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PubMed2006

Estimating the external force acting on the human eye lens during accommodation by finite element modelling.

Using new geometric information on the shape of the lens that has recently become available, a finite element model has been developed in order to estimate the forces that act on the lens during accommodation for a typical 29-year-old human eye. To investigate the influence of the anterior, posterior and central zonular fibres insertion regions, three models with different configurations were built. All three configurations appeared to be capable of inducing the required accommodative changes in the lens. Based on material properties from the literature, the estimated summed net force for each of the three models was approximately 0.08 N.

Accommodation, Ocular↗
PubMed2006

Visual training improves underwater vision in children.

Children in a tribe of sea-gypsies from South-East Asia have been found to have superior underwater vision compared to European children. In this study, we show that the improved underwater vision of these Moken children is not due to better contrast sensitivity in general. We also show that European children can achieve the same underwater acuity as the Moken children. After 1 month of underwater training (11 sessions) followed by 4 months with no underwater activities, European children showed improved underwater vision and distinct bursts of pupil constriction. When tested 8 months after the last training session in an outdoor pool in bright sunlight-comparable to light environments in South-East Asia-the children had attained the same underwater acuity as the sea-gypsy children. The achieved performance can be explained by the combined effect of pupil constriction and strong accommodation.

Accommodation, Ocular↗
PubMed2006

Peripheral defocus does not necessarily affect central refractive development.

PURPOSE: Recent experiments in monkeys suggest that deprivation, imposed only in the periphery of the visual field, can induce foveal myopia. This raises the hypothesis that peripheral refractive errors imposed by the spectacle lens correction could influence foveal refractive development also in humans. We have tested this hypothesis in chicks. METHODS: Chicks wore either full field spectacle lenses (+6.9 D/-7 D), or lenses with central holes of 4, 6, or 8mm diameter, for 4 days (n=6 for each group). Refractions were measured in the central visual field, and at -45 degrees (temporal) and +45 degrees (nasal), and axial lengths were measured by A-scan ultrasonography. RESULTS: As previously described, full field lenses were largely compensated within 4 days (refraction changes with positive lenses: +4.69+/-1.73 D, negative lenses: -5.98+/-1.78 D, both p<0.001, Dunnett's test, to untreated controls). With holes in the center of the lenses, the central refraction remained emmetropic and there was not even a trend of a shift in refraction (all groups: p>0.5, Dunnetts test). At +/-45 degrees , the lenses were partially compensated despite the 4/6/8mm central holes; positive lenses: +2.63 / +1.44 / +0.43 D, negative lenses: -2.57 / -1.06 / +0.06 D. CONCLUSIONS: There is extensive local compensation of imposed refractive errors in chickens. For the tested hole sizes, peripherally imposed defocus did not influence central refractive development. To alter central refractive development, the unobstructed part in the central visual field may have to be quite small (hole sizes smaller than 4mm, with the lenses at a vertex distance of 2-3mm).

Accommodation, Ocular↗
PubMed2006

Vergence accommodation and monocular closed loop blur accommodation have similar dynamic characteristics.

Retinal blur and disparity are two different sensory signals known to cause a change in accommodative response. These inputs have differing neurological correlates that feed into a final common pathway. The purpose of this study was to investigate the dynamic properties of monocular blur driven accommodation and binocular disparity driven vergence-accommodation (VA) in human subjects. The results show that when response amplitudes are matched, blur accommodation and VA share similar dynamic properties.

Accommodation, Ocular↗
PubMed2007

Conceptual model of human blur perception.

An empirically based, conceptual model of human blur perception is presented. It incorporates the concepts of blur detection and blur discrimination in depth, and across the central and peripheral retina, in two- and three-dimensional visual space. Key aspects of the model are its dynamic nature, predictability regarding the blur-based depth-ordering of objects, patterns of retinal defocus with far and near viewing, and interactions related to retinal defocus between the central and peripheral retina. Furthermore, a two-dimensional schematic representation of the blur-free region during near viewing is depicted in dioptric space. This model has implications with respect to accommodative control, depth perception, and refractive error development and progression.

Accommodation, Ocular↗
PubMed2003

The polaroid suppression test in a pediatric population with ophthalmologic disorders.

