Pneumococcal keratitis at the flap interface after laser in situ keratomileusis

The cholesterol-dependent cytolysin pneumolysin from Streptococcus pneumoniae binds to lipid raft microdomains in human corneal epithelial cells

Streptococcus pneumoniae (pneumococcus) is an opportunistic bacterial pathogen responsible for causing several human diseases including pneumonia, meningitis, and otitis media. Pneumococcus is also a major cause of human ocular infections and is commonly isolated in cases of bacterial keratitis, an infection of the cornea. The ocular pathology that occurs during pneumococcal keratitis is partly due to the actions of pneumolysin (Ply), a cholesterol-dependent cytolysin produced by pneumococcus. The lytic mechanism of Ply is a three step process beginning with surface binding to cholesterol. Multiple Ply monomers then oligomerize to form a prepore. The prepore then undergoes a conformational change that creates a large pore in the host cell membrane, resulting in cell lysis. We engineered a collection of single amino acid substitution mutants at residues (A370, A406, W433, and L460) that are crucial to the progression of the lytic mechanism and determined the effects that these mutations had on lytic function. Both Ply^WT and the mutant Ply molecules (Ply^A370G, Ply^A370E, Ply^A406G, Ply^A406E, Ply^W433G, Ply^W433E, Ply^W433F, Ply^L460G, and Ply^L460E) were able to bind to the surface of human corneal epithelial cells (HCECs) with similar efficiency. Additionally, Ply^WT localized to cholesterol-rich microdomains on the HCEC surface, however, only one mutant (Ply^A370G) was able to duplicate this behavior. Four of the 9 mutant Ply molecules (Ply^A370E, Ply^W433G, Ply^W433E, and Ply^L460E) were deficient in oligomer formation. Lastly, all of the mutant Ply molecules, except Ply^A370G, exhibited significantly impaired lytic activity on HCECs. The other 8 mutants all experienced a reduction in lytic activity, but 4 of the 8 retained the ability to oligomerize. A thorough understanding of the molecular interactions that occur between Ply and the target cell, could lead to targeted treatments aimed to reduce the pathology observed during pneumococcal keratitis.

Two Cases of Pneumococcal Keratitis Following Myopic LASIK

PURPOSE

To report two cases of pneumococcal keratitis after LASIK.

METHODS

Retrospective interventional small case series of two patients who underwent bilateral LASIK for myopia and developed pneumococcal keratitis after surgery. This complication was encountered 2 days after surgery in one eye in both cases. The corneal flap was lifted, and irrigation and cultures from the stromal bed performed. Topical and subconjunctival antibiotics were started.

RESULTS

Culture revealed Streptococcus pneumoniae in both cases. The infiltrates responded well to treatment. One year after the procedure, uncorrected visual acuity is > 20/40 in both cases.

CONCLUSIONS

Pneumococcal keratitis can complicate LASIK. Patients should be informed of this potential complication, as prompt treatment is crucial.

Nontuberculous (atypical) mycobacterial keratitis after LASIK: current status and clinical implications

PURPOSE

Corneal infection with unfamiliar organisms such as nontuberculous (atypical) mycobacteria after laser in situ keratomileusis (LASIK) can be a significant clinical problem, and mismanagement of such corneal infection in an otherwise healthy, young individual can lead to significant medicolegal issues for the refractive surgeon. Because nontuberculous (atypical) mycobacterial keratitis is the most common infection after LASIK, the refractive surgeon should be aware of all aspects of this dreaded infection to be better prepared to manage such cases.

METHODS

Literature search.

RESULTS/CONCLUSIONS

This article provides a comprehensive compilation of all reported cases of nontuberculous (atypical) mycobacterial keratitis in the English literature and provides some useful recommendations for the clinical management of such corneal infection after LASIK.

Unusual anaerobic bacteria in keratitis after laser in situ keratomileusis

Laser in situ keratomileusis (LASIK) was performed in the left eye of a 57-year-old man for residual ametropia after phacoemulsification. The patient was given topical tobramycin and a corticosteroid for 1 week postoperatively. Fifteen days later, he developed 3 corneal infiltrates beneath the flap with a gas bubble, suggesting an anaerobic infection. Tobramycin and ofloxacin were administered every 2 hours, but the condition worsened. Corneal scrapings were taken from beneath the flap for microbiological cultures and a polymerase chain reaction (PCR) test. The PCR amplification was negative for fungi and mycobacteria and positive for bacterial DNA. Sequence analysis showed Propionibacterium granulosum as the causal agent, but cultures were negative. Treatment with vancomycin and cefazolin led to clinical improvement, with resolution of corneal infiltrates. Anaerobic microorganisms can cause keratitis after LASIK. Polymerase chain reaction amplification and DNA typing can help detect microorganisms involved in these ocular infections.

