Factors influencing the detection of visual developmental deficits in 3-year-old kindergarten children

PURPOSE/BACKGROUND

In the 'Tübingen Kindergarten study', an orthoptic screening program for amblyopia in three-year-olds was evaluated. In the retrospective analysis presented here, the association between a child's history--especially participation in the regular preventive care examinations in Germany (U4 to U7)--and the time of detection of target diseases was investigated.

METHODS AND SUBJECTS

The parents of three groups of children were interviewed by telephone. Group 1 consisted of 21 children already treated for amblyopia before orthoptic screening; group 2 of 26 children with target conditions newly detected by orthoptic screening; and group 3 of 32 children with newly detected moderate ametropia. The groups were tested for differences in history and utilization/results of the regular preventive care examinations.

RESULTS

Participation in regular preventive care ranged from 82% to 92%. There were no significant differences between the groups. Nearly 90% of parents from groups 2 and 3 had not heard of amblyopia before orthoptic screening. Only one child had been referred after regular preventive care examinations.

CONCLUSIONS

The regular preventive care examinations contributed little to the detection of amblyopia. The strong position of the pediatrician should be used for the early information of parents.

Magnetosomal matrix: ultrafine structure may template biomineralization of magnetosomes

The organic matrix surrounding bullet-shaped, cubo-octahedral, D-shaped, irregular arrowhead-shaped, and truncated hexa-octahedral magnetosomes was analysed in a variety of uncultured magnetotactic bacteria. The matrix was examined using low- (80 kV) and intermediate- (400 kV) voltage TEM. It encapsulated magnetosomes in dehydrated cells, ultraviolet-B-irradiated dehydrated cells and stained resin-embedded fixed cells, so the apparent structure of the matrix does not appear to be an artefact of specimen preparation. High-resolution images revealed lattice fringes in the matrix surrounding magnetite and greigite magnetosomes that were aligned with lattice fringes in the encapsulated magnetosomes. In all except one case, the lattice fringes had widths equal to or twice the width of the corresponding lattice fringes in the magnetosomes. The lattice fringes in the matrix were aligned with the [311], [220], [331], [111] and [391] related lattice planes of magnetite and the [222] lattice plane of greigite. An unidentified material, possibly an iron hydroxide, was detected in two immature magnetosomes containing magnetite. The unidentified phase had a structure similar to that of the matrix as it contained [311], [220] and [111] lattice fringes, which indicates that the matrix acts as a template for the spatially controlled biomineralization of the unidentified phase, which itself transforms into magnetite. The unidentified phase was thus called pre-magnetite. The presence of the magnetosomal matrix explains all of the five properties of the biosignature of the magnetosomal chain proposed previously by Friedmann et al. and supports their claim that some of the magnetite particles in the carbonate globules in the Martian meteorite ALH84001 are biogenic. Two new morphologies of magnetite magnetosomes are also reported here (i.e. tooth-shaped and hexa-octahedral magnetosomes). Tooth-shaped magnetite magnetosomes elongated in the [110] direction are reported, and are distinct from arrowhead-shaped and bullet-shaped magnetosomes. Elongation of magnetite magnetosomes in the [110] direction has not been reported previously. A Martian hexa-octahedral magnetite particle was previously characterized by Thomas-Keptra et al. and compared with truncated hexa-octahedral magnetite magnetosomes. Hexa-octahedral magnetite magnetosomes with the same morphology and similar sizes and axial ratios as those reported by Thomas-Keptra et al. are characterized here. These observations support their claim that ALH84001 contains evidence for a past Martian biota.

Porous nanocomposites of zirconium dioxide and silicate

Highly porous nanocomposites of zirconium dioxide and silicate are synthesised in an aqueous system from an inorganic salt of zirconium; the nanacomposites, with tailorable pore structures, exhibit superior performance as catalyst supports.

Phakometric measurement of ocular surface radius of curvature and alignment: evaluation of method with physical model eyes

Ophthalmophakometric measurements of ocular surface radius of curvature and alignment were evaluated on physical model eyes encompassing a wide range of human ocular dimensions. The results indicated that defocus errors arising from imperfections in the ophthalmophakometer camera telecentricity and light source collimation were smaller than experimental errors. Reasonable estimates emerged for anterior lens surface radius of curvature (accuracy: 0.02-0.10 mm; precision 0.05-0.09 mm), posterior lens surface radius of curvature (accuracy: 0.10-0.55 mm; precision 0.06-0.20 mm), eye rotation (accuracy: 0.00-0.32 degrees; precision 0.06-0.25 degrees), lens tilt (accuracy: 0.00-0.33 degrees; precision 0.05-0.98 degrees) and lens decentration (accuracy: 0.00-0.07 mm; precision 0.00-0.07 mm).

