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PubMed1995

Soft lens movement: effects of humidity and hypertonic saline on lens settling.

Hydrogel contact lenses require a settling period before lens fit stabilizes, but the process underlying the initial reduction in lens mobility is poorly understood. Explanations for this phenomenon include base curve steeping with dehydration, expulsion of postlens tear fluid, and osmotic flow of hypotonic tears into the cornea. We conducted two randomized, single-masked interocular comparisons for ten subjects wearing HEMA lenses for 1 h. We investigated potential mechanisms of dehydration-dependent lens tightening, by limiting dehydration in one eye using a high humidity environment (experiment 1), and of a hypotonic lacrimation-dependent decrease in lens movement, by presoaking lenses in isotonic (0.9%) or hypertonic (1.5%) saline (experiment 2). Lens mobility profiles were not significantly affected by modification of environment; lenses in both normal and high humidity environments displayed a significant reduction in lens movement during the first 15 min of wear (ANOVA, p = 0.0001), and no change in lens mobility thereafter. Lens mobility profiles were identical for lenses presoaked in isotonic and hypertonic saline, with initial lens movement being significantly greater than for subsequent measurements (ANOVA, p < 0.05). These studies find no evidence to support dehydration-dependent steepening of base curve, or osmotic-dependent binding from hypotonic lacrimation as mechanisms for the initial postinsertion decrease in lens movement.

Adult↗
PubMed2002

Use of contact lenses to correct aphakia in children.

BACKGROUND: Contact lenses play an important role in the management of childhood aphakia. However, the use and care of the lenses can be challenging. The aim of this study was to determine how parents coped and what problems they encountered. METHODS: Thirty-one families of aphakic children who were fitted with contact lenses between 1990 and 1997 were contacted and invited to participate in a telephone survey. RESULTS: Thirty families agreed to participate. Eighteen families (60%) were still using contact lenses successfully at the time of the study. Four families (13.3%) stopped using contact lenses within a year because of overwhelming difficulties handling the lenses. There was an initial learn-ing process that was often stressful and frustrating. The learning curve lasted from 1 to 24 months (first quartile 2.0 months; median 3.3 months; third quartile 15.0 months). The personality of the parent, temperament of the child and the frequency at which problems occurred may all have contributed to how each family coped with the lenses. Common initial problems included inserting the lenses into the eyes of an uncooperative child and the loss of lenses. Other problems included irritation associated with dryness, and the financial cost of maintaining the lenses. CONCLUSION: Although most parents initially found contact lenses daunting, 70% of families surveyed eventually learned to cope well. Parents felt that proper education of both parents and children on why the lenses were required, a good appreciation of problems that may occur, a strong social support network and adequate financial aid were important factors in learning to cope.

Adaptation, Psychological↗
PubMed2003

The effects of ocular and lens parameters on the postlens tear thickness.

PURPOSE: To assess the effects of soft contact lens base curve radius (BCR), sex, ethnicity, central corneal curvatures, and vertical palpebral aperture size (PAS) on the postlens tear thickness (PLTT). METHODS: The PLTT was measured using optical pachometry on 114 experienced lens wearers who were fitted with lathe-cut soft lenses (Alden 47, polymacon, 35.5% H2O, -2.00 diopter, and 14.0 mm). Each subject was randomly allocated to one lens group receiving a BCR of 7.9, 8.3, or 8.7 mm. Pachometry measurements were taken at 30 min after lens insertion. Vertical PAS and keratometry readings were measured for 94 of the 114 subjects. RESULTS: The mean (95% confidence interval) PLTT was 15.7 microm (13.2-18.0 microm), 12.8 microm (10.9-14.7 microm), and 12.1 microm (10.2-14.0 microm) for the 7.9-mm, 8.3-mm, and 8.7-mm BCR groups, respectively. The differences in PLTT among the three BCR groups was significant (analysis of variance F-test; P=0.039). Post hoc testing using the Tukey honestly significant difference statistic showed that only the two extreme BCR groups (7.9 mm and 8.7 mm) were significantly different. Sex had no effect on the PLTT; however, the PLTT was significantly thinner for the Asian compared with non-Asian eyes (P=0.0001). The Asian PLTT did not vary with different soft lens BCRs. The non-Asian PLTT was thicker with lenses of the steep BCR compared with the flat BCR. CONCLUSION: These results show that the base curve radius of a soft contact lens and several ocular characteristics can affect the thickness of the postlens tear film.