PURPOSE: The Polaroid suppression test (PST) is a new method for early detection of amblyogenic factors by screening for suppression. The apparatus can elicit suppression with the use of Polaroid filters. The aim of the present study was to examine a population of children with known ophthalmologic disorders using the PST to determine the rate of false-negative results of the PST. METHODS: Six hundred four children, varying in age between 3 and 15 years (mean, 7.9) were examined using the PST. Ophthalmologic disorders ranged from strabismus and amblyopia to refractive disorders. RESULTS: Mean testing time for the PST was 43 seconds. The PST could not be administered to 34 children (5.6%); 443 children (73.3%) had abnormal results; and 127 children (22.2%) showed no suppression. The suppression in constant strabismus was detected in almost all cases. The sensitivity for accommodative forms of strabismus was lower, but amblyopia was never missed in these cases. In children with normal eye alignment, only 2.7% with an interocular acuity difference of more than 0.1 logMAR had no suppression. Of all 119 children with clinical defined amblyopia, only 1 (0.8%) did not have suppression. Overall sensitivity of the PST for strabismus and/or abnormal interocular acuity difference was 96.2% and specificity was 41.1%. CONCLUSIONS: The PST has great potential as a visual screening tool in young children. Only few children with amblyogenic factors were missed. Thus, the test can differentiate those children at risk for amblyopia from normally sighted children. Because specificity is lower, all children showing suppression with the PST in a screening situation should have further examination by the health care worker before being referred to the ophthalmologist.

Accommodation, Ocular↗
PubMed2000

Influence of astigmatism on multifocal and monofocal intraocular lenses.

PURPOSE: To examine the influence of astigmatism on the visual acuity of patients with multifocal and monofocal intraocular lenses. METHODS: Thirty eyes of 30 patients who underwent five-zone refractive multifocal intraocular lens implantation and 30 eyes of 30 age-matched patients who had monofocal intraocular lens implantation were included. The visual acuities of these patients at 5.0, 3.0, 2.0, 1.0, 0.7, 0.5, and 0.3 m were measured by means of an all-distance vision tester after addition of a cylindrical lens of 0, 0.5, 1.0, 1.5, 2.0, and 2.5 diopters. RESULTS: Mean visual acuity at all distances decreased in proportion to the diopters of astigmatism in both the multifocal and monofocal intraocular lens groups. When astigmatism was 0.5, 1.0, or 1.5 diopters, distance visual acuity in the multifocal group was significantly worse than that in the monofocal group; with astigmatism of 2.0 diopters or more, intermediate visual acuity was also worse in the multifocal group. In contrast, near visual acuity in the multifocal group was significantly better than that in the monofocal group at all astigmatic diopters. When astigmatism was within 1.0 diopter, visual acuity in the multifocal group reached 20/29 at distance and 20/50 at near. Mean contrast sensitivity was also worse in the multifocal group than in the monofocal group. CONCLUSIONS: Both distance and intermediate visual acuity deterioration caused by astigmatism was greater with a multifocal intraocular lens than with a monofocal intraocular lens, whereas near visual acuity was better with the multifocal intraocular lens. When astigmatism was within 1.0 diopter, eyes with a multifocal intraocular lens achieved good visual acuity at both distance and near.

Accommodation, Ocular↗
PubMed2002

Accommodation and convergence palsy caused by lesions in the bilateral rostral superior colliculus.

PURPOSE: To report a patient who developed accommodation and convergence palsy caused by lesions in the bilateral rostral superior colliculus. DESIGN: Observational case report. METHODS: A 30-year-old right-handed man experienced sudden onset of diplopia and blurred vision at near vision. RESULTS: The patient showed accommodation and convergence palsy. Magnetic resonance imaging revealed lesions located in the bilateral rostral superior colliculus. CONCLUSION: These findings suggest that the rostral superior colliculus is involved in the control of accommodation and vergence eye movements.

Accommodation, Ocular↗
PubMed2002

Implantation of scleral expansion band segments for the treatment of presbyopia.

