Acid injury
Mechanism: Denatures and coagulates tissue proteins
Penetration: Coagulated proteins form a barrier, so damage often remains superficial
Exceptions: Hydrofluoric acid and strong acids penetrate deeply
Chemical Injury of the Conjunctiva and Cornea (Alkali and Acid)
Key points at a glance
Section titled “Key points at a glance”1. What Is Chemical Injury of the Conjunctiva and Cornea
Section titled “1. What Is Chemical Injury of the Conjunctiva and Cornea”Chemical injury of the conjunctiva and cornea (chemical burn) is a condition in which the cornea and conjunctiva are damaged by chemicals such as acids or alkalis entering the eye. Immediate treatment is required as an ophthalmic emergency.
The incidence of ocular chemical injury is estimated at 65–78 cases per 100,000 people1). The mean age is 48 years, but there is also a bimodal peak in those under 1 year of age1). Alkali injuries are more common than acid injuries1). Workplace injuries are the most frequent, and they are the second most common type of occupational eye injury after metallic foreign bodies1).
Causative substances include acids, alkalis, surfactants, organic solvents, and various others. Alkaline substances are found in cement, slaked lime, quicklime (desiccant), mold removers, hair dyes, and similar products. Acidic substances such as toilet bowl cleaners (hydrochloric acid) and battery fluid (sulfuric acid) can be the cause.
Q
Which is more severe: alkali injury or acid injury?
A
Alkali injuries are generally more severe. Alkalis are lipid-soluble and saponify cell membrane lipids, causing liquefactive necrosis, and penetrate deep into tissues within a short time without forming a barrier. Ammonia has high permeability and penetrates the cornea instantly, while sodium hydroxide reaches the anterior chamber within minutes. In contrast, weak acids often cause superficial protein denaturation that forms a barrier, limiting damage to the surface layers. However, strong acids and hydrofluoric acid have high deep-tissue penetrability and cause severe damage similar to alkalis.
2. Main Symptoms and Clinical Findings
Section titled “2. Main Symptoms and Clinical Findings”Subjective Symptoms
Section titled “Subjective Symptoms”- Eye pain: mild cases present with foreign body sensation, severe cases with intense pain
- Vision loss: due to corneal opacity and edema
- Tearing and blepharospasm: reflex reactions caused by chemical irritation
Clinical Findings
Section titled “Clinical Findings”Mild cases show conjunctival hyperemia and corneal epithelial defects. In severe cases, the entire cornea becomes degenerated and appears white and opaque. When conjunctival necrosis is present, the conjunctiva lacks hyperemia and appears white and edematous. This finding can appear mild at first glance, requiring caution.
Fluorescein staining is used to evaluate corneal epithelial defects. When the corneoconjunctival epithelium is extensively damaged, the entire area may stain uniformly and faintly, potentially masking the appearance of epithelial defects.
| Evaluation Item | Finding |
|---|---|
| Corneal Opacity | Clear to white opacity |
| Limbal ischemia | Extent of POV loss |
| Conjunctival necrosis | White edema with absence of hyperemia |
Severe chemical injuries can cause complications such as iritis, cataract, secondary glaucoma, symblepharon, and pseudopterygium.
3. Causes and Risk Factors
Section titled “3. Causes and Risk Factors”Mechanisms of Acid and Alkali Injury
Section titled “Mechanisms of Acid and Alkali Injury”Alkali Injury
Mechanism of action: Saponifies lipids in the cell membrane, causing liquefactive necrosis
Penetration: Does not form a barrier and penetrates deep tissues rapidly
Anterior chamber penetration: Can cause secondary iritis, cataract, and glaucoma
Chemical injuries due to assault often reach Roper-Hall Classification Grade IV, and ammonia-related assault has been reported to result in the most severe outcomes1).
4. Diagnosis and Examination Methods
Section titled “4. Diagnosis and Examination Methods”Initial Assessment
Section titled “Initial Assessment”Measure tear pH using pH test paper. If not neutral (pH 7–7.2), irrigate the eye immediately. Recheck pH 20 minutes after irrigation and repeat irrigation if necessary.