Adult↗
PubMed2004

Bone-anchored hearing aid in unilateral inner ear deafness: a study of 20 patients.

OBJECTIVE: To evaluate the benefit of a bone-anchored hearing aid (BAHA) contralateral routing of sound (CROS) in 20 patients with unilateral inner ear deafness. SUBJECTS: 21 patients were recruited; 15 had undergone acoustic neuroma surgery and 6 patients had unilateral profound hearing loss due to other causes; 1 patient was excluded. Only patients with thresholds of better than 25 dB HL (500-2000 Hz) and an air-bone gap of less than 10 dB in the best ear were included. METHODS: Evaluation involved audiometric measurements before intervention, when fitted with a conventional CROS and after implementation and quantification of the patients' subjective benefit with a hearing aid-specific instrument: the Abbreviated Profile of Hearing Aid Benefit (APHAB). RESULTS: Lateralization scores were not significantly different from chance (50%) in any of the three conditions. Measurements of speech perception in noise showed an increase in the signal to noise ratio (S/N ratio) with the conventional CROS (p = 0.001) and with the BAHA CROS compared to the unaided condition when speech was presented at the front with noise on the poor hearing side. On the other hand, a lower S/N ratio was seen with the BAHA CROS (p = 0.003) compared to the unaided situation when noise was presented at the front with speech on the poor hearing side. The patient outcome measure (APHAB) showed improvement, particularly with the BAHA CROS. CONCLUSIONS: The poor sound localization results illustrate the inability of patients with unilateral inner ear deafness to localize sounds. The speech-in-noise measurements reflect the benefit of a BAHA CROS in lifting the head shadow while avoiding some of the disadvantages of a conventional CROS. The benefit of the BAHA CROS was most clearly reflected in the patients' opinion measured with the APHAB.

Adult↗
PubMed2004

Apical clearance rigid contact lenses induce corneal steepening.

PURPOSE: Anecdotal reports suggest that steeply fitted rigid contact lenses can induce corneal steepening and myopic shifts in refraction. This study investigated changes in corneal topography, corneal thickness, and refraction after short-term wear of apical clearance lenses. METHODS: : Ten young adults participated in the study in which apical clearance lenses (Conoid, Hydron Pty. Ltd., Frenchs Forest, NSW, Australia), fitted approximately 0.3 mm steeper than the flattest keratometric reading, were worn for 4 h. A polymethyl methacrylate (PMMA) lens was worn in one eye, and a Boston XO lens (Bausch & Lomb, Rochester, NY) was worn in the other. Lenses were nonfenestrated in the first trial, and a single midperipheral fenestration was incorporated for a second trial. Corneal topography was monitored using the EyeSys topographic analysis system (EyeSys Vision, Inc., Houston, TX); central corneal thickness was quantified using ultrasonic pachometry; and refraction and anterior ocular response were also monitored. RESULTS: Significant central corneal edema (8.2 +/- 2.2%) was demonstrated in the PMMA lens-wearing eye only. Fenestration did not reduce the edema response. We found significant corneal steepening over a 5- to 6-mm central zone, which was more pronounced in the PMMA lens-wearing eye and was modified by lens fenestration. The curvature changes altered central corneal shape from prolate (Q = -0.06 +/- 0.10) to oblate (Q = -0.26 +/- 0.31). A slight myopic shift in refraction (-0.38 +/- 0.60 D) was found with the PMMA lenses only. CONCLUSIONS: : Apical clearance lenses induce corneal steepening after short-term wear. Although corneal molding is implicated as the primary factor driving the shape change, corneal edema and postlens tear film pressures can modify this response.

