Dendritic corneal ulcer
It is a primary corneal ulcer caused by Herpes simplex virus type I. It is dendritic in shape (linear and branched).
It is caused by Herpes simplex virus (a large DNA virus) type I which is responsible for infection above the waste. The primary infection occurs in early childhood leading to follicular conjunctivitis (not dendritic ulcer) that heals usually without residual damage. The virus becomes dormant in the trigeminal ganglion waiting for drop of the immunity to cause recurrences. The recurrent attacks are dangerous for vision because central corneal opacities are common.
Precipitating factors of recurrence = Causes of drop immunity:-
- Exposure to cold, so that recurrences are more common in winter.
- Fevers as influenza, common cold, ....
- Local or systemic steroids.
- Immunosuppressive drugs.
Symptoms (it is usually recurrent):
- Marked drop of vision is common because the ulcer is commonly central.
- Pain is usually mild because of corneal hyposthesia.
- Ciliary injection (See before).
- Cornea: The ulcer runs in 2 stages; infiltration and ulceration:
* Early stages: there is punctate and stellate epithelial keratitis with positive rose bengal stain. The infected cells did not shed yet, so that the fluorescein stain is negative in this stage.
* Stage of ulceration: It is characterized by:
- The ulcer is superficial and dendritic shape (linear and branched). The branches end by knobs
- Loss of lustre and transparency in the area of ulcer.
- The ulcer is stained by fluorescein 2% due to shedding of the infected epithelial cells and its edges (infected epithelium) are stained by rose bengal.
- Corneal hyposthesia as diagnosed by weak blink response on touching the cornea by a sterile piece of cotton.
Complications of dendritic ulcer:-
1. Recurrences always in the same eye.
2. Iridocyclitis that may be severe.
3. Secondary glaucoma due to iridocyclitis.
4. Disciform keratitis due to invasion of stroma by viral antigen, not due to stromal infection. It may occur several months after healing of the ulcer.
- If peripheral and not affecting vision steroids are not indicated.
- If it is central local steroids under umbrella of zovirax should be given to avoid corneal scarring and vascularization.
5. Amoeboid (geographical) ulcer formation: Here most of the corneal epithelium is infected due to marked weakness of immunity or local steroids. The ulcer will be large and amoebic in shape.
6. Keratitis metaherpetica: There is shedding of the epithelium at the site of the previous ulcer due to improper healing, not due a recurrence. There will be positive fluorescein staining, but rose bengal staining is negative (why). It is treated by:
- Bandage or bandage contact lens.
- Vitamin A and local lubricant preparations as regepithel eye ointment.
7. Neurotrophic ulcer due to destruction of corneal sensation. It is deep and perforating.
8. Corneal scars: Nebula is the commonest type of scars because the ulcer is superficial. However, deeper scars can sometimes occur.
I. Treatment of uncomplicated ulcer:
1. Local antiviral drugs.
2. Atropine (See before).
3. Prophylactic antibiotics in small doses to prevent secondary infection.
The local antiviral drugs:
Mechanism of action:
They are local antimetabolites. They are structurally similar to the nitrogenous bases necessary for viral DNA synthesis. So that they interfere with DNA synthesis by competitive inhibition with these bases.
They are toxic to the corneal epithelium causing epithelial erosions and delayed healing of the ulcer especially on long term treatment.
Examples of antiviral drugs:
1. Trifluorothimidine (TFT) 1 % eye drops.
2. Adenine arabinoside (Ara A): 3 % eye ointment.
3. Acycloguanosine (Zovirax = Acyclovir): 3 % eye ointment. It has 2 advantages:
a. It penetrates into the substantia propria of the cornea.
b. It is absorbed only by the infected cells not by the healthy cells. So that its toxicity is minimal and accordingly it can be given for long time as in cases of disciform keratitis.
II. Treatment of resistant dendritic ulcer:-
Beside the above treatment the following is added:
1. Debrdiment by wiping the ulcer by a sterile cotton tipped applicator to remove the infected cells. It has 2 very helpful advantages:
- Protects the adjacent cells from infection.
- Removes the antigen which causes disciform keratitis.
a. Chemical cautery by 7% iodine in absolute alcohol (superficial effect).
b. Cryo at - 50 degrees for 5 seconds.
3. Therapeutic lamellar keratoplasty may be needed.
III. Treatment of complications:-
1. Treatment of secondary glaucoma (See before).
2. Treatment on disciform keratitis (See before).
3. Treatment of keratitis metaherpetica (See before).
4. Treatment of nebula (See before).