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PubMed2002

Anisotropic water transport in the human eye lens studied by diffusion tensor NMR micro-imaging.

We report in vitro measurements of effective diffusion tensors characterising the anisotropic transport of water in human eye lenses ranging in age from 13 to 86 years. The measurements were obtained by means of a pulsed field gradient spin echo (PFGSE) magnetic resonance imaging (MRI) technique at a spatial resolution of 218 x 218 x 1000 microm(3). The results show that water diffusion is both spatially inhomogeneous and highly anisotropic on the timescale of the measurements (approximately 15 msec). Diffusion parallel to the long axes of the lens fibre cells is relatively unrestricted, whereas that between cells is substantially inhibited by the cell membranes, particularly in the inner cortex region of the lens. The data confirm the presence of a diffusion barrier surrounding the lens nucleus, which inhibits transport of water and other small molecules into and out of the nucleus. The results shed light on factors that may influence the onset of presbyopia and senile cataract. They also have implications for delivery of drugs to the lens nucleus.

Adolescent↗
PubMed1995

The optics of the eye-lens and lenticular senescence. A review.

Although the lens of the eye is structurally a biological tissue, it functions as an optical element providing one third of the refracting power of the human eye, and a variable focus in younger years. Throughout a life-time the optical properties of the eye-lens alter, resulting in changes in function: there is a gradual depletion of the focussing amplitude from infancy to middle age, and a loss of transmittance in the later decades of life. The optical properties of the lens depend on its power, which in turn is determined by its physical dimensions (curvatures and thickness) and its refractive index as well as transmissivity and the organization of its internal components. The power of the functional lens is, however, modifiable by virtue of the lens being attached via the zonule to the ciliary muscle. The contraction and relaxation of the latter respectively increases and decreases lens power in accordance with innervations determined by the physical distance of external objects to be imaged on the retina. This review will consider many of these features and how alterations in any of them may lead to changes in lenticular function. However, as we have recently devoted a detailed study to presbyopia [1] its mechanism will not be considered here.

Accommodation, Ocular↗
PubMed2000

[Analysis of the dynamics of the ciliary muscle during accommodation].

BACKGROUND: The magnitude of anterioaxial shift of the human ciliary muscle during accommodation and its ceasing of ciliary function with advanced age are still unknown. PATIENTS AND METHODS: A total 105 patients (aged 10-91 years) were examined by high-resolution ultrasound biomicroscopy during disaccommodation and voluntary accommodation. Accommodative changes in the total area of the ciliary muscle and in the outer contour were quantified with a specially developed software program for automatic contour determination. RESULTS: A significant anterior shift independent of age was observed in the total area of the ciliary muscle and defined points on the outer contour of the muscle in the range of 56-121 microns, while the inward displacement was less obvious. A decrease in the magnitude of configurational changes during accommodation was observed with age. CONCLUSION: The new software program could be useful in further investigations of the accommodative process and evaluation of the potential causes of presbyopia.

Accommodation, Ocular↗
PubMed2005

Three-dimensional ultrasound biomicroscopy, environmental and conventional scanning electron microscopy investigations of the human zonula ciliaris for numerical modelling of accommodation.

PURPOSE: Biomechanical modelling of the accommodation process is a useful tool for studying the mechanism of accommodation and presbyopia and can aid in the development of accommodative lens-replacing materials. Existing biomechanical models, however, use a very simplified zonula structure. The aim of this study was to use three-dimensional ultrasonic imaging and scanning electron microscopy to provide a more detailed, three-dimensional description of the structure of the human zonula to improve the modelling of accommodation. METHODS: Five human eyes were examined without invasive manipulation using a custom-made three-dimensional ultrasonic imaging technique that allows scanning of features with a spatial resolution of 30 microm. Environmental and conventional scanning electron microscopy (SEM) provided information to complement the ultrasonic images for use in development of a more anatomically correct finite-element model of the zonula structures. These data along with the material properties of the ocular tissue structures were used to construct an advanced geometric model for finite-element simulation of the accommodation process. RESULTS: Images were obtained through three-dimensional ultrabiomicroscopy (3D-UBM) of anatomical features heretofore not directly imagable in their native state. Ciliary processes and zonula structures were clearly separated by both the 3D-UBM and the SEM methods. It was found that fibres inserting on the anterior and posterior lens capsule emerge anteriorly at the ciliary body. Fibres emerging near the pars plana insert on the lens and the ciliary body. No X-shaped crossing fibres were found. Modelling of the accommodation process with both the simple and the more complex geometric models produced refractive power changes comparable with in vivo findings. CONCLUSIONS: The 3D-UBM allowed examination of zonula structures in their native state with minimized preparation artefacts. While these data were incorporated into a complex and more anatomically correct finite-element simulation of intraocular features including lens, zonular system and ciliary body it was found that a simplified zonular model is sufficient for the numerical simulation of the accommodation process.