Non-cycloplegic screening for amblyopia via refractive findings with the Nikon Retinomax hand held autorefractor in 3 year old kindergarten children

AIMS

To assess non-cycloplegic screening for amblyopia with the hand held Nikon Retinomax autorefractor in 3 year old kindergarten children.

METHODS

427 three year old children were examined in kindergarten with the Retinomax without cycloplegia. A gold standard was established in all children by two orthoptic examinations in kindergarten. If there were missing, abnormal, or inconsistent findings, children were referred for ophthalmological examination. If, by the ophthalmological examination, a new case of amblyopia requiring treatment was diagnosed, the gold standard was set "positive."

RESULTS

In 404 children the gold standard was obtained. 10 children (2.5%) had a "positive" gold standard of unknown and untreated amblyopia. Screening sensitivity was 0.80, specificity 0.58, accuracy 0.58, and the likelihood ratio 1.89.

CONCLUSION

Non-cycloplegic refractive screening with the Retinomax led to many false positive referrals due to instrument myopia and "inconclusive" results. Hence specificity, accuracy, and the likelihood ratio were too low to conduct screening effectively.

A nanometre-scale non-periodic structural variation in high temperature superconducting ceramics and the implications for properties

Non-periodic structural variation has been found in the high Tc cuprates, YBa2Cu3O7-x and Hg0.67Pb0.33Ba2Ca2Cu3O8+delta, by image analysis of high resolution transmission electron microscope (HRTEM) images. We use two methods for analysis of the HRTEM images. The first method is a means for measuring the bending of lattice fringes at twin planes. The second method is a low-pass filter technique which enhances information contained by diffuse-scattered electrons and reveals what appears to be an interference effect between domains of differing lattice parameter in the top and bottom of the thin foil. We believe that these methods of image analysis could be usefully applied to the many thousands of HRTEM images that have been collected by other workers in the high temperature superconductor field. This work provides direct structural evidence for phase separation in high Tc cuprates, and gives support to recent stripes models that have been proposed to explain various angle resolved photoelectron spectroscopy and nuclear magnetic resonance data. We believe that the structural variation is a response to an opening of an electronic solubility gap where holes are not uniformly distributed in the material but are confined to metallic stripes. Optimum doping may occur as a consequence of the diffuse boundaries between stripes which arise from spinodal decomposition. Theoretical ideas about the high Tc cuprates which treat the cuprates as homogeneous may need to be modified in order to take account of this type of structural variation.

Structural and morphological anomalies in magnetosomes: possible biogenic origin for magnetite in ALH84001

We report biogenic magnetite whiskers, with axial ratios of 6 : 1, elongated in the [1 1 1], [1 1 2] and [1 0 0] directions, resembling the magnetite whiskers detected in the Martian meteorite ALH84001 by Bradley et al., and interpreted by those authors as evidence of vapour-phase (abiogenic) growth. Magnetosomal whiskers with extended defects consistent with screw dislocations and magnetosomes resembling flattened twinned platelets, as well as other twinning phenomena and other structural defects, are also reported here. Magnetosomes with teardrop-shaped, cuboidal, irregular and jagged structures similar to those detected in ALH84001 by McKay et al., coprecipitation of magnetite possibly with amorphous calcium carbonate, coprecipitation of magnetite possibly with amorphous silica, the incorporation of titanium in volutin inclusions and disoriented arrays of magnetosomes are also described. These observations demonstrate that the structures of the magnetite particles in ALH84001, their spatial arrangement and coprecipitation with carbonates and proximity to silicates are consistent with being biogenic. Electron-beam-induced flash-melting of magnetosomes produced numerous screw dislocations in the [1 1 1], [1 0 0], and [1 1 0] lattice planes and induced fusion of platelets. From this, the lack of screw dislocations reported in the magnetite particles in ALH84001 (McKay et al., and Bradley et al.) indicates that they have a low-temperature origin.

[Experiences with cycloplegic drops in German-speaking centers of pediatric ophthalmology and stabology--results of a 1999 survey]

BACKGROUND

Because of its advantages, topical cyclopentolate is often preferred over the gold standard, atropine. The purpose of the study was to obtain an overview over current cycloplegia protocols and to estimate the likelihood of severe complications due to the use of cycloplegics.

