A 42-year-old woman with no past ocular history presents with worsening blurry vision, irritation, and redness in her right eye two weeks after sodium hydroxide drain cleaner splashed into her eye. At the time of the injury, she irrigated her eye with tap water for approximately 10 minutes. She did not seek medical care and has only been using artificial tears since.
Her visual acuity is 20/200 OD and 20/20 OS. On examination of the right eye, there is conjunctival injection, perilimbal ischemia, diffuse corneal haze, and a persistent corneal epithelial defect. The intraocular pressure is 28 mmHg. The pH of the ocular surface is now physiologic, the fornices have been cleared of any remaining material, and the B-scan ultrasonography shows that the retina is attached.
Which of the following best describes the primary mechanism of this patient’s injury?
A. Coagulation of tissue proteins, forming a barrier that limits deeper chemical penetration
B. Saponification of cell membrane lipids causing rapid penetration and liquefactive necrosis
C. Immune complex deposition within the corneal stroma, leading to complement-mediated inflammation
D. Thermal denaturation of superficial epithelial proteins
E. Hyperosmotic injury causing epithelial dehydration and cellular shrinkage
Correct answer: B. Saponification of cell membrane lipids causing rapid penetration and liquefactive necrosis
Sodium hydroxide found in drain cleaners, soaps and detergents is a strong alkali. Alkali-based agents rapidly penetrate ocular tissues because hydroxyl ions cause saponification of fatty acids within cell membranes, disrupting cellular barriers and producing liquefactive necrosis. This allows for continued penetration through the cornea and into the deeper parts of the ocular tissues. The patient's corneal haze, persistent epithelial defect, perilimbal ischemia and elevated intraocular pressure are characteristic of a severe alkali ocular injury. Limbal ischemia reflects damage to the limbal vasculature and stem-cell population, and elevated IOP may result from inflammation and direct injury to the trabecular meshwork.
(A) explains the mechanism of acidic ocular injuries from coagulative necrosis. Protein precipitation can create a barrier that limits deeper penetration, although severe acid injuries can still cause substantial ocular damage.
(C) is not the primary mechanism of chemical alkali injury since immune-mediated inflammation may contribute to later tissue damage rather than the inciting injury.
(D) describes a thermal burn where heat-induced protein denaturation occurs. However, the damage from thermal burns does not explain the progressive deep tissue damage beyond the epithelium caused by alkali burns.
(E) is not the primary mechanism of chemical alkali injury since hyperosmotic epithelial injury does not account for the progressive stromal, limbal, and trabecular damage seen after exposure to a strong alkali.
References:
Dua HS, Ting DSJ, Al Saadi A, Said DG. Chemical eye injury: pathophysiology, assessment and management. Eye (Lond). 2020 Nov;34(11):2001-2019. doi: 10.1038/s41433-020-1026-6. Epub 2020 Jun 22. PMID: 32572184; PMCID: PMC7784957.
https://eyewiki.org/Chemical_(Alkali_and_Acid)_Injury_of_the_Conjunctiva_and_Cornea