Infectious keratitis is a global cause of visual impairment and blindness, generally affecting marginal populations. In the United States, infectious keratitis is usually associated with contact lens use, but in developing countries the most common cause is ocular trauma during rural work.
In the present study, the current literature on new methods of diagnosis and treatment of infectious keratitis was investigated.
An adequate diagnosis of the organism of origin is essential and although cultures continue to be the main diagnostic tool, there are new techniques such as confocal microscopy that are used to diagnose fungi and Acanthamoeba, Nocardia and larger organisms in general.
Viral keratitis is usually diagnosed in the office due to the characteristic dendritic appearance, although polymerase chain reaction is sometimes used to confirm the diagnosis with greater sensitivity. Optical coherence tomography has recently been used to determine the magnitude of corneal infiltrates or scar size and to monitor corneal thinning during treatment.
| Bacterial keratitis |
The best treatment remains topical antibiotics for bacterial keratitis; a recent study concluded that all commonly indicated topical antibiotics are equally effective. However, the results are usually not as good due to ulcers, scarring and perforation of the cornea.
Corneal culture is recommended for all corneal ulcers due to methicillin resistance. It is important to monitor the response to treatment and if the patient worsens, the antibiotic should be changed. If treatment was started with a broad-spectrum antibiotic, the toxicity of the drops may be the factor that is affecting healing and it is recommended to reduce treatment.
Treatment should be intended to stabilize the cornea and reduce the incidence of serious complications, such as corneal perforation requiring penetrating keratoplasty.
Adjuvant treatment to control the immune response associated with keratitis is with topical corticosteroids. Those who favor the use of corticosteroids claim that they improve results by reducing inflammation. Others consider that its use delays the healing of the epithelium and may even worsen the infection.
According to important studies, corticosteroids are effective in certain subgroups: patients with low baseline vision, central ulcers covering 4 mm of the pupil, and deep ulcers. The timing of steroid administration is also important, with best results when started 2 or 3 days after administering antibiotics.
After analyzing the subgroups, we recommend administering steroids as adjuvant treatment in positive cultures of non-Nocardia bacterial keratitis, starting 48 hours after administering topical antibiotics. This needs to be confirmed by a well-designed randomized controlled clinical trial.
Participant of the SCUT (Steroids for Corneal Ulcer Trial) study, a 64-year-old manual worker with an ulcer with a positive culture for Norcadia , treated with corticosteroids as an adjuvant. A) At the beginning, his visual acuity was 1.2 log MAR. B) At 3 weeks, visual acuity 1.46 logMAR. C) At 12 months, his visual acuity continued to decrease by 1.9 logMAR.
Participant of the SCUT (Steroids for Corneal Ulcer Trial) study, a 67-year-old manual worker with an ulcer with a positive culture for Pseudomona aeruginosa , treated with corticosteroids as an adjuvant. A) At the beginning, his visual acuity was 1.7 log MAR. B) At 3 weeks, visual acuity 0.62 logMAR. C) At 12 months, his visual acuity continued to improve by 0.24 logMAR.
| fungal keratitis |
Fungal ulcers have worse results than bacterial ulcers and the treatment since 1960 is topical natamycin. It represents a small percentage of infectious keratitis in areas with a temperate climate, however in tropical climates it can cause up to 50% of infectious ulcers.
The main risk factor in the United States is contact lens use. In addition to topical natamycin 5%, Voriconazole is being used for its excellent penetration.
Studies that have compared both treatments concluded that natamycin gives better results than voriconazole for the treatment of fungal keratitis, especially Fusarium keratitis.
Despite these results in the comparison of both treatments, there are reasons to believe that oral voriconazole may be effective as a treatment.
Firstly, if you miss a dose of topical medication, oral medication provides a more stable level of the drug at the site of infection. However, the MUTT II investigated the effect of adjuvant oral voriconazole versus placebo for fungal keratitis and found no difference in the results and there were more adverse effects in the group treated with oral voriconazole.
| 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.
