A summary of the findings from the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. CLEK Study Group.

BACKGROUND: This summary of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study includes the study design and results to date. METHODS: The CLEK Study is a longitudinal, observational study of 1,209 patients with keratoconus. The study's main outcome measures are corneal scarring, visual acuity, corneal curvature, and quality of life. RESULTS: These patients' mean age at baseline was 39.3 +/- 10.9 years, and they had moderate to severe keratoconus. Ninety-five percent of the patients had steep keratometric readings of at least 45 D, and 78% had best-corrected visual acuity of 20/40 or better in both eyes. Sixty-five percent of the patients wore rigid gas-permeable contact lenses in both eyes, and most of those (73%) reported that their lenses were comfortable. Most rigid gas-permeable contact lens wearers were fitted with apical touch (88%). Fifty-three percent had corneal scarring in one or both eyes, and corneal scarring was associated with corneal staining, contact lens wear, age, the presence of a Fleischer's ring, and a steeper cornea. Corneal scarring was associated with decreased high- and low-contrast visual acuity. CONCLUSIONS: These results characterize keratoconus patients as rigid gas-permeable contact lens wearers with moderately steep corneas. Corneal scarring is associated with decreased vision in keratoconus.     

The prevalence and pattern of contact lens use in a Singapore community.

PURPOSE: We conducted a cross-sectional survey to determine the prevalence, socio-demographic patterns, and characteristics of contact lens use in an electoral community in Singapore. METHODS: One thousand eight hundred fifteen persons aged between 12-55 years from 768 households were surveyed using a standardized pre-tested questionnaire. RESULTS: The percentage of contact lens wearers in the survey populations was 9.0%. Forty-two percent of surveyed individuals were myopes, 21.8% of whom wore contact lenses. Contact lens wearers tended to be young Chinese females with higher level education and incomes. Most wore monthly disposable or daily wear soft contact lenses. Convenience and cosmesis were the main reasons cited for contact lens wear. Optometrists, who prescribed the bulk of contact lenses, were also the most influential in determining consumers' choice of lenses. CONCLUSION: Information gathered in this population-based survey may be used to facilitate national eye-care planning and provide a baseline for comparison with rates of lens wear found in other countries and in future surveys.     

Keratocyte density in keratoconus. A confocal microscopy study(a)

PURPOSE: To estimate keratocyte density in human corneas with keratoconus by confocal microscopy. DESIGN: Prospective, observational cohort study. METHODS: Twenty-nine unscarred corneas of 19 patients with keratoconus and 29 corneas of 19 controls matched for age (+/-3 years) and contact lens wear were examined by using confocal microscopy. Images were recorded from the full-thickness central cornea. A masked observer manually counted bright objects (keratocyte nuclei) in images without motion blur. Cell densities in anteroposterior stromal layers of keratoconus corneas were compared with densities in corresponding layers of control corneas. RESULTS: In keratoconus patients, age 40 +/- 15 years (mean +/- standard deviation), keratocyte density was 19% lower in those who wore contact lenses (16,894 +/- 4032 cell/mm(3), n = 12) than in those who did not wear contact lenses (20,827 +/- 4934 cell/mm(3), n = 17, P =.03). In control patients, age 39 +/- 16 years, there was no difference in keratocyte density between those who wore contact lenses (n = 12) and those who did not wear contact lenses (n = 17, P =.80). Among contact lens wearers, keratocyte density was 25% lower in keratoconus corneas (16,894 +/- 4, 032 cell/mm(3), n = 12 [9 = rigid gas-permeable lenses, 3 = soft lenses]) than in control corneas (22,579 +/- 2, 387 cell/mm(3), n = 12 [3 = rigid gas-permeable lenses, 9 = soft lenses], P =.002), the result of cell density being lower in the most anterior keratocyte layer (P =.001) and the layers between 0% to 10% (P <.001), 67% to 90% (P <.001), and 91% to 100% (P <.001) of stromal thickness. Among noncontact lens wearers, there was no difference in cell density between keratoconus and controls (P =.41). CONCLUSION: Keratocyte density is decreased in the anterior and posterior stroma of keratoconus patients who wear contact lenses.     

