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Soflens (polymacon) contact lenses were subjected to long-term heat disinfection in a carefully controlled laboratory study and in a patient clinical study. No adverse effects were observed on the physical or chemical properties of the lenses other than the deposition of some tear components in a portion of the patient-worn lenses. This was not unexpected since no enzyme or surfactant cleaners were used.
A soft contact lens, because of its elasticity, can re-center itself over the cornea after it has been displaced by a blink. In this paper, a potential energy method is used to simulate the centering mechanism. Specifications for commercially available soft contact lenses and realistic eye shapes are used for the examples. With this technique we can compare the centering attributes of different lens and eye geometries.
PURPOSE: To establish proper contact lens care as a common practice by discovering the quantity and condition of protein deposition on various types of soft contact lenses. METHODS: The amounts of deposition of two proteins found in tear fluid, lysozyme and albumin, on various types of contact lenses were measured. Lenses deposited with albumin and lenses deposited with lysozyme were stained with Coomassie brilliant blue (CBB). Frozen cross-sections of these lenses were examined using a microscope. RESULTS: A considerably larger amount of lysozyme was found on group IV (U.S. Food and Drug Administration classification) contact lenses. Conversely, there were no significant differences between the four groups in the quantity of albumin found. When various lenses were stained with CBB, only the lysozyme-deposited lenses of group IV obtained a strong tint. When cross-sections of the tinted group IV contact lenses were examined, not only the surface, but also the matrix of the lens was stained. CONCLUSIONS: Results suggested that the reason group IV lenses accumulated a considerably greater amount of lysozyme than did lenses of other groups is that lysozyme accumulates not only on the surface, but also in the matrix of group IV lenses.
Complications associated with rigid contact lenses are more frequent in aphakia. The limited dexterity of older patients not only may prove an insurmountable barrier to the mastery of daily contact lens insertion and removal, but also may produce significant direct eye trauma, its seriousness determined by the integrity of the cataract wound. Since prolonged wear of aphakic contact lenses is the rule rather than the exception, the risk of irreversible corneal changes such as vascularization and erosions is greater. A poorly fitted aphakic contact lens that does not permit adequate oxygenation of all corneal areas makes such complications even more likely to occur. Decreased corneal sensitivity associated with cataract surgery permits continued wear of a poorly fitted lens, which does not allow the cornea to recover between wearing periods. Detection of keratoconjunctivitis sicca, more prevalent in the older age group, may prevent the associated complications of corneal erosion, iritis, and infection. Complications of aphakic contact lenses can be controlled by patient instruction, appropriate contact lens adjustments, and regularly scheduled follow-up examinations.
Extended wear contact lenses are now a reality. Unfortunately, the physiological basis for their apparent success is less based on knowledge than wishful thinking. This paper discusses both what we know and what we don't know with the goal of giving the practitioner in the field a global view of this important and controversial procedure.
Hydrogel (HEMA) contact lenses of increased thickness were worn by owl monkeys (Aotus tivergatus) under open and closed eye conditions to study ultrastructurally the corneal epithelial response to increased stress. The 0.07 mm thick lens with a calculated Dk/L of 4.2-2.2 caused an epithelial thinning without oedema. This thinning was due to a loss of superficial cells and a flattening of the remaining ones. Factors in the mechanism of epithelial thinning without oedema may include anoxia, trauma, lid pressure, and lens weight. The 0.4 mm thick lens offers negligible gas transmission in the closed eye, and after 48 hours much of the epithelium was stripped, while oedema and degenerative cytoplasmic changes were prominent in areas of surviving cells. In such areas the thickness of the epithelium was reduced to one or two layers of cells. The basement membrane was in all experiments unharmed by hydrogel contact lens wear. The epithelial innervation was maintained in all corneas except those of the closed eye, and finding correlates well with the good corneal touch threshold in soft contact lens wearers.
