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PubMed1985

Clinical factors in proximal vergence.

Using forced vergence fixation disparity curves, proximal vergence was analyzed in two asymptomatic patient samples; 20 young adults (average age 25.2 +/- 4.71 years) and 20 presbyopes (average age 61.6 +/- 7.8 years). Total proximal vergence was significantly larger when measured under binocular (closed loop) conditions than monocular (open loop) conditions for pre-presbyopes (binocular 10.51 delta +/- 4.7 vs. 6.4 delta +/- 3.84 monocular) and presbyopes (binocular 11.59 delta +/- 3.13 vs. 4.71 delta +/- 2.15 monocular). Associated proximal vergence was shown to predict associated phoria magnitude in presbyopes and in pre-presbyopes when vergence adaptation and convergence accommodation (CA/C) interactions with accommodative convergence (AC/A) are included. A vergence/accommodation model is presented which includes influences of proximal vergence. Clinical implications of the findings relating to diagnosis and therapy are discussed.

Accommodation, Ocular↗
PubMed1985

Performance characteristics of a hydrophilic concentric bifocal contact lens.

Hydrophilic bifocals designed to achieve simultaneous vision with a central distance zone and annular add zone were evaluated on 15 presbyopic subjects. Simultaneous vision was demonstrated for distance zone diameters from 2.25 to 3.25 mm. Both zones affected over-refraction at distance and near resulting in extra minus required for distance and extra plus required for near. On average, visual acuity was worse than with equivalent spectacle correction. Effects of a night viewing simulation were also studied.

Adult↗
PubMed1985

Adaptation to lens-induced heterophorias.

In previous studies we have shown that subjects with normal binocular vision adapt to prism-induced heterophorias. In this study we have continued the work by investigating whether the oculomotor system can also adapt to lens-induced heterophorias. It was found that subjects gradually adapted to the esophoria induced when viewing a distance chart through negative lenses. Adaptation also occurred to lens-induced esophoria and exophoria at near, while at distance, where the visual feedback was unaltered, the phoria remained virtually constant. These findings demonstrate the flexibility of the oculomotor system.

Adaptation, Ocular↗
PubMed1986

Eye and head contribution to gaze at near through multifocals: the usable field of view.

Presbyopes show that for targets presented within a 28 degrees clear field of view, gaze is accomplished by head and eye movements with head movements making an average contribution of 24%. A clear field of view which incorporates the factor of segment width provides an underestimation because of the factor of head movements. By including the effect of head movements, a fixed segment width provides a much wider clear field of view which we term the usable field of view.

Eye Movements↗
PubMed1986

A system of retinoscopy for the aged eye.

A method of retinoscopy is described in which an optical arrangement magnifies the patient's pupil and makes it easier to see the retinoscopic reflex. At the same time, the method permits retinoscopic observation by the emmetropic examiner without need for accommodation, a distinct advantage to the presbyopic examiner. The relationship between retinoscope position and dioptric power-error is linear, a feature that facilitates cylinder determination using a variable-distance technique.

Accommodation, Ocular↗
PubMed1987

Ocular dominance and the interocular suppression of blur in monovision.

Presbyopic contact lens patients with monocular corrections (monovision) see clearly at all distances by virtue of an interocular suppression of anisometropic blur that occurs regionally between corresponding retinal areas. This suppression fails to occur with small high-contrast targets viewed under low luminance conditions. The effect of target size and contrast upon interocular suppression of blur was quantified by reducing contrast of a bright test spot, viewed binocularly while wearing various plus lenses monocularly, until the out-of-focus image was suppressed. The strength of interocular suppression was equivalent when the plus lens was before either eye. However, after subjects wore a plus lens over their nonsighting eye for one day, interocular suppression of blur became enhanced when the nonsighting eye was blurred, and it became reduced when the sighting eye was blurred. Successful monovision subjects suppressed blur at higher contrast levels than did unsuccessful subjects. These results suggest a possible clinical test for quantifying adaptation to monovision.

Adaptation, Physiological↗
PubMed1987

Effect of head and eye positions on fixation disparities, phorias, and ductions at near.

