Evaluation of the Lenstar LS 900 non-contact biometer.

BACKGROUND/AIMS: Evaluation of the reproducibility of the Lenstar LS 900 non-contact biometer, and a comparison with the Visante anterior-segment optical coherence tomography (AS-OCT) and the IOLMaster. METHODS: Central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), keratometry (K) values, corneal diameter (CD) and axial length (AL) were obtained in 38 healthy volunteers (76 eyes) to determine the reproducibility of the Lenstar. CCT, ACD, CD, K values and AL measurements measured with the Lenstar were compared with the AS-OCT and IOLMaster. Intraocular lens (IOL) power calculations were done to study the significance of the difference between AL measurements. RESULTS: The reproducibility of the Lenstar was better than 0.9% for CCT, ACD, LT, K values and AL measurements. Although all correlations were highly significant (p<0.001), all comparisons showed a significant difference, except for the comparison of CD measurements using the Lenstar and IOLMaster (p = 0.175). The differences in IOL power calculations for an AL of 20, 25 and 30 mm with a mean difference between Lenstar and IOLMaster AL measurements of 0.03 mm, were 0.13 D, 0.10 D and 0.08 D, respectively. CONCLUSION: The reproducibility of the Lenstar was excellent. Small but significant differences exist between the Lenstar, Visante OCT and the IOLMaster. Therefore, measurements of the Lenstar, AS-OCT and IOLMaster are not interchangeable. Despite the significant difference between AL measurements, there is no clinically significant difference in the IOL power calculation results.

Neuronal changes in normal human aging and Alzheimer's disease.

This article discusses age-related changes in brain weight, total number of cortical neurons, cortical dendrites, spine, and synapse density. The conclusion is that the present outlook is less grim than it was 30 years ago. Age-related reduction appears to be specific to brain region and cortical layer rather than a general feature. In addition, we describe a different pattern of changes that occur in Alzheimer's disease patients. This review concludes that the association cortices in particular are affected in aging and Alzheimer's disease and that the primary visual and somatosensory cortices are relatively spared.

A practical approach to and long-term results of fitting silicone contact lenses in aphakic children after congenital cataract.

PURPOSE: This prospective study investigated characteristics of fit and performance of silicone contact lenses under conditions of permanent wear in cases of aphakia after congenital cataract. METHODS: Seventeen aphakic children (8 eyes unilateral, 18 eyes bilateral) were fitted with silicone contact lenses on an empirical basis without the use of keratometry. The lenses were worn on a permanent basis, with a routine replacement every 3 months. The follow up was 6 years, with evaluation lens parameters, fitting characteristics, lens condition, replacement rate, wearing time, complications, and visual acuity. RESULTS: The back optical zone radius (BOZR) remained stable at 7.50 mm, up to the age of 1.5 years old. At the age of 4 years, almost all eyes needed a BOZR of 7.90 mm. Mean +/- SD contact lens power was +25.47 diopter (D) +/- 4.0 (range +32.00 D - +20.00 D) at 3 months of age, and +17.94 D +/- 3.8 (range +29.00 D - +15.00 D) at 3 years of age. This represents an average decrease of 0.23 D per month. The power decrease in unilateral cases was significantly lower (P < 0.01) than in bilateral aphakia. Snellen visual acuity at 4 years of age was 0.1 to 0.3 (20/200-20/60) in 15 eyes, 0.3 to 0.5 (20/60-20/40) in 10 eyes and greater than 0.5 (>20/40) in 1 eye. Lens usage over a total period of 90 wearing years was 5.6 lenses/eye/year, including the regular exchange every 3 months. No serious complications occurred. A positive correlation (r = 0.89) was found between age and deposit buildup. With the need for permanent wear reduced, therefore, 73% of the eyes were refitted with high-water content soft lenses or high gas-permeable (HGP) lenses, when the patients ranged in age from 4 to 6 years old. CONCLUSIONS: The procedure for fitting silicone lenses in aphakic children is feasible in an easy and logical way without keratometry. Permanent wear with a low complication rate is possible up to the age of 3. with a lens usage (including a 3-month regular exchange) of 5.6 lenses/eye/year. From the age of 3, deposit formation is the determining factor for refitting with high-water content soft or HGP lenses.

Evaluation of a new system of lens parameter selection and comparison of traditional vs one-step lens care systems for aspheric high-Dk RGP contact lenses.