Infections following laser in situ keratomileusis: an integration of the published literature

Infections occurring after laser in situ keratomileusis (LASIK) surgery are uncommon, but the number of reports have steadily increased in recent years. This systematic, comprehensive review and analysis of the published literature has been performed in order to develop an integrative perspective on these infections. We have stratified the data by potential associations, microbiology, treatment, and the degree of visual loss, using Fisher's exact tests and Student's t-tests for analysis. In this review, we found that Gram-positive bacteria and mycobacterium were the most common causative organisms. Type of postoperative antibiotic and steroid use was not associated with particular infecting organisms or severity of visual loss. Gram-positive infections were more likely to present less than 7 days after LASIK, and they were associated with pain, discharge, epithelial defects, and anterior chamber reactions. Fungal infections were associated with redness and tearing on presentation. Mycobacterial infections were more likely to present 10 or more days after LASIK surgery. Moderate or severe visual reductions in visual acuity occurred in 49.4% of eyes. Severe reductions in visual acuity were significantly more associated with fungal infections. Flap lift and repositioning preformed within 3 days of symptom onset may be associated with better visual outcome.

Acremonium fungal infection in 4 patients after laser in situ keratomileusis

We present 4 patients who had laser in situ keratomileusis and were referred to our clinic with a diagnosis of infectious keratitis. Laser in situ keratomileusis was performed in all cases in the same operating room by different surgeons between April and May 2002. A partial penetrating keratoplasty was performed in all patients to control the process. A study of the corneas demonstrated the presence of the fungus Acremonium in all cases. Rigid asepsis during the surgical procedure is important to prevent this serious complication.

Repositioning the Laser in situ Keratomileusis Flap at the Slit Lamp

PURPOSE

To describe the indications and technique for repositioning the laser in situ keratomileusis (LASIK) flap at the slit lamp.

METHODS

We present a description of patients with striae or slippage of the flap who had repositioning of the flap at the slit lamp.

RESULTS

Indications for repositioning at the slit lamp are mostly flap striae. However, it can also be done for a displaced flap and small amounts of debridement. This procedure is not recommended for taking cultures, irrigation of diffuse lamellar keratitis, suturing the flap, or epithelial ingrowth. Repositioning the flap is done by finding the edge of the flap with the cannula, lifting the flap, sweeping the cannula to release the entire wound, and infusing balanced salt solution under the entire flap. We did not encounter infection or recurrent epithelial erosion in these patients.

CONCLUSIONS

Repositioning the LASIK flap at the slit lamp was effective and safe in the treatment of striae or flap slippage. It saved time, money, and, anxiety for the patient.

Ulcerative keratitis caused by Serratia marcescens after laser in situ keratomileusis

We report 2 cases of severe corneal infections caused by Serratia marcescens after laser in situ keratomileusis (LASIK). Twenty-four hours after LASIK, 2 patients developed infectious keratitis, 1 bilaterally. In each eye, the corneal flap was edematous, ulcerated, and detached from the stromal bed. Treatment included removal of the necrotic flap and aggressive antibiotic therapy. Cultures from corneal exudates were positive for S marcescens. After 1 year, both patients had a loss of best corrected visual acuity (BCVA) ranging from 20/40 to 20/22 because of irregular astigmatism. Overrefraction with a hard contact lens resulted in a BCVA of 20/20 in the 3 affected eyes. Slitlamp examination showed trace subepithelial haze without severe corneal scarring. Videokeratography disclosed areas of paracentral inferior steepening resembling keratoconus. Refraction and videokeratography remained stable after 6 months of follow-up. Ulcerative keratitis caused by S marcescens is a potential complication of LASIK. Bilateral involvement may occur if bilateral simultaneous surgery is performed.

Infectious keratitis after laser in situ keratomileusis: Results of an ASCRS survey

To investigate the incidence, culture results, treatment, and visual outcomes of infectious keratitis after laser in situ keratomileusis (LASIK) worldwide, the Cornea Clinical Committee of the American Society of Cataract and Refractive Surgery (ASCRS) contacted 8600 United States and international ASCRS members by e-mail and asked them to respond to a questionnaire about post-LASIK infectious keratitis. One hundred sixteen infections were reported by 56 LASIK surgeons who had performed an estimated 338 550 procedures. Seventy-six cases presented in the first week after surgery, 7 during the second week, 17 between the second and fourth weeks, and 16 after 1 month. Forty-seven cases were not diagnosed on initial presentation. The most common organisms cultured were atypical mycobacteria and staphylococci. Empiric therapy is not recommended as most of the organisms are opportunistic and not responsive to conventional therapy. Flap elevation and culturing should be performed when post-LASIK infectious keratitis is suspected.