This study evaluated the effects of head and gaze position on near fixation disparity, phoria, and duction findings. A population of 104 non-complaining subjects divided by age into 3 groups participated in the study. The primary head and gaze position along with two others approximating the positions used for reading by nonbifocal and bifocal wearers were used. A statistically significant effect was found for the phoria data from the young group, but the magnitude was clinically insignificant. Changes in head and/or gaze positions did not significantly affect fixation disparities or duction recovery ranges. Phorias and fixation disparities showed statistically significant increases in exo deviation with increasing age regardless of head and/or gaze position. Nine of 23 presbyopic subjects gave erratic findings during fixation disparity testing and this casts doubt upon the clinical usefulness of this procedure with presbyopes.

Adolescent↗
PubMed1988

Monovision contact lens wear and occupational task performance.

The effects of monovision (MV) contact lens wear on the performance of occupational-type nearpoint tasks was evaluated on 18 presbyopic subjects (ages 44 to 67 years) by comparing MV performance (MV condition) to that with distance contact lenses with reading glasses (BV condition). Each subject had correctable distance visual acuity of 6/6 (20/20) in each eye, at least 60 sec arc of near stereopsis, good ocular health, and no previous MV experience. Time performance and error performance for 3 nearpoint occupational tasks (pointers and straws, card filing, and letter editing) were measured with the MV correction and BV correction. Measurements were taken at dispensing and at 2 weeks and 8 weeks after dispensing. Subjects were instructed to wear the MV soft spherical contact lenses at least 8 h per day. We measured BV time performance to be better than MV time performance by 2.8 to 5.7% and also measured an increased number of errors with MV.

Aged↗
PubMed1988

Comparative investigations of progressive lenses.

Different types of progressive addition lenses were compared with each other. It was our aim to measure all parameters in such a way that they were consistent with the normal wearing situation. The distribution of the spherical power and astigmatism was measured with a special focimeter. The induced distortion, which is important for patient acceptance, was determined by a photographic method. There are significant differences between the various types of progressive addition lenses. However, objective information is not sufficient to resolve the subjective question of patient acceptance.

Eyeglasses↗
PubMed1988

Patterns of binocular suppression and accommodation in monovision.

The binocular depth of focus of monovision wearers was compared to the sum of the two monocularly determined depths of focus. Observers fell into three groups based upon ocular sighting dominance. Complete binocular summation of the monocular depths of focus was observed in subjects without a preferred fixating eye. Subjects who preferred to fixate with one eye had difficulty suppressing blur of that eye while the binocular target was within the depth of focus of the nonpreferred eye. A third group showed partial summation of the two monocular depths of focus. Similar patterns of accommodative response, measured objectively with the SRI optometer, were observed in subjects wearing monovision corrections. Accommodative response to sinusoidal variations in blur was controlled primarily by the dominant sighting eye. These results demonstrate the effectiveness of interocular suppression of anisometropic blur in monovision correction and the influence of ocular dominance upon this suppression process.

Accommodation, Ocular↗
PubMed1989

Factors influencing vision with rigid gas permeable alternating bifocals.

This study assessed the fitting and visual performance of a rigid, gas permeable (RGP), monocentric, alternating bifocal. Fourteen presbyopic eyes each wore 24 different lenses consisting of all combinations of 2 diameters, 2 segment heights, 2 prism ballasts, and 3 fitting relations. The influence of parameter selection on visual performance and the usefulness of clinical measurements in predicting visual performance were determined statistically by multivariate logistic regression. Our results showed that prism, segment height, and the fitting relation can influence distance and near visual performance. Lens movement, postblink segment positioning, and return time were the most useful measured predictors of visual performance.

Aged↗
PubMed1991

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.

Adult↗
PubMed1991

Prevalence of spectacle wear among U.S. Army aviators.

The advanced avionic and electro-optical systems installed in Army rotary wing aircraft are becoming increasingly incompatible with spectacle wear. Therefore, the prevalence of spectacle wear among Army aviators is an important consideration in the development of future systems. A review of spectacle prevalence data from the Aviation Epidemiology Data Register (AEDR) for the years 1986, 1987, 1988, and 1989 was performed. Data were consistent across all 4 years, with mean prevalence of spectacle wear being 22% for active component forces. Reserve and National Guard components displayed mean spectacle wear prevalences of 27% and 32%, respectively. These prevalence rates are higher than those previously obtained in 1985 by a similar, but slightly different paradigm. Spectacle-wearing aviators exist in greater numbers than previously documented and represent a segment of the aviation population that will have increasing compatibility problems with advanced flight systems. Therefore, system planners will need to address these incompatibilities in future hardware developments.