Accommodation, Ocular↗
PubMed1988

Age changes in rhesus monkey ciliary muscle: light and electron microscopy.

The ciliary muscle from 44 rhesus monkeys ranging in age from 137-day fetuses and a 3-week neonate to 35-year-old adults was studied by light and electron microscopy. In the fetuses and the neonate, the muscle cells appeared immature, and the muscle consisted mainly of longitudinally oriented fibers. By age 1 year, the muscle fibers were aggregated into bundles, and within each bundle the individual fibers were packed tightly together. In sagittal section, the muscle now exhibited longitudinal, reticular and circular portions. The individual muscle cells exhibited ultrastructural characteristics which set them apart from other smooth muscle cells. Age-related structural changes occurred in the ciliary muscle and intramuscular nerves, beginning at 6 years. These included increasing numbers of lysosomes, 'fingerprints', and the appearance of myelin figures within some nerve endings and nerve fibers. These alterations became more frequent and pronounced with age, and in elderly animals were seen in all regions of the muscle and around its entire circumference. Additionally, the elderly animals exhibited overt degeneration of some muscle cells and some myelinated nerve fibers. The time-course of these age-related structural neuromuscular alterations parallels the decline of functional accommodative amplitude (i.e. presbyopia) and of the ciliary muscle's configurational response to peripheral pharmacologic and central electrical stimulation. This suggests a pathophysiologic, albeit (given the relatively moderate overall abnormalities) not necessarily causal, relationship. An age-related increase in the number of pigmented cells between the ciliary muscle bundles also occurred, with the anterior longitudinal region being affected last. This might reflect an age-related decline in uveoscleral drainage of aqueous humor.

Aging↗
PubMedDate not supplied

Progressive power lenses.

With the rapidly increasing public awareness of progressive power lenses for the correction of presbyopia, there has been a corresponding proliferation of manufacturers and types of progressive lens designs. This paper discusses the various lens design philosophies, often grouped in "hard" and "soft" categories. In the absence of visible multifocal segment lines, problems arise in attempting to identify the various lens types, in neutralizing progressive lens powers and in dispensing. These problems are discussed from the viewpoint of the refractionist. The advantages and disadvantages of progressives are considered, together with their indications and contraindications.

Eyeglasses↗
PubMedDate not supplied

Complications of radial and transverse keratotomy.

Radial keratotomy for myopia and transverse keratotomy for astigmatism are the most commonly performed refractive surgical procedures. A decade of experience with modern techniques has produced considerable literature on the complications of keratotomy. Vision-threatening complications (bacterial keratitis, traumatic rupture of the globe through weakened keratotomy scars, endophthalmitis, cataract formation from surgical trauma to the lens) are quite rare, occurring in less than 1% of eyes in published series. The most common side effects affect most patients in the first few months after surgery: pain for 24 to 48 hours, transient glare and light sensitivity, and fluctuating visual acuity. The most common persistent complications are overcorrection and undercorrection. Persistent irregular astigmatism occurs in almost all cases in the region of the incision scars, but it is rarely severe enough to reduce spectacle acuity. Most individuals have mild glare, but this is rarely disabling. Diurnal variation of refraction in visual acuity occurs commonly, but the magnitude of the fluctuation is seldom enough to require multiple pairs of spectacles. Longterm refractive stability occurs in approximately half of eyes by six months, but approximately one in four eyes will experience continued change over six months to four years. Complications, such as scarring from intersecting keratotomy incisions, irregular astigmatism resulting from multiple reoperations, and overcorrections with the attendant early onset of symptomatic presbyopia are becoming much less frequent.

