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PubMed1993

[Contact lenses--medical indications and problems].

Today, hard and soft contact lenses are useful visual aids. In common with any other effective medication, however, they can also produce side effects. They are medically indicated whenever spectacles fail to optimally compensate poor vision. They are not easy to customize, and wearers must be examined by the ophthalmologist more frequently than wearers of eye glasses. Complications are more common with contact lenses than with other visual aids. Nevertheless, modern lens systems do provide optimal correction of impaired sight in any age group. The present paper offers an overview of the limitations and possibilities of treatment with contact lenses, and discusses the medical indications.

Adolescent↗
PubMedDate not supplied

Field restriction and vignetting in contact lenses with opaque peripheries.

BACKGROUND: Some previous researchers have shown empirically that visual fields can be restricted by contact lenses with opaque and semi-opaque peripheral zones. However, there has been no formal statement of the optical theory behind such restriction. METHODS: Calculations are made of fields of view with opaque periphery contact lenses, based on paraxial theory and meridional finite ray tracing in the Gullstrand-Emsley schematic eye. RESULTS: This analysis shows that paraxial theory is adequate for predicting 'half fields of full illumination' for ocular pupil diameters smaller than six millimetres, although paraxial estimates of 'half total field' can substantially underestimate those obtained by finite ray tracing for a wide range of ocular pupil sizes. Therefore finite ray tracing may be a more appropriate method of calculating half total field. 'Total field' will be smaller with smaller ocular pupils and smaller contact lens apertures. A clinical method is suggested for assessing total field with such contact lenses in situ. The analysis applied to opaque periphery contact lenses is extended to the semi-opaque periphery contact lenses used for cosmetic alteration of eye appearance. CONCLUSION: Semi-opaque periphery contact lenses will decrease retinal illuminance most at regions outside those tested by previous empirical static perimetry studies.

Journal Article↗
PubMed2003

Oculocardiac reflex caused by contact lenses.

PURPOSE: To report two cases of patients who fell unconscious because of the oculocardiac reflex when attempting to wear contact lenses. CASE REPORTS: Case 1: A 15-year-old healthy boy came to our clinic to be fitted with contact lenses. As soon as a hard contact lens was inserted forcibly, he became unconscious. Case 2: A 22-year-old man fell unconscious the instant that the eye was compressed with a hard contact lens. Neither patient had used glasses or contact lenses before. Their blood pressure was decreased while unconscious. They recovered consciousness after about 10 min, and nausea and vomiting settled subsequently. Contact lens insertion was tried again carefully after 1 week avoiding compression of the eyes and there were no problems. They are currently using contact lenses without any problems. CONCLUSION: Insertion of contact lenses may rarely provoke the oculocardiac reflex.

Adolescent↗
PubMed2006

Cellular retention on diagnostic contact lenses: an evaluation of current cleaning protocol.

AIMS: To compare cellular contamination of diagnostic contact lenses after two different cleaning methods. METHODS: Twenty-five used diagnostic contact lenses were cleaned by two different methods and the material retained on their contact surface examined for cells. Two diagnostic contact lenses were examined using electron microscopy and surface debris was subjected to x-ray photoelectron spectroscopy. RESULTS: Significantly more cells were present on used lenses compared with controls (P<0.001). There was no significant difference in total cell count between the lenses subjected to the two cleaning strategies but the lenses simply wiped clean retained marginally more nucleated cells than controls (P=0.039). Electron microscopy showed the majority of the debris on or close to the rim of the lens. X-ray photoelectron spectroscopy confirmed the presence of proteinaceous material. CONCLUSIONS: Regardless of cleaning method, significant cellular debris is retained on the surface of diagnostic contact lenses after use.

Cell Count↗
PubMed1998

The efficacy of SimulVue and Unilens RGP aspheric bifocal contact lenses in the treatment of esotropia associated with a high accommodative convergence/accommodation ratio.