METHODS

A questionnaire was sent to 107 German-speaking centres with a supposed high cycloplegia frequency.

RESULTS

57 centres answered, whereby 1,112 cumulated years of experience with cycloplegia were available for analysis. The frequency of cycloplegias varied between 2 and 180/week/centre, median 25/week/centre. A cumulated amount of 1.7 million cycloplegias was computed. The average extrapolated experience with cycloplegia was 49,000 cycloplegias/30 years. Severe complications which would cause a medical follow up of several hours or which led to a follow up in a ward were named 47 times and 2 times, respectively.

CONCLUSIONS

During 30 years of a cycloplegia career with an average of 34 cycloplegias/week, one may expect 2-10 severe complications. In current practice, the patient risk of severe complications is very small. Health care professionals and parents should be informed about the frequent occurrence of light side effects in order to reach a good compliance with cycloplegia.

Adhesion of microbes using 3-aminopropyl triethoxy silane and specimen stabilisation techniques for analytical transmission electron microscopy

A variety of adhesive support-films were tested for their ability to adhere various biological specimens for transmission electron microscopy. Support films primed with 3-amino-propyl triethoxy silane (APTES), poly-L-lysine, carbon and ultraviolet-B (UV-B)-irradiated carbon were tested for their ability to adhere a variety of biological specimens including axenic cultures of Bacillus subtilis and Escherichia coli and wild-type magnetotactic bacteria. The effects of UV-B irradiation on the support film in the presence of air and electrostatic charge on primer deposition were tested and the stability of adhered specimens on various surfaces was also compared. APTES-primed UV-B-irradiated Pioloform was consistently the best adhesive, especially for large cells, and when adhered specimens were UV-B irradiated they became remarkably stable under an electron beam. This assisted the acquisition of in situ phase-contrast lattice images from a variety of biominerals in magnetotactic bacteria, in particular metastable greigite magnetosomes. Washing tests indicated that specimens adhering to APTES-primed UV-B-irradiated Pioloform were covalently coupled. The electron beam stability was hypothesised to be the result of mechanical strengthening of the specimen and support film and the reduced electrical resistance in the specimen and support film due to their polymerization and covalent coupling.

Cost-effectiveness of orthoptic screening in kindergarten: a decision-analytic model

PURPOSE

The purpose of this study was to analyze the cost-effectiveness of orthoptic screening for amblyopia in kindergarten.

METHODS

A decision-analytic model was used. In this model all kindergarten children in Germany aged 3 years were examined by an orthoptist. Children with positive screening results were referred to an ophthalmologist for diagnosis. The number of newly diagnosed cases of amblyopia, amblyogenic non-obvious strabismus and amblyogenic refractive errors was used as the measure of effectiveness. Direct costs were measured form a third-party payer perspective. Data for model parameters were obtained from the literature and from own measurements in kindergartens. A base analysis was performed using median parameter values. The influence of uncertain parameters was tested in sensitivity analyses.

RESULTS

According to the base analysis, the cost of one orthoptic screening test was 7.87 euro. One ophthalmologic examination cost 36.40 euro. The total cost of the screening program in all kindergartens was 3.1 million euro. A total of 4,261 new cases would be detected. The cost-effectiveness ratio was 727 euro per case detected. Sensitivity analysis showed considerable influence of the prevalence rate of target conditions and of the specificity of the orthopic examination on the cost-effectiveness ratio.

CONCLUSIONS

This analysis provides information which is useful for discussion about the implementation of orthoptic screening and for planning a field study.

The use of cycloplegic agents. Results of a 1999 survey of German-speaking centers for pediatric ophthalmology and strabology

INTRODUCTION

Because of its advantages, topical cyclopentolate is often preferred over the gold standard, atropine. The purpose of this study was to obtain an overview over current cycloplegia protocols and to estimate the likelihood of severe complications due to the use of cycloplegics.

METHODS

A questionnaire was sent to 107 German-speaking centers with a supposed high frequency of cycloplegias.

RESULTS

57 centers answered, whereby 1,112 cumulated years of experience with cycloplegia were available for analysis. The frequency of cycloplegias varied between 2 and 180/week/center, median 25/week/center. A cumulated total of 1.7 million cycloplegias was computed. The extrapolated average experience with cycloplegia was 49,000 cycloplegias/30 years. Complications which would warrant a medical follow-up of several hours (severe complications) or which led to a follow-up in a ward (very severe complications) were named 47 times and 2 times, respectively.