PURPOSE: To evaluate the effect of soft contact lenses with different lens power on the measured value of the intraocular pressure with non-contact pneumotonometry. METHODS: 120 eyes (80 healthy volunteers: 50 women, 30 men, aged 22 to 61 years) were included in this study. Intraocular pressure was measured with a pneumotonometer Canon X-10 before and after insertion of the Ciba Vision Focus Night&Day soft contact lens. We used contact lenses with different lens power of + 0.25 D, + 1.00 D, + 4.00 D, - 1.00 D, and - 4.00 D. The averages of three measurements were taken as representative IOP values that were statistically evaluated. RESULTS: IOP measured over myopic lenses of - 1.00 and - 4.00 D showed lower values within the mean range of 1 mm Hg. The difference between the measurements over the myopic lenses was mostly smaller than +/- 2 mm Hg (78% when using - 1.00 D and 90% when using - 4.00 D contact lens). All the differences using + 0.25 D contact lens were smaller than +/- 2 mm Hg. The difference was considerably higher in measurements over + 1.00 and + 4.00 hyperopic contact lenses and showed strong increase with the lens power. CONCLUSIONS: In our study we showed that intraocular pressure can be reliably measured with non-contact pneumotonometry over myopic lenses or hypermetropic lenses with small lens power. This suggests that non-contact pneumotonometry is a useful method in patients wearing therapeutic contact lenses and contact lens wearers who, when measuring the eye pressure, would not need to remove the contact lenses before the examination.
Contact lenses can be worn in a variety of environmental conditions and do not increase the wearers risk of injury. In many situations they offer significant corneal protection. Currently firefighters are prohibited from using contact lenses. To evaluate whether contact lenses are a safe form of visual correction 50 firefighters were fitted, and examined after 1, 4 and 10 months of contact lens wear. Twenty-nine were fitted with soft contact lenses, and 21 with rigid gas permeable contact lenses. Statistically significant increase in lid sulcus hyperaemia was found in both the SCL and RGPCL groups (P < 0.01, P = 0.02, respectively), as well as an increase in hyperaemia of the vertical quadrant of the bulbar conjunctivae (P = 0.01, P = 0.02, respectively). In addition the RGPCL group showed a statistically significant increase in hyperaemia of the lateral portion of the bulbar conjunctivae (P < 0.01), consistent with exposure epitheliopathy. The SCL group showed statistically significant increase in corneal staining in the vertical quadrant for all visits (P = 0.02, P = 0.01, P = 0.02 for all visits, respectively), indicative of lens dehydration. These findings although clinically significant are not unique to firefighting, and are found within a "normal" population of contact lens wearers. In conjunction with questionnaire data (Owen et all, 1996) we conclude that soft contact lenses can be worn safely by firefighters without additional risk.
Standard methods of contact angle analysis include sessile drop, captive bubble and Wilhelmy plate techniques; however, these methodologies are not particularly well suited for assessing the wettability of the surfaces of formed hydrogel contact lenses. This paper describes two methodologies that are adaptations of previously described techniques. The maximum adherent force method is an adaptation of the dynamic Wilhelmy plate technique that allows the assessment of whole, finished contact lenses. The dynamic photographic method allows the simultaneous assessment of the front and back surfaces of strip samples for the assessment of advancing and receding contact angles. Lenses investigated were made from polyhydroxyethyl methacrylate, hydroxyethyl methacrylate/methacrylic acid and hydroxyethyl methacrylate/glycerol methacrylate. The lenses were manufactured by lathing, spin-casting or cast-moulding techniques. Overall, both techniques demonstrated few differences between the wettability of different lens materials and no differences between materials of the 'same' lens type but manufactured by different methods. These findings are consistent with the results of clinical studies, which have shown little difference between contact lens surface wettability in vivo, which may be due to the apparent natural surface wettability-enhancing properties of the pre-lens tear film.