PURPOSE: We investigated the value of newly developed systems for parameter selection on the performance of high Dk rigid gas permeable (RGP) contact lenses with a spheric-aspheric design made of Boston Equa material in normal daily wear conditions. A comparison was also made between the safety and efficacy of a traditional care system vs a one-step chemical care system during the follow-up period of 1 year. METHODS: A total of 66 patients were randomly assigned to traditional and newly developed systems for computing the back optical zone radius (BOZR) and the total diameter (TD) of the lenses. Evaluation parameters incorporated assessment of fit, visual acuity, wearing time, comfort, and lens condition. RESULTS: The traditional method of computing the BOZR, using a method based on flat-K, predicted the BOZR successfully in 83% of the cases. Corneal topometry reached a lower, but not significantly different (P > 0.01) value of 75% correct prediction of BOZR. Analysis of the differences in eccentricity (E) values between quadrants per eye was a significant (P < 0.001) factor in fault predictions in the topometric system. A newly developed guide forTD selection performed, with 90% correct predictions, significantly (P < 0.01) better than a traditional method (72%) based on corneal diameter on supraversion. No significant differences (P > 0.05) were found in the capabilities of care systems (a traditional care system using a surfactant cleaner vs a one-step solution) to keep the lenses in proper condition and without deformation, over the 1 year follow-up period. The final success rate was 85%. CONCLUSIONS: Although high Dk RGP contact lenses can be fit and used with a 85% success rate using advanced systems for determining the BOZR and TD, it remains necessary to evaluate the fit before dispensing high Dk RGP lenses in 15% of the cases. The one-step solution used in this study was a good starting point for lens care. If needed, surfactant cleaning in the traditional care system can be done without the risk of lens deformation.

Clinical evaluation of a custom-made toric soft lens.

PURPOSE: The fitting of toric soft contact lenses is often complicated by interference between the toric optics and the geometry need to stabilise the lens on the eye. The use of a spherical trial lens to determine the parameters of a toric soft contact lens can lead to unintended positioning and movement of the lens ordered. The purpose of this study was to evaluate clinically the success. PURPOSE: The fitting of toric soft contact lenses is often complicated by interference between the toric optics and the geometry needed. METHOD: The design of the lenses used was such that optical correction and stabilisation were separated. The lenses had a back tonic surface limited to the central optical zone and base down prism stabilisation in the periphery. The empirical system used corneal radii, spectacle refraction and horizontal visible iris diameter as lens design parameters. RESULTS: This multi-centre trial, comprised of 105 patients (193 eyes), revealed an overall success rate of 86%. The total number of lenses ordered to achieve success was 1.46 per eye in new patients and 1.69 per eye in patients who were failures with other toric soft lenses. In 14% of the cases success could not be achieved despite ordering several lenses (up to 4 lenses/eye). Many of these patients (60%) were also failures with other toric soft lenses. CONCLUSION: It is concluded that in new patients successful toric soft contact lens fitting can be achieved with an empirically based method. When refitting former toric soft lens failures, we recommend discontinuation after two further unsuccessful fittings.

Tailoring of new polymeric biomaterials for the repair of medium-sized corneal perforations.

The aim of this study was to investigate whether polymeric biomaterials can be designed such that they become suitable for surgical closure of medium-sized perforations in the cornea, the transparent tissue in the front of the eye. Such a biomaterial must meet stringent requirements in terms of hydrophilicity, strength, transparency, flexibility, and biocompatibility. Four different copolymers of n-butyl methacrylate (BMA) and hexa(ethylene glycol) methacrylate (HEGMA) were prepared and characterized. Poly(BMA) was made as a reference material. Physicochemical properties were measured (contact angles, glass-transition temperatures, thermal degradation, water uptake and swelling), and cytotoxicity in vitro was assessed with a MTT test. Moreover, the interaction between the materials and cultured human corneal epithelial cells was studied. The copolymers may be useful for temporary closure of corneal perforations.

Synthesis and initial structure--activity relationships of modified salicylihalamides.

[reaction:see text] The first stereoselective total synthesis of the potent antitumor compound (-)-salicylihalamide A is presented. The practicality of our approach provides for high material throughput and is highlighted by the rapid construction of a variety of modified congeners. Initial structure-activity relationships are derived from growth inhibition experiments with a human melanoma cancer cell line.

Review and classification of corneal topographers.

Corneal topography has, due to developments in refractive surgery and contact lens fitting, become a widely used diagnostic tool. Many types of topographers have been introduced, but there is some confusion on classification and subsequent principal possibilities of the various devices offered to the practitioner. The purpose of the study reported here was to make an inventory of developed devices, analyse the basic principles and create a classification based on optical principles. A literature search was done using Medline, the IBM Patent Server, and references found in articles and patents. This search resulted in a variety of descriptions that could be classified into 12 groups according to their use of light source and light-matter interaction of which four groups have representatives on the commercial market. This classification can be used by researchers and practitioners to gain insight into the possibilities of a given device in relation to the desired application.

