Change in the accommodative force on the lens of the human eye with age.

The aim of the study was to determine the age-dependence of the accommodative force on the lens in order to make it clear whether the causes of presbyopia are due to lenticular or extralenticular changes. A finite element model of the lens of an 11-, 29- and 45-year-old human eye was constructed to represent the fully accommodated state. Subsequently, the force that was needed to mould the lens into its unaccommodated state was calculated. The force on the lens appeared to be preserved with age, with only a slight increase to a value of approximately 0.06N. In conclusion, the preservation of the net force delivered by the extralenticular ciliary body indicates that the causes of presbyopia must be ascribed to lenticular changes.

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.

The shape of the anterior and posterior surface of the aging human cornea.

PURPOSE: To determine the shape and astigmatism of the posterior corneal surface in a healthy population with age, using Scheimpflug photography corrected for distortion due to the geometry of the Scheimpflug imaging system and the refraction of the anterior corneal surface. METHODS: Scheimpflug imaging was used to measure in six meridians the cornea of the right eye of 114 subjects, ranging in age from 18 to 65 years. RESULTS: The average radius of the anterior corneal surface was 7.79+/-0.27 (SD) mm and the average radius of the posterior corneal surface was 6.53+/-0.25 (SD) mm. Both surfaces were found to be flatter horizontally than vertically. The cylindrical component of the posterior surface of 0.33 mm is twice that of the anterior surface (0.16 mm). The asphericity of both the anterior and the posterior surface was independent of the radius of curvature at the vertex, refractive error and gender. In contrast with that of the anterior corneal surface, the asphericity of the posterior corneal surface varied significantly between meridians. With age, the asphericity of both the anterior and the posterior corneal surface changes significantly, which results in a slight peripheral thinning of the cornea. CONCLUSION: On average, the astigmatism of the posterior corneal surface (-0.305 D) compensates the astigmatism of the anterior corneal surface (0.99 D) with 31%. The results show that the effective refractive index is 1.329, which is lower than values commonly used. There is no correlation between the asphericity of the anterior and the posterior corneal surface. As a result, the shape of the anterior corneal surface provides no definitive basis for knowing the asphericity of the posterior surface.

Change in shape of the aging human crystalline lens with accommodation.

The objective was to measure the change in shape of the aging human crystalline eye lens in vivo during accommodation. Scheimpflug images were made of 65 subjects between 16 and 51 years of age, who were able to accommodate at least 1D. The Scheimpflug images were corrected for distortion due to the geometry of the camera and the refraction of the cornea and anterior lens surface, which is necessary to determine the real shape of the lens. To ensure accurate correction for the refraction of the anterior lens surface, the refractive index of the crystalline lens must be determined. Therefore, axial length was also measured, which made it possible to calculate the equivalent refractive index of the lens and possible changes in this index during accommodation. The results show that during accommodation there is a decrease in both the anterior and the posterior radius of the lens, although the change in mm per diopter of the latter is much smaller. The increase in lens thickness with accommodation is higher than the decrease in the anterior chamber depth, indicating that the posterior lens surface moves backwards with accommodation. During accommodation the anterior lens surface becomes more hyperbolic. Furthermore, an increase in the equivalent refractive index during accommodation was determined.

Changes in the internal structure of the human crystalline lens with age and accommodation.

Scheimpflug images were made of the unaccommodated and accommodated right eye of 102 subjects ranging in age between 16 and 65 years. In contrast with earlier Scheimpflug studies, the images were corrected for distortion due to the geometry of the Scheimpflug camera and the refraction of the cornea and the lens itself. The different nuclear and cortical layers of the human crystalline lens were determined using densitometry and it was investigated how the thickness of these layers change with age and accommodation. The results show that, with age, the increase in thickness of the cortex is approximately 7 times greater than that of the nucleus. The increase in thickness of the anterior cortex was found to be 1.5 times greater than that of the posterior cortex. It was also found that specific parts of the cortex, known as C1 and C3, showed no significant change in thickness with age, and that the thickening of the cortex is entirely due to the increase in thickness of the C2 zone. With age, the distance between the sulcus (centre of the nucleus) and the cornea does not change. With accommodation, the nucleus becomes thicker, but the thickness of the cortex remains constant.