INTRODUCTION: Increasingly aspherical optics are used in contact lens designs to produce a varifocal effect to correct presbyopia. Whilst no current ISO standard describes a method to verify these products, the vertex power needs to be verified by the manufacturer and optometrist. Visionix claim that the VC2001 instrument is able to resolve the vertex power of complex contact lenses and that it has been adopted by contact lens manufacturers as their "gold standard" method of measure. Practitioners rely on the focimeter for contact lens verification and accept that it has poorer resolution. This raises the question of whether practitioners can verify the vertex powers of varifocal contact lenses to a sufficient sensitivity. The purpose of this study is to determine whether a focimeter can differentiate between various vertex powers incorporating differing degrees of asphericity that are used in contact lens designs. METHODS: A range of varifocal contact lenses were used with single vision contact lenses as controls. Three types of focimeters were used: a manual focimeter, a projector focimeter and a computerised focimeter (standard and contact lens modes). The VC2001 assessed the vertex powers over the optical zone and was used as a reference for the focimeters. The measures from the VC2001 and the focimeters were analysed by discrepancy analysis. RESULTS: All discrepancy measures fell outside two standard deviations for either the varifocal contact lenses or the single vision contact lenses when the focimeters were compared to the VC2001. This raises the issue of whether the focimeters are measuring the same parameter as the VC2001. Only the analysis of the repeated measurements from the manual focimeter for single vision contact lenses demonstrated an acceptable measure of precision (+/-0.21, 2S.D.) with a very small degree of bias (mean difference -0.024, +/-0.02 [2S.E.]). CONCLUSION: These results suggest that the manual focimeter can measure the vertex powers for single vision contact lenses to an acceptable degree of precision. The vertex powers of varifocal lenses cannot be verified using standard practice equipment. The VC2001 has poor precision for power measurements and may not be measuring the same parameter as the focimeters and therefore questions the validity of the VC2001 as the "gold standard" for vertex power measurement.
Disposable soft contact lenses have been marketed as a safer alternative to conventional soft lenses. We undertook a case-control study of patients attending the casualty unit of an eye hospital to quantify the relative risk of keratitis in disposable lens wear and to establish associated patterns of use. All eligible contact lens users were identified and asked to complete a questionnaire (n=242). Keratitis, microbial or sterile, was the most common complication in disposable lens users, occurring in 16 of 41 subjects. The relative risks for all lens types were estimated by comparison with rigid lenses (the referent). Both extended- and daily-wear disposable lenses were associated with higher risks of keratitis than other lens types including conventional extended-wear lenses. Poor hygiene, disinfectant system failure, and lens type may all account for these statistically significant trends.
Convex-surfaced contact lenses increase the power of the laser optically for surgery on the iris. Their power-increasing faculty becomes obvious by their power of image magnification. When linked by functions, lens power, laser power, and magnification increases. The laser power, which is multiplied by the lenses, contains a safety feature for the tissues outside the focus of the laser beam as the beam increases in angle. Safety and power is gained by the appropriate use of power-multiplying contact lenses for argon laser surgery.
AIMS: To describe the fitting of patients with high or irregular astigmatism following penetrating keratoplasty with contact lenses and to answer the question whether or not contact lenses with special back surface design can improve visual acuity in complex cases after penetrating keratoplasty. METHODS: 28 eyes were included. They were fitted with contact lenses with a special back surface that was designed for optical rehabilitation after penetrating keratoplasty. Four different types of these lenses (tricurve, keratoconus, reverse, oblong) were used selectively depending on abnormal eccentricity determined by videokeratoscope. The patients were followed up for an average period of 15.5 months. Lens tolerance and corrected visual acuity were evaluated and compared with that corrected with spectacles. RESULTS: The visual acuity was significantly improved in nearly all eyes with an average increase of 3.6 lines (maximal nine lines) accompanied by good contact lens tolerance and satisfactory contact lens fit. No noticeable complications were observed. CONCLUSION: Contact lenses with special back surface design can improve visual results and lens tolerance, and minimise problems in contact lens fitting. This is in favour of contact lenses as an alternative to surgical procedures for correction of high or irregular astigmatism after penetrating keratoplasty. This procedure is recommended especially in cases of patients who decline further operative interventions.
