The effects of long-term contact lens wear on corneal thickness, curvature, and surface regularity

PURPOSE

To evaluate the effect of long-term contact lens wear on corneal thickness, curvature, and surface regularity.

DESIGN

A prospective, clinic-based, case-control study.

PARTICIPANTS

A total of 40 eyes of 20 normal subjects and 64 eyes of 35 subjects wearing contact lenses for more than 5 years were evaluated.

METHODS

The Orbscan Corneal Topography System was used to evaluate the entire corneal thickness and curvature, anterior curvature and the anterior and posterior elevation topographic patterns in normal eyes and subjects wearing contact lenses on a regular basis for more than 5 years. Indices of TMS-1 Corneal Topography System were used to determine corneal surface regularity in subjects wearing contact lenses and normal eyes. All topographic examinations were performed after contact lenses had been removed for at least 2 weeks.

MAIN OUTCOME MEASURES

The entire corneal thickness, curvature, surface regularity index (SRI), surface asymmetry index (SAI), potential visual acuity (PVA) and topographic patterns were compared between normal eyes and subjects wearing contact lenses for more than 5 years.

RESULTS

The 64 eyes of 35 subjects evaluated by the Orbscan instrument had an average of 13.45 +/- 6.42 years of contact lens wear. The mean corneal thickness in the center and in eight peripheral areas measured in contact lens wearing subjects was significantly reduced by about 30 to 50 microm compared to normal subjects (P < 0.001 for central and peripheral sites). No correlation was noted between central corneal thickness and degree of myopia in diopters (r = 0.15, 0.10 < P < 0.25). The corneal curvature, maximum keratometry (Max K) and minimum keratometry (Min K) readings, were significantly steeper in eyes wearing contact lenses than normal eyes (P < 0.01 for Max K and Min K measured by both instruments). No difference in the mean corneal astigmatism was noted between groups. The SRI and SAI, but not the PVA index, of the TMS-1 were significantly greater in contact lens wearers than in the control group (P < 0.01 for both SRI and SAI, P = 0.15 for PVA). The color-coded patterns of all curvature and elevation maps made with both instruments showed no significant difference between subjects wearing contact lenses and the control group. There was no significant difference between corneal curvature measurements taken with the Orbscan System or the TMS-1 System in both normal and contact lens groups.

CONCLUSIONS

Long-term contact lens wear appears to decrease the entire corneal thickness and increase the corneal curvature and surface irregularity.

Management of pediatric aphakia with silsoft contact lenses

PURPOSE

To evaluate the performance of silicone elastomer lenses in pediatric eyes with aphakia.

METHODS

We retrospectively studied pediatric aphakic eyes fit with Silsoft lenses (elastofilcon A, Bausch & Lomb) at the L.V. Prasad Eye Institute, India.

RESULTS

Seventy-four children (106 eyes) with a median age of 9.0 months (range: 1 month to 12 years) were included in the study. Congenital cataract was the pre-existing pathology in 84 eyes. Lenses were fit between 1 week and 5 years following surgical intervention (median: 25 days). The most frequently used base curves were 7.5 mm (n=46 eyes) and 7.7 mm (n=39 eyes); lens diameter was 11.3 mm (n=103 eyes). Satisfactory fit was achieved in 86 eyes (81.1%). One-week extended wear was the most commonly recommended mode of wear (n=95 eyes). Lenses (n=118) were replaced for change of power, lens loss, and deposits or damage. Lenses were worn for > or =6 months in 68 eyes (64.2%). Twenty-three contact lens related adverse events occurred, all of which resolved uneventfully. On survival analysis, the probability of not having a lens related complication was 75.5% (95% CI; 61.5-89.5) at 24 months.

CONCLUSIONS

In the management of pediatric aphakia, Silsoft lenses are safe, provide satisfactory optical correction, and are easy to handle. Limited availability and the financial costs associated with frequent lens replacement are limitations in our socioeconomic circumstances.

