Cornea microscopically in order from outside to inside
1. Epithelium,
2. Bowman's layer,
3. Stroma,
4. Descemet's membrane
5. It consists of the endothelial layer.
The perfect arrangement of the epithelial layer and its avascularity, the arrangement of the lamellar system formed by the collagen fibers in the stroma and the apparent effect of the endothelium on the fluid dynamics, keeping the intrastromal water level constant (76%) ensures the transparency of the cornea. The endothelium is the layer that has the most effective role in ensuring the transparency of the cornea.
0 When damaged, epithelium regenerates, while Bowman's layer and endothelium do not.
0 The limbus is 1-2 mm thick and contains the trabecular meshwork.
Infection and Inflammation of the Cornea (Keratitis)
0 Two important features of the corneal epithelium are its barrier function against microorganisms and its ability to regenerate. However, diphtheria bacillus, Neisseria, Listeria and Haemophilus species can also penetrate through intact epithelium.
0 Injury, infection and allergy involving the deep layers of the cornea stimulate inflammatory reactions and cause structural changes (ulcer, necrosis, neovascularization) and permanent visual disturbances with corneal opacities that occur as a result.
There are three types of corneal opacities: nebulae, nephelion, and leukoma.
• The first two do not affect vision much. If the leukoma covers all layers of the cornea and closes the pupil area, vision is severely reduced. In this case, corneal transplantation (keratoplasty) may be required.
Superficial Punctate Keratitis
• There are small, pin-tip dye-holding defects in the corneal epithelium. Since it is a nonspecific picture, its etiology is diverse.
Dry eye syndrome, blepharitis
Hypersensitivity reactions to Staphylococci
Adenovirus, chlamydia, herpes simplex infections
• Treatment is directed to the cause. Artificial tears and bandages, therapeutic contact lens applications provide symptomatic relief.
Bacterial Keratitis
• Bacteria other than Neisseria, Corynebacterium, Listeria and Haemophilus that penetrate the intact corneal epithelium; however, they can cause keratitis when the corneal epithelial integrity is impaired.
• Risk factors: Use of contact lenses (especially Pseudomonas) Trauma (refractive surgery, etc.)
Ocular surface damage (dry eye, etc.)
Other (immunosuppression, diabetes, vitamin A deficiency, etc.)
• The most common agents in etiology are staphylococci (S. aureus, S. epidermidis), streptococci (S. pneumoniae and others), Pseudomonas aeruginosa and enterobacter (Proteus, Enterobacter, Serratia).
• Clinical symptoms include pain, photophobia, blurred vision, mucopurulent or purulent discharge.
• Clinical findings; chemosis (conjunctival edema), conjunctival deep ciliary hyperemia, corneal stromal edema, corneal ulcers and perforations, anterior uveitis, hypopyon, posterior synechia, endophthalmitis etc.
• Topical fortified (fortified) vancomycin+ceftazidime combination and systemic quinolone derivatives are used in the treatment.
Viral Keratitis
Herpes slmplex keratitis (dendritic keratoconjunctivitis)
• HSV type I is responsible.
• There is blepharoconjunctivitis, as well as preauricular lymphadenopathy.
• Patients have symptoms such as foreign body sensation, photophobia.
• Corneal sensitivity is decreased. Neurotrophic keratitis and ulceration may develop due to corneal anesthesia. It is characterized by painless corneal ulcers.
• It has 3 forms: epithelial, disciform (endothelitis) and stromal (interstitial).
Varicella zoster keratitis
• It is characterized by dendritic lesions similar to herpes simplex dendrites.
• Symptomatology and clinical types are similar to herpetic keratitis.
Fungal keratitis (keratomycosis)
• Corticosteroid use increases the risk.
• The most common agents are Candida and filamentous fungi (Aspergillus, Fusarium)
• Candida keratitis usually occurs in association with pre-existing chronic corneal disease or in immunosuppressed and frail patients.
• Filamentous fungal keratitis commonly occurs in agricultural areas as a result of ocular trauma caused by an organic substance (tree branch, etc.).
Protozoal keratitis (acanthamoeba)
• Annular corneal abscess It is the most common protozoan keratitis in the community.
• It can live freely in soil, fresh and salt waters.
• It creates ring (ring-shaped) corneal abscesses and ulcerations.
• The most common mode of transmission in developed countries is the use of contact lenses contaminated with tap water.
Neurotrophic keratitis
• Occurs due to corneal anesthesia (loss of innervation of the 5th nerve).
• The disappearance of protective sensory stimuli; It causes intracellular edema, epithelial defects and persistent ulcerations in the cornea.
• Herpes simplex, Herpes zoster oticus, n. surgical cutting of the trigeminus (after sinus surgeries), radiation treatments, etc. found after.
Lagophthalmic (exposure) keratitis
It occurs especially in 7th cranial nerve palsies. Dry eye and secondary corneal infections develop as a result of keeping the eye open.
Keratomalacia
• It occurs due to vitamin A deficiency.
• There is dryness and necrosis of the cornea and conjunctiva.
• Foamy "Bitot" spots appear on the conjunctiva.