The vascular response to contact lens wear

The ocular limbal blood vessels were studied in daily wearers of soft contact lenses and hard contact lenses, and in eyes of subjects who had never worn a contact lens. The degree of filling of vessels and the number of vessels crossing the limbus were measured photographically at the inferior limbus. The extent to which vessel filling in contact lens wearers could be considered as capillary injection, as apposed to new vessel growth, was estimated by comparing the degree of injection in lens wearers to that found in nonwearers given a vasodilating stimulus. It was found that soft lens wearers showed greater limbal injection than hard lens wearers. The limbal vasculature of hard lens wearers was indistinguishable from that of nonwearers. The vascular response to soft lens wear was similar in magnitude to that produced by vasodilating agents in noncontact lens wearers, and was therefore considered to be due to the filling of preexisting capilliaries rather than new vessel growth. The chronic level of vessel dilation in soft lens wearers is cause for concern, as sustained dilation of the limbal vessels may be a precursor to new vessel growth.     

Corneal endothelial polymegathism after the extended wear of rigid gas-permeable contact lenses

To determine if there are any corneal endothelial cell size and shape changes in subjects wearing rigid gas-permeable contact lenses for cosmetic extended wear, six unadapted lens wearers were fitted using four different lens materials. Each subject wore one lens extended-wear and the other daily-wear for 3 months. Before lens wear and after 3 months, noncontact endothelial photographs were taken. Cell tracings were analyzed by a digitizing computer. This study showed significant endothelial polymegathism, an increase in maximum cell area to minimum cell area, and a significant decrease in percent frequency of hexagonal cells in the extended-wear eyes. There existed in these subjects a significant correlation between changes in cell size (polymegathism) and cell shape (pleomorphism).     

Comparison of tear-film osmolarity in different types of contact lenses.

PURPOSE: To investigate the tear-film osmolarity of contact lens wearers for different types of contact lenses. METHODS: Fifty six eyes of 56 cases were evaluated in four different groups according to the type of contact lens worn, with 14 eyes in each group. Groups 1 and 2 consisted of subjects who wore frequent-replacement daily wear soft contact lenses; group 1 lenses had 55% water content, and lenses in group 2 had 38% water content. Groups 3 and 4 consisted of subjects who wore rigid gas-permeable contact lenses, with a Dk value of 90 in group 3 and a Dk value of 52 in group 4. Tear-film osmolarity values in milliosmole (mosm) units were determined by auto-osmometer (Orstat 6030, Daiichi Kagacu, Kyoto, Japan) before and after contact lens wear for each group, and the results were compared statistically by ANOVA test. RESULTS: Before the period of contact lens wear, the tear-film osmolarity values of group 1, 2, 3, and 4 were 283.61+/-12.83 mosm, 285.23+/-8.94 mosm, 285.57+/-11.39 mosm, and 280.15+/-12.07 mosm, respectively. After the period of contact lens wear, these values were measured at 312.15+/-16.03 mosm in group 1, 316.54+/-12.14 mosm in group 2, 313.14+/-9.66 mosm in group 3, and 316.38+/-11.60 mosm in group 4. Although the difference between the values before and after the period of contact lens wear was statistically significant for each group (F=291.45; P=0.0005), there was no statistically significant difference among the groups. CONCLUSIONS: When a contact lens is placed in the eye, the lens alters the normal structure of the tear film and affects its rate of evaporation; therefore tear-film osmolarity may increase. In our study, all contact lenses produced a similar effect on tear-film osmolarity.     

Rigid gas-permeable lenses for extended wear--a 1-year clinical evaluation

A 1-year evaluation of the feasibility of the use of gas-permeable rigid lenses for extended wear was carried out, using two different materials. Forty subjects were entered into the study. Fifteen were fitted with the Polycon II lens and another 15 with the Boston IV lens. These two groups wore the lenses on a weekly basis for the duration of the study. Two other groups, the controls, were fitted with the same types of lenses as the experimental groups, but wore the lenses on a daily basis. All lenses were made to the Syntex specifications for the Polycon lens and the groups were comparable with regard to age, sex, refractive error, corneal astigmatism, and any pre-existing ocular pathology. All subjects carried out the same care regimen for their lenses and were examined after 24 h, 1 week, 1 month, 3 months, 6 months, and 1 year. Examinations performed at the follow-up visits were to determine any clinically observable effects of lens wear in each patient in all groups. The results of the study suggest that the extended wear of gas-permeable rigid materials is a viable option. However, the results also indicate that extended wear is not without problems, and these need to be studied more fully before the use of gas-permeable rigid lenses for extended wear can be recommended.     

Visual acuity in contact lens wearers.