Contact lens-induced peripheral ulcers with extended wear of disposable hydrogel lenses: histopathologic observations on the nature and type of corneal infiltrate

PURPOSE

Contact lens-induced peripheral ulcer (CLPU), a sudden-onset adverse event observed with extended wear of hydrogel lenses, is characterized by a single, small, circular, focal anterior stromal infiltrate in the corneal periphery or midperiphery. The condition is always associated with a significant overlying epithelial loss and resolves in a scar. The aim was to determine, by using histopathologic techniques, the nature and type of the corneal infiltrate of these events.

METHODS

Three CLPUs observed in three patients using disposable hydrogel lenses on an extended-wear schedule were examined. The eye was topically anesthetized, and a corneal section including all of the infiltrate was taken. A small triangular piece of conjunctiva immediately adjacent to the infiltrate was sectioned. The tissue was immediately fixed, processed, stained using hematoxylin and eosin and periodic acid-Schiff stains, and examined by using light microscopy.

RESULTS

The diameter of these three corneal infiltrates varied from 0.3 to 0.6 mm. Histopathology of the corneal sections revealed a focal epithelial loss corresponding to the infiltrated stroma in all three patients. The adjacent epithelium was thinned. Bowman's layer was intact in two patients and had a localized area of loss in the remaining patient. The anterior stroma was densely infiltrated with polymorphonuclear leukocytes and had focal areas of necrosis. The infiltration was most dense in the region immediately underlying Bowman's layer. No other infiltrative cell type was seen in any of the sections. Histopathology of the conjunctiva revealed features consistent with normal conjunctival tissue.

CONCLUSIONS

On histopathology of CLPU, distinctive features (i.e., focal corneal epithelial loss, an intact Bowman's membrane, and a localized infiltration of the anterior stroma with polymorphonuclear leukocytes) were seen. These features suggest that the event is an acute inflammatory process and probably noninfective in nature.

Great expectations and the grapes of wrath: contamination of contact lenses

The results of an analysis of complications in contact lens wearers in The Netherlands indicate that there is an increased risk of keratitis associated with the extended wear of the lenses. This article discusses some of the underlying issues.

Adverse events with extended wear of disposable hydrogels: results for the first 13 months of lens wear

OBJECTIVE

To determine the type and incidence of adverse events seen in the first 13 months of extended wear from a prospective clinical trial involving the use of disposable hydrogels on a 6-night extended wear and replacement schedule.

DESIGN

A prospective, noncomparative clinical trial.

PARTICIPANTS

Three hundred thirty subjects were enrolled in the study from March 1993 to August 1996 and commenced in extended wear. The subjects were new contact lens users with ages ranging from 16 to 39 years and refractive errors from -1.00 to -6.50-diopter (D) sphere with cylindrical component less than 1.0 D.

INTERVENTION

Disposable hydrogel lenses on a 6-night extended wear and replacement schedule.

MAIN OUTCOME MEASURES

To determine the incidence of adverse events in the first 13 months of lens wear with the use of disposable hydrogels on an extended wear schedule. In addition, corneal infiltrative events observed with lens wear were classified based on their presenting signs and symptoms.

RESULTS

A total of 137 adverse events were seen in 102 subjects in the first 13 months of extended wear. The type of adverse events and the incidence per 100 patients per year of lens wear were as follows: corneal infiltrative events (44.4 events), contact lens papillary conjunctivitis (6.4 events), neovascularization and corneal wrinkling (1.7 events each), corneal striae and superior epithelial arcuate lesions (1.3 events each), and blepharokeratoconjunctivitis (0.4 event). Viral keratoconjunctivitis was also observed (0.8 event). The corneal infiltrative events were further subclassified as follows: contact lens-induced peripheral ulcers (13.6 events), contact lens-induced acute red eyes (12.3 events), infiltrative keratitis (9.7 events), and asymptomatic infiltrative events (8.9 events). There were no events of infectious keratitis. Except for all events of contact lens-induced peripheral ulcers and two isolated events of infiltrative keratitis that resulted in scarring, all of the corneal infiltrative events resolved without sequelae. None of the events caused any loss of best-corrected visual acuity.