Adult↗
PubMedDate not supplied

Clinical evaluation of a full-digital in-the-ear hearing instrument.

In this study we measured the efficacy of a digital hearing aid with compression and noise reduction in a well-controlled clinical field trial in two independent centres. The experiments focused on a number of aspects of the application of the digital hearing aids. The study combines a field test of 2x4 weeks with laboratory experiments. We used objective measurements (speech perception tests in background noise, loudness scaling) and subjective assessments (questionnaires). The measurements were performed before and after the field test. The questionnaires were collected after each field test. The results of the digital hearing aids were compared to the results of similar tests with newly fitted analogue reference aids. The study involved 27 sensorineural hearing-impaired subjects, wearing new hearing aids. They comprised a representative sample of in-the-ear users. We used a crossover design in which the subjects used successively digital hearing aids and analogue reference aids in a randomized order. On average, the subjective data are more positive than the objective data. In the end, 20 out of 27 subjects had an overall preference for the digital hearing aid. The financial implications were not taken into consideration. However, objective data do not support this strong subjective preference. A reason could be that the method of analysis (short sentences in a short-duration background noise) is not suited for the digital hearing aid; the testing procedure does not allow the noise-reduction algorithm to adapt to the background noise. There was a striking difference between the results for the two centres. This difference can, to at least a certain extent, be attributed to the timing of speech relative to the background noise in the objective tests. This illustrates that the test conditions are critical in modern non-linear signal-processing hearing aids with long time constants. New evaluation techniques should be developed for this new generation of active non-linear hearing aids.

Adult↗
PubMed2001

Maximizing effective audibility in hearing aid fitting.

OBJECTIVE: This paper examines why more audibility is not always better than less audibility if hearing-impaired people are to best understand speech. DESIGN: We used speech perception data from 14 normally hearing and 40 hearing-impaired people to quantify the contribution of audibility to speech intelligibility. The quantification revealed that the effectiveness of audibility decreased with hearing loss, and the decrement was greater at high frequencies than at lower frequencies. To apply the Speech Intelligibility Index (SII) model to predict speech intelligibility for hearing-impaired people, we modified the model to take account of effective audibility rather than physical audibility. RESULTS: The modified SII model provided an adequate description of speech performance of people with a wide range of hearing threshold levels. We applied the model to the evaluation of two prescriptions for a sloping audiogram at prescribed levels and at equated loudness levels to demonstrate the necessity of considering loudness and effective audibility in prescribing amplification. Effective audibility is defined as audibility corrected for the effects of level distortion and hearing loss desensitization, and this paper proposes a method of estimating effective audibility from hearing threshold level at different frequencies. CONCLUSIONS: The practical implication of considering effective audibility in prescribing hearing aids is that for a given listening level, less gain is provided at frequencies where the hearing is most impaired to allow more gain at frequencies where audibility is most useful. In developing the NAL-NL1 prescription for nonlinear hearing aids, we adopted the modified SII model together with a loudness model to derive optimal gain-frequency response characteristics that maximize predicted speech intelligibility for people with different degrees of hearing losses.

Audiometry, Speech↗
PubMed1998

Aided speech recognition abilities of adults with a severe or severe-to-profound hearing loss.