Adult↗
PubMed1992

Comparative visual performance of three presbyopic contact lens corrections.

We compared the visual performance of a soft diffractive (DIFF) bifocal contact lens, a near center (CN) concentric bifocal design, and monovision (MV), using a comprehensive vision testing protocol. Fifteen presbyopic subjects who were successfully wearing DIFF bifocal contact lenses participated in the study. Of the three systems tested, MV provided best visual acuity at distance and near; less than one line of acuity was lost relative to best spectacle acuity under all lighting and contrast conditions, and there was less disturbance of a point source of light. Both bifocal corrections gave similar visual acuity performance, with more lines of acuity lost relative to spectacles at near compared to distance. However, the concentric bifocal induced more ghosting at near than the other two systems. Stereopsis was compromised at distance with MV correction, but all systems performed worse than spectacles at near. An understanding of the strengths and weaknesses of presbyopic contact lens options allows the clinician to improve management of the presbyope who wishes to wear contact lenses.

Contact Lenses, Hydrophilic↗
PubMed1992

Vision and task performance with monovision and diffractive bifocal contact lenses.

We measured vision and task performance on 26 presbyopes, ages 46 to 65 years, fitted with diffractive bifocal contact lenses (BFCL) and monovision contact lenses (MVCL). Distance contact lenses combined with reading spectacles (DCL) served as the control condition. Twenty subjects completed the 6-week study. All subjects wore BFCL and MVCL daily for a period of 3 weeks each. Performance times for three near tasks were 6 to 8% longer with BFCL compared with DCL and 2 to 6% longer for MVCL compared with DCL. There were significant reductions in distance visual acuity with BFCL (0.4 to 1.5 Snellen lines) and MVCL (0.5 to 0.8 Snellen lines) compared to DCL. At the conclusion of the study, given a choice between BFCL and MVCL, 2 of the 20 subjects chose to continue wearing BFCL, whereas 18 of the 20 subjects chose MVCL. Our results show greater visual compromise and decreased task performance with BFCL and MVCL compared to DCL and greater patient preference for MVCL.

Aged↗
PubMed1992

Interest of presbyopes in contact lens correction and their success with monovision.

The presbyopic population is seen as a large potential source of contact lens wearers. The aims of this study were: (1) to estimate the percentage of presbyopes interested in contact lenses, (2) to ascertain the success of interested presbyopes with monovision correction, and (3) to determine the percentage willing to continue wearing monovision lenses after 1 month's trial. Seven practitioners in Sydney surveyed consecutive presbyopes attending their practices about their interest in contact lenses. Of the 1133 presbyopes surveyed, 314 (28%) were interested in trying monovision lenses. A total of 72 patients were subsequently fitted with monovision in high water content hydrogel form. After 1 month, 46 of these patients (64%) were still wearing the lenses, and 39 (54%) expressed willingness to continue with monovision correction. The major reasons for discontinuation from lens wear during the 1-month trial were inadequate vision and difficulty in lens handling.

Adult↗
PubMed1992

Twelve-month success rates with a hydrogel diffractive bifocal contact lens.

In this study we assessed success rates over 12 months with a hydrogel diffractive bifocal contact lens. A total of 108 presbyopes were fitted with lenses, and after 12 months 46% were still wearing the lenses. Subjects with previous presbyopic lens-wearing experience achieved greater success (58% of those fitted) than neophyte lens wearers (33% of those fitted, and 17% of all neophyte presbyopes initially expressing an interest in contact lenses before screening). More neophytes failed for nonvision-related reasons than experienced subjects (31% vs. 12% of those fitted). Consequently, when nonvision-related failures were excluded from the calculation of success rates, 59% of those fitted with lenses (49% of neophytes and 66% of experienced subjects) were still wearing the lenses at 12 months. Most discontinuations from lens wear occurred in the first month of the study, the major reason for discontinuation being poor near vision (blur and/or ghosting; 47% of discontinuations).

Aged↗