Adherence of Daily Wear
RGP Contact Lenses

BY S. BARRY EIDEN, O.D., F.A.A.O. & CRISTINA SCHNIDER, O.D., M.SC., F.A.A.O.
FEB. 1996

Lens adherence is common in extended RGP wear but it can be a complication of daily RGP wear as well, as this study illustrates. Despite a lack of clinical evidence, lens adhesion among daily wear RGP patients may be more common than we think. A variety of physical characteristics, subjective symptoms and ocular complications have been previously supported secondary to RGP adherence. The following study proves that this complication, also termed lens binding or stuck lens syndrome, is not isolated to extended wear RGP lens use.

PROPOSED ETIOLOGIES OF LENS ADHERENCE

In 1979, Fatt proposed that a negative pressure or a suction effect is created by deformation of a steeply fit flexible contact lens. Swarbrick challenged this theory by fenestrating a lens worn by a patient who demonstrated frequent adherence with extended wear RGP use. Following fenestration of the lens, binding still occurred in eight out of nine nights.

Direct contact adhesion between the corneal epithelium and the posterior contact lens surface may be a mechanism for lens adherence for both silicone elastomers and RGP lenses. This theory is also challenged by the fact that significant epithelial disruption would be expected in the area of maximum adherence, i.e., the peripheral indentation zone. Yet staining of this area is an infrequent finding.

Ghormley, in 1991, suggested that the specific gravity of lens materials may be related to the frequency of adherence. He observed clinically that lenses made from materials of higher specific gravity tended to bind more frequently than materials of low specific gravity. He hypothesized that due to their weight the lenses would position inferiorly (a common position of adherent lenses) more often. Although material specific gravity may play a role in lens adherence, decentration of an RGP lens while mobile has not been shown to increase the likelihood of adherence.

In 1988, Swarbrick proposed that eyelid pressure during eye closure thins the retro-lens tear film by preferentially expelling the aqueous tear layer component during overnight wear. The remaining tear film is a thin, highly viscous layer of mucus, lipid and cellular debris that acts as an adhesive between the cornea and the lens surface. Physics lubrication theory supports Swarbrick's proposal. It states that as a fluid's viscosity increases or thickness decreases between a surface and an object, one must use more force to move or slide the object over the surface.

METHODS

We analyzed the clinical records of 15 daily wear patients who routinely displayed lens adherence. We reviewed the time period from lens dispensing to first visit demonstrating lens adherence, subjective symptoms, objective biomicroscopic findings, central fluorescein pattern, lens material and Dk, remediation methods, and results of remediation methods.

We matched a subgroup of five adherence patients according to age, sex, lens fit characteristics and lens materials with five non-adherence controls. After one week without contact lens wear, we performed the following tests and measurements for each subject and control:

1. Schirmer test after instillation of one drop of proparacaine (mm wet in five minutes).

2. Rose Bengal staining after instillation of one drop of dye (grade 0-4).

3. Sequential fluorescein staining by applying three instillations of fluorescein 10 minutes apart (a positive result indicated any increased staining following repeated instillation).

FIG. 1: CHARACTERISTIC ADHERENT LENS IN A DECENTERED POSITION.

FIG. 2 RETRO-LENS DEBRIS COMMONLY FOUND BEHIND THE MID-PERIPHERY OF AN ADHERENT LENS.

RESULTS

Patients presented with lens adherence two weeks to 24 months from initial dispensing visit. The mean time period was 6.8 months with a median of 7 months. Prior to the adherence visit, there were no subjective or objective signs or symptoms suggesting adherence during routine follow-up care.

The most common subjective symptoms were difficulty with lens removal, and irritation and spectacle blur following lens removal (Table 1). Only two patients reported no subjective symptoms.

We detected a corneal indentation ring corresponding to the lens periphery in the bound position in all 15 patients. None of our patients demonstrated staining within the indentation zone. Corneal staining peripheral to the lens edge and central staining were common findings, as was corneal distortion detected by keratometry. There was one case of localized infiltrative keratitis peripheral to the edge of the bound lens. This patient was diagnosed previously with chronic staph blepharitis. Another patient developed corneal dellen, again peripheral to the lens edge in the bound position. This patient also demonstrated heavy 3 and 9 o'clock staining and injection patterns associated with lens adherence. Unilateral epithelial basement membrane dystrophic-like (EBMD) anomalies developed in one patient. We detected lens adherence only in the eye with the EBMD anomalies (Table 2).