CONCLUSIONS

Based on the observations from the first 13 months of extended wear in the trial, the majority of the complications associated with extended wear of disposable hydrogels are corneal infiltrative events. No events of microbial keratitis were seen in the first 13 months of extended wear. None of the events were associated with loss in best-corrected visual acuity. Clearly, frequent and regular disposing of lenses does not eliminate adverse effects, and better materials and designs are required for extended wear to be a successful method.

Incidence of contact-lens-associated microbial keratitis and its related morbidity

BACKGROUND

The incidence of contact-lens-associated microbial keratitis is uncertain and its related morbidity in the general population of contact-lens wearers is not known. We examined these issues in a prospective epidemiological study.

METHODS

We surveyed all practising ophthalmologists in the Netherlands to identify all new cases of microbial keratitis reported during a 3-month period in 1996. Follow-up telephone calls were made to examine ocular morbidity. We undertook annual nationwide telephone surveys between 1994 and 1997 to estimate the prevalence of contact-lens wear.

FINDINGS

Of 440 ophthalmologists contacted, 379 provided information. There were 92 cases of microbial keratitis; 17 used daily-wear rigid gas-permeable lenses, 63 daily-wear soft lenses, and 12 extended-wear soft lenses. The estimated annualised incidence of microbial keratitis was 1.1 per 10,000 (95% CI 0.6-1.7) users of daily-wear rigid gas-permeable lenses, 3.5 per 10,000 (2.7-4.5) users of daily-wear soft lenses, and 20.0 per 10,000 (10.3-35.0) users of extended-wear soft lenses (p<0.00001 for comparison between all groups), Five of the 92 patients achieved a final visual acuity of 20/70 or less. Pseudomonas and Serratia spp were the organisms most commonly isolated. Pseudomonas keratitis accounted for the largest mean diameter of corneal ulcers, the highest mean number of days in hospital, the greatest number of mean outpatients visits, and the poorest visual acuity outcome.

INTERPRETATION

The incidence of microbial keratitis among users of extended-wear soft contact lenses in the Netherlands is similar to that reported in the USA during 1989. Awareness of risk factors and improvement in contact-lens materials have not led to a decrease in incidence. Overnight wear should be strongly discouraged.

Giant papillary conjunctivitis in frequent replacement contact lens wearers: a retrospective study

PURPOSE

We conducted a retrospective study of 47 patients who wore frequent replacement contact lenses on a daily-wear basis to determine the incidence of giant papillary conjunctivitis (GPC) and to assess the potential risk factors that may predispose frequent replacement contact lens wearers to develop GPC.

METHODS

We reviewed the records of patients with no prior contact lens experience who were fit with frequent replacement contact lenses from September 1993 to February 1997.

RESULTS

Forty-seven of 260 patients met the requirements for inclusion in the study. Ten (21.27%) patients had developed GPC. The incidence varied with the frequency of contact lens replacement. The contact lens replacement schedule ranged from 1 day to 12 weeks. In those patients replacing their contact lenses every 4 weeks or at a longer interval, the incidence of GPC was 36%, while for patients who replaced their lenses more frequently, the incidence was 4.5%. Coated contact lenses were also more common among patients who replaced their lenses at 4 weeks or longer (P = 0.23). A significantly greater number of patients in the GPC group incorporated enzymatic cleaning into their contact lens care system (P = .0004). A history of allergy was more prevalent in patients who developed GPC and was statistically significant (P = .012). There was no significant difference found between the groups for age, gender, average daily wearing time, FDA classification of contact lens material, time in contact lenses from fitting to diagnosis or last follow-up period, or the parameters and fitting characteristics of the contact lenses.

CONCLUSION

The frequency at which patients replace their contact lenses appears to be an important variable in developing GPC. Although frequent replacement contact lenses do not eliminate GPC, patients on a 1-day to 3-week replacement cycle had a significantly lower risk of developing GPC than patients who replaced their lenses at longer intervals. Lens coating was present less often on contact lenses replaced daily and up to 3 weeks. For patients who are at high risk for GPC, replacing lenses at intervals ranging of one day to two weeks appears to offer a better strategy for avoiding GPC than incorporating enzymatic cleaning into their lens care system.