DISCUSSION

During 30 years of a cycloplegia career with an average of 34 cycloplegias/week, one may expect 2-10 severe or very severe complications. In current practice, the patient risk of severe complications is very small. Health care professionals and parents should be informed about the frequent occurrence of harmless side effects in order to achieve a good compliance with cycloplegia.

[Cost effectiveness of mass orthoptic screening in kindergarten for early detection of developmental vision disorders]

PURPOSE

Orthoptic screening in the kindergarten is one option to improve early detection of amblyopia in children aged 3 years. The purpose of this study was to analyse the cost-effectiveness of such a screening programme in Germany.

METHODS

Based on data from the literature and own experience gained from orthoptic screening in kindergarten a decision-analytic model was developed. According to the model, all children in kindergarten, aged 3 years, who had not been treated for amblyopia before, were subjected to an orthoptic examination. Non-cooperative children were reexamined in kindergarten after one year. Children with positive test results were examined by an ophthalmologist for diagnosis. Effects were measured by the number of newly diagnosed cases of amblyopia, non-obvious strabismus and amblyogenic refractive errors. Direct costs were estimated from a third-party payer perspective. The influence of uncertain model parameters was tested by sensitivity analysis.

RESULTS

In the base analysis the cost per orthoptic screening test was DM 15.39. Examination by an ophthalmologist cost DM 71.20. The total cost of the screening programme in all German kindergartens was DM 6.1 million. With a 1.5% age-specific prevalence of undiagnosed cases, a sensitivity of 95% and a specificity of 98%, a total of 4,261 new cases would be detected. The cost-effectiveness ratio was DM 1,421 per case detected. Sensitivity analysis showed considerable influence of prevalence and specificity on the cost-effectiveness ratio. It was more cost-effective to re-screen non-cooperative children in kindergarten than to have them examined by an ophthalmologist straight-away.

CONCLUSIONS

The decision-analytic model showed stable results which may serve as a basis for discussion on the implementation of orthoptic screening and for planning a field study.

[Estimating squint angle according to the degree of refixation saccades. Model trial fixation saccades]

BACKGROUND

Objective, linear strabismometric methods are used preferentially to assess the eye alignment in patients with bad eyesight or with a deeply amblyopic eye, and also in uncooperative subjects, for instance children. The common point of these methods is that a distance must be measured or estimated, from which the eye rotation, or alignment, is computed through a conversion factor, the angular ratio. Such a ratio was introduced by Hirschberg in the 19th century. The purpose of the study was to examine the influence of the size of angular ratios and examiners influence upon the accuracy of estimation of eye alignment from the limbus position.

METHODS

As an experimental test, 9 trained examiners estimated the amount of refixation movements between 0.5 degree and 26 degrees (1 cm/m and 48.8 cm/m). These refixation movements were simulated by a test person who executed fixation saccades in front of a tangent scale designed for a distance of 2.5 m.

RESULTS

The magnitude of a refixation movement was estimated best by looking at the limbus shift, with a ratio of about 5 degrees/mm (8.7 cm/m/mm), and an accuracy of +/- 2 degrees (3.5 cm/m) (95% confidence interval) was reached for refixation movements up to +/- 5 degrees (8.7 cm/m). The threshold for detection of microtropia reached about 0.5 degree (1 cm/m). Accuracy was limited by two factors: the difference between the individual and average angular ratio, and estimating errors.

CONCLUSIONS

Experienced examiners estimate the angle of strabismus from the magnitude of refixation movements up to +/- 5 degrees (8.7 cm/m) almost as accurately as with the prism and cover test.

[Hirschberg erred here: the correct angle factor is 12 degrees pro mm corneal reflex decentration. Geometric optical analysis of various methods in strabismometry]

BACKGROUND

The use of prisms and cover is the established clinical method to measure eye alignment, the accuracy of which may reach 0.5 degree (1 cm/m). By contrast, there are contradictory recommendations in the literature regarding the measurement with corneal reflections. The purpose of the study was to present a synopsis of the foundations on which such measurements are based, and to derive parameters for the measurement of eye alignment.