[Improvement of vision in nursing home patients through eyeglasses]. / Visusverbetering door brilcorrectie bij verpleeghuispatiënten.

Adequate refraction correction may contribute to the quality of life of elderly persons who will be less dependent on care in daily life and will be less prone to fall. In nearly 20% of 102 nursing home residents binocular visual acuity improved with at least one line on the Snellen Chart by adjustment of refractive correction.

Involvement of the peripheral nervous system in primary Sjögren's syndrome.

BACKGROUND: Involvement of the peripheral nervous system in patients with primary Sjögren's syndrome (SS) has been reported, but its prevalence in neurologically asymptomatic patients is not well known. OBJECTIVE: To assess clinical and neurophysiological features of the peripheral nervous system in patients with primary SS. PATIENTS AND METHODS: 39 (38 female) consecutive patients with primary SS, aged 20-81 years (mean 50), with a disease duration of 1-30 years (mean 8) were studied. The peripheral nervous system was evaluated by a questionnaire, physical examination, quantified sensory neurological examination, and neurophysiological measurements (nerve conduction studies). To assess autonomic cardiovascular function an orthostatic challenge test, a Valsalva manoeuvre, a forced respiration test, and pupillography were done. RESULTS: Abnormalities as indicated in the questionnaire were found in 8/39 (21%) patients, while an abnormal neurological examination was found in 7/39 (18%) patients. Abnormalities in quantified sensory neurological examination were found in 22/38 (58%) patients. In 9/39 (23%) patients, neurophysiological signs compatible with a sensory polyneuropathy were found. No differences were found in the autonomic test results, disease duration, serological parameters, or erythrocyte sedimentation rate between the patients with primary SS with and those without evidence of peripheral nervous involvement. CONCLUSION: Subclinical abnormalities of the peripheral nervous system may occur in patients with primary SS selected from a department of rheumatology, but clinically relevant involvement of the peripheral nervous system in this patient group is rare.

The thickness of the aging human lens obtained from corrected Scheimpflug images.

Commonly, measurements of lens thickness are performed using A-scan ultrasonography or slitlamp Scheimpflug photography. Both techniques have their drawbacks in the study of presbyopia: ultrasonography requires the velocity of sound in the lens which may change with age, whereas Scheimpflug photography requires knowing the refractive index of the lens to enable correction of the photographs for the distortion due to the refraction of the cornea and lens. By combining Scheimpflug photography and axial optical eye-length measurements, we were able to individually correct the Scheimpflug images for distortion and calculate the refractive index and thickness of the human lens. Lens thickness of 90 subjects ranging in age between 16 and 65 years was measured, and an average increase of 24 microm/year was found. This value is consistent with ultrasonographic measurements assuming an age-independent velocity of sound in the lens of 1641 m/s. The posterior lens surface recedes from the cornea with age, and this backward movement does not differ significantly from the forward movement of the anterior lens surface.

The shape of the aging human lens: curvature, equivalent refractive index and the lens paradox.

Scheimpflug slit images of the crystalline lens are distorted due to the refracting properties of the cornea and because they are obliquely viewed. We measured the aspheric curvature of the lens of 102 subjects ranging in age between 16 and 65 years and applied correction for these distortions. The procedure was validated by measuring an artificial eye and pseudophakic patients with intraocular lenses of known dimensions. Compared to previous studies using Scheimpflug photography, the decrease of the radius of the anterior lens surface with age was smaller, and the absolute value for the radius of the anterior and posterior lens surface was significantly smaller. A slight decrease of the posterior lens radius with age could be demonstrated. Generally, front and back surfaces were hyperbolic. Axial length was measured of 42 subjects enabling calculation of the equivalent refractive index of the lens, which showed a small, but highly significant decrease with age. These new findings explain the lens paradox and may serve as a basis for modelling the refractive properties of the lens.

Histopathologic ocular examination after lensectomy in a Macacus rhesus monkey, an unexpected event of secondary glaucoma.

In a Macacus rhesus monkey an unilateral lensectomy was performed on the 15th day of life to study the emmetropization proces. During a period of 20.5 months refractional state, axial length, corneal dioptric power and intraocular pressure were measured in the aphakic and fellow eye. Results showed that axial elongation of the aphakic eye was larger in comparison to the phakic fellow eye. Histopathologic examination of the aphakic eye revealed glaucomatous changes due to obstruction in the anterior chamber angle.