Contact Lenses↗
PubMedDate not supplied

Prevalence of eye disorders among the elderly in Los Angeles.

A series of 431 vision screening records of seniors 55 years of age and older were analysed. Patients were examined by the UCLA Mobile Eye Clinic at two senior centers in the Los Angeles area, between the years 1982 and 1990. Sixty-eight percent of patients were females and 32% were males. The mean (+/-S.D.) age was 69 (+/-7.5) years. Common diagnoses were refractive errors (65.2%) and impaired visual acuity (37.0%). The prevalences of refractive errors were: hyperopia, 24.8%; myopia, 10.4%; presbyopia, 54.1%; and astigmatism, 31.8%. In most patients (94.0%), impaired visual acuity was corrected by spectacles. The prevalence of cataract was 29.5% and age-specific prevalences of cataract increased with age. The prevalences of other eye disorders were as follows: glaucoma, 6.3%; diabetic retinopathy, 1.2%; and macular degeneration, 5.1%. This study highlights the degree of ophthalmic disorders identified by vision screenings in the elderly population in senior centers; our results are consistent with previously reported studies of eye diseases in the elderly.

Journal Article↗
PubMed2006

Mapping age-related elasticity changes in porcine lenses using bubble-based acoustic radiation force.

Bubble-based acoustic radiation force aims to measure highly localized tissue viscoelastic properties. In the current investigation, acoustic radiation force was applied to laser-induced bubbles to measure age-related changes in the spatial distribution of elastic properties within in vitro porcine lenses. A potential in vivo technique to map lens elasticity is crucial to understanding the onset of presbyopia and develop new treatment options. Bubble-based acoustic radiation force was investigated as a technique to measure the spatial elasticity distribution of the lens in its natural state without disrupting the lens capsule. Laser-induced optical breakdown (LIOB) generated microbubbles in a straight line across the equatorial plane of explanted porcine lenses with 1mm lateral spacing. Optical breakdown occurs when sufficiently high threshold fluence is attained at the focus of femtosecond pulsed lasers, inducing plasma formation and bubble generation. A two-element confocal ultrasonic transducer applied 6.5 ms acoustic radiation force-chirp bursts with the 1.5 MHz outer element while monitoring bubble position within the lens using pulse-echoes with the 7.44 MHz inner element. A cross-correlation method was used to measure bubble displacements and determine exponential time constants of the temporal responses. Maximum bubble displacements are inversely proportional to the local Young's modulus, while time constants are indicative of viscoelastic properties. The apparent spatial elasticity distributions in 41 porcine lenses, ranging from 4 months to 5 years in age, were measured using bubble-based acoustic radiation force. Bubble displacements decrease closer to the porcine lens center, suggesting that the nucleus is stiffer than the cortex. Bubble displacements decrease with increasing lens age, suggesting that porcine lenses become stiffer with age. Bubble-based acoustic radiation force may be well-suited as a potential in vivo technique to spatially map elastic properties of the lens and guide therapeutic procedures aimed at restoring accommodation.

Aging↗
PubMedDate not supplied

Unmet visual needs of Alzheimer's disease patients in long-term care facilities.