MATERIALS AND METHODS

Simple eye models for an adult average eye were derived. From these the dependence of the shift of the corneal reflex and of the limbus upon eye rotation was derived and expressed as rotation versus shift ratio WF, in degrees per millimeter or prism diopters per mm.

RESULTS

This study confirmed the findings of a number of studies in that the frequently quoted Hirschberg ratio of 7-8 degrees/mm (13 cm/m/mm) is much too low. The correct ratio is 12 degrees/mm (21 cm/m/mm).

CONCLUSIONS

Without covering, a misalignment is estimated best by judging the difference between the positions of the corneal reflexes in both eyes. Due to the limited accuracy of this test of at best +/- 5 degrees (8.7 cm/m), pseudotropia may not be distinguished from microtropia. The magnitude of a refixation movement may be estimated best by looking at the limbus shift, with a ratio of about 5 degrees/mm (8.7 cm/m/mm).

[Bilateral optic disk edema in polyneuropathy, organomegaly, endocrinopathy, monoclonal proteins and skin changes (POEMS syndrome)]

BACKGROUND

POEMS occurs only in about 1% of plasmocytoma cases, but in more than 50% of the rare osteosclerotic subtypes and plasma cell dyscrasias. The estimated frequency is 20 cases per year in Germany. Swelling of the optic disks is an early sign of the syndrome.

CASE REPORT

An osteosclerotic plasmocytoma type IgA lambda was known in a 63-year-old farmer for 4 years. The primary lesion in the left femur was irradiated at diagnosis. Half a year prior to our examination the patient experienced edema of the legs and recurrent diarrhea. A staging confirmed the earlier diagnosis of a POEMS syndrome. The patient was presented for ophthalmologic examination because of optic disk swelling and progressive visual field defects: raster perimetry revealed enlarged blind spots and increased thresholds. Neurologic examination revealed polyradiculitis, increased protein levels in the cerebrospinal fluid and intracranial hypertension. The patient was treated with oral steroids which entailed improvement of the visual fields and decrease of optic disk swelling.

CONCLUSIONS

Ophthalmologists play an active role in the staging, in the ruling out of other causes, and in the treatment. Symptomatic treatment with oral steroids should be monitored with visual acuity, raster perimetry and fundus examinations.

[Construction of a model eye for simulation of Purkinje reflections for determining the radii of curvature and the position of the crystalline lens]

Specular reflections at the optical interfaces of the eye, the Purkinje reflections, are used in physiologic optics and ophthalmology for biometric measurements. To date, there is no standard in the measurement of crystalline lens radii of curvature and position. To that end model eyes were designed.

MATERIALS AND METHODS

The most important goal was to simulate the Purkinje reflections I, III, and IV, in the human eye as realistically as possible. The casing of the model eye was made of brass; the optical components were made from contact lens material.

RESULTS

Several variants of components were manufactured to reproduce the range of variations in human eyes. By combining different components it was possible to vary the radii of curvature of the cornea and of the crystalline lens, axial separations, crystalline lens rotations and decentrations independently and reproducibly. First applications included devices for biometry of the crystalline lens (phacometry), validation of methods for eye alignment measurement, and refractometry.

CONCLUSIONS

The properties of the specular reflections of the model eye are very close to the target values in human eyes. One of the advantages of the model eye is the compact design. This model eye is the first measuring standard for phakometry.

[Computer aided, examiner independent screening for inapparent eye misalignment among 590 infants and preschoolers--a pilot study with an orthoptic gold standard]

BACKGROUND

The purpose of the study was to investigate the computer aided screening method using Purkinje image I and IV reflection patterns for the detection of inapparent eye misalignment and to compare this to an orthoptic examination.

MATERIALS AND METHODS

590 subjects up to 72 months of age with inapparent eye misalignment were recruited from the orthoptic outpatient department and externally. The computer aided screening consisted of taking a series of still video pictures with Purkinje reflection patterns. These were evaluated in an examiner independent way to reach a recommendation whether the child needed an ophthalmological referral or not. As gold standard, an orthoptic examination was performed. For analysis, the data were split by age groups. The orthoptic results were tested for certainty and repeatability.

RESULTS

The computer aided examination had the highest sensitivity of 0.82 in the age group up to 2.5 years of age, and a specificity of 0.90. With an estimated prevalence for microtropia of 0.01, the extrapolated positive predictive value was 0.08, and the negative predictive value was 0.998. In the age group up to 2.5 years of age, the percentage of orthoptic examinations without clear result (neither non-referral, nor strabismic) was 22.4%, and 6.1% in the screening examination. Among the cases which were examined repeatedly, some were classified as "strabismic" in the beginning, and as "non-referral" in the end in the orthoptic examinations.

