progressive and vision-threatening.

Complications

Potential complications include:

• Persistent epithelial defect
• Neurotrophic keratopathy
• Limbal stem-cell deficiency
• Severe dry eye
• Filamentary keratitis
• Corneal ulceration
• Infectious keratitis
• Stromal thinning
• Corneal neovascularization
• Scarring
• Lipid keratopathy
• Corneal perforation
• Endothelial decompensation
• Secondary visual loss

Ophthalmology Pearls

• Radiation keratopathy includes both acute UV photokeratitis and chronic corneal injury from therapeutic ionizing radiation; these are clinically distinct entities.
• Photokeratitis classically causes severe bilateral pain, photophobia, tearing, and diffuse punctate epithelial erosions beginning about 6–12 hours after UV exposure.
• Common UV causes include welding arcs, snow reflection, tanning beds, and high-altitude sunlight.
• Uncomplicated photokeratitis usually heals within 24–72 hours with lubrication and analgesia.
• Do not prescribe topical anesthetics for repeated unsupervised home use because of potentially severe corneal toxicity.
• Routine pressure patching is not recommended for uncomplicated photokeratitis.
• Chronic therapeutic radiation injury can damage not only the cornea but also the limbus, corneal nerves, lacrimal gland, meibomian glands, and conjunctival goblet cells.
• Persistent epithelial defects after periocular radiation should prompt evaluation for neurotrophic keratopathy, exposure, severe dry eye, infection, and limbal stem-cell deficiency.
• Check corneal sensation in any unexplained nonhealing radiation-associated epithelial defect.
• Frequent preservative-free lubrication is the foundation of chronic treatment.
• Severe neurotrophic disease may require serum tears, amniotic membrane, scleral lens, tarsorrhaphy, or cenegermin.
• Radiation-induced LSCD may cause conjunctivalization, superficial vascularization, recurrent epithelial breakdown, and chronic corneal opacity.
• Corneal transplantation should generally be delayed until the underlying ocular surface, exposure, neurotrophic disease, and LSCD are controlled.
• Radiation planning with corneal, limbal, and lacrimal-gland sparing whenever feasible is the most effective preventive strategy.
• Acute UV injury usually has an excellent prognosis, whereas severe therapeutic radiation keratopathy can produce lifelong ocular-surface disease and permanent visual loss.