Photodynamic therapy to tackle fungal keratitis

A new paper by Dr Bhupesh Bagga and others from the Ramoji Foundation Centre of Ocular Infection and The Cornea Institute, L V Prasad Eye Institute discusses the success of photodynamic antimicrobial therapy, with Rose Bengal as an adjuvant, in tackling moderate fungal infection of the cornea, specifically by Fusarium sp. The prospective case series bolsters its clinical findings by correlating them with in vitro experiments.

Fungal keratitis is an infection of the cornea caused by a set of fungus genera, commonly Fusarium Sp. and Aspergillus Sp. Treatment for fungal keratitis ranges from prolonged use of antifungals to therapeutic penetrating keratoplasty. However, there are only a handful of antifungal drugs, and those have poor outcomes for patients with fungal keratitis. The last decade has seen the emergence of a new technique to tackle microbial keratitis: Photodynamic Antimicrobial Therapy (PDAT), with a photosensitizer as an adjuvant. This therapy reduces the dependence on antimicrobials, and when successful, reduces the need for a keratoplasty.  

PDAT combines green light optical irradiation with a photosensitizer like riboflavin to destroy microbial DNA and reduce infection in the cornea. PDAT also stimulates cross-links across the stromal collagen fibers of the cornea, girding it and stopping its dissolution due to the infection. A variety of studies have been looking into various combinations of photosensitizers, their concentrations, the fluence of UVA, the delivery protocol and so on in tackling microbial keratitis, especially in its refractory stage. PDAT with a synthetic dye like ‘Rose Bengal’ is reported to have better ‘in-vitro efficacy’ than riboflavin, and possibly, better outcomes.

A prospective case series report by Dr Bhupesh Bagga and others in the Current Eye Research journal is a new addition to the literature on this therapy. The report explores two new aspects of photodynamic therapy: it focuses on cases with moderate fungal keratitis, and it compares the cases to analogous isolates in a lab. Such a correlation is important because previous studies have reported discrepancies between lab and clinical outcomes of PDAT. 

The case series reports on the clinical outcomes of PDAT with Rose Bengal (PDAT-RB) to treat seven patients (five males and two females) with fungal keratitis. Three patients with Fusarium keratitis saw complete clinical resolution when treated with PDAT-RB, which also correlated with the therapy’s in vitro success. However, patients with other fungal infections, due to Aspergillus sp. and Acremonium sp., worsened and needed therapeutic keratoplasty. While the Aspergillus in vitro sample also did not respond to PDAT-RB, the Acremonium sp. sample saw growth inhibition (which does not correlate with the clinical findings).

'This article provides evidence of PDAT-RB’s efficacy against Fusarium keratitis and baseline information for further research to promote this as an adjuvant and alternate treatment of Fungal keratitis,' says Dr Bhupesh Bagga, Head of the Ramoji Foundation Centre for Ocular Infections, L V Prasad Eye Institute. 

Bagga B, Sharma S, Ahirwar LK, Sheba E, Vaddavalli PK, Mishra DK. Clinical Outcomes of Rose Bengal Mediated Photodynamic Antimicrobial Therapy on Fungal Keratitis with Their Microbiological and Pathological Correlation. Curr Eye Res. 2022 Apr 14:1-8. doi: 10.1080/02713683.2022.2058019. Epub ahead of print. PMID: 35385332.  

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