Parasympathetic failure does not contribute to ocular dryness in primary Sjögren's syndrome.

OBJECTIVE: To investigate the sympathetic and parasympathetic cardiovascular function in primary Sjögren's syndrome (SS) and to investigate the possible relation with ocular dryness. METHODS: 41 (40 women) patients with primary SS, mean age 50 years (range 20-80) with a mean disease duration of eight years (range 1-30), were studied. In each patient direct arterial blood pressure (BP), heart rate (HR) and respiration were measured continuously for two hours. The function of the autonomic circulatory regulation was evaluated by measuring the heart rate response to deep breathing (6 cycles/min) and by means of the Valsalva manoeuvre and the responses of BP, HR and plasma noradrenaline (norepinephrine) concentrations to a 10 minute 60 degree head up tilt test. Pupillography was done to evaluate ocular autonomic function. RESULTS: The HR-Valsalva ratio was abnormal in 24% of the patients, and the HR variability during forced respiration was abnormal in 56% of the patients. The HR responses to both the Valsalva manoeuvre and deep breathing, as indicators of parasympathetic function, were abnormally low in 6 of 41 (15%) patients. In only two patients the decrease in systolic BP in response to the head up tilt test, as indicator of sympathetic function, was more than 20 mm Hg. However, increment of plasma noradrenaline concentration during head up tilt test and the overshoot of BP in phase IV of the Valsalva manoeuvre, as indicators of sympathetic function, were normal in both patients. Thus, no evidence for sympathetic dysfunction was found, whereas evidence for parasympathetic failure occurred sometimes. Autonomic pupillary function in patients with primary SS and healthy controls, as well as the Schirmer test in patients with or without evidence for parasympathetic dysfunction as based on the results of the Valsalva and deep breathing tests, were not significantly different. CONCLUSION: Parasympathetic, but not sympathetic dysfunction seems to occur in a subgroup of primary SS. Results show that this does not necessarily contribute to the typical ocular dryness in this condition.

[Aging of the crystalline lens and presbyopia]. / Veroudering van de ooglens en presbyopie.

The crystalline lens changes both optically and mechanically with age: it becomes less transparent and more difficult to deform. Using a new ultrasound technique, Continuous Ultrasonographic Biometry (CUB), we were able to demonstrate that presbyopia is caused by increased stiffness of the lens due to changes in lens fibre membranes and cytoskeleton. These results are important for further research on the ageing processes that lead to cataract and presbyopia, and the treatment of these conditions.

Parasympathetic dysfunction in rheumatoid arthritis patients with ocular dryness.

OBJECTIVE: To determine whether abnormalities in the function of the autonomic nervous system are associated with oral and ocular dryness in rheumatoid arthritis. METHODS: Pupillography was done using an infrared light reflection method (IRIS) to measure both parasympathetic function (constriction latency and the latency of maximum constriction velocity (MCV)) and sympathetic function (dilatation latency) in rheumatoid arthritis patients with and without ocular dryness. The Schirmer and Saxon tests were used to measure the tear and saliva production respectively. RESULTS: The Schirmer and Saxon test results in rheumatoid arthritis patients with ocular dryness were reduced (P < 0.05) compared with rheumatoid arthritis patients without ocular dryness and healthy controls. Constriction latency and MCV latency were prolonged in rheumatoid arthritis patients with ocular dryness compared to the other two groups (P < 0.05). A negative correlation was found between the degree of ocular dryness and both constriction latency and MCV latency. No correlation was found between the results of pupillography and saliva production. CONCLUSIONS: Parasympathetic dysfunction may play a role in ocular dryness in patients with rheumatoid arthritis.

Microfluctuations of steady-state accommodation measured with ultrasonography.