CONCLUSIONS

The examiner independent, computer aided screening method is a cost effective option for the screening for inapparent eye misalignment, especially in the age group up to 2.5 years of age. If an orthoptic examination was carried out for screening, one should expect a higher rate of false positives, which entails more costly ophthalmological checks. Future studies should assess the validity of the single ortoptic examination as the gold standard in this age group.

[Measuring the effect of eyeglasses on determination of squint angle with Purkinje reflexes and the prism cover test]

BACKGROUND

The alternating prism and cover test is the conventional test for the measurement of the angle of strabismus. The error induced by the prismatic effect of glasses is typically about 27-30%/10 D. Alternatively, the angle of strabismus can be measured with methods based on Purkinje reflex positions. This study examines the differences between three such options, taking into account the influence of glasses.

MATERIALS AND METHODS

The studied system comprised the eyes with or without glasses, a fixation object and a device for recording the eye position: in the case of the alternate prism and cover test, a prism bar was required; in the case of a Purkinje reflex based device, light sources for generation of reflexes and a camera for the documentation of the reflex positions were used. Measurements performed on model eyes and computer ray traces were used to analyze and compare the options.

RESULTS

When a single corneal reflex is used, the misalignment of the corneal axis can be measured; the error in this measurement due to the prismatic effect of glasses was 7.6%/10 D, the smallest found in this study. The individual Hirschberg ratio can be determined by monocular measurements in three gaze directions.

CONCLUSIONS

The angle of strabismus can be measured with Purkinje reflex based methods if the fundamental differences between these methods and the alternate prism and cover test, and if the influence of glasses and other sources of error are accounted for.

[Model for cost-benefit relations of amblyopia screening]

BACKGROUND AND PURPOSE

In Germany, 750,000 children are born per year who should be screened for developmental visual defects in the age range 24-48 months. However, the established pediatric screening program is not sufficient to prevent amblyopia. The purpose of this study was to examine the cost-effectiveness of alternatives for amblyopia and microtropia screening.

METHODS

Three options were compared: (1) an orthoptic screening carried out in the field, for instance in kindergartens, (2) an examiner-independent objective apparatus-based screening, and (3) a complete ophthalmological and strabismological examination carried out in a practice. The costs of screening, follow-up examinations and of the treatment were modelled for prevalences of 1% (microtropia) and 5% (amblyopia). The benefit due to treatment was calculated as the result of an avoided whole-person impairment of 3% and 1%. The income related, increased tax and health care payments were used to cover the costs.

RESULTS AND CONCLUSIONS

In options (1) and (2) there were favorable cost-effective ratios. The practice-based option 3 was economically less promising. The higher the prevalence was, the higher the resulting cost-effectiveness.

Limbus versus pupil center for ocular alignment measurement with corneal reflexes

PURPOSE

To investigate the accuracy of ocular misalignment measurement, using corneal reflections.

METHODS

Corneal reflex positions were measured relative to two landmarks, the limbus center and the entrance pupil center, using high-resolution digital images for cyclopean gaze angles from 0 degree to 18.8 degrees (34.04 prism diopters; PD) to the right and to the left in 10 subjects. Distance h from the center of the corneal curvature to each landmark was determined from linear regressions and showed significant differences between both conditions: mean hlimbus was 5.243 mm, and mean hpupil was 4.884 mm. From these, limbus- and entrance-pupil-center-related Hirschberg ratios were determined as 11 degrees/mm (19.43 PD/mm) and 11.82 degrees/mm (20.92 PD/ mm), respectively; and ocular alignment was calculated for both conditions. Simulated angles of strabismus were calculated as the binocular difference between ocular alignment of the right and left eyes (condition 1), and as the monocular difference between the ocular alignment of right eyes and left eyes separately (condition 2).

RESULTS

Condition 1: Errors in simulated angles of strabismus were approximately twice as large for entrance pupil center compared with those in limbus-center-based evaluation; in the primary position, the 95% pupil-related confidence interval of the binocular difference was +/- 5.217 degrees (9.1 PD), compared with +/- 3.174 degrees (5.5 PD) for the limbus-related option. Condition 2: Errors were approximately equal.