Adults with severe or severe-to-profound hearing losses constitute between 11% and 13.5% of the hearing-impaired population. A detailed investigation of the speech recognition of adults with severe (n = 20) or severe-to-profound (n = 14) hearing loss was conducted at The University of Melbourne. Each participant took part in a series of speech recognition tasks while wearing his or her currently fitted hearing aid(s). The assessments included closed-set tests of consonant recognition and vowel recognition, combined with open-set tests of monosyllabic word recognition and sentence recognition. Sentences were presented in quiet and in noise at +10 dB SNR to replicate an environment more typical of everyday listening conditions. Although the results demonstrated wide variability in performance, some general trends were observed. As expected vowels were generally well perceived compared with consonants. Monosyllabic word recognition scores for both the adults with a severe hearing impairment (M = 67.2%) and the adults with a severe-to-profound hearing impairment (M = 38.6%) could be predicted from the segmental tests, with an allowance for lexical effects. Scores for sentences presented in quiet showed additional linguistic effects and a significant decrease in performance with the addition of background noise (from 82.9% to 74.1% for adults with a severe hearing loss and from 55.8% to 34.2% for adults with a severe-to-profound hearing loss). Comparisons were made between the participants and a group of adults using a multiple-channel cochlear implant. This comparison indicated that some adults with a severe or severe-to-profound hearing loss may benefit from the use of a cochlear implant. The results of this study support the contention that cochlear implant candidacy should not rely solely on audiometric thresholds.

Adolescent↗
PubMed2004

Hearing AIDS and music.

Historically, the primary concern for hearing aid design and fitting is optimization for speech inputs. However, increasingly other types of inputs are being investigated and this is certainly the case for music. Whether the hearing aid wearer is a musician or merely someone who likes to listen to music, the electronic and electro-acoustic parameters described can be optimized for music as well as for speech. That is, a hearing aid optimally set for music can be optimally set for speech, even though the converse is not necessarily true. Similarities and differences between speech and music as inputs to a hearing aid are described. Many of these lead to the specification of a set of optimal electro-acoustic characteristics. Parameters such as the peak input-limiting level, compression issues-both compression ratio and knee-points-and number of channels all can deleteriously affect music perception through hearing aids. In other cases, it is not clear how to set other parameters such as noise reduction and feedback control mechanisms. Regardless of the existence of a "music program,'' unless the various electro-acoustic parameters are available in a hearing aid, music fidelity will almost always be less than optimal. There are many unanswered questions and hypotheses in this area. Future research by engineers, researchers, clinicians, and musicians will aid in the clarification of these questions and their ultimate solutions.

Audiometry↗
PubMed2003

Nomogram for spherical RGP contact lens fitting in patients with pellucid marginal corneal degeneration (PMCD).

PURPOSE: To present a nomogram for spherical rigid gas-permeable (RGP) contact lens fitting in patients with pellucid marginal corneal degeneration (PMCD). METHODS: Retrospective review of the medical records of 24 patients diagnosed with PMCD who underwent an RGP contact lens trial at the Bausch & Lomb contact lens center between April 1995 and March 2002 at L.V. Prasad Eye Institute in Hyderabad, India. Data collected included age and sex of patients, duration of presenting symptoms, associated ocular conditions, presenting visual acuity, and degree of astigmatism. For the purpose of analysis, the astigmatism was classified into four groups: group 1, less than 5.00 diopters (D); group 2, 5.00 to 10.00D; group 3, 10.00 to 15.00D; and group 4, 15.00 to 20.00D. The final lens parameters, the patient's comfort level, and the duration of follow-up were analyzed. RESULTS: Forty eyes of 24 patients were fitted with RGP contact lenses during the study period. Sixteen were male patients and eight were female patients. The age of the patients ranged from 13 to 59 years, with a mean of 35.5 years. Twenty-two (91.7%) patients had typical inferior PMCD, whereas the other two (8.3%) had superior PMCD. The mean corneal curvature was 7.1 mm (range, 5.9-7.8 mm) in group 1, 6.9 mm (range, 6.6-7.9 mm) in group 2, 7.5 mm (range, 6.5-7.8 mm) in group 3, and 7.9 mm (range, 6.8-7.8 mm) in group 4. The mean base curve of the final fitting lens was 6.3 mm (range, 5.7-7.8 mm) in group 1, 6.8 mm (range, 5.9-7.8 mm) in group 2, 7.5 mm (range, 6-8.2 mm) in group 3, and 7.2 mm (range, 6.6-7.8 mm) in group 4. The mean lens diameter of the final fitting lens was 8.7 mm (range, 8.6-10.6 mm) in group 1, 9.5 mm (range, 8.8-10.5 mm) in group 2, 10.2 mm (range, 8.8-11.5 mm) in group 3, and 10.4 mm (range, 8.8-11.3 mm) in group 4. The common fluorescein patterns were central touch with midcentral peripheral pooling in 14 (35%) and dumbbell pattern in seven (17.%). The final visual acuity range with an RGP lens in the four astigmatism groups was 20/40 to 20/20 in group 1, 20/30 to 20/20 in group 2, 20/40 to 20/20 in group 3, and 20/200 to 20/50 in group 4. Twenty-one patients were comfortable with an RGP lens, and the mean duration of follow-up was 13 months. Three patients discontinued lens wear. In one patient, the lens was not stable, and the other two experienced discomfort with their lenses. CONCLUSIONS: Spherical rigid gas-permeable lenses are a good option for patients even with advanced PMCD. In patients with astigmatism of less than 10D, a lens with a base curve of 6.0 to 7.0 mm and a diameter of 8.0 to 9.5 mm seems to be a good initial lens for trial, and for patients with astigmatism of more than 10D, a lens with a base curve of 7.0 to 7.5 mm and a diameter of 10.0 to 10.5 mm seems to be a good initial lens.

