Contact lenses and corneal shields

Contact lens wear has been associated with a wide spectrum of corneal complications. Disposable contact lenses have not eliminated the problem of corneal ulcers associated with extended-wear contact lenses. Rigid, gas-permeable extended-wear lenses may be considered as an acceptable alternative to extended wear of soft contact lenses. Collagen corneal shields are a clinical indicator of collagenase activity on the ocular surface and serve as a collagenase inhibitor.     

Contact lenses and corneal shields

Contact lenses are widely used all over the world. If fitted and handled properly, contact lenses can be good cosmetic and therapeutic tools. In this review, the different indications for contact lens wear are discussed. Contact lenses can also lead to serious problems. Tear film and morphologic alterations of the cornea, as well as corneal infections of microbial origin, are reviewed. Collagen bandage lenses have been used for some time in the treatment of corneal epithelial defects. Currently, these lenses are being tested as drug delivery systems, especially for use with poorly penetrating drugs, in serious infections of the cornea.     

Contact lenses and corneal shields

This article reviews literature regarding contact lenses and corneal shields published between February 1996 and January 1997 that will help the ophthalmologist to better understand some of the clinical effects of contact lenses and corneal shields. Progress has been made in understanding the interaction between contact lenses and the eye, and this may improve fitting. However, fitting presbyopic patients with contact lenses still remains a challenge. There is new insight in the pathomechanism of serious corneal infections caused by Acanthamoeba species and Pseudomonas aeruginosa, which may lead to decreases in these complications. Furthermore, in the era of different wear modalities and replacement schedules and the advent of daily disposable lenses, an update of contact lens terminology is provided.     

The clinical use of contact lenses and collagen shields

Contact lens wear before and after photorefractive or phototherapeutic keratectomy with excimer lasers has become an increasingly interesting subject. No negative side effects of contact lens wear prior to photorefractive keratectomy have yet been shown and refractive errors postoperatively do not seem to constitute a major practical problem. Normal side effects include the risk of bacterial infection and keratitis. The major pathogen in this context is still Pseudomonas aeruginosa, although increased insight into the mechanisms of bacterial adhesion and improvements in cleaning procedures now allow more effective preventive care of contact lenses themselves and of contact lens cases. Tear fluid research using leucotriene C4 as a possible indicator for subclinical inflammation has led to interesting results, and the importance of the arachidonic pathway and its metabolites has become more evident. These advances contribute considerably to the safe use of contact lenses in clinical ophthalmology, although major innovations such as the multifocal contact lenses have not reached the stage of perfection.     

Use of collagen corneal shields versus soft contact lenses to enhance penetration of topical tobramycin

We compared the corneal penetration in rabbits of topical tobramycin in the presence of collagen corneal shields and bandage soft contact lenses. A collagen corneal shield was placed on six albino rabbit eyes, while therapeutic soft contact lenses (61.4% poly-2-hydroxyethyl-methacrylate/38.6% water) were placed on six eyes. Four control eyes received no shield or contact lens. Topical tobramycin was applied to all 16 eyes every five minutes for six doses. Samples of aqueous humor were removed at 15 and 60 minutes following the last dose. Collagen corneal shields allowed a significant (P less than .05) increase in tobramycin penetration into the anterior chamber at 60 minutes compared with hydrophilic soft contact lenses or controls.     

Clinical uses of collagen shields

Collagen shields immersed in tobramycin solution for one minute were applied to one eye each of 60 patients who had had cataract extraction, penetrating keratoplasty, or epikeratophakia or who had nonsurgical epithelial healing problems. The shields were well tolerated; one patient had the shield removed and one patient lost the shield in the early postoperative period. The surgical patients showed more rapid healing of epithelial defects after surgery with the use of the collagen shield. Patients with acute nonsurgical epithelial problems, such as contact lens abrasions and recurrent erosion, responded to the use of the collagen shield with improved healing. Patients with chronic epithelial defects responded poorly, presumably because underlying abnormalities in Bowman's layer prevented epithelial growth in the area of the defect. No infections were noted in any of the patients. The collagen shields appear to promote enhanced healing in patients with postsurgical and acute epithelial defects and to provide adequate antibiotic prophylaxis against infection in these vulnerable eyes.     

Oxygen permeability of collagen shields

The oxygen permeability (Dk) of ten 24-hr collagen shields was measured directly by polarographic methodology at approximately 2 hr of hydration. Edge and boundary effects were included in the calculations. Dk was found to be approximately 26 x 10(-11) cm ml O2/sec ml mmHg at 35 degrees C. Mean water content of the shields was 65.7% (SD = 1.0%) as measured by a hand refractometer. Therefore, the projected oxygen transmissibility of collagen shields is expected to be compatible with normal corneal metabolism.     

Contact lenses and keratitis

Keratitis is a rare but important and possibly sight threatening complication of Contact Lens wearing. Despite of the number of only about 1.7 keratitis cases per ophthalmolgist per year, this serious side effect needs knowledge and special diagnosis and treatment. Global changes of infectious agents and increase of previously unsuspicious pathogens in combination with a high degress of non-compliance indicate that Contact Lens wearing must be accompanied careful ophthalmologist's medical care and after-care.     

Cyclosporine-containing collagen shields suppress corneal allograft rejection

Thirty-seven rabbit eyes with penetrating keratoplasty grafts placed in vascularized beds to enhance the possibility of graft rejection were treated with cyclosporine delivered in collagen shields or drops of olive oil. Treatment was begun either immediately after grafting or at the first sign of immune graft reaction. Mean survival time of the grafts in the collagen shield treated eyes was significantly longer than in the eyes treated with drops. In the eyes treated at the first sign of graft reaction, cyclosporine in collagen shields halted the rejection process; seven of these eyes survived the 120-day observation period, compared to one of the eyes treated with drops. These results indicate that the collagen shield is an effective delivery system for cyclosporine and the topically administered cyclosporine is effective in suppressing the initiation of graft rejection and in reversing a graft reaction in progress.     

Contact lenses in hypoxia

Seven women with soft contact lenses were examined during a 4 h period in a decompression chamber. The atmospheric pressure was lowered from the normal value of 1000 millibars (750 mmHg) to 560 millibars (420 mmHg), which corresponds to the altitude of 4000 m above sea level. The humidity, temperature, percentage of carbon acid and illumination were attempted to be kept even. Five test subjects developed subjective, and all the 7 also developed objective eye symptoms. It was concluded that hypoxia itself may cause eye discomfort for aircraft passengers with contact lenses. The most serious objective findings were corneal erosions in 3 and opacities of corneal stroma in 5 test persons. The control group without contact lenses did not develop any symptoms during the test.     

Contact lenses following keratoplasty

Bandage contact lenses can be used following keratoplasty to protect the ocular surface and promote epithelial healing. Rigid gas permeable contact lenses are indicated to correct irregular astigmatism and anisometropia. The Rotterdam Eye Hospital fit 77 keratoplasty patients with contact lenses following their surgery. The methods of fitting contact lenses over the irregular or highly astigmatic surface of a graft are discussed.