The effect of rigid gas permeable contact lens wear on proliferation of rabbit corneal and conjunctival epithelial cells

PURPOSE

To study the effect of rigid contact lens oxygen transmissibility on cell proliferation of the corneal, limbal, and conjunctival epithelium in vivo following 2 days of extended wear in the rabbit model.

METHODS

Fourteen adult New Zealand White rabbits were divided equally into two groups. Each group was assigned to one of two test rigid gas permeable (RGP) contact lenses (Dk/Ltotal = 10 and 97) with uniform thickness (0.15 mm) and diameter (14.0 mm). One eye of each rabbit randomly received a contact lens for two days (48 hrs) extended wear, and the fellow eye was used as a control. Rabbits were injected intravenously with 5-bromo-2-deoxyuridine (200 mg/kg) in sterile phosphate buffered saline (pH 7.4) 24 hours before being killed. Corneas with a limbal rim of episclera and overlying conjunctiva were fixed in situ and excised. Nuclei labeled with BrdU were detected with a monoclonal anti-BrdU antibody and an FITC-conjugated secondary antibody. Digital images were collected and BrdU-labeled nuclei of whole-mount corneas were counted from superior limbus to inferior limbus using epifluorescence microscopy.

RESULTS

Twenty-four hours after intravenous injection of BrdU, labeled nuclei were confined to and appeared as pairs in the basal epithelial layer. The density of BrdU-labeled nuclei were found to be 258 +/- 42, 167 +/- 43, 372 +/- 64, and 310 +/- 46 (pairs/mm2, mean +/- SD, n = 14) in normal controls for adjacent conjunctiva, limbus, peripheral cornea, and central cornea, respectively. By contrast,there was significant 81.35% (low Dk)and 22.46% (ultra-high Dk) suppression of cell proliferation in the central cornea after two days lens wear (n = 7). In addition, significant increases in the labeling of limbal and conjunctival epithelium were also noted.

CONCLUSIONS

Significantly less BrdU labeling of epithelial cells at the normal rabbit limbus was noted as compared to the peripheral and central cornea (P < 0.05) and is consistent with the presence of slow-cycling limbal basal cells and the limbal stem cell theory; however, this is the first report of up-regulation of limbal cell proliferation induced by contact lens wear. This study also revealed, for the first time, that short-term extended wear of RGP lenses inhibits central corneal epithelial cell proliferation. This effect was significantly more pronounced for a low-oxygen vs. a hyper-oxygen transmissible test lens. This data also suggests that corneal epithelial layer thinning seen following extended contact lens wear may be explained, in part, by suppression of basal epithelial cell proliferation. Further study is clearly necessary to validate and extend these preliminary findings.

Effect of lens wear on corneal stroma: preliminary findings

PURPOSE

The aim of the study was to measure the effects of long-term extended wear of hydrogel lenses.

METHODS

Nine subjects wearing disposable hydrogel lenses and age- and sex-matched non-lens-wearing control subjects were enrolled. Using confocal microscopy, stromal keratocyte cell densities were measured.

RESULTS

Anterior stromal keratocyte density was reduced in the lens-wearing group (544+/-206 cells/mm2) compared to the non-lens-wearing group (804+/-145 cells/mm2) (P < 0.01). Posterior stromal keratocyte density was lower in the lens-wearing group (514+/-111 cells/mm2) than in the control group (628+/-101 cells/mm2) (P < 0.05).

CONCLUSIONS

These preliminary findings indicate that extended wear of hydrogel lenses reduces stromal keratocyte density. The mechanisms for this alteration may include hypoxic, cytokine-mediated or mechanical effects.

Papillary hypertrophy of the upper tarsal conjunctiva during contact lens wear: a 4-month study with ethyl-6-O-decanoyl-glucoside

PURPOSE

We studied the potential effect of ethyl-6-O-decanoyl-glucoside (EDG) on papillary hypertrophy in contact lens wearers who were recruited on the basis of papillary hypertrophy and a long history of contact lens wear. The contact lens care solutions were 0.00025% chlorhexidine acetate (CHX) with or without 0.005% EDG.