PURPOSE: This was a prospective study assessing the efficacy of the SimulVue bifocal contact lens and the Unilens RGP aspheric multifocal contact lens (Unilens, Largo, Fla.) in the treatment of high accommodative convergence/accommodation (AC/A) esotropia in an adolescent and postadolescent population. METHODS: Those patients meeting the inclusion criteria were fit with contact lenses with use of full cycloplegic refraction and later retested by an examiner masked to the previous binocular status. Particular attention was given to the sensory status and the motor fusion of each patient in their bifocal spectacles and then in their bifocal contact lenses. All patients were followed up for at least 6 months after the contact lenses were fitted. RESULTS: Five of the six patients demonstrated larger angles of esophoria or tropia at near with the contact lenses than with bifocal spectacles. The only patient who maintained excellent stereopsis in bifocal contact lenses was the one who normalized her AC/A ratio during this study and no longer required a bifocal in her spectacle correction for fusion. The two patients who initially had no stereopsis but good alignment in spectacle correction had a large esotropia at near fixation with bifocal contact lenses. CONCLUSIONS: The SimulVue and Unilens RGP aspheric bifocal contact lenses did not adequately treat adolescent patients who had esotropia associated with a high AC/A ratio.

Accommodation, Ocular↗
PubMed1999

Process capability measurement of frequent replacement spherical soft contact lenses.

Frequent replacement soft contact lenses must have good reproducibility in order to avoid clinical problems arising from manufacturing variations in lens parameters. This study assessed the actual and potential process capability of eight frequent replacement lenses (monthly or 2-weekly replacement) in relation to back vertex power, back optic zone radius, total diameter and centre thickness. Twenty-four lenses in three powers (-1.00, -3.00, -6.00 D) were measured for eight frequent replacement lenses: Acuvue, Acuvue 2, Biomedics 55, Encore, Focus, Optima FW, Soflens 66, Surevue. In general, the lenses showed adequate reproducibility in respect of those parameters likely to affect lens fit, namely back optic zone radius, total diameter and centre thickness. The process capability results showed some variation in reproducibility of BVP between lens types and between lens powers. Process capability was found to be a useful measure of contact lens reproducibility.

Journal Article↗
PubMed1983

Pseudomonas corneal ulcer with extended-wear soft contact lenses for myopia.

Extended-wear soft contact lenses for myopic correction are becoming a more frequent alternative to spectacles. The risk of corneal ulceration with their use exists. In our patient, a 29-year-old woman, a severe Pseudomonas aeruginosa corneal ulcer developed after the use of extended-wear contact lenses for myopia.

Adult↗
PubMed1984

Surface deposits on worn hard contact lenses.

Giant papillary conjunctivitis (GPC) is associated with deposits on contact lenses. We used scanning electron microscopy to study the anterior surface of 30 hard contact lenses, both cleaned and not cleaned, worn by patients with GPC and with keratoconus and by asymptomatic subjects. Uncleaned lenses worn by asymptomatic subjects for one day had deposits on about 5% of the surface. In most cases, the deposits were removed completely by one cleaning. Uncleaned lenses worn by patients with GPC or keratoconus had deposits on about 90% of the surface. Most of these deposits were removed by one cleaning. However, residual deposits after cleaning were greater on lenses from patients with keratoconus than on those from patients with GPC. Lenses from asymptomatic subjects rarely had residual deposits after cleaning. We found that the types of deposits on worn soft and hard contact lenses are similar, that there are fewer deposits on hard lenses than on soft lenses, and that deposits on hard lenses, unlike those on soft lenses, generally can be removed by one cleaning.

Conjunctivitis↗
PubMed1989

Microwave disinfection of soft contact lenses.

We evaluated the effectiveness and convenience of microwave irradiation as a method of disinfecting soft contact lenses. Soft contact lenses from each of the four Food and Drug Administration (FDA) categories were placed in sterile vials and immersed in 2 ml of saline which had been contaminated with one of three common species of bacteria. The contaminated lens vials were placed in a standard 600 W microwave oven and exposed to microwave irradiation times ranging from 30 to 180 s. Significant reductions in bacteria colony counts were found after 30 s of microwave irradiation. Few of the bacteria survived 60 s of microwave exposure and none survived 90 s. Our findings indicate that microwave disinfection can be an effective and rapid means of killing bacteria on soft lenses and in the storage solution. However, further studies are necessary to determine the minimum exposure time required, the effect of microwave disinfection on other microorganisms, and the effect of microwave irradiation on contact lens polymers and lens dimensions.