Severity Classification
Section titled “Severity Classification”Severity is assessed after irrigation. Corneal and conjunctival epithelial defects, limbal ischemia, and conjunctival necrosis are evaluated. Corneal opacity, anterior chamber inflammation, and intraocular pressure are also recorded. Initial classification is used to determine treatment intensity and timing of reconstruction.
| Classification | Main evaluation criteria | Clinical application |
|---|---|---|
| Kinoshita classification | Remaining POV and conjunctival necrosis | Estimates corneal epithelial regeneration capacity and prognosis |
| Roper-Hall classification | Corneal opacity and limbal ischemia | Used for severity comparison in international literature |
| Dua classification | Clock hours of limbal involvement and percentage of conjunctival involvement | Further stratifies the most severe cases in greater detail |
Kinoshita Classification
Section titled “Kinoshita Classification”Kinoshita Classification is based on the remaining POV. POV is the site where corneal epithelial stem cells reside. Fluorescein staining reveals epithelial defects. The extent of limbal whitening and conjunctival necrosis is also assessed. Grades 3a and 3b represent an important branching point. They are not distinguished by the presence or absence of total corneal epithelial defect. The determination is based on whether POV remains.
| Grade | Main findings | Interpretation |
|---|---|---|
| Grade 1 | Conjunctival hyperemia only. No corneal epithelial defect observed | Limbal stem cells are preserved. Prognosis is favorable |
| Grade 2 | Conjunctival hyperemia. Partial corneal epithelial defect observed | Epithelial defect is confined within the cornea. Re-epithelialization occurs easily with conservative treatment. |
| Grade 3a | Partial conjunctival necrosis. Total corneal epithelial defect. Partial preservation of POV. | Limbus function is partially preserved. Re-epithelialization is delayed but corneal epithelial regeneration can be expected. |
| Grade 3b | Partial conjunctival necrosis. Total corneal epithelial defect. Complete loss of POV. | Limbus function is lost. Watch for conjunctival invasion, persistent epithelial defect, and corneal melting. |
| Grade 4 | Limbal-conjunctival necrosis extending over half or more of the circumference. Total corneal epithelial defect. Complete loss of POV. | Most severe. High likelihood of severe LSCD, symblepharon, corneal perforation, and need for ocular surface reconstruction. |
In Grades 1 and 2, limbal stem cells are preserved. The prognosis is favorable. In Grade 3a, POV remains. Regeneration can be expected even with total corneal epithelial defect. In Grades 3b and 4, limbal epithelium is also lost. Regeneration of transparent corneal epithelium is difficult. Conjunctival epithelium with blood vessels covers the cornea. In the cicatricial stage, consider limbal transplantation or cultured epithelial cell sheet.
Roper-Hall classification and Dua classification
Section titled “Roper-Hall classification and Dua classification”| Grade | Roper-Hall Classification Findings | Prognosis |
|---|---|---|
| I | Corneal epithelial defect. No limbal ischemia | Good |
| II | Mild corneal opacity with visible iris details. Limbal ischemia <1/3 | Good |
| III | Total corneal epithelial defect and stromal opacity. Iris details obscured. Limbal ischemia 1/3 to 1/2 | Guarded |
| IV | Severe corneal opacity. Iris and pupil not visible. Limbal ischemia exceeds 1/2 | Poor |
The Dua classification evaluates limbal involvement by clock hours. Conjunctival involvement is assessed by area percentage.
| Dua Grade | Limbal involvement | Conjunctival involvement |
|---|---|---|
| I | None | None |
| II | 3 clock hours or less | 30% or less |
| III | More than 3 clock hours, up to 6 clock hours | More than 30%, up to 50% |
| IV | More than 6 clock hours, up to 9 clock hours | More than 50%, up to 75% |
| V | More than 9 clock hours, less than 12 clock hours | More than 75%, less than 100% |
| VI | 12 clock hours (full circumference) | 100% |
Grade IV in the Roper-Hall classification is subdivided into grades IV to VI. Suitable for stratifying severe cases1).
AS-OCTA is useful for evaluating limbal ischemia. AS-OCTA is anterior segment optical coherence tomography angiography. Clinical evaluation alone may underestimate limbal ischemia. AS-OCTA enables more objective assessment2).
Q
What are the differences between severity classifications for chemical injuries?
A
The Kinoshita classification focuses on the preservation of POV. It facilitates prediction of corneal epithelial regeneration capacity. The Roper-Hall classification assesses corneal opacity and limbal ischemia. The Dua classification quantifies limbal and conjunctival involvement. It is particularly suitable for prognosis evaluation in severe cases1).
5. Standard Treatment
Section titled “5. Standard Treatment”Initial Response: Eye Irrigation
Section titled “Initial Response: Eye Irrigation”Immediate eye irrigation regardless of the type of chemical is the most important step. The time to irrigation and the volume of irrigant determine the prognosis.
At the scene, irrigate the eye with running tap water for at least 10 minutes. At the ophthalmology clinic, after topical anesthesia, thoroughly irrigate the conjunctival sac with 500 to 2,000 mL of saline. For severe alkali injuries, irrigate for 30 minutes or longer. Since tap water is hypotonic and increases water influx into the corneal stroma, saline or lactated Ringer’s solution is preferable.
Conservative Treatment
Section titled “Conservative Treatment”Acute-Phase Pharmacotherapy
Anti-inflammation: Topical and systemic administration of steroids suppresses secondary tissue damage.