METHODS

Nineteen subjects wearing both ionic and non-ionic contact lenses for 6-18 hours used either CHX or CHX+EDG as a cleaning and disinfecting agent. CHX and CHX+EDG was used simultaneously by each subject but in different eyes during two consecutive periods of 8 weeks. Symptoms and signs were recorded at three examinations during the study. The protein content of contact lenses and tryptase activity of tear fluids were measured.

RESULTS

The degree of papillary hypertrophy did not decrease in either the CHX or CHX+EDG groups. Also, there were no differences in protein content of lenses nor tryptase activity of tear fluids in either group. There was a significant correlation between papillary hypertrophy and tryptase activity during the study.

CONCLUSIONS

Despite the earlier finding that EDG prevents development of papillary hypertrophy in contact lens wearers, EDG still cannot reverse established signs of papillary hypertrophy.

Morphologic changes in corneal endothelial cells during 3 years of fluorocarbon contact lens wear

PURPOSE

To record morphologic changes that occur in corneal endothelial cells during daily wear of rigid, gas-permeable fluorocarbon contact lenses during 3 years.

METHODS

Nineteen new wearers and 32 previous wearers were fitted with daily-wear fluorocarbon contact lenses. Photographic images of the central corneal endothelium and central corneal thickness measurements were recorded at baseline, 2 months, and 1, 2, and 3 years after fitting.

RESULTS

In the new wearers, an increase in the coefficient of variation of cell area was present by 2 months after lens fitting and increased further over the subsequent 3 years. The increase in coefficient of variation of cell area was correlated with the oxygen transmissibility of the lens. Endothelial cell density was decreased at 2 and 3 years. Corneal thickness did not change. In the previous lens wearers after 3 years, there were no significant changes from baseline in any morphologic value. Corneal thickness was decreased significantly.

CONCLUSIONS

Although oxygen transmissibility in fluorocarbon contact lenses is improved over previous hard and soft lenses, polymegethism still was induced within 2 months by these lenses, and morphologic changes present from past lens wear did not improve during 3 years of daily wear.

An ocular strain of Pseudomonas aeruginosa is inflammatory but not virulent in the scarified mouse model

Pseudomonas aeruginosa is the most common pathogen among contact lens-associated infections. This study investigated the response of the murine cornea to infection with an ocular strain of P. aeruginosa isolated from a subject with an inflammatory adverse response to contact lens wear termed CLARE. Although this bacterium was isolated in confluency (greater than 2000 cfu lens-1) from the lens at the time of the inflammatory episode, no infection of the cornea subsequently developed. Male C57BL/6J mice (20 per strain) had their corneas scratched with a 26 gauge needle (3 parallel 1.0 mm wounds in the left eye only). The incisions were centered over the pupillary axis and penetrated the epithelial cell basal lamina and into the superficial stroma. The CLARE strain was found to persist (viable bacteria could be cultured from corneal homogenates) up to 8 hr, as did the virulent control strain ATCC 19660. At 24 hr, only ATCC 19660 could be cultured, indicating an inability of the strain isolated from CLARE, Paer1, to persist in the eye consistent with the human inflammatory episode. Histological examination of the mouse tissue showed further differences between infection by the two strains. Infection with ATCC 19660 resulted in tissue necrosis and a large population of polymorphonuclear leukocytes (PMNs) recruited to the wound site. In contrast, during infection with the CLARE strain, PMN recruitment was reduced and temporally delayed. The CLARE strain grew as well as ATCC 19660 in vitro but produced less protease activity, in particular less elastase. The decreased PMN response and decreased protease production by the CLARE strain may have been responsible for the lack of ocular damage and apparent healing of the wound. P. aeruginosa strains are considered to be invasive or cytotoxic to corneal tissue, however this strain may represent a third inflammatory type consistent with its differing pathology.

Ophthaproblem. Contact lens (Acanthamoeba) keratitis

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Contact lens induced peripheral ulcers during hydrogel contact lens wear

PURPOSE

Ulcerative keratitis is the most serious adverse response associated with contact lens wear. However, some reports of microbial keratitis in the literature may refer to a less severe form of corneal ulceration, which we have termed contact lens induced peripheral ulcers (CLPU).