PURPOSE: The difference between high- and low-contrast visual acuity provides a sensitive indicator of vision loss in ocular disease; however, the effect of refractive error correction on this difference is still debated. METHODS: High- and low-contrast visual acuity was measured in 116 rigid gas permeable contact lens wearers, 51 spectacle wearers, and 50 soft contact lens wearers with habitual and best correction. Twenty-nine of the soft contact lens wearers reported that they wore disposable contact lenses (discarded on a monthly or more frequent basis), whereas the other 21 soft contact lens wearers wore traditional soft contact lenses. RESULTS: Rigid gas permeable contact lens wearers had statistically worse high-contrast habitual visual acuity than spectacle wearers (Tukey-Kramer, p = 0.0075). Traditional soft contact lens wearers had significantly worse low-contrast visual acuity compared with all other groups (Tukey-Kramer, p < 0.02 for each comparison). Traditional soft contact lens wearers had a significantly larger difference between high- and low-contrast visual acuity with best correction compared with rigid gas permeable wearers (Tukey-Kramer, p = 0.0099). CONCLUSIONS: Rigid gas permeable contact lens wearers had statistically worse habitual high-contrast visual acuity compared with spectacle wearers, but no difference was present under best-corrected conditions. We hypothesize that rigid gas permeable contact lens wearers were not wearing their optimal correction habitually. Traditional soft contact lens wearers had significantly worse low-contrast visual acuity. They also had a larger difference between their best-corrected high- and low-contrast visual acuity scores compared with rigid gas permeable contact lens wearers.     

A 6-month follow-up of successful refits from daily disposable soft contact lenses to continuous wear of high-Dk silicone-hydrogel lenses

PURPOSE: To compare, in routine optometric practice, the outcome of keeping successful soft contact lens (SCL) wearers in their lenses to re-fitting them with continuous wear of silicone hydrogel (SiH) lenses. METHODS: Forty-nine successful daily disposable lens wearers were recruited; 19 continued to wear daily SCLs and 30 were refitted with high-Dk SiH lenses on a 30-day/night schedule. Patients were assessed at baseline, 3 and 6 months by slit lamp examination along with the Efron grading scales, and central corneal thickness (CCT) and the corneal endothelium were assessed by non-contact specular microscopy. RESULTS: No substantial changes in subjective vision, refraction, visual acuity or overall lens comfort occurred for those completing the study, although five SiH lens wearers did discontinue due to reduced comfort, eyelid problems or seasonal allergy. Contact lens induced peripheral ulcers (CLPU) were observed in three patients in the first 3 months in the SiH lens group and these were also discontinued. Over the 6 month period, a complete set of records was obtained for 16 in each group. For those completing the study, lens dryness scores were variable, but there was a slight improvement in favour of SiH lenses. Small, but statistically significant, reductions in corneal staining, bulbar hyperaemia, and limbal neovascularisation in favour of the SiH lenses were also evident but mainly because of further increases in the daily lens wearers. Contact lens induced papillary conjunctivitis (CLPC) and corneal endothelial polymegethism were mild to moderate and showed slight increases in the daily lens wearers at 6 months. CONCLUSIONS: The present studies confirm that the continuous wear of SiH lenses for up to 30 days can be considered as an alternative to daily disposable soft lens wear, but is not suitable for everyone.     

Acanthamoeba keratitis. A growing problem in soft and hard contact lens wearers

Eleven contact lens-wearing patients presented with Acanthamoeba keratitis. Eight cases were culture- and/or stain-positive for Acanthamoeba and three were presumed to have Acanthamoeba keratitis based on history and clinical findings. Six wore daily wear soft contact lenses, two wore extended-wear soft contact lenses, one wore a polymethylmethacrylate hard contact lens, one wore a gas-permeable hard contact lens, and one wore a Saturn lens (combined hard and soft lens). Four patients used distilled water and salt tablet saline, three used tap water and salt tablet saline, two used tap water rinse, two used well water rinse or storage, and one used intravenous (IV) saline. It is apparent that all contact lens wearers are at some risk for Acanthamoeba keratitis developing if proper contact lens care is not maintained. Of great concern is the inability of most current chemical sterilization methods to kill the organism if the lens becomes contaminated. Heat disinfection will kill Acanthamoeba trophozoites and cysts but the lens must not be placed into contaminated solutions afterward. Prevention is very important because medical and surgical treatment failures are frequent. Eye care practitioners who fit contact lenses are advised to use heat disinfection for low-water content stock soft contact lenses, and to use hydrogen peroxide without a catalyst for a minimum of 6 hours for all other stock lens fitting sets, to specifically inquire about contact lens care habits used by their patients, and to discourage the use of homemade saline solutions.     