Over the past 30 years investigators have noted fluctuations in accommodation when the eye views a stationary target. These microfluctuations have been studied mainly with the use of infrared optometers. Two dominant components have been found: a low frequency component (LFC; 0.05-0.5 Hz) and a high frequency component (HFC; 1.0-2.2 Hz). The LFC probably has a neurological origin. The HFC is supposed to be related to the arterial pulse. The aim of this study was to investigate accommodative fluctuations and gain more information about their origin by using a non-optical method. We used continuous ultrasonographic biometry to measure changes in anterior chamber (AC) depth, lens thickness and vitreous length during steady-state accommodation. Simultaneously, the electrocardiogram (ECG) was recorded. Changes in axial length were calculated offline by taking the sum of the changes in the three intraocular distances. Results show that fluctuations with an LFC were present in all three intraocular distances but not in the axial length, proving that only the lens was involved. In contrast with the findings of investigators using optical methods, no HFC was present in fluctuations of AC depth and lens thickness. However, a small HFC was found in registrations of the vitreous and axial length, which appeared to correspond with the heart rate.

Age-related changes in the accommodation mechanism.

Presbyopia is caused by changes in the visco-elastic properties of the lens or the choroid or both. Far-to-near (FN) accommodation dynamics are dominated by the properties of the lens, whereas near-to-far (NF) accommodation dynamics depend on the properties of the lens as well as the choroid. The aim of this study was to gain more insight into the cause of presbyopia by analyzing how FN and NF accommodation dynamics change as a function of age. Changes in axial lens thickness during accommodation were measured in vivo using continuous ultrasonographic biometry. The measurements were analyzed with the use of a biomechanical model of the mechanism of accommodation. Fitting the model to the responses yields time constants of FN and NF accommodation. The time constants FN and NF increase with age at an approximately equal rate: 7 ms/year (+/- 1.8 SEM) and 6 ms/year (+/- 1.6 SEM), respectively. This result supports a lenticular cause of presbyopia. In addition, estimations of the lens damping coefficients at different ages are given for the first time: the damping coefficient of the lens increases 20-fold between 15 and 55 years of age.

Analysis of accommodation function with ultrasonography.

The aim of this study was to present a new method that uses ultrasonography to analyse accommodation function, and to do a preliminary investigation of its possible use in clinical practice. Using the method of continuous ultrasonographic biometry, changes in lens thickness were measured during accommodation. From these measurements response latency and duration were determined. Normal values for latency and duration were obtained by measuring 20 healthy subjects of different ages. Measurements were also performed on three patients with different accommodation disorders: diabetes, Adie's syndrome and third nerve palsy. Normal response latency is 394 ms (+/-46 SD) and independent of are. Normal response duration increases with age from an average 306 ms at 15 years-of-age to an average 954 ms at 55 years-of-age. Normal latency as well as duration appear to have a large interindividual variability. The diabetic patient had a delayed latency but a normal response duration. The patient with Adie's syndrome had a delayed latency and prolonged duration. The patient with third nerve palsy had a normal latency and duration. We conclude that ultrasonographically determine latency and duration give additional information on accommodation function that is more complete and objective than maximum accommodative amplitude alone. The results in our patients suggest that, in selected cases, this information may aid in the diagnosis and management of patient's complaints.

In vivo determination of the biomechanical properties of the component elements of the accommodation mechanism.

A method of obtaining in vivo information about the component elements of the accommodation mechanism is described. Changes in axial lens thickness during accommodation are measured continuously by ultrasonographic biometry. The measurements are fitted with a dynamic biomechanical model of the mechanism of accommodation. This gives a time constant that depends both on the direction of accommodation and on the properties of the lens, zonules and choroid. Two ratios can be calculated that give information about the visco-elastic properties of the lens, zonules and choroid. This information is especially useful to evaluate the changes that lead to presbyopia.

Presbyopia and velocity of sound in the lens.

The elastic properties of lens matter change with age and this contributes to presbyopia. The changes in elasticity of lens matter could be the result of a change in water and soluble proteins (1) or a change in lens fiber cytoskeleton and membranes (2). If it is caused by (1) then the velocity of sound in the lens should change with age. If it is caused by (2) the velocity of sound in the lens will not change. Using the technique of continuous ultrasonographic biometry, the velocity of sound in clear lenses was measured in vivo in a group of 24 healthy subjects aged 15 to 45 years with a visual acuity of 6/6 or better. In this group maximum accommodative amplitude decreased with age. It was found that, despite the occurrence of presbyopia, the velocity of sound did not change with age. Our results support the hypothesis that age-related changes in lens fiber cytoskeleton and membranes are responsible for the change in elastic properties of lens matter and thus contribute to presbyopia.