METHODS

We present details of 11 cases of CLPU which occurred in clinical trials at our research unit.

RESULTS

CLPU episodes are characterized by a single, small (< 2 mm diameter) circular lesion in the corneal mid-periphery or periphery, involving a focal loss of the full thickness of the epithelium associated with subepithelial stromal infiltrates. Patient symptoms may include ocular irritation, pain, photophobia, and lacrimation. They are usually associated with the use of hydrogel extended wear contact lenses. The lesions are self-limiting, typically healing within 7 days without treatment. After resolution, a small circular scar remains, which does not affect vision because of its peripheral location. The etiology of CLPU is unclear. In our studies, the incidence of CLPU was similar in conventional (2.9% per patient year) and disposable (2.0% per patient year) hydrogel extended wear, but lower during intermittent extended wear (1.6% per patient year); only one case occurred during daily wear (< 0.5% per patient year).

CONCLUSIONS

A conservative approach to patient management of all suspected cases of corneal ulceration is encouraged. However, we suggest that future reports of ulcerative keratitis associated with various lens types and wearing schedules should differentiate between potentially devastating microbial keratitis and the relatively innocuous peripheral ulceration described in this paper.

Extended wear in perspective

BACKGROUND

Convenience and safety are major motivating factors in the choice of a mode of correction for refractive errors. Extended wear of contact lenses is associated with greater convenience than daily wear, but questions remain concerning the safety and risks associated with this modality. This paper investigates the hurdles that have rendered extended wear an unfavorable option thus far and seeks to identify strategies to overcome these obstacles.

METHOD

We review the history of extended contact lens wear, focusing on soft extended wear for cosmetic use. Results of incidence and relative risk studies for the major complications are scrutinized. The factors that are associated with increased risk together with mechanisms which have been proposed on based on scientific research are analyzed to derive strategies for preventing adverse reactions in extended wear.

RESULT

Infectious keratitis associated with extended wear of contact lenses has been identified by the community as a major issue, although the degree of concern may be disproportionate. Current perceptions of the relative risk of extended wear versus daily wear in the context of the risk for nonwearers may be misplaced, and the role of eye closure versus consistency and duration of wear remains open to debate. In the minds of practitioners and patients, other adverse reactions may be of greater significance in rejecting extended wear. Nonetheless, the potential extent of injury from infection demands attention. Studies collectively attest that corneal hypoxia during extended wear is a potential causative mechanism in infectious keratitis, suggesting that the provision of higher oxygen levels to the cornea will reduce morbidity rates from this unwanted complication. However, the issues of stagnation of the post-lens tear film during eye closure, mechanical properties of the lens, and lens movement remain unresolved and may prove to be contributing factors to adverse responses.

CONCLUSIONS

Attention to oxygen permeability and mechanical properties of soft contact lenses should solve the remaining problems with extended wear. Materials currently under development promise to meet at least some of the desired properties and may lead to the long-awaited advent of safe extended wear.

[Contact lenses. 2: Contact lens associated infections]

Contact lens wearers, especially those who wear soft or extended wear contact lenses, are at increased risk of suffering from keratitis. Among the causes of corneal infections, an inadequate hygiene or overextended wear play an important role. An insufficient cleaning and disinfection leads to contamination with pathological germs. Sites of entry for these germs are corneal microlesions, caused by the setting and removal of contact lenses, and epithelial defects, as a result of the wearing of old or defective contact lenses. Primary eye diseases of patients who wear contact lenses can be altered by their wearing, and vice-versa. Even more, miscellaneous infections may lead to infectious corneal ulcerations. Having an adequate hygiene, a proper patient orientation during the medical visit, and a regular control are therefore of great importance for the reduction in the frequency of such infections by patients who wear contact lenses.

Extended wear disposable soft contact lenses as an alternative to photorefractive keratectomy: report of 4 years experience

PURPOSE

To establish whether, in a well-informed population, the use of extended wear disposable soft contact lenses (EWDSCL) poses an unacceptable risk to vision and corneal health due to complications associated with their use.