INTRODUCTION: The purpose of this study was to determine the prevalence of uncorrected visual disorders in nursing home patients with Alzheimer's disease (AD) and to determine whether appropriate corrective measures were taken by nursing home staff. This study was conducted at 2 community nursing homes in the St Louis area. Whereas previous studies have shown that visual impairment is common among all residents of nursing facilities, our study was focused specifically on residents with AD. This population is less able to effectively express needs and more likely to endure unaddressed visual deficits. For AD patients, it is important to offer appropriate corrective remedies in order to maintain as much functional independence as possible. METHODS: A retrospective cohort study was conducted in 2 private, skilled nursing facilities in St Louis County thought to be representative of community nursing homes in the United States. All subjects were patients with a diagnosis of dementia of probable AD. Demographic information collected included age, sex, and race. Mini-Mental State Examination scores were also obtained. The patients, their families, and nursing staff were interviewed to determine the patients' visual history, corrective measures, and the usage of corrective eyewear before and after admission to the nursing homes. The data were summarized to demonstrate how many patients suffered from uncorrected errors of refraction and what factors contributed to their visual status. RESULTS: Of the total of 85 patients included in the study, 80 (94.1%) required glasses for correction of presbyopia, myopia, or both. However, 25 of the 80 residents had not actively been using glasses since entering the nursing home. Of these 25 residents not wearing proper eyewear, 9 residents were too cognitively impaired to request them, 8 residents had broken or misplaced them, and 8 residents had prescriptions that were no longer sufficient to correct their vision. DISCUSSION: Our study found that nearly one third of the visually impaired nursing home residents with AD (25 of 80 patients) were not using their required eyewear. These 25 patients were the population of most interest because they were most likely to benefit from intervention. Many of these patients were not using glasses because they had been lost, damaged, or were no longer sufficient to correct their vision. CONCLUSIONS: We have presented 3 recommendations intended to prevent uncorrected visual acuity in nursing home residents with dementia: (1) Label eyewear in appropriate patient populations to provide rapid identification in the event of misplacement, (2) recommend that an extra pair of glasses be made available if the current pair would be lost or damaged, and (3) ensure that all residents have annual or biannual eye exams. If adequate steps are taken to prevent unnecessary visual impairment in AD patients, it would limit their dependence on others, reduce the burden on nursing staff, and improve the patients' overall quality of life.

Aged↗
PubMed2005

First safety study of femtosecond laser photodisruption in animal lenses: tissue morphology and cataractogenesis.

PURPOSE: To determine through safety studies the tissue effects and potential cataractogenesis of laser modification of the crystalline lens (photophaco modulation). SETTING: Laser Zentrum Hannover, Hannover, Germany. METHODS: Six fresh porcine lenses and 6 living rabbit eyes (with the contralateral eye as a control) were radiated with a low-energy femtosecond laser to induce lens fiber disruption. After 3 months, the rabbit eyes were extracted and tested for light scatter and lens function and fixed for histology and ultrastructure. RESULTS: After laser treatment, all lenses displayed a tightly packed array of intralenticular bubbles, which resolved with time. In the porcine eyes, the bubbles coalesced unless spacing of 9 mum or greater was applied at an energy of 2 microJ. In the rabbit eyes, an energy of 1 microJ and spacing of 10 microm was chosen for transcorneal delivery, showing minimum bubble coalescence. After 3 months, the rabbit lenses showed good transparency, with only 1 rabbit having cataract formation unrelated to the laser. Laser scanning studies show essentially identical values for the back focal length and sharpness of focus (variability of back focal length). Ultrastructurally, the rabbit eyes showed a 0.5 microm electron dense border layer with adjacent normal lens architecture. CONCLUSIONS: Femtosecond laser photodisruption of the ocular lens yields a self-limited lesion with bubbles that resolve with time. In living animal eyes, no cataract formation was found with no loss of lens function or induced light scatter after 3 months. These results suggest that use of a low-energy femtosecond laser might be safe when modifying the lens for presbyopia correction.

Animals↗
PubMed2004

Anterior segment imaging: ultrasound biomicroscopy.

Ultrasound biomicroscopy technology has become an indispensable tool in qualitative and quantitative assessment of the anterior segment. Advances in soft-ware design and algorithms will improve theoretical understanding of the pathophysiology of anterior segment disorders. Future applications of quantitative techniques will yield important information regarding mechanisms of angle closure, improving understanding of the dynamic functions of the iris,accommodation, presbyopia, and other aspects of anterior segment physiology and pathophysiology.

Anterior Eye Segment↗
PubMed2006

Accommodation: mechanism and measurement.