Layer-specific dendritic regression of pyramidal cells with ageing in the human prefrontal cortex.

The dendritic field of pyramidal neurons in cortical layers IIIc and V of the prefrontal cortex in ageing humans was studied. The three-dimensional branching pattern of the basilar dendrites of Golgi-Cox impregnated neurons was analysed in the middle frontal gyrus (areas 9 and 46) in eight subjects between the ages of 49 and 90 years, all without a neurological or psychiatric disorder. The results revealed a significant regression of the layer V dendritic pattern with increasing age, but the layer IIIc neurons did not show any age-related changes. Together with our earlier data on the postnatal development of the same cell types in the prefrontal cortex, we hypothesize that the layer V neurons in the prefrontal cortex start to regress from the fifth decade onwards, in contrast to the layer IIIc neurons which remain stable from puberty on. We conclude that pyramidal cells in layer IIIc and V in a similar cortical region undergo a differential ageing effect.

Disinhibition of the mediodorsal thalamus induces fos-like immunoreactivity in both pyramidal and GABA-containing neurons in the medial prefrontal cortex of rats, but does not affect prefrontal extracellular GABA levels.

Stimulation of the mediodorsal and midline thalamic nuclei excites cortical neurons and induces c-fos expression in the prefrontal cortex. Data in the literature data suggest that pyramidal neurons are the most likely cellular targets. In order to determine whether cortical interneurons are also impacted by activation of mediodorsal/midline thalamic nuclei, we studied the effects of thalamic stimulation on (1) Fos protein expression in gamma-aminobutyric acid (GABA)-immunoreactive neurons and on (2) extracellular GABA levels in the prefrontal cortex of rats. Perfusion of the GABA-A receptor antagonist bicuculline for 20 minutes through a dialysis probe implanted into the mediodorsal thalamus induced Fos-like immunoreactivity (IR) approximately 1 hour later in the thalamus and in the medial prefrontal cortex of freely moving rats. Immunohistochemical double-labeling for Fos-like IR and GABA-like IR showed that about 8% of Fos-like IR nuclei in the prelimbic and infralimbic areas were located in GABA-like IR neurons. Fos-like IR was detected in three major subsets of GABAergic neurons defined by calbindin, parvalbumin, or vasoactive intestinal peptide (VIP)-like IR. Dual probe dialysis showed that the extracellular levels of GABA in the prefrontal cortex did not change in response to thalamic stimulation. These data indicate that activation of thalamocortical neurons indeed affects the activity of GABAergic neurons as shown by the induction of Fos-like IR but that these metabolic changes are not reflected in changes of extracellular GABA levels that are sampled by microdialysis.

Contrast sensitivity with soft contact lenses compensated for spherical aberration in high ametropia.

BACKGROUND: In optical systems, it is usual to compensate for longitudinal spherical aberration. In order to increase image quality, lens surfaces can be made aspheric to bring all object light rays into focus at the image plane. Theoretically, soft contact lenses with high power and spherical surfaces show significant amounts of spherical aberration. The use of spherical aberration-free soft contact lenses could therefore improve retinal image quality in the case of high ametropia. However, because of ocular aberration, accommodation effects, pupil dynamics, contact lens flexure, and positioning, the computation of the spherical aberration induced when a contact lens is placed on the eye is complicated. METHODS: In this study, the spatial contrast sensitivity (CS) of 61 high ametropes wearing soft contact lenses with, and without, in-air spherical aberration compensation is measured. RESULTS: A slightly better overall performance was found with the standard lenses. There was no significant influence by the type of ametropia, age, and gender. If individual results are considered, clinically significant differences between the two lens groups are observed in approximately 30% of the cases. CONCLUSIONS: It seems that correcting in-air soft contact lens spherical aberration systematically is of no clinical interest. However, selective manipulation of spherical aberration could, in high power soft contact lenses, significantly improve CS in individuals.

Development of a wide field height eye topographer: validation on models of the anterior eye surface.