The characteristics of corneal staining in successful daily and extended disposable contact lens wearers

Purpose : The aim of this investigation was to measure levels of corneal staining in successful daily and extended wearers of disposable hydrogel contact lenses. Methods : Twenty-four subjects on a daily wear (DW) schedule and 20 subjects on an extended wear (EW) schedule were examined at six-monthly intervals over a two-year period. Subjects wore two types of disposable hydrogel lenses. Measurements were taken from the eye wearing an etafilcon A contact lens only. The cornea was divided into five equally sized zones and the extent and depth of corneal staining were assessed on a zero to four scale. Results : The overall levels of corneal staining were low with median values below or equal to grade 0.5 in all groups. There was no difference in the extent, depth or geographical distribution of corneal staining between the DW and EW groups. Staining was more frequently recorded in the superior and inferior areas of the cornea than in the central, nasal or temporal regions (Pearson's Chi-Square, p < 0.10). Conclusions : The mode of wear with disposable contact lenses is not a contributing factor to the amount of corneal staining seen in successful wearers. Low levels of corneal staining should be expected in successful DW and EW wearers.     

The frequency of ocular symptoms during spectacle and daily soft and rigid contact lens wear.

PURPOSE: Ocular discomfort is the primary reason for discontinuation of contact lens wear. The purpose of the study was to quantify and compare the frequency of ocular symptoms experienced by spectacle wearers and wearers of soft and rigid daily contact lenses. METHODS: We analyzed the results of an ocular symptom survey of prospective volunteers for contact lens clinical trials during the period 1989 to 1995. Questions pertaining to lens-wear experience and ocular symptoms were answered by 883 untrained individuals without active ocular disease. The sample included 664 spectacle wearers, 171 soft contact lens (SCL) wearers, and 48 rigid gas-permeable (RGP) lens wearers. The frequencies of 10 ocular symptoms were compared for each group. Spearman's Rank Correlation was used to test for correlations between symptoms. The chi2 test was used to determine differences between subject groups, adjusted for multiple comparisons. RESULTS: There were no significant differences in the frequency of ocular symptoms between the soft contact lens (SCL) and RGP wearers. The most common symptom was ocular tiredness (27%). None of the symptoms were highly correlated, indicating that they are somewhat different "sensations." Despite ocular discomfort being the primary reason for discontinuation of lens wear, contact lens wearers experienced the same type and severity of symptoms as spectacle wearers. Thus (in order of frequency of occurrence), tiredness, itchiness, watering, pain, aching, excessive blinking, and burning had similar rates of occurrence for all three groups. The two major distinguishing symptoms were dryness and redness, which were reported far more frequently and with greater severity in both contact lens groups (p < 0.001). Grittiness was also reported more with RGP wearers than with spectacle wearers (p < 0.001). CONCLUSIONS: Contact lenses disturb the ocular environment, as evidenced by responses of increased ocular dryness, redness, and grittiness. Despite fundamental differences in SCL's and RGP contact lenses, both groups of contact lens wearers surveyed experienced a similar type and frequency of ocular symptoms.     

Visual acuity,spectacle blur and slit-lamp biomicroscopy on asymptomatic contact-lens-wearing recruits

Refraction data of 644 Dutch Army and Air Force recruits wearing contact lenses or spectacles were statistically compiled and correlated with the type of lenses worn. Visual acuity with contact lenses was far from optimal because the power of the lenses was incorrect or the optical quality poor. This applied particularly to soft contact lenses. On the other hand, spectacle blur was rare with soft lenses and less evident with gas-permeable hard lenses compared with conventional hard lenses. Less corneal staining occurred with gas-permeable hard lenses compared with conventional hard lenses (P=0.02). Corneal neovascularization, conjunctival hyperaemia, papillary changes in the tarsal conjunctiva, corneal opacifications and ghost vessels were seen more often in wearers of soft rather than hard lenses. In this study, in which we examined objective parameters of contact lens efficiency, the gas-permeable hard lenses appeared most favourable.     

Hypoxic effects on the anterior eye of high-Dk soft contact lens wearers are negligible.