Adolescent↗
PubMedDate not supplied

Field trials using a digital hearing aid with active noise reduction and dual-microphone directionality.

In this study, we measured the effects of a digital hearing aid on speech recognition or reception in noise for two noise reduction concepts: active noise reduction by speech-sensitive processing (SSP) and improved directionality by a dual- or so-called twin-microphone system (TMS). This was conducted in a well-controlled clinical field trial in 16 hearing-aid users, using a single-blind crossover design. The hearing aid fitting was controlled by insertion gain measurements and measurements with loudness scaling. This study combined laboratory experiments with three consecutive field trials of 4 weeks each. We used performance measurements (speech recognition tests in background noise), paired comparisons, and self-report measurements (questionnaires). The speech recognition or reception tests were performed before and after each field trial, the paired comparisons were performed in weeks 4 and 12, and the questionnaires were administered after each field trial. For all subjects, results were obtained for three different settings: no noise reduction, SSP alone, and TMS alone. In the last week, we also performed speech recognition or reception tests in background noise with both noise reduction concepts combined. Three types of results have been reported: "objective" results from the critical signal to noise ratios for speech recognition or reception in different background noises for different settings and "subjective" results: paired comparisons and questionnaires. The subjective scores show the same trend as the objective scores. The effects of TMS were clearly positive, especially for the speech reception threshold tests and for the paired comparisons. The effects of SSP were much smaller but showed significant benefits with respect to aversiveness and speech perception or reception in noise for specific acoustical environments. There was no extra benefit from the combined effect of SSP and TMS relative to TMS alone.

Adult↗
PubMed2002

A 1-year prospective clinical trial of balafilcon a (PureVision) silicone-hydrogel contact lenses used on a 30-day continuous wear schedule.

