| viral keratitis |
Herpes simplex virus (HSV) keratitis is the most common cause of blindness due to infectious keratitis in most developed countries. Viral keratitis, unlike bacterial and fungal keratitis, can become chronic and recurrent.
In addition to being painful and a threat to vision, it significantly affects quality of life even when the patient is not suffering from an active infection. Other less common viral keratitis is caused by the varicella zoster virus and cytomegalovirus.
Topical treatment for viral keratitis consists of antiviral medication and corticosteroids as an adjuvant. In the United States the most prescribed topical antiviral is trifluridine, although it is effective in treating HSV keratitis, it has low bioavailability and can cause ocular surface toxicity.
Its use is being replaced by new antivirals. Topical acyclovir is the most indicated in Europe against HSV keratitis, it has been shown to be as effective as trifluridine and with less toxicity. Ganciclovir is the newest medication with a greater antiviral spectrum and less toxicity, it is even effective for treating cytomegalovirus. In addition, resistance to the drug is less likely to develop.
Corticosteroids are sometimes used as an adjuvant to antiviral treatment.
Oral acyclovir has been shown to be effective against varicella zoster virus keratitis and could generally improve results in terms of visual acuity according to the HEDS I study.
Valanciclovir is a newer and well-tolerated antiviral. There is evidence that its ocular penetration is better. The treatment is 1 g, three times a day, while acyclovir is 400 g. 5 times a day, which makes it easier to comply with valanciclovir treatment.
Oral valganciclovir is the best treatment against cytomegalovirus stromal keratitis, but it has important side effects, such as aplastic anemia, and must be strictly monitored.
In practice, we generally use oral antivirals to avoid ocular toxicity that can complicate topical treatment and obscure the clinical picture. We reserve topical medication for adjuvant treatment when oral medication is not appropriate and for patients who are not good candidates for systemic treatment.
The HEDS II study investigated the long-term use of oral acyclovir as prophylaxis against herpes simplex virus recurrence, observing that recurrence was 45% lower in the group treated with acyclovir.
Herpes zoster ophthalmicus infection occurs by reactivation after varicella zoster infection. Vaccination of older adults is recommended to prevent herpes zoster ophthalmicus and other zoster infections. Long-term use of oral valanciclovir as prophylaxis is being investigated.
Collagen cross-linking is a treatment used to strengthen corneal tissue in cases of keratoconus. Such treatment could be used to treat infectious ulcers due to its antimicrobial effect and its potential to improve corneal resistance.
In a study 16 cases of bacterial keratitis were treated with collagen cross-linking. In 14 patients the ulcer resolved without other treatment, only 2 required topical treatment with antibiotics. The use of collagen cross-linking instead of antibiotics would serve to treat drug-resistant infections and avoid ocular surface toxicity that can complicate the treatment of bacterial ulcers.
There is no solid evidence for the use of collagen cross-linking to treat fungal keratitis, but it is used together with antifungal in some cases to try to obtain better results, given the poor prognosis of these cases. We must wait for new research to evaluate the use of this treatment for infectious keratitis.
| Conclusions: |
Despite having adequate antimicrobial treatments for most of the pathogens involved in infectious keratitis, results are often poor.
The strategy to reduce the morbidity associated with this pathology should try to avoid the ulcer, improve the condition as soon as possible and use precise diagnostic techniques to avoid the development of drug resistance.
Adjuvant treatments focus on modifying the immune response to the infection, trying to maintain the integrity of the cornea, avoiding its degradation and scarring that affects vision loss. Such treatments will have the greatest potential to improve clinical outcomes.
