Monovision vs. soft diffractive bifocal contact lenses: A crossover study

The relative clinical performance of monovision and the Hydro® ECHELON® soft diffractive bifocal contact lens were evaluated in a 1 -month, two-period, open-label crossover study. Wearers' subjective impressions were also elicited. Monovision provided superior low contrast acuity and the bifocal better stereopsis. No difference was found for high-contrast visual acuity or physiological signs. Although monovision was subjectively preferred for reading, no difference was found for other subjective variables. These included visual quality ratings at far and intermediate viewing distances, under dimly lit conditions, when driving at night, and for overall preference. Similiar patient acceptance can be expected for both modalities. The results of this study reflect a significant improvement in performance of the diffractive bifocal lens over previous simultaneous vision bifocal contact lens damage.     

Patient response to concentric bifocal contact lenses.

We evaluated the visual results and success rate with a center-near concentric simultaneous vision bifocal contact lens. Forty subjects (screened from 175 presbyopic applicants) entered the study and were fitted with the CIBA Spectrum bifocal lenses (BCL) and also with single vision distance contact lenses combined with reading glasses (DCL). Visual acuity and stereoacuity measurements were made at dispensing and after 8 weeks of regular bifocal contact lens wear. At both times, visual acuity measurements with BCL were significantly reduced by 1-1.5 lines compared to DCL. Stereoacuity was reduced by 32-36" with BCL compared to DCL. Thirty-two patients completed the study and 27 chose to continue wearing BCL after completion of the study. None of the subjects had adverse corneal findings or problems of discomfort. The primary reason for BCL discontinuation was blurred vision. The data was retrospectively analyzed to identify risk factors for discontinuance--none were significant.     

Pupil dependency of bifocal contact lenses

The advantages and the problems associated with use of alternating vision and simultaneous vision bifocal contact lenses are analyzed. The changes in pupil diameter associated with changes in illumination and in the distance of the task make the selection of the best bifocal design complex.     

Clinical evaluation of three bifocal contact lenses

The ACC, Alges, and Tangent Streak bifocal contact lenses were fit in separate populations of presbyopic patients, some of whom had not previously worn contact lenses. Complete eye examinations were performed on fitting and at 6 and 12 months after fitting to determine how effectively the lenses corrected presbyopic symptoms. Patients were examined for subjective comfort, visual acuity, contrast sensitivity, and by slit lamp. Sixteen of the 24 ACC lens wearers (67%), 23 of 31 Alges lens wearers (74%), and 25 of 27 Tangent Streak lens wearers (93%) wore their lenses comfortably after 12 months. Nine of 18 failures (50%) were successfully refit in one of the other bifocal lenses. Most patients read 20/25 and J1 with contrast sensitivity in the normal range at distance and near. Twelve of 16 patients (75%) with no prior contact lens experience continued to wear the lenses at 12 months. We believe that bifocal contact lenses provide an acceptable alternative for the correction of presbyopia. Lens fitting requirements and patient selection are discussed.     

The design characteristics of bifocal contact lenses

Problems associated with the correction of presbyopia with bifocal contact lenses are discussed. The designs of bifocal contact lenses manufactured by the major foreign firms are analyzed.     

Traditional methods for the treatment of presbyopia: spectacles, contact lenses, bifocal contact lenses

Today, many options are available for the correction of presbyopia. New technology perpetually surfaces to offer better ideas and designs to meet the visual demands of the presbyopic population. This article provides information on various modalities for spectacle and contact lens correction of presbyopia. It is based on current information at the time of publication and is not intended to be a fitting guide.     

Inspection of back surface aspheric contact lenses

Two methods of clinically inspecting and verifying rigid back surface aspheric contact lenses were investigated. A modification of the Radiuscope was found to be an accurate method for making such measurements. Measurement data of a number of aspheric lenses obtained by using this procedure are presented.     

Visual performance with aspheric rigid contact lenses

Single vision aspheric contact lens designs may be able to enhance visual performance by controlling spherical aberration. In this study, we have compared the visual performance provided by two front surface aspheric rigid contact lenses with that of a spherical rigid contact lens and spectacle correction. These 4 corrections were worn by ten subjects while visual acuity was determined as a function of aperture size. The possibility that front surface aspheric lens designs may enhance visual performance was confirmed, although individual subjects varied significantly in this visual response. Contributions to the visual performance, other than contact lens surface shape, may include lens position and stability.     

Predicting and assessing visual performance with multizone bifocal contact lenses.

PURPOSE: To investigate how bifocal contact lenses, when combined with the aberrations of the eye, will affect visual performance. Also, to investigate the relationship between the patient's predicted and actual visual benefit with bifocal contact lenses. METHODS: The monochromatic aberrations of 16 subjects were measured and used to simulate visual quality with three bifocal contact lens designs. Actual and computed visual benefit was compared for an Acuvue bifocal contact lens in 5 of the 16 subjects. RESULTS: Subjects were predicted to have either a bifocal response or an increase in depth of focus for all lens designs. Our subjects were predicted to have a decrease in visual benefit for distance viewing and a gain in visual benefit at near compared with not wearing a contact lens. We found a statistically significant association between our subjects' predicted and actual visual benefit with the Acuvue Bifocal contact lens (r = 0.685, p = 0.008). CONCLUSIONS: Bifocal contact lens designs, when combined with the aberrations of the eye, will not always provide bifocal vision. Visual quality with a bifocal contact lens can be predicted based on a patient's ocular aberrations.     