PURPOSE: To determine whether the eyes of high-Dk soft contact lens wearing subjects can be discriminated from non-contact lens wearing subjects. METHODS: This study was a prospective masked assessment of 32 subjects, 16 of whom wore experimental high-Dk soft contact lenses and 16 of whom did not wear contact lenses. Subjects wore high-Dk lenses on a 30-night replacement schedule for an average of 9 months. Tear film characteristics, staining and vascularization of the cornea, conjunctival staining, and the presence of microcysts in the corneal epithelium were assessed using slitlamp microscopy. The endothelium was examined for polymegethism. RESULTS: No differences were found between the two groups in any of the variables that were examined (p > 0.05) except that the high-Dk lens wearing group had about twofold more tear film debris and 2.5-fold more severe conjunctival staining (p < 0.05). CONCLUSIONS: Hypoxia-associated effects were not apparent in the eyes of subjects wearing experimental high-Dk soft contact lenses. Conjunctival staining can generally distinguish lens wearers from non-lens wearers and can be used to discriminate between high-Dk lens wearing subjects and non-lens wearing subjects.     

Vascular response to extended wear of hydrogel lenses with high and low oxygen permeability.

PURPOSE: The purpose of this study was to determine the impact of extended wear of high and low oxygen permeability (Dk) lenses on the development or resolution of limbal hyperemia and corneal neovascularization in a randomized prospective clinical trial. METHODS: Adapted daily-wear contact lens wearers were randomly assigned to one of two groups. The low-Dk group (N = 23) wore etafilcon A lenses (Dk/t = 40) for up to 7 days and 6 nights, and the high-Dk group (N = 39) wore lotrafilcon A lenses (Dk/t = 175) for up to 30 days and nights. Limbal hyperemia and neovascularization were assessed and graded during 9 months of extended wear. A stratified analysis to determine how change in ocular redness depended on initial presentation was also conducted. RESULTS: On a 0 to 100 scale, extended wear of low-Dk lenses resulted in a 16-point increase in limbal hyperemia (p < 0.0001); no significant change occurred with the high-Dk lenses. The difference was greatest for low-Dk participants who initially presented with lower levels of hyperemia (N = 18). There was a slight resolution of redness in participants who initially presented with higher levels of hyperemia (N = 10) after wearing the high-Dk lenses. Neovascularization increased by an average of 0.5 on a scale of 0 to 4 in low-Dk lens wearers (p < 0.0001) but remained unchanged in the high-Dk lens wearers. The increase was most marked for the low-Dk group with lower levels of neovascularization at baseline. CONCLUSIONS: Subjects who wore lenses with higher oxygen permeability for 9 months of extended wear exhibited a lower vascular response of the ocular surface compared with subjects who wore lenses of lower oxygen permeability for the same period. This result was found both for the surface limbal vessels and in the deeper neovascular stromal vessels. Moderate neovascularization also developed after 3 months of extended wear of low-Dk hydrogels, whereas high-Dk lenses caused no neovascularization.     

Corneal epithelial permeability during extended wear of disposable contact lenses versus daily wear of soft contact lenses.

AIMS--The corneal epithelial permeability during extended wear of disposable contact lenses was compared with that during daily wear of soft contact lenses. The study was performed to verify whether the extended wear of disposable contact lenses would result in a higher permeability value than the daily wear of soft contact lenses. A higher permeability makes the cornea more vulnerable for bacterial infections and thus could explain the higher incidence of bacterial keratitis found in extended wear of disposable contact lenses in comparison with the daily wear of soft contact lenses. METHOD--The corneal epithelial permeability was determined by fluorophotometry in 33 healthy volunteers after the wear of soft, daily wear contact lenses for at least 6 months. Thereafter the determination was repeated in each volunteer after extended wear of disposable contact lenses for 1 month. The permeability in 34 healthy non-contact lens wearing volunteers was determined as a control. The permeability value was calculated from the amount of fluorescein that passed into the cornea after application by means of an eyebath. RESULTS--The mean permeability values after daily and extended wear were 0.032 nm/s and 0.031 nm/s, respectively. The values were not significantly different (Wilcoxon paired test p > 0.5). The mean permeability for the non-contact lens wearing controls was 0.042 nm/s. CONCLUSION--The results do not sustain the explanation that a difference in permeability value is the main cause of the increased incidence of keratitis during extended wear of disposable contact lenses in comparison with daily wear.     

Nitric oxide levels in tears of patients with mild forms of papillary conjunctivitis induced by rigid gas-permeable contact lenses.