PURPOSE: To evaluate silicone-hydrogel balafilcon A (PureVision, Bausch & Lomb Inc., Rochester, NY) contact lenses worn on a 30-day continuous wear basis when compared with a traditional hydrogel (Acuvue, Vistakon, Johnson and Johnson Vision Products, Inc., Jacksonville, FL) worn on a 7-day extended wear schedule. DESIGN: Prospective, comparative, paired-eye, interventional, multicenter clinical trial. PARTICIPANTS: Two hundred twelve ametropes with no significant ocular pathology. METHODS: Subjects with normal ocular health who conformed to a set of standard criteria were monitored at seven different sites around the globe. Subjects wore both study lenses simultaneously, one on each eye. Lenses were assigned to right and left eyes according to a randomized schedule. The silicone hydrogel was removed and replaced every month and the traditional hydrogel was removed every 7 days and replaced at 14-day intervals. Subjects were followed for up to 1 year with discontinuation on indication divided between lens-related causes, unrelated factors, and loss to follow-up. MAIN OUTCOME MEASURES: Discontinuations, symptoms, vision, lens fit, lens surface assessment, slit-lamp assessment, and patient preferences. RESULTS: One hundred twenty three subjects completed the 12-month wearing period. There were no vision-threatening events with either lens type. The silicone-hydrogel lenses showed statistically superior performance in physiologic terms with regard to epithelial microcysts, striae, corneal staining, limbal injection, and bulbar injection. Inflammatory reactions, such as corneal infiltrates and tarsal conjunctival abnormalities occurred at similar rates between the lens types. Visible deposition and postlens debris with associated transient corneal indentation were significantly lower with the traditional hydrogel material at specific time points in the study. Visual acuity was comparable with the two lens types. Subjects rated the silicone-hydrogel material as preferable on subjective scales of dryness, comfort, and lens handling. Overall subjective performance was rated superior with the silicone-hydrogel material. CONCLUSIONS: The high oxygen performance of the silicone-hydrogel lenses provides a superior physiologic environment compared with a traditional hydrogel material during continuous wear. Despite the slightly higher levels of visible deposit on the silicone-hydrogels, superior subjective responses suggest that the plasma coating technology on these lenses is effective in providing comfortable lens wear. The results look promising for the success of silicone-hydrogels as the material of choice for continuous wear contact lenses.

Adolescent↗
PubMed2001

Fitting low ratio compression to people with severe and profound hearing losses.

OBJECTIVE: In this study, we aimed to determine the extent to which wide dynamic range compression and compression limiting could benefit severely and profoundly hearing-impaired adults. DESIGN: Subjects were fitted with multi-memory hearing aids incorporating frequency independent input-controlled compression with a 2:1 compression ratio and output-controlled compression limiting. The input compression threshold (CT) was varied to establish the lowest level that maintained audibility for conversational intensity speech without acoustic feedback oscillation. Where a low (40 to 57 dB SPL) CT was possible, this was compared with a moderate (65 to 74 dB SPL) level. The preferred input compression setting was subsequently compared with linear, compression-limited amplification in the same aids. In the three cases where 2:1 input compression could not be used, because of feedback or loudness insufficiency problems, compression limiting was compared with peak clipping. Field trials were conducted over a 2- or 3-mo period to establish preferences. RESULTS: Nine of the 16 subjects preferred the inclusion of the higher level input compression, and one preferred lower level input compression. Four subjects preferred linear, compression-limited amplification, one favored peak clipping, and one could not be satisfied with any of the options provided. CONCLUSIONS: 2:1 input compression was useful, and preferred by 10 of the subjects, but for nine subjects the preferred CT was relatively high. With a group 4-frequency average loss of 87 dB HTL, the results demonstrate that fast-acting, low compression ratio systems can be useful for losses traditionally regarded as the domain of linear amplification.

Adult↗
PubMed2003

Successful monovision contact lens wearers refitted with bifocal contact lenses.

PURPOSE: Should successful monovision contact lens wearers be refitted with bifocal lenses? METHODS: Fifty current monovision lens wearers were fitted with ACUVUE Bifocal contact lenses (Johnson & Johnson Vision Care, Jacksonville, FL). Visual function and subjective vision ratings were assessed with habitual monovision lenses at the first visit and then were repeated at the end of 6 months while wearing bifocal lenses. Lens preference was determined at the end of the 6-month study, and the subjects were called 1 year later to repeat the lens preference questionnaire. RESULTS: Forty (80%) subjects completed the 6-month study; nine discontinued for visual reasons. At the end of 6 months of wear, 68% preferred bifocal lenses and 25% preferred monovision. Of the subjects who were contacted a year later, 53% were still wearing bifocal lenses. High-contrast visual acuity and letter contrast sensitivity at distance was the same for monovision and bifocal lenses, but low-contrast acuity was better with monovision. Intermediate low- and high-contrast acuity and 3-meter and near stereoscopic acuity were better with bifocal lenses. Near high- and low-contrast acuity were better with monovision. All subjective ratings, except near vision in poor lighting, were significantly greater with bifocal lenses. CONCLUSIONS: It is possible to refit successful monovision lens wearers with simultaneous vision bifocal lenses, and these lenses should be considered as an alternative method for the correction of presbyopia. In addition, subjective responses to bifocal lenses may not be reflective of visual function measurements.