Deposits on soft contact lenses of high water content were investigated morphologically and chemically and compared with those on conventional soft contact lenses of poly (2-hydroxyethyl methacrylate). The material of the lenses examined in this investigation was the crosslinked copolymer of methyl methacrylate and N-vinylpyrrolidone with a water content higher than 70%. Morphologically, the deposits on the lenses with high water content were found to have no characteristics distinguishable from those on conventional lenses. By the electron microscopic observation of the cross section of a lens that had become opaque, it was confirmed that the deposit was on the lens surface and that no deposit was within the lens. Some spots on the lenses were recognized as colonies of microorganisms, but the majority of the spots had no involvement by microorganisms. Surface analysis with Fourier transform infrared spectrometer (FT-IR) confirmed that the main component of the filmy deposit was protein. Protein was detected in most of the deposits. The amino acid compositions of the proteins were found to be close to that of lysozyme. From the elemental analysis of several spots, silicon, aluminum, iron, and some other elements were detected. The structural analysis of some spots by a laser Raman microprobe (MOLE) revealed the existence of lipids. In several cases, the deposits were found to have grown around a defect of the lens surface. A mechanism for the formation of deposits is suggested.
The number of contact lenses worn has increased steadily in the last decades. The number and types of complications have increased in approximately the same degree. New, hitherto unknown, complications are continually described. The complications are classified according to the factors which cause them: complications of mechanical origin; complications due to metabolic disorders; allergic reactions; exogenous infections; disorders of tear production. The lesions found in the cornea and the conjunctiva are described. The complications caused by hard lenses are usually noticed earlier by the patient than those due to soft lenses, because the lesions caused by hard lenses are usually painful, whereas those due to soft lenses are not.
The visual results, stereopsis, and complications have been assessed on 50 patients in a presenile age group treated for uniocular aphakia. Twenty-five patients received a Binkhorst four-loop lens implant at the time of cataract surgery and 25 were offered a conventional hard contact lens trial postoperatively. The period of follow-up ranged from one to three years.
PURPOSE: Giant papillary conjunctivitis in patients wearing contact lenses occurs after intolerance and/or allergy to contact lenses. Eotaxin is a CC chemokine with a potent and specific chemotactic effect for eosinophils, which are involved in allergies. The purpose of this study is to measure the eotaxin levels in tears of patients wearing contact lenses and in normal subjects. Eotaxin levels were also correlated with the grade of giant papillary conjunctivitis. METHODS: Around 10 microL of tears were collected with glass capillaries in 16 patients wearing contact lenses and in 10 normal volunteers. Giant papillary conjunctivitis was graded from 0 to 4 by reference to standard slit-lamp photographs of the superior tarsal conjunctiva. Eotaxin concentration in tears was measured by ELISA using mouse anti-human eotaxin monoclonal antibodies. For the statistical analysis of the results, the paired Wilcoxon/Kruskal-Wallis test was used. RESULTS: The mean concentration of eotaxin was 2698+/-233 (SEM) pg/mL in patients wearing contact lenses and 1498+/-139 pg/mL in normal subjects. The difference was statistically significant (P=0.0004). The mean score of papilla grade was 1.75+/-0.19 in patients wearing contact lenses and 0.2+/-0.13 in normal subjects (P<0.0001). Papilla grade could be correlated to the eotaxin level in tears (R2=0.6562 and P<0.0001). CONCLUSION: An increase of eotaxin levels in tears was measured in patients wearing contact lenses. Eotaxin levels correlated with the severity of giant papillary conjunctivitis. These data suggest that eotaxin could play a role in papilla formation.
Contact lenses in the elderly patient are often prescribed for visual correction and/or corneal rehabilitation. The success of contact lenses in the geriatric patient is often limited by such factors as abnormal adnexal physiology, decreased manual dexterity, high degrees of refractive error, and low vision. Assessment of these factors prior to contact lens fitting can greatly increase the success of these unique contact lens applications. Indications and contraindications for contact lenses in the elderly, the need for special lens handling and care by family members, and available specialty lenses will be discussed.