PURPOSE: To determine whether nitric oxide (NO) is detectable in the tear fluid of patients with mild forms of papillary conjunctivitis who wear rigid gas-permeable contact lenses. METHODS: Tear samples were taken from 12 users of rigid gas-permeable contact lenses and 12 healthy controls. Samples were analyzed, and the levels of NO were determined. RESULTS: The mean level of NO in those who wore contact lenses was 118.98 micromol/L (95% CI: 91.85-146.10 micromol/L); whereas the level of NO found in the control subjects was 114.84 micromol/L (95% CI: 102.54-127.14 micromol/L). The difference was statistically insignificant (P>0.05). CONCLUSION: Nitric oxide levels in the tear fluid of rigid gas-permeable contact lens users did not correlate with the presence of mild symptoms of papillary conjunctivitis.     

Corneal endothelial polymegethism and pleomorphism induced by daily-wear rigid gas-permeable contact lenses.

PURPOSE: To determine if there are any corneal endothelial cell size and shape changes (and the time course of these changes) in subjects wearing rigid high gas-permeable (RGP) contact lenses for daily wear. METHODS: Ninety-seven eyes of 57 new wearers were fitted with a fluoroperm contact lens material (Persecon92E, oxygen transmissibility (Dk)= 92 x 10(-11)). Prior to lens wear and after 1 week, 1 month, 3 months, 6 months, and 1 year, noncontact endothelial photographs were taken. Maximum cell size/Minimum cell size (Max/Min) was measured as an index of polymegethism and the relative frequency of 5-, 6-, and 7-sided cells was evaluated. RESULTS: An increase in the ratio of Max/Min was present 1 week after lens fitting and increased further over the subsequent year. This study showed significant increase in endothelial polymegethism and in the relative frequency of 7-sided cells, but a significant decrease in the relative frequency of 6-sided cells. CONCLUSIONS: Daily-wear high Dk gas-permeable contact lenses can cause endothelial polymegethism and pleomorphism similar to those caused by soft and hard contact lenses.     

A market survey of contact lens practice in Hong Kong

Purpose : The aim of this survey was to evaluate the use of contact lenses, current prescribing habits of practitioners and the development of the contact lens market in Hong Kong. Methods : Questionnaires were sent to all registered contact lens practitioners in Hong Kong. This questionnaire sought information about their choices on prescribing contact lenses and lens care products and their opinions on continuing education and future trends of contact lens development. Results : A total of 286 responses (22 per cent) were returned. On average, the respondents reported that 36 per cent of their patients were contact lens wearers and most were myopes. The ratio of new fittings to refittings was 1:3. Of the contact lens wearers, 66 per cent were fitted with planned replacement lenses, mostly daily disposable lenses. Multipurpose solution was the most popular lens care regimen prescribed. Only 48 per cent of astigmatic patients were fitted with toric lenses and the use of overnight orthokeratology and silicone hydrogel lenses was limited. Single vision contact lenses with over‐spectacles and monovision contact lenses were the most popular management for presbyopes. Dryness was the major problem reported by contact lens wearers. Practitioners look forward to further development of custom‐made toric, multifocal and silicone hydrogel lenses. The major source of new contact lens information was communication with contact lens suppliers. Conclusion : Compared to previous reports, there was no significant change in the prescribing habits of practitioners. The major complaint of contact lens wearers is still ocular dryness. The contact lens market is driven by younger contact lens wearers, and planned replacement soft contact lenses together with multipurpose solutions dominate. The use of bifocal/multifocal lenses remained low and practitioners want low cost bifocal/multifocal contact lenses with better visual performance and toric lenses with a wider range in parameters. The use of overnight wear lenses such as silicone hydrogel and ortho‐k lenses is limited and 30 days continuous wear silicone hydrogel lenses are prescribed mainly for daily wear.     

Six-month evaluation of extended wear soft contact lenses among armor troops: Part I,clinical findings

This report addresses the clinical aspects of wearing contact lenses in an operational military environment. Male volunteers in an armored division wore extended wear soft contact lenses (SCL) or spectacles for up to six months, participating fully in their units' normal activities. Seventy-four percent of those successfully fitted with SCL wore their lenses for the duration of the study when administrative losses were factored out. More than one-third of the SCL wearers experienced one or more ocular conditions requiring at least a temporary suspension of lens wear. Corneal edema and corneal staining occurred rarely at clinically significant levels. High rates of corneal vascularization were influenced by reporting criteria. Relatively frequent conjunctival injection appeared to be largely due to environmental factors.