A clear understanding of the anatomy of accommodative structures, the mechanism of accommodation, and the causes of presbyopia is necessary to understand whether accommodation may be restored to the presbyopic eye. Not withstanding the significant challenges that are faced owing to age-related changes in the eye, theoretically, it may be possible to restore accommodation to a presbyopic eye with an artificial accommodative intraocular lens.

Accommodation, Ocular↗
PubMed2006

Artificial crystalline lens.

If presbyopia is caused by hardening of the crystalline lens, replacing it with a material with mechanical properties similar to the young crystalline lens should restore accommodative ability. Such a silicone material has been developed. Refilling the capsular bag with this material results in 3 to 5 D of accommodation in primates in response to pilocarpine.

Animals↗
PubMed2006

Keratorefractive approaches to achieving pseudoaccommodation.

Although presbyopia is ostensibly an age-related disease of the lens, ciliary body, and zonular apparatus, surgeons have nonetheless persevered in their attempts to create a solution to the problem of diminished near vision by performing keratorefractive procedures. This article discusses two approaches of varying technological sophistication, beginning with surgically induced astigmatism and continuing through enhanced monovision. Sometimes simple solutions are the best, and the technological innovation in cataract and refractive surgery has met with unrivalled success in the last three decades.

Accommodation, Ocular↗
PubMedDate not supplied

Superstitions of George Bartisch.

George Bartisch was a 16th century German ophthalmologist who published the first ophthalmology textbook in the vernacular for laymen and non-university-trained practitioners. His treatments and understanding of diseases rested firmly on Greek tradition, but he also was very involved in the superstitions of the day. This essay looks at the man and his mores. Bartisch believed that much of the suffering of patients had to do with sins they had committed, and that the devil was the active force in the world inflicting this punishment. Often, he believed, witches would carry out the devil's hexes, in the form of either hot or cold witchcraft. Bartisch also felt that astrology played a major role in the outcome of surgery. Because of that he practiced only during certain astrological signs, and in the proper waxing and waning phases of the moon. He also linked many common problems to sins. For example, presbyopia was presented as due to excessive use of alcohol. Glasses were to be avoided because he felt they destroyed vision in themselves. Despite these superstitions and misconceptions, Bartisch was an honorable professional and his books give insight into the making of a good ophthalmologist.

Germany↗
PubMed2005

Age related changes in accommodative dynamics in humans.

Age related changes in the dynamics of accommodation (far to near focus) and disaccommodation (near to far focus) are reported in this study. Dynamic responses to step stimulus demands from 1D to 6D, in 1D steps, were recorded with a PowerRefractor in 66 subjects in the age range 14-45 years. The accommodative and disaccommodative responses were fit with exponential functions to calculate response amplitude, time constant and peak velocity. The latency of accommodation did not change and the latency of disaccommodation increased with age. For accommodation, time constant increased and peak velocity decreased with age. For disaccommodation, no change in time constant or peak velocity was found with age. The form of the peak velocity vs response amplitude relationship (main sequence) of accommodation changed with age. The differences in the dynamics of accommodation and disaccommodation with age are discussed with reference to the age related changes in the eye leading to presbyopia.

Accommodation, Ocular↗
PubMed2001

Dynamics of the accommodation response to abrupt changes in target vergence as a function of age.

The dynamic accommodation responses to small, abrupt changes in an accommodation stimulus were studied in two experiments. In the first, responses of 19 subjects with ages distributed between 18 and 49 years were measured for step stimuli of +/- 1.05 D. In the second, responses to small step stimuli (+/- 0.75, +/- 1.75 D) were recorded for a group of six 'young' (mean age 22, range 16-26 years) and six 'old' (mean age 42, range 36-48 years) subjects. In both experiments, the low target vergences always lay within the accommodation range of all subjects. Whether the data were analysed in terms of simple reaction and response times, or in terms of the frequency response, no marked systematic changes with age were found in the dynamics of the response in either of the experiments. It is concluded that, for small stimuli within the amplitude of accommodation, the response dynamics over the adult age range studied remain remarkably constant, even though the amplitude progressively reduces with age as complete presbyopia is approached.

Accommodation, Ocular↗