Adult↗
PubMed2000

Bone response to implant-supported frameworks with differing degrees of misfit preload: in vivo study in rabbits.

PURPOSE: To study the bone response around implants placed in tibia of rabbits that supported misfitting superstructures secured with different degrees of preload. MATERIALS AND METHODS: Twelve rabbits were provided with two terminal 10-mm and one intermediate 7-mm-long implant in each tibia. After an integration time of about 9 weeks, nine of the animals received one control framework each (n = 9), designed with good fit to all three implants. In the other tibia of these animals, and in both tibias in the remaining three rabbits, test frameworks (n = 15) were connected with a vertical misfit of about 1 mm to the intermediate implant. The intermediate set screws were tightened with a torque ranging from 15 Ncm to 26 Ncm in the different test frameworks. The fascia and skin was then sutured back over the implants. After a loading period of 2 to 3 weeks, the animals were sacrificed, and histomorphometric measurements were made and correlated to the different levels of preload of the central implant. RESULTS: The mean bone-to-metal contact for the three best consecutive threads of the central implant was 40% for both test and control sites (p > .05). Compared to the other regions of the implant thread, less bone-to-metal contact was found at the tip of the test implant threads in the low preload group (p < .05). However, the same relation was not observed in the high preload group. A significant correlation was observed between increasing degree of preload in the central screw joint and increasing bone-to-metal contact, most obviously noticed at the tip of the implant thread (p < .01). CONCLUSIONS: Misfit stress levels of clinical magnitudes do not seem to jeopardize osseointegration per se. On the contrary, clinical levels of preload stress seem to significantly promote bone remodeling at the tip of the implant thread.

Animals↗
PubMed2005

Investigation of the performance of the Menifocal Z gas-permeable bifocal contact lens during continuous wear.

PURPOSE: The Menifocal Z is an alternating vision, concentric, bifocal gas-permeable (GP) contact lens; center distance is connected to near periphery by a smooth transition zone. The lens is produced using tisilfocon A (Menicon Z material), which is approved for up to 30 days of continuous wear (CW). The aim of this study was to evaluate the clinical performance of the Menifocal Z when worn for up to 30 days of CW for 6 months. METHODS: Thirty-five existing GP lens wearers were enrolled in the study. Subjects were fitted with Menifocal Z lenses and follow-up visits were conducted after 2 weeks of daily wear and 1 day, 1 week, 6 weeks, 3 and 6 months of CW. A range of objective and subjective clinical performance measures were assessed, including distance and near visual acuity, the physiological response to CW, and subjective evaluation of vision and comfort. RESULTS: Twenty-seven subjects (77%) completed the study and eight (23%) discontinued: five (14%) as a result of lens-related problems (four vision, one comfort) and three (9%) as a result of non-lens related reasons. Average CW time achieved by the subjects was 22 +/- 2 days. Mean binocular logarithm of the minimum angle of resolution (logMAR) acuities at 6 months were: high contrast distance 0.03 (20/20-), low contrast distance 0.63 (20/80-), and high contrast near 0.26 (20/25, N4). Adverse responses and lens binding were minimal, and there were no significant increases in corneal staining, corneal vascularization, or superior palpebral conjunctival papillae over time (p > 0.05). Problems with night vision (distance and near) with the lenses were the most common difficulties reported by the subjects. CONCLUSIONS: The Menifocal Z appears to be a promising option for presbyopic vision correction, providing successful correction of distance and near vision in a group of experienced GP lens wearers. The hyper Dk tisilfocon A (Menicon Z) material allowed for safe wear of the lenses on a CW basis.