Central fluorescein pattern evaluation revealed an alignment pattern in 10 patients, mild bearing in two patients, and minimal clearance in three patients. Nine patients wore fluoro-silicon-acrylate materials and six wore silicon-acrylate lenses. The Dk values were fairly evenly distributed. Four patients wore lenses with Dk's of less than 20, four between 20 and 50, and six above 50.

We attempted a variety of remediation methods (Table 3) based on the physical fitting characteristics of the lens that exhibited binding while in a mobile state. We successfully remediated 10 of the 15 patients by modifying the physical fitting characteristics. We refit the five patients who were not successfully remediated into hydrogel lenses or we prescribed spectacles.

In the subgroup evaluation of tear function, all subjects who displayed adherence showed signs of an aqueous-deficient dry eye. The most common feature was positive sequential staining. In contrast, none of the control subjects showed more than one abnormal finding in the tear film test battery (Table 4).

DISCUSSION

RGP lens adherence, with its resulting subjective symptoms and ocular complications, is a significant concern in daily wear as well as extended wear. To develop effective management strategies, we must establish a clear understanding of the potential etiologies and contributing factors associated with lens adherence.

FIG. 3: CORNEAL INDENTATION RING CORRESPONDING TO THE POSITION OF THE EDGE OF THE ADHERENT LENS (LENS HAS BEEN REMOVED).

FIG. 4: CENTRAL CORNEAL STAINING AND CORNEAL INDENTATION RING SECONDARY TO LENS ADHERENCE (LENS HAS BEEN REMOVED).

The most plausible etiology for lens adherence is similar to Swarbrick's theory that implicates a thinning of the post-lens tear film. The remaining thin tear film, being highly viscous and mucoid, imparts an adhesive effect between the lens and cornea that is not overcome by the force of eyelid movement during blinking. In the extended wear use of RGP lenses, the thinning of the post-lens tear film may occur secondary to eyelid pressure during closure. In the daily wear use of RGP lenses, the thin and viscous tear film behind the lens surface may be associated with aqueous-deficient tear film abnormalities as suggested by our study. Other factors that may contribute to lens adherence are hydrophobic lens surface, and lens parameters that promote greater surface contact between the cornea and contact lens and hinder both tear exchange and lens movement (i.e., flat central fits, large overall diameters, low axial edge lift).

RGP wear could result in a gradual increase in the lens-to-cornea surface area contact and thus promote molding and adherence. Large, flat fits with low edge lift and higher specific gravity materials may come into play. Patient-dependent factors could include lid tension, corneal topographic characteristics, and the variable compactness or resistance to molding of the corneal tissue itself.

We remediated our subjects' lens adherence by manipulating their lens parameters. Swarbrick and Holden found that flat central fits, low axial edge lift, large overall diameters, and limited lens movement while mobile were all statistically associated with lens adherence. Remediation of adherence is, therefore, successfully achieved by fitting lenses with apical clearance, moderate edge lift, and good movement of the lens with blinking. If adherence cannot be remediated by changing lens fitting characteristics, then consider a hydrogel lens fit.

CONCLUDING REMARKS

The mechanism for daily wear RGP lens adherence is likely similar to that of extended wear use. An adhesive effect between the cornea and the posterior lens surface is created by a thin, highly viscous retro-lens tear film. This condition may be more common in patients with aqueous-deficient dry eyes or highly viscous tear film qualities. Lens parameters that promote increased lens-to-cornea surface area contact or inhibit tear exchange and lens movement tend to promote adherence.

Future investigations of RGP lens adherence should evaluate patient-dependent characteristics such as tear chemistry, lid tensions and corneal topography. Prospective controlled studies of the influence of corneal molding on adherence via sequential corneal topography should be conducted as well as controlled studies of the effects of various remediation methods such as design and parameter changes, material selection, lens care systems and tear film enhancement (both pharmacological and mechanical means such as punctal occlusion). CLS

Dr. Eiden is in a private group practice in Deerfield, Ill. He is an assistant clinical professor at the University of Illinois Medical Center and president of United Vision Assoc., Ltd., that provides continuing education for the eyecare field. Dr. Schnider is an associate professor at Pacific University College of Optometry in Forest Grove, Ore. and a diplomate of the Cornea and Contact Lens Section of the AAO.