CONCLUSIONS

The entrance pupil center is a less reliable landmark than is the limbus center for measuring ocular alignment by using corneal reflections, because of unreliable positions of the entrance pupil center; different mean Hirschberg ratios should be used in both conditions.

Algorithm for Purkinje images I and IV and limbus centre localization

PURPOSE

To develop a fast and reliable image processing algorithm for the extraction of Purkinje reflection data for measurement of ocular alignment with standard PC hardware.

METHODS

Purkinje images I and IV are specular reflections of light sources, the positions of which are proportional to eye rotation. Fast histogram-based thresholding and gradient techniques were used to localize Purkinje images I and IV, the pupil centre and the limbus centre in images obtained with near infrared light.

RESULTS AND CONCLUSIONS

Execution time was 500 ms per eye. A set of 540 images was evaluated of which 94% were automatically analysed.

Improved computing scheme for measuring eye alignment with Purkinje images I and IV

This study introduces an improved computing scheme for determining eye rotation from Purkinje images I and IV. The original computing scheme systematically underestimated eye rotation. Paraxial raytracing calculations revealed that this error resulted from failure to account for the fact that Purkinje images I and IV fall at different distances behind the cornea. The error could be overcome with a correction factor derived from paraxial raytracing calculations. A series of experiments were carried out to test the validity of this correlation factor, involving exact raytracing calculations as well as measurements on physical model eyes and human eyes. The influence on the correction factor of ocular surface asphericity, accommodation, age and ocular component variations were examined. The new method was also compared to Hirschberg's technique, which makes use of Purkinje image I alone, as a means of screening for strabismus.

Catoptric properties of eyes with misaligned surfaces studied by exact ray tracing

PURPOSE

Historically, Purkinje images have been used to calculate ocular surface curvature and misalignment. The purpose of this report is to introduce an exact ray-tracing program that can be used to examine the influence of ocular component variations on the size and position of Purkinje images I, III, and IV.

METHODS

Ray tracing was carried out on Le Grand's four-surfaced schematic eye to demonstrate the main features of the program. Any location may be chosen for the point light source and the observer. Ocular component dimensions, eye rotation, and crystalline lens decentering and rotation are fully adjustable. The program computes the coordinates of the Purkinje images in three-dimensional space from the point of view of the observer. It also offers the option of exhibiting Purkinje images seen through standard and telecentric imaging devices. Both options yield Purkinje image positions in relation to the rotating center of the limbus, observed clinically.

RESULTS

The resulting program compared favorably with current ray-tracing software and with data from the literature.

CONCLUSIONS

The program has many research and teaching applications. For example, our requirement was to calculate a series of linear coefficients that closely approximate Purkinje-image behavior in any given eye. These coefficients may be used to measure misalignment of intraocular components in phakic and pseudophakic eyes.

[Detection and diagnosis of small ocular misalignment with the Purkinje reflex pattern method]

BACKGROUND

Application test for an automatic classification strategy for ocular alignment data for the detection of ocular misalignment in strabismic patients.

METHODS

Photographic Purkinje Reflection Pattern Evaluation was used a) with a handheld device for the detection and measurement of ocular misalignments in near fixation (group 1, n = 64 strabismic patients) and b) with a stationary device for the detection and measurement of ocular misalignments in near fixation (group 2, n = 38 patients) and in distance fixation (group 3, n = 36 patients). The orthoptic diagnoses were mostly primary and secondary microtropia with manifest angles of strabismus from naught or 0.25 degrees to 3-4 degrees, with maximum angles up to 6-9 degrees. The ocular alignment data were classified using the computer based strabismus index procedure. This strategy relies on thresholds derived from means and standard deviations in orthotropic control populations. In this way the data sets were classified automatically as "no referral" or "referral". In addition, an automatic diagnosis of the type of misalignment was given and the results were compared to the orthoptic gold standard.

RESULTS

The sensitivity for the detection of a manifest ocular misalignment was a ca. 80% in group 1 and 2, and 90% in group 3, with specificities from 90% to 100%. All manifest angles of strabismus larger than 1 degree were correctly classified as "referral". There was good agreement between the diagnoses of the type of misalignment in most cases. Discrepancies were observed with very small ocular misalignments or with incomplete data sets, or they could be explained by a switch of fixation. The amount of the misalignment varied markedly as compared to the orthoptic measurement in a number of cases.