Adult↗
PubMed2001

The Berkeley Contact Lens Extended Wear Study. Part I : Study design and conduct.

OBJECTIVE: The primary aim of the Berkeley Contact Lens Extended Wear Study (CLEWS) was to test the hypotheses that extended wear of rigid gas-permeable (RGP) contact lenses with greater oxygen permeability (Dk) reduces the incidence of contact lens-associated keratopathy (CLAK) and increases the survival rate in RGP extended wear (EW). In this article we describe the clinical trial design in detail, present the results of subject recruitment and retention, and provide the baseline demographic and ocular characteristics of the CLEWS subjects, whose data will be analyzed to address the study aims in a companion article. DESIGN: A randomized, concurrently controlled clinical trial. INTERVENTION: Subjects were fitted with day wear (DW) high-Dk RGP lenses and then adapted to EW. Subjects who adapted to EW were then randomly assigned to either high- or medium-Dk RGP lenses for 12 months of 6-nights/week EW. MAIN OUTCOME MEASURES: Slit-lamp assessment and grading of 17 possible keratopathies, measurement of refractive error and corneal curvature, and symptoms. Follow-up data were collected every 3 months. RESULTS: From 545 subjects entering the DW adaptation phase, 201 adapted to EW and were randomly assigned to medium- or high-Dk lenses for 12 months of EW. The baseline characteristics of the two study groups were similar and did not differ from the 344 DW subjects who failed to adapt to EW. The distributions of oxygen transmissibility for the two study groups were disjoint, indicating that each group received distinctly different levels of hypoxia. CONCLUSIONS: We show that CLEWS was appropriately designed to address the study hypotheses, was conducted with regard for the safety of the subjects, and adhered to rigorous protocols designed to control for bias and ensure the integrity of study data. We establish the internal validity of between-group statistical comparisons and characterize our study population to permit informed evaluation of the applicability of our results to the contact lens-wearing population in general.

Adult↗
PubMed2002

EAP recordings in ineraid patients--correlations with psychophysical measures and possible implications for patient fitting.

OBJECTIVE: Objective measurements can be helpful for cochlear implant fitting of difficult populations, as for example very young children. One method, the recording of the electrically evoked compound action potential (EAP), measures the nerve recruitment in the cochlea in response to stimulation through the implant. For coding strategies implemented at a moderate stimulation rate of 250 pps per channel, useful correlations between EAP data and psychophysical data have been already found. With new systems running at higher rates, it is important to check these correlations again. DESIGN: This study investigates the correlations between psychophysical data and EAP measures calculated from EAP amplitude growth functions. EAP data were recorded in 12 Ineraid subjects. Additionally, behavioral thresholds (THR) and maximum acceptable loudness levels (MAL) were determined for stimulation rates of 80 pps and 2,020 pps for each electrode. RESULTS: Useful correlations between EAP data and psychophysical data were found at the low stimulation rate (80 pps). However, at the higher stimulation rate (2,020 pps) correlations were not significant. They were improved substantially, however, by introducing a factor that corrected for disparities due to temporal integration. Incorporation of this factor, which controls for the influence of the stimulation rate on the threshold, improved the correlations between EAP measures recorded at 80 pps and psychophysical MALs measured at 2,020 pps to better than r = 0.70. CONCLUSIONS: EAP data as such can only be used to predict behavioral THRs or MCLs at low stimulation rates. To cope with temporal integration effects at higher stimulation rates, EAP data must be rate corrected. The introduction of a threshold-rate-factor is a promising way to achieve that goal. Further investigations need to be performed.

Auditory Threshold↗