Comparison of acridine orange and Gram stains in bacterial keratitis

Diagnostic armamentarium of infectious keratitis: A comprehensive review

Infectious keratitis (IK) represents the leading cause of corneal blindness worldwide, particularly in developing countries. A good outcome of IK is contingent upon timely and accurate diagnosis followed by appropriate interventions. Currently, IK is primarily diagnosed on clinical grounds supplemented by microbiological investigations such as microscopic examination with stains, and culture and sensitivity testing. Although this is the most widely accepted practice adopted in most regions, such an approach is challenged by several factors, including indistinguishable clinical features shared among different causative organisms, polymicrobial infection, long diagnostic turnaround time, and variably low culture positivity rate. In this review, we aim to provide a comprehensive overview of the current diagnostic armamentarium of IK, encompassing conventional microbiological investigations, molecular diagnostics (including polymerase chain reaction and mass spectrometry), and imaging modalities (including anterior segment optical coherence tomography and in vivo confocal microscopy). We also highlight the potential roles of emerging technologies such as next-generation sequencing, artificial intelligence-assisted platforms. and tele-medicine in shaping the future diagnostic landscape of IK.

Correlation between surface water contamination with amoeba and the onset of symptoms and diagnosis of amoeba-like keratitis

AIM

A seasonal variation was noted in the incidence of amoeba-like keratitis in Iowa. The level of contamination of amoeba in surface water has been found previously to vary on a monthly basis for Tulsa, Oklahoma, a region with a similar climate. It was hypothesised that this seasonal variation in amoeba-like keratitis correlated with the concentration of amoeba in surface water.

METHODS

The monthly variation in the onset of symptoms was determined and date of diagnosis in 137 cases of amoeba-like keratitis, in Iowa, from January 1993 to the end of December 1996.

RESULTS

Over a 4 year period a significant variation was found, on a monthly basis, in the onset of symptoms as reported by the patient. There were two peak periods per year when the onset of symptoms was most frequent: June and November. This corresponded closely with the concentration of amoeba in the ground water reported for a similar region in the mid-west (Tulsa, Oklahoma). A yearly increase was found in the number of cases diagnosed from January 1993 to the end of December 1996.

CONCLUSIONS

This study supports the hypothesis that the concentration of amoeba in surface water may influence the rate of an amoeba-like keratitis infection.

Outbreak of keratitis presumed to be caused by Acanthamoeba

PURPOSE

A sharp increase of Acanthamoeba keratitis from two cases per year to 30 cases per year at our institution prompted this study to determine whether there was a change in the clinical characteristics, basic epidemiology, and outcome of this disease.

METHODS

We reviewed all cases of Acanthamoeba keratitis diagnosed at the University of Iowa Hospitals and Clinics from mid-1993 through 1994.

RESULTS

We screened 217 patients with keratitis by tandem scanning confocal microscopy and suspected Acanthamoeba in 51 patients. Diagnosis was confirmed by cytology in 43 patients (48 eyes). There were no positive cultures. Patients examined within four weeks of onset of symptoms were younger (mean age, 32.6 +/- 15.4 years) and wore contact lenses (11 of 18 patients), and infrequently herpes simplex keratitis (four of 18 patients) was diagnosed. Patients examined after four weeks were older (mean age, 54.0 +/- 19.5 years), infrequently wore contact lenses (six of 25 patients), and often had herpes simplex keratitis (12 of 25 patients).

CONCLUSIONS

Corneal examination with tandem scanning confocal microscopy was associated with a marked increase in the detection of Acanthamoeba, strongly suggesting that the disease is more prevalent than suspected. Acanthamoeba may account for many cases of clinically presumed herpes simplex keratitis, the leading cause of corneal blindness in the United States. Acanthamoeba should be considered in the differential diagnosis of any unexplained keratitis, even those of short duration.

Acridine orange staining in early diagnosis of mycotic keratitis

We have assessed the comparative sensitivities of acridine orange staining and 10% potassium hydroxide wet mount in the examination of corneal scrapings from one hundred and sixty-one clinically suspected cases of mycotic keratitis. The sensitivity of acridine orange was found to be 76% as compared to that of potassium hydroxide (65%). The predictive value for culture result was also seen to be higher. Although both the values were not statistically significant (P greater than 0.05), acridine orange staining was a rapid and simple technique with an added advantage of detecting inflammatory cells in corneal scrapings.

Microbial keratitis--the false negative

The investigation of presumed microbial keratitis includes microscopy and culture of corneal specimens obtained by scraping the infiltrated cornea. Routine microscopy fails to identify the infecting organism in about 15% of cases. We discuss the problems presented by 20 such eyes which required further investigation. We present a diagnostic algorithm aimed at reducing the delay in identifying the pathogen and increasing the rate of positive culture. This is important since unusual pathogens may require treatment with drugs other than the 'first line' broad spectrum combination of an aminoglycoside and a cephalosporin. The algorithm allows sequential restaining and reculturing of specimens for more thorough investigation. In addition to the use of special stains and culture conditions, it presents indications for further corneal scrapes and biopsies. Uncontrolled infection resulted in five perforations and penetrating keratoplasty was indicated in 11 cases. The visual outcome for these patients was poor with fewer than 30% achieving 6/12 acuity. The delay in diagnosis increases morbidity and this should be significantly reduced by adopting the algorithm we propose.

Bacterial keratitis after radial keratotomy

The authors identified nine patients with culture-proven keratitis after radial keratotomy (RK). Three patients became infected in the immediate post-operative period, and six patients had delayed-onset keratitis. Gram-negative rods were the predominant pathogens in late-onset keratitis (4 of 6 infections). Gram-positive cocci were implicated in all three postoperative infections. The inferior corneal quadrants were involved in seven of nine patients. Two episodes of late-onset keratitis were associated with contact lens wear. Five of these patients had transverse incisions or greater than eight radial cuts. All six patients regained visual acuity of 20/40 or better. Two additional cases of early-onset and six cases of late-onset keratitis with many features similar to these cases have been reported previously.