Optical and visual performance of aspheric soft contact lenses.

PURPOSE: This study was conducted to investigate whether aspheric design soft contact lenses reduce ocular aberrations and result in better visual acuity and subjective appreciation of clinical performance compared with spherical soft contact lenses. METHODS: A unilateral, double-masked, randomized and controlled study was undertaken in which ocular aberrations and high and low contrast logMAR visual acuity were measured on myopic subjects who wore aspheric design (Biomedics 55 Evolution, CooperVision) and spherical design (Biomedics 55, CooperVision) soft contact lenses. Ten subjects who had about -2.00 D myopia wore -2.00 D lenses and 10 subjects who had about -5.00 D myopia wore -5.00 D lenses. Measurements were made under photopic and mesopic lighting conditions. Subjects were invited to grade comfort, vision in photopic and mesopic conditions, and overall impression with the two lens types on 100 unit visual analogue scales. RESULTS: There was no significant difference in high contrast or low contrast visual acuity between the two lens designs of either power under photopic or mesopic conditions. Both lens designs displayed lower levels of spherical aberration compared with the "no lens" condition under photopic and mesopic light levels (p < 0.0001); however, there were no differences in aberrations between aspheric and spherical lens designs. There were no statistically significant differences in subjective appreciation of clinical performance between lens designs or lens powers. CONCLUSIONS: At least with respect to the brand of lenses tested, the fitting of aspheric design soft contact lenses does not result in superior visual acuity, aberration control, or subjective appreciation compared with equivalent spherical design soft contact lenses.     

Corneal topographic data: its use in fitting aspheric contact lenses.

We conducted a retrospective assessment of the fitting characteristics obtained with the Boston Envision rigid gas permeable contact lens to determine the best parameter for selecting an initial base curve. We fit 13 subjects (11 successfully) with the Envision lens, using computerized videokeratoscopy to evaluate prefitting corneal topography. The selected base curve of the lenses fit most closely to the flattest K at the 5 mm zone. This value may be the best parameter for selection of an initial base curve, especially in eyes with keratoconus. Using topographic information may give quicker and more accurate initial fits than keratometry alone.     

Task and visual performance with concentric bifocal contact lenses

We evaluated the effects of concentric simultaneous vision bifocal contact lenses on task performance, visual acuity, and stereopsis. Forty extensively screened presbyopes were fitted with CIBA Spectrum center-near bifocal contact lenses (BCL) and with distant contact lenses combined with reading spectacles (DCL) which served as the control. Thirty-two subjects completed the 8-week study. At dispensing and after 8 weeks of regular BCL wear, performance times with BCL were significantly greater than with DCL for all three near tasks. BCL generally resulted in more errors per trial. Visual acuities with BCL were reduced significantly by 0.8 to 1.4 acuity lines compared to DCL. Stereopsis was reduced significantly by 32 to 36 sec arc with BCL compared to DCL at both measurement sessions. It is likely that the decreased task performance with the simultaneous vision BCL is caused by the decreased visual acuity with these lenses. Nonetheless, 27 patients (58.7% of those selected to be fitted; 67.5% of those who were fitted) chose to wear the BCL on a regular basis at the study conclusion. Thus, even though BCL reduced task and visual performance, thoroughly screened and properly fitted presbyopic patients can become satisfied BCL wearers. However, the reduced task and visual performance with BCL should be considered when evaluating prospective BCL candidates.     

Maximum disparity with acuvue bifocal contact lenses with changes in illumination.

PURPOSE: To assess the visual performance of Acuvue bifocal contact lenses at different illumination levels using a stereoscopic parameter, the maximum disparity. We compare the results with those for progressive spectacle lenses. METHODS: We used a modified Wheatstone stereoscope and random-dot stereograms (RDS) as tests. The maximum disparity was measured for each observer at different luminance levels. RESULTS: Maximum disparities did not show statistically significant differences for a wide range of luminance levels with contact lenses. The maximum disparities found when some contact-lens users wore progressive spectacle lenses were similar. CONCLUSIONS: The results show that the Acuvue bifocal lenses offer good performance for a near visual task, in this case the maximum disparity, for changes in illumination and are similar to that with progressive spectacle lenses.     

Soft bifocal contact lenses for patients with nearpoint asthenopia

Bifocal contact lenses have generally been considered solely for the presbyopic population. However, pre-presbyopic individuals with accommodative or vergence disorders who respond favorably to plus lenses at near may be good candidates for bifocal contact lenses. A group of ten non-presbyopic patients who manifest accommodative dysfunctions or near point esophoria were fit with the Ciba BI-SOFT contact lenses. Nearpoint accommodative and vergence findings were evaluated through both near point plus spectacle lenses and the bifocal soft lenses. Results indicate that the BI-SOFT bifocal contact lens was effective in changing the near point visual posture. However, poor distance vision acuity due to ghost images reduced the subjective success rate of the BI-SOFT lens on this non-presbyopic population.