CONCLUSIONS

The examination allows for a detection of small manifest ocular misalignments with a very high sensitivity. The deviated eye and the type of the misalignment in the primary position are evaluated automatically by a data base computer algorithm. The differences between the measured angles of strabismus indicate that the photographic examination conditions and the orthoptic simultaneous prism and cover test conditions are not exactly alike. Purkinje Reflection Pattern Evaluation represents a step towards an examiner-independent measurement of the angle of strabismus.

Statistical validation of a strabismus index calculated from objective ocular alignment data

PURPOSE

Statistical analysis of a strabismus index used for objective interpretation of eye alignment data and improvement of this strabismus index.

MATERIALS AND METHODS

Primary position eye alignment data of 330 subjects aged from a few months to young adulthood were collected with Purkinje Reflection Pattern Evaluation. Among these there were 95 strabismic subjects with inapparent, very small ocular misalignments from o° to about ±5°. The subjects were split into four age groups: up to 12 months of age, between 12 and 24 months, between 24 and 48 months and above 48 months of age. The measured and calculated angular variables and the strabismus index were tested statistically for age dependence and differences between the three orthoptic groups 'strabismus', 'referral' and 'non-referral'. The level of significance chosen was $aL=0.05.

RESULTS

There was a significant dependence of most of the angular variables on the orthoptic group. A dependence of the variables on age was not found except for a few angular variables which seemed to be related to the somewhat larger fluctuations of fixation in the two lower age groups. There was no age dependence of the strabismus index. With a strabismus index threshold of 0.7, the sensitivity was 85% for the detection of cases who needed referral according to the orthoptic examination.

CONCLUSIONS

This study provides the statistical basis for the strabismus index procedure which was initially introduced as an empirical procedure. It indicates that the strabismus index does not depend on age, so that limited cooperation in toddlers and infants has no major influence on the result of the data classification with the strabismus index. The strabismus index is a suitable means for objective, examiner-independent decision making in screening for very small ocular misalignment.

Self-assessment of angles of strabismus with photographic Purkinje I and IV reflection pattern evaluation

BACKGROUND

Accurate assessment of the angle of strabismus, e.g. of variable angles of strabismus, is crucial in preoperative patient management and is usually performed in a clinical environment. Objective assessment by patients themselves, under everyday conditions, could contribute to a better preoperative work-up. A new objective evaluation procedure for the measurement of manifest angles of strabismus for near and distance fixation by the patient himself is presented.

METHODS

To account for the modified experimental setup used for the self-assessment, an amended computation procedure of Purkinje reflection pattern evaluation was developed. For measurement, patients and controls placed their head on a head/chin rest and fixated at 33 cm or 4 m distance in primary position. A reflex camera and three photo flash units were positioned on a special frame underneath the visual axis and in front of the subject so that both eyes could be photographed simultaneously. The camera's remote shutter control was released together with the photo flash units by the properly fixating subject. The angles of strabismus were obtained from the series of pictures through later evaluation of the Purkinje I and IV reflection patterns recorded in the photographs of the eyes.

RESULTS

Measurements of the ocular alignment in two control groups and in a group of strabismic subjects showed satisfactory accuracy of the "self-assessment" method compared to "standard" Purkinje reflection pattern evaluation and orthoptic measurements of the angle of strabismus.

CONCLUSION

The modified "self-assessment" method can be used for the objective recording of angles of strabismus as needed in the preoperative work-up of patients with variable angles of strabismus, over prolonged periods of time, and outside a clinical setting.

Measurement of ocular alignment with photographic Purkinje I and IV reflection pattern evaluation

PURPOSE

To provide reference data for the measurement of ocular alignment and of angles of strabismus with a new stationary photographic apparatus at near and at distance fixation; to verify quantitative relations between the data by comparing experimental data with theoretical predictions.

METHODS

Use of Purkinje I and IV Reflection Pattern Evaluation in conjunction with a new stationary photographic apparatus; application of previously derived equations; simulation of angles of strabismus of 5 degrees and 10 degrees in the primary position.

RESULTS

Data from 62 subjects with orthotropia show good linearity of measured angles in different directions of gaze; a 95% confidence interval for errors up to 18.6% in the simulated angles of strabismus; no need for individual calibration of the apparatus; no bias due to wearing of spherical corrections, and a detection threshold for microstrabismus of +/- 0.35 degrees.

CONCLUSIONS

Data concerning orthotropic and simulated strabismus prove the accuracy of Reflection Pattern Evaluation to assess ocular alignment, for instance, for the diagnosis