METHODS

A 4 year retrospective review of EWDSCL, involving 371 patients in Melbourne from a single general ophthalmology practice. The important aspects of this group were that all patients were given written instructions about the methods of ensuring initial and ongoing cleanliness of lenses, no lenses were cleaned and reinserted, and no solutions other than the saline in the original packaging, and comfort crops, were used. Two types of EWDSCL were used in powers from -9.0 to +6.0 D, and with an initial aim of 4 weeks uninterrupted extended wear. Follow-up was from 2 to 52 months, with an average of 24 months.

RESULTS

Of the 354 patients followed up, 236 (66%) regularly wore them on an extended overnight basis, and of these 180 (76%) wore them for the suggested 4 week period before renewal of lenses. In the 471 eyes of 236 patients, adverse reactions occurred at the following rates, marginal infiltrates (12 cases, 2.5%); corneal oedema (10 cases, 2%) peripheral corneal vascularization (2 cases, 0.4%); and presumed infective keratitis (1 case, 0.2%). No eyes lost one or more lines of Snellen acuity.

CONCLUSIONS

When disposable soft contact lenses do not come into contact with cleaning solutions, saline from bottles or aerosol cans, or storage cases, their use on an extended wear basis (up to 4 weeks continuous) appears to be associated with a low risk of minor or major complications. The results of this review indicate that controlled usage of EWDSCL is safer than previous reports have indicated.

Conjunctival impression cytology in patients wearing contact lenses

PURPOSE

Evaluation of contact lens-induced cytologic changes on the conjunctival surface.

METHODS

Fifty eyes of 25 patients wearing soft or rigid gas-permeable contact lenses, and 50 healthy eyes of 25 control subjects were examined with conjunctival impression cytology. Of the patients wearing contact lenses, 40% did not have any contact lens-related complaints, whereas 60% had some minor complaints related to contact lens intolerance. The material obtained by impression cytology was examined with regard to epithelial cell morphology, goblet cell density, and snake-like nuclear chromatin changes.

RESULTS

When epithelial cell morphology was graded according to the system described by Nelson, specimens from the control group revealed 90% of the eyes to be grade 0 and 10% to be grade 1, whereas of the eyes wearing contact lenses, 8% were grade 0, 36% grade 1, 32% grade 2, and 24% grade 3. Thus statistically significant differences were observed between the control group and the contact lens group with regard to each grade (p < 0.05) as well as to the goblet cell densities (p < 0.05). Snake-like chromatin changes, on the other hand, were observed in 30 and 27% of the eyes wearing soft and rigid gas-permeable contact lenses, respectively, whereas these were not encountered in any eye in the control group.

CONCLUSION

Epithelial changes were noted to be more frequent and more severe in symptomatic patients than in those without any complaints. No correlation was found between average duration of contact lens wear and the risk of contact lens intolerance or development of squamous metaplasia.

Prospective trial of daily and extended wear disposable contact lenses

PURPOSE

The current study prospectively evaluates the response to daily and extended wear of disposable lenses with each patient acting as his/her own control. This paradigm allowed for elimination of individual variation as a confounding factor, as well as determining whether an intrinsic factor, other than lens wear, predisposed patients to complications.

METHODS

One hundred thirty-four patients were randomly assigned to contralateral daily wear (DW) or extended wear (EW) with Acuvue lenses for 1 year. All lenses were disposed of on a weekly basis. Bilateral bacteriology of lids, conjunctivae, lenses, and fingers was carried out on those patients presenting with complications.

RESULTS

The results after 1 year indicate a higher incidence of complications in the EW eye (peripheral infiltrative keratopathy, 12%; corneal striae, 3%). No significant clinical complications occurred in the DW eye. Microbiological cultures did not reveal any significant difference between those eyes with keratopathy and those of controls. The most common pathogen was Staphyloccocus epidermidis. No gram-negative organisms grew from any of the culture sites.

CONCLUSIONS

The results of this study indicate that extended wearing schedules, and not the lens entity, predispose the patient to a higher risk of keratopathy with disposable contact lenses. No microbiological association with the adverse events could be determined, and no intrinsic patient factor could be demonstrated that would predict the likelihood of complications.