Infection prevention: topical instillation of new quinolone antibacterial agents
Mydriasis: atropine sulfate eye drops to prevent iritis and reduce pain
Epithelial regeneration promotion: sodium hyaluronate eye drops, therapeutic contact lens, autologous serum eye drops
Medications to be cautious with
NSAID eye drops: do not use as they delay epithelial healing
Preservative-containing eye drops: preservative-free preparations are preferred as preservatives inhibit regenerating epithelium
Secondary glaucoma: manage intraocular pressure with beta-blockers or acetazolamide
Surgical Treatment
Section titled “Surgical Treatment”Roper-Hall classification grade III or higher, or Kinoshita classification grade 3b or higher, is likely to require additional surgical treatment.
Acute-phase surgical treatment: necrotic tissue removal, amniotic membrane transplantation (to reduce inflammation and promote epithelialization), and tenonplasty are performed. Tenonplasty is a procedure in which the Tenon capsule is advanced to the limbus to restore vascular supply in eyes with limbal or scleral ischemia; it is useful as an eye-salvaging surgery in severe chemical injuries2). The rate of re-epithelialization after surgery is high, but symblepharon is the most common complication2).
Scar-phase surgical treatment: ocular surface reconstruction is performed by combining limbal stem cell transplantation (autologous or allogeneic), amniotic membrane transplantation, and penetrating keratoplasty. In severe bilateral cases, femtosecond laser-assisted large-diameter lamellar keratolimbal transplantation enables simultaneous transplantation of limbal stem cells and corneal stroma, and good visual improvement has been reported3).
Q
In what cases is Tenon capsule plasty indicated?
A
The main indication for Tenon capsule plasty is limbal ischemia and scleral ischemia associated with severe chemical injury2). By advancing and fixing the Tenon capsule from the orbital side to the limbus, vascular supply to the ischemic area is restored and conjunctival epithelial migration is promoted. It is performed in severe cases when established ischemia is observed. However, in the most severe cases presenting with 360-degree circumferential limbal and scleral ischemia, the Tenon capsule itself may also be ischemic, limiting its effectiveness2).
6. Pathophysiology and Detailed Mechanism
Section titled “6. Pathophysiology and Detailed Mechanism”The severity of chemical injury is determined by the type of agent, pH, concentration, duration of contact, and extent of injury.
Alkaline substances saponify cell membrane lipids via hydroxide ions, causing liquefactive necrosis of cells. Being lipophilic, they easily pass through the epithelial layer and penetrate deep into the stroma within a short time. Alkali that penetrates into the anterior chamber causes iritis, cataract, and glaucoma.
Acidic substances denature and coagulate tissue proteins, forming insoluble proteins. This coagulated protein acts as a barrier, so damage often remains superficial. However, hydrofluoric acid has high penetrability and causes severe destruction of the anterior segment of the eye.
The course after chemical injury is classified into the acute phase, early reparative phase, and late reparative phase. In the acute phase, damage to the corneal and conjunctival epithelium and inflammation occur. When corneal epithelial stem cells located in the limbal region are damaged, epithelial regeneration becomes impossible, and conjunctival epithelium invades the cornea (conjunctivalization). Limbal ischemia increases the risk of developing limbal stem cell deficiency (LSCD), leading to corneal scarring and permanent visual impairment2). Disruption of goblet cells, tear film instability due to mucin reduction, symblepharon, and conjunctival fornix shortening also worsen the ocular surface environment.
7. Latest Research and Future Outlook
Section titled “7. Latest Research and Future Outlook”AS-OCTA enables objective quantification of limbal ischemia in the acute phase of chemical injury, providing more accurate severity assessment and prognosis prediction than clinical evaluation. AS-OCTA results correlate well with final visual prognosis, and integration into existing classification systems is anticipated2).
Femtosecond laser-assisted large-diameter lamellar corneal limbal transplantation can simultaneously transplant corneal stroma and limbal stem cells as a single-stage surgery for bilateral severe chemical injury. Compared with conventional manual dissection, it enables uniform lamellar dissection, and good visual improvement has been reported3).
The application of femtosecond laser is limited to a small number of cases, and further research is needed to establish long-term efficacy3). Standardization of AS-OCTA and its incorporation into classification systems remain future challenges2).
8. References
Section titled “8. References”- Chemical injuries of the eye. Ann Eye Sci. 2023;8:13.
- Sharma S, Kate A, Donthineni PR, Basu S, Shanbhag SS. The role of Tenonplasty in the management of limbal and scleral ischemia due to acute ocular chemical burns. Indian J Ophthalmol. 2022;70:3203-12.
- Lin L, Xu Y, Ou Z, et al. Femtosecond laser-assisted large-diameter lamellar corneal-limbal keratoplasty in ocular chemical burns. Am J Ophthalmol Case Rep. 2025;37:102246.