PURPOSE: To assess the effects of scleral expansion band (SEB) segments on accommodative amplitude (primary measure), along with near and distance vision, refraction, pupil size and function, keratometry, axial length, intraocular pressure, contrast sensitivity, stereopsis, and other parameters (secondary measures) in a cohort of 29 emmetropic, presbyopic patients. DESIGN: Multicenter, prospective, nonrandomized, unmasked clinical trial in which the nonoperated eye served as the control. METHODS: Four polymethylmethacrylate segments were surgically implanted in quadrantic scleral pockets created in the dominant eye of 29 emmetropic patients who were between the ages of 51 and 60 (mean age 54). Patients were examined preoperatively and up to 6 months postoperatively. The aforementioned tests were performed on the operated and control eye of each patient. Data were analyzed using two-sided rank tests. Medians, means, and standard deviations are provided for all measurements. RESULTS: Accommodative amplitude was measured monocularly using a near-point "push" technique from both a 70-cm and 30-cm starting point. An increase in accommodative amplitude of surgical eyes by +1.7 +/- 1.5 diopters and +1.5 +/- 1.2 diopters, at these two testing distances, respectively, was noted at 6 months postoperatively (P <.0001). A smaller increase was also seen in control eyes (+1.2 +/- 1.1 diopters and +1.3 +/- 1.2 diopters, respectively). There was notable intercenter variation in gains in accommodation, with three of seven centers showing significant improvement in near-point accommodative amplitudes relative to the others (P =.0003). There was a median improvement of uncorrected near acuity in surgical eyes by 0.3 logarithm of the minimal angle of resolution (logMAR) at 30 and 40 cm and by 4 lines at 20 cm, with the difference in near acuity improvement at 6 months between SEB eyes and control eyes statistically significant at 20 cm (P <.030). Changes in spherical equivalence, axial length, and central keratometry readings were not statistically significant. There were no reports of anterior segment ischemia or malignant glaucoma. Adverse effects were limited to a transient elevation of intraocular pressure in one patient and misalignment of individual SEB segments, due to inadequate scleral pocket formation, in three patients. Only one SEB segment in one eye was replaced. It appears that the thickness and uniformity of the scleral belt loop is critical to the proper positioning and efficacy of the SEB segments. CONCLUSION: While the safety profile of SEB segments for the treatment of presbyopia was high, a modest improvement in near vision was noted in approximately half the patients using subjective methods of testing. The mechanisms that underlie improvement in near vision in the nonoperated eye await explanation. This may be due to a centrally controlled consensual response, potentiated convergence generating increased intravitreal pressure and hydraulic lift of the vitreo-zonular-lens diaphragm, or artifact from current testing techniques. Future studies of the SEB procedure should address the issue of intercenter variation by further standardizing and automating specific aspects of the surgical technique, as well as incorporating objective testing methods into the study design.

Accommodation, Ocular↗
PubMed2003

Aging changes in apparent accommodation in eyes with a monofocal intraocular lens.

PURPOSE: To examine the aging changes in the amplitude of apparent accommodation in eyes with a monofocal intraocular lens (IOL). DESIGN: Prospective comparative observational study. METHODS: Two hundred eyes of 200 patients who were scheduled for phacoemulsification and monofocal IOL implantation were studied. Forty patients in each of five age groups-younger than 40 years of age or in their 50s, 60s, 70s, and 80s-were prospectively recruited. Using an accommodopolyrecorder, the amplitude of apparent accommodation of these patients was measured approximately 1 month after surgery. Visual acuities from far to near distances after best-corrected distance were examined using an all-distance vision tester, and the region of accommodation at which each patient achieved a visual acuity of 20/29 or 20/40 was determined and converted to the diopteric range. Contrast sensitivity was also examined using a vision contrast test system. RESULTS: The amount of apparent accommodation as measured with the accommodopolyrecorder was decreased significantly in proportion to patient age (P <.0001). Furthermore, significant negative correlation was found between the amount of apparent accommodation and actual age of each patient (r = -.491). The diopteric range of accommodation at which the patients achieved 20/29 or 20/40 also reduced in proportion to the age. Although no significant differences were found in the mean far visual acuities between age groups, the intermediate and near visual acuities worsened significantly with age. The contrast sensitivity was also reduced in proportion to the age. CONCLUSIONS: The amplitude of apparent accommodation in eyes with a monofocal IOL decreases significantly in proportion to age, resulting in worsening of best-corrected intermediate and near visual acuities.

Accommodation, Ocular↗
PubMed1997

Is myopia related to amplitude of accommodation?