PURPOSE: The aim of this research was to develop a corneal topographer that determines the shape of the entire anterior surface of an eye without assumptions, and with uniformly high accuracy in the center and periphery. METHODS: Based upon a double projection of two sine wave gratings and analysis of the distortion of the sine wave gratings due to the corneal-scleral shape, point-by-point measurements of surface elevation were obtained with a sample density equal to the pixel density of the CCD-detector. Using this principle, a prototype topographer, called the Maastricht Shape Topographer (MST), was developed. The accuracy and reproducibility of the instrument were evaluated using bispheric models of the anterior surface of the eye. RESULTS: The average accuracy of height measurements was +/- 0.55 micron in the 10-mm central area and +/- 22.50 microns in the periphery (14 to 19 mm). Reconstruction accuracy of the radius of curvature was +/- 0.0155 mm (+/- 0.88 D) in the center and +/- 0.0313 mm in the periphery (sclera). Average height reproducibility standard error was 0.0282 micron in the center and 2.6156 microns in the periphery. CONCLUSIONS: With the MST, unambiguous shape measurements of the entire anterior surface of the eye are possible, with accuracy up to clinically accepted standards. MST is able to measure height over a wide area of 20 mm, with a 6-mm depth of field. The tested prototype of the device can be further improved by the use of custom-made optics in order to increase signal to noise ratio in the periphery of the image. This height topographer could offer a reliable method in cases where shape is of paramount importance, e.g., in (scleral) contact lens fitting and refractive surgery.

Response learning of rats in a Morris water maze: involvement of the medical prefrontal cortex.

This study is concerned with the question whether the medial prefrontal cortex mediates spatial navigation requiring the expression of response learning. It consists of two parts. In the first experiment it was investigated whether intact male Wistar rats can learn a spatial response task in a Morris water maze, and, if so, how the learning of this task compares with the learning of a place task, in the same water maze. The data illustrate that rats can indeed learn the response task demands, but also demonstrate that this task is more difficult to learn than the place task. This is evidenced by a slower and more capricious acquisition. Based on these findings a second experiment was conducted, in which sham-operated rats and rats with damage of the medial prefrontal cortex (mPFC) were compared for their acquisition in the response task in the Morris water maze. The results showed that both escape latency and path length of the mPFC-damaged animals were significantly higher than those of the sham-operated animals. A behavioral analysis of the swimming paths demonstrated that the mPFC-damaged rats were more persistent in their use of a place strategy, while the sham-operated animals sooner switched to the more successful taxon-orientation strategy. Taken together with previous findings these data support the hypothesis of a functional dissociation of the mPFC with regard to its involvement in the expression of place and response learning.

Development of pyramidal cells in medial frontal cortex following neonatal lesions of anterior midline cortex.

The anterior midline cortex of rats was removed on postnatal day 10. The development of layer II, III and V pyramidal cells in the tissue that subsequently formed the presumptive medial frontal cortex in these animals was studied in Golgi-Cox stained material on postnatal days 15, 25, 35, and 120. The results showed that the number of branch segments of both basilar and apical dendrites were significantly reduced relative to controls at the early developmental stages but by adulthood all regions analyzed were similar in operates and controls. Thus, the cells migrating into the lesion area were delayed in development but did eventually grow to resemble cells that were in the same region in normal controls. This anatomical development correlates with the functional recovery of animals with day 10 frontal lesions in other studies, and suggests that the growth of this tissue may play a role in functional recovery.

Infrared pupillometry in presbyopes fitted with soft contact lenses.

The influence of pupil size, lens centration, and translation on multifocal contact lens performance suggests that these parameters should be accounted for in the optical design of presbyopic contact lenses. The purpose of the present article is to complete the existing experimental data with clinical measurements of pupil diameter and lens position relative to the pupil in a group of presbyopes, with controlled target luminance, stimulus distance, gaze angle, and convergence. The experiments involve an infrared video-pupillometer and ring-marked contact lenses. Results on pupil aperture show that the effect of changing target distance is comparable in magnitude to that of varying luminance within the photopic range. The measured data on lens position confirm that soft contact lenses are generally decentered from the pupillary axis, usually in inferior temporal direction, and that their average translation between primary and downward gaze is very small. It is also found that the average relative position between lens and pupil centers is slightly modified by changes of luminance in far vision. All these results provide characteristic values which are helpful for the optical modelling of presbyopic contact lenses.

Ineffectiveness of GM1 and ORG2766 on behavioural recovery after prefrontal cortical lesions in adult rats.

This study examines whether treatment with GM1 ganglioside or the corticotropin (ACTH)(4-9) analogue ORG2766 can facilitate the behavioural recovery of adult rats with medial prefrontal cortex (mPFC) lesions, as animals are impaired in their food hoarding and spatial delayed alternation performance following mPFC lesions. No ameliorating effects of GM1 treatment on performance of these behaviours were observed. Although treatment with ORG2766 somewhat improved the hoarding performance of lesioned animals, the intermediate amount of pellets hoarded was not significantly different from that of either sham-operated or vehicle-treated lesioned rats. No effect of ORG2766 treatment was observed in the spatial delayed alternation test. Further, no changes were detected in the mesocortical dopamine innervation, presumed to be involved in the neural mechanism of behavioural sparing, in response to either treatment.

