[Infection immunology in silicone hydrogel contact lenses for continuous wear--a review].
BACKGROUND
The patient's wish for permanent refractive solution and optimal comfort must be weighed against the risk of infections. In order to meet these wishes and the demand for minimising associated risks, hyperoxygen-transmissible silicone hydrogel contact lenses have been developed.


METHODS
Colonisation and sensitivity to antibiotics of bacteria in vitro, expression of bacterial ligands of the corneal epithelium (rabbit model), and the morphology of complications in patients have been reported to characterise HOTL.


RESULTS
Bacterial adherence to hydrophobic silicone elastomers is low. The reduction of sensitivity towards antibiotics is higher for PMMA-adherent bacteria with respect to the conventional antibiotics compared to the silicone-elastomer adherent bacteria. Colonising bacteria are not significantly different in asymptomatic CL wearers concerning CFU and species: asymptomatic: CNS (54 vs. 47 %), propioni- (43 vs. 48 %), coryne- (6 vs. 10 %) and gram-negative bacteria (2 vs. 3 %), S. aureus (2 vs. 1 %), and in patients with keratitis are not significantly different concerning species: CLARE (H. influenzae, S. pneumoniae), CLPU (S. aureus, S. pneumoniae), IK (P. aeruginosa), however, concerning the CFU (gram-negative) 23.7 % (keratitis) vs. 3.8 %, (asymptomatic), S. pneumoniae 7.6 % vs. 0.6 %. The epithelial expression of bacterial ligands like WGA is lower for HOTL (3230 p/750 micro) than for low oxygen-transmissible (4611 p/750 micro) consistent with a decreased adherence of pseudomonas of 5.31 - 5.98 vs. 5.9 - 7.81 bacteria/cell. Asymptomatic morphological anomalies and keratitis are less frequent in HOTL. Apoptosis-induced desquamation and the central epithelial thickness decreased. In a one-year study of 504 patients wearing continuous wear HOTL for 30 days, corneal staining was seen in 10.6 vs. 10.5 % 30-day 7 day extended wear, infiltrates in 2.3 vs. 4.6 %, epithelial oedema in 3.6 vs. 2.0 % und tarsal conjunctival anomalies in 3.0 vs. 1.6 %. Individual reports on infectious keratitis in HOTL wearers have been published.


CONCLUSIONS
Fewer morphological anomalies and a decreased incidence of infections (on the basis of duration of wear) can be associated with the higher oxygen transmission of HOTL. From the clinical point of view, colonisation of HOTL with the same bacterial species as in conventional biomaterials, and the extended wear demand clear patient counseling and vigilant follow-up by an ophthalmologist.
Bialasiewicz
Alexander A
AA
Dept. of Ophthalmology & School of Ophthalmic Technicians, Sultan Qaboos University Hospital, University of Oman.
D000818:Animals; D001422:Bacterial Adhesion / Q000187:drug effects / Q000276:immunology; D001424:Bacterial Infections / Q000188:drug therapy / Q000276:immunology* / Q000382:microbiology; D003262:Contact Lenses, Extended-Wear / Q000382:microbiology*; D019573:Epithelium, Corneal / Q000276:immunology / Q000382:microbiology; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D008826:Microbial Sensitivity Tests; D019904:Polymethyl Methacrylate; D011474:Prosthesis Design; D016459:Prosthesis-Related Infections / Q000188:drug therapy / Q000276:immunology* / Q000382:microbiology; D011817:Rabbits; D012826:Silicone Elastomers
D012826:Silicone Elastomers; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D019904:Polymethyl Methacrylate