PURPOSE: To report the association between amplitude of accommodation and refractive error. METHODS: Refractive error and amplitudes of accommodation were measured in 1,148 eyes of 696 patients as part of the Early Treatment Diabetic Retinopathy Study. RESULTS: Eyes with myopia, defined as those with a refractive error of -0.75 diopter or more, have lower accommodative amplitudes (P = .005). After multivariate logistic regression analysis adjusting for age, occupation, and white race, lower amplitudes of accommodation remained associated with myopia (P = .03). CONCLUSIONS: Eyes with lower amplitudes of accommodation must use more of their accommodative reserve for near work. Myopia may be an adaptation that develops in eyes with reduced accommodative amplitudes.

Accommodation, Ocular↗
PubMed1996

Accommodation in primate eyes after implantation of refilled endocapsular balloon.

PURPOSE: To restore accommodation after crystalline lens removal. METHODS: The crystalline lens of one eye of each of four primates was removed by phacoemulsification. Each operated-on eye underwent endocapsular silicone balloon implantation followed by filling with an organosilicone mixture. Seven months postoperatively, the anterior chamber depth and refractive power changes were measured before and after topical application of 4% pilocarpine. RESULTS: In the refilled eyes, the average anterior chamber depth reduction was 0.50 mm and the average maximal myopic change was 6.74 diopters. CONCLUSION: After lens removal, measurable accommodation was restored in the eyes with the endocapsular balloon filled with an organosilicone mixture.

Accommodation, Ocular↗
PubMed1993

The effect of optical defocus on the pattern electroretinogram in normal subjects and patients with Alzheimer's disease.

The pattern electroretinogram, thought to originate from the spatially sensitive inner retinal layers, was recorded in 16 patients with Alzheimer's disease and 16 age- and gender-matched control subjects under the following two test conditions: (1) optical defocus or inattention, without laser pointer, and (2) optical focus or attention, with laser pointer. By correcting for optical defocus with the laser pointer, control subjects increased their pattern electroretinogram amplitudes by 8% from a mean value of 2.65 microV (standard deviation, 1.12) to 2.87 microV (standard deviation, 0.93), whereas patients with Alzheimer's disease had a 19% increase in pattern electroretinogram amplitude from 2.20 microV (standard deviation, 0.86) to 2.62 microV (standard deviation, 0.64). By controlling for optical defocus, the coefficient of variation (standard deviation/mean) was reduced by 10% (from 42% to 32%) in normal subjects and by 14% (from 39% to 25%) in patients with Alzheimer's disease. A two-way analysis of variance (ANOVA) did not show a significant difference in amplitudes between populations, which indicates that the pattern electroretinogram may not be valuable in establishing an early diagnosis of Alzheimer's disease. In a second study conducted in 20 young, healthy normal subjects, plus lenses were used to defocus the checkerboard stimuli, before recording the pattern electroretinogram. We found that the pattern electroretinogram was extremely sensitive to optical defocusing such that the response amplitude decreased by 13% at 20/25 visual acuity and 19% at 20/30. Reduction of pattern electroretinogram amplitude caused by change in visual acuity is an independent source of artifact.(ABSTRACT TRUNCATED AT 250 WORDS)

Accommodation, Ocular↗
PubMed1987

Spasm of the near reflex associated with organic disease.

Spasm of the near reflex is characterized by transient attacks of convergence, accommodation, and miosis. It is usually observed in young individuals and considered functional. We studied seven patients with spasm of the near reflex who had associated neurologic disorders or head trauma. Two patients had posterior fossa abnormalities (cerebellar tumor, Arnold-Chiari malformation), two patients had pituitary tumors, one patient had a vestibulopathy, and two patients had a history of antecedent head trauma.

Accommodation, Ocular↗
PubMed1980

Early-onset accommodative esotropia.

Twenty-one patients had esotropia diagnosed before age 12 months. In all of these patients esotropia was eliminated, at least initially, by antiaccommodative therapy consisting of either full hypermetropic spectacles or miotics, or both. Clinical findings evaluated in these patients were comparable to similar clinical factors studied in a larger series of patients with accommodative esotropia, most with onset after 12 months of age. In approximately 50% of these patients early-onset accommodative esotropia deteriorated to a nonaccommodative esotropia that required surgery despite aggressive antiaccommodative therapy. All but one of the surgically treated patients continued to need hypermetropia spectacles postoperatively to maintain alignment.

Accommodation, Ocular↗