Monoamine concentrations in rat prefrontal cortex and other mesolimbocortical structures in response to partial neonatal lesions of the medial prefrontal cortex.

In an earlier study it was found that partial neonatal lesions of the medial prefrontal cortex (mPFC) resulted in an increased dopaminergic innervation in the remaining part of mPFC along with functional sparing. The present study assessed whether this response is restricted to this part of the cortex or whether also other structures of the mesolimbocortical system are involved. Furthermore, it was investigated whether the other monoaminergic systems were affected by neonatal mPFC lesions. In 6-day-old rats, the mPFC was partially ablated or a sham operation was made. The concentrations of dopamine (DA) and its metabolites increased to 250-350% in the remaining part of the mPFC compared to the sham-operated controls. The response was most prominent in this part of the cortex; no other mesolimbocortical structure showed such major changes of DA and its metabolites. In addition, a small increase in the concentrations of noradrenaline, serotonin and their metabolites was also spotted in the remaining mPFC and some other mesolimbocortical structures of the lesioned animals. The present data support the suggested involvement of DA in the neural mechanism of sparing of function, and this DA response seems to be most prominent in the remaining mPFC. However, the responses of the noradrenergic and serotonergic systems may also be important for sparing of function to occur.

Activation of mesocortical dopaminergic system in the rat in response to neonatal medial prefrontal cortex lesions. Concurrence with functional sparing.

Neonatal lesions of the medial part of the rat prefrontal cortex (mPFC) (performed at the age of 6 days) resulted in a sparing in the performance of spatial delayed alternation (SDA) and an increase in dopaminergic (DA) innervation. The increased DA innervation was primarily observed in the remaining part of the mPFC. The DA fibre density was considerably higher in the non-ablated part of the mPFC, and the fibres were thicker with more large varicosities compared with sham-operated controls. Biochemical measurements showed a 3.5-fold increase in DA concentration in the remaining part of the mPFC of the animals with neonatal lesions when compared with the mPFC of sham-operated animals. In addition the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were increased. The metabolite/transmitter ratios, indicating DA utilisation, did not significantly differ from controls. The increased DA innervation and the increased concentration of DA and its metabolites in the animals with neonatal lesions further support our hypothesis that the mesocortical DA system is involved in the neural mechanism of sparing of function observed after neonatal mPFC lesions. However, sparing of function in animals with no discernable mPFC forces us to conclude that this DA response cannot be the only factor involved in the mechanism of sparing of function.

Neuroanatomical correlates of sparing of function after neonatal medial prefrontal cortex lesions in rats.

In rats, the possibility of neuroanatomical changes in response to partial medial prefrontal cortex lesions at postnatal day 6, concomitant with behavioural sparing, was investigated. The projections from the mediodorsal nucleus of the thalamus (MD) and the mesocortical dopaminergic (DA) projection were examined. No indications were found for a changed pattern of projection from MD in response to either a neonatal or an adult medial prefrontal cortex (mPFC) lesion. However, the DA innervation was changed after neonatal mPFC lesions. In the remainder of the mPFC, the DA fibre network proved to be denser, fibres were thicker, had more varicosities, and often the background staining was higher. None of these phenomena were seen in operated adult rats or in controls. It is postulated that the changes in DA innervation might contribute to the sparing of function observed in the spatial delayed alternation task.

Comparison of the effects of neonatal and adult medial prefrontal cortex lesions on food hoarding and spatial delayed alternation.

Performance in food hoarding, a species-typical task, and spatial delayed alternation, a learning task, was investigated in male rats with bilateral medial prefrontal cortex (mPFC) lesions sustained in adulthood or at the age of 6 days. Animals with adult mPFC lesions hoarded significantly fewer food pellets than their controls. The mPFC lesion effect on hoarding behaviour of the neonatally operated rats was unclear because of the unexpectedly low hoarding score of their controls. In the spatial delayed alternation task, the animals with mPFC lesions in adulthood exhibited a permanent deficit, while the animals with neonatal mPFC lesions showed no significant deficits. It is concluded that a bilateral lesion in adulthood, mainly affecting the frontal area 2 and the dorsal anterior cingulate area of the mPFC, results in a permanent deficit in food hoarding and spatial delayed alternation performance, whereas a similarly restricted mPFC lesion at the age of 6 days shows a complete sparing of the spatial delayed alternation task performance.