Bacterial Infections↗
PubMed1978

Light transmission of hydrogel contact lenses.

The visible-light transmission of various Bausch & Lomb Soflens contact lenses and HydrocurveTM contact lenses was measured with a Perkin-Elmer model 202 UV spectrophotometer. The light transmission for both types of lenses ranged from 96-99%, and was almost constant over the visible spectrum. Neither the power, the thickness, nor the posterior apical radius of the lenses had a significant effect on the amount of light they transmitted.

Contact Lenses, Hydrophilic↗
PubMed1990

Experimental Pseudomonas aeruginosa keratitis from extended wear of soft contact lenses.

We used a rabbit model to investigate the pathogenesis of soft contact lens-induced bacterial keratitis. Rabbit eyes underwent complete tarsorrhaphy for 7 days either with (group A, n = 14) or without (group B, n = 13) new sterile soft contact lenses. On day 7, an increase in mean corneal thickness (20.3% in group A and 17.2% in group B) was detected. New or rabbit-worn soft contact lenses were then inoculated with 10(7) colony-forming units of Pseudomonas aeruginosa or by 0.1 mL of P aeruginosa suspension. On day 9, conjunctival cultures of all eyes yielded P aeruginosa. Corneal infection developed in 11 of 14 eyes wearing new or worn, contaminated soft contact lenses. Bacterial keratitis did not develop in any of the 13 eyes inoculated with P aeruginosa suspension. Light and electron microscopy of infected eyes showed abundant polymorphonuclear neutrophils destroying the epithelium, basement membrane, and stroma. Few bacteria could be detected and only in the deep stroma. Since bacterial suspension alone caused no inflammation, soft contact lens-wear appears crucial to corneal infection in this model.

Animals↗
PubMedDate not supplied

Aberration generation by contact lenses with aspheric and asymmetric surfaces.

PURPOSE: We explored the potential of aberration correction in the human eye by using a new generation of soft contact lenses with aspheric and asymmetric surfaces. METHODS: Soft contact lens samples were designed with one asymmetrical surface (front) and one spherical (back) to produce predetermined amounts of desired pure defocus, astigmatism, trefoil, coma, and spherical aberration. Contact lens wavefront aberrations were measured ex vivo using a Fizeau-Tolanski interferometer and compared with the in vivo wavefronts obtained by subtracting the aberrations of the eye with and without the contact lenses. These second set of measurements were obtained using a Shack-Hartmann sensor. RESULTS: We found that an aberration-free contact lens sample induced in the eye a small amount of residual aberration. We obtained a good match between the ex vivo and in vivo wavefront measurements for most of the samples of the contact lenses. CONCLUSIONS: The aberrations generated by soft contact lenses on the eye were predictable. Rotations and translations of the contact lenses with respect to correct position on the eye were, however, the main limitation for precise correction of the ocular aberrations.

Adult↗
PubMed1983

[Papillomatous hyperplastic conjunctivitis caused by contact lenses].

The characteristic features of contact lens-induced giant papillary conjunctivitis, as observed in 64 cases between 1978 and 1980, are described. The main symptoms are increasing lens intolerance with foreign body sensation, mucus discharge and reduced vision. The typical subtarsal sign is cobblestone formation resembling vernal conjunctivitis. Therapy must achieve complete disappearance of the conjunctival lesions, to avoid recurrences. Discontinuing lens wear is sufficient only in the less pronounced cases (stage I and II). In the fully developed cases, additional cryocoagulation of the lesions proved to be effective. The differences in the clinical pattern between our group of patients and that of Allansmith et al. (1977) support the opinion that surface deposits on the contact lenses are pathogenetically of prime importance.

Adult↗
PubMed2003

Do daily wear opaquely tinted hydrogel soft contact lenses affect contrast sensitivity function at one meter?

PURPOSE: To investigate the effects of daily wear opaquely tinted hydrogel soft contact lenses on contrast sensitivity functions, as measured using the Pelli-Robson chart viewed at 1 meter. METHODS: Contrast sensitivity was measured in 48 healthy individuals before and 6 hours after soft contact lens wear. Twenty-four subjects used clear soft contact lenses and 24 used tinted soft contact lenses. RESULTS: The contrast sensitivity scores were significantly decreased monocularly and binocularly (P = 0.000 and P = 0.002, respectively) in the colored contact lens group whereas there were no significant changes in the clear contact lens group (P = 0.317 and P = 0.317, respectively). CONCLUSIONS: Color-tinted contact lenses were associated with a reduction of contrast sensitivity function. Therefore, those who wear colored contact lenses should be informed about the possible consequences of tinted contact lens wearing.

Adult↗
PubMed1996

Infrared pupillometry in presbyopes fitted with soft contact lenses.

The influence of pupil size, lens centration, and translation on multifocal contact lens performance suggests that these parameters should be accounted for in the optical design of presbyopic contact lenses. The purpose of the present article is to complete the existing experimental data with clinical measurements of pupil diameter and lens position relative to the pupil in a group of presbyopes, with controlled target luminance, stimulus distance, gaze angle, and convergence. The experiments involve an infrared video-pupillometer and ring-marked contact lenses. Results on pupil aperture show that the effect of changing target distance is comparable in magnitude to that of varying luminance within the photopic range. The measured data on lens position confirm that soft contact lenses are generally decentered from the pupillary axis, usually in inferior temporal direction, and that their average translation between primary and downward gaze is very small. It is also found that the average relative position between lens and pupil centers is slightly modified by changes of luminance in far vision. All these results provide characteristic values which are helpful for the optical modelling of presbyopic contact lenses.

Adult↗
PubMed1979

Problems associated with prolonged wear soft contact lenses.

Complications of prolonged wearing of soft contact lenses are corneal infection, peripheral vascularization, giant papillary conjunctivitis and allergy, sterile ulcers, corneal warping, lens infection, protein and calcium deposits, lens fragility, and problems with disinfecting solutions. Further long-term studies are needed to compare the safety of prolonged wear soft contact lenses with the safety of intraocular lenses, on which long-term studies are currently being done.

Conjunctivitis↗
PubMed2000

Accelerated photostability testing of precision UV(TM) contact lenses.

Precision UV(TM) contact lenses were photoaged beyond their expected lifetime in an accelerated manner with a SUNTEST(R) CPS(+) system, which is a solar spectrum equivalent. Ultraviolet spectra of lenses irradiated for 30 h in saline at 41 degrees C and 44 degrees C at the highest power setting were statistically indistinguishable from those measured prior to the exposure. In a similar experiment run at 79 degrees C, the UVB range of the spectra showed small but statistically significant differences, whereas the UVA range of the spectra were not distinguishable. Lenses photoaged at half power and twice the time at 43 degrees C gave UV spectra that could be distinguished. Refractive indices of lenses were indistinguishable before and after irradiation. Eluted materials could not be detected in the saline used to maintain lenses in any irradiation experiment. Lens parameters and water contents remained within manufacturing specifications before and after irradiation.

Journal Article↗
PubMed1984

Contact lenses and the work environment.

Controversial opinions have been presented about the use of contact lenses in industrial environments. Work environments contain few obstacles to the use of contact lenses, but many occupations are associated with the risk of excessive difficulties, spoilation , irritation, or complications. From the radiant energy the shorter (280 nm) ultraviolet (UV) wavelengths and the longer (1300 nm) infra-red (IR) wavelengths are absorbed by contact lenses, the absorption increases their temperature and may cause corneal complications. Protective glasses, however, absorb more than 99.5% of the UV and IR energy and thus provide sufficient protection for contact lens wearers exposed to UV or IR radiation. The advantages and risks of contact lenses in industrial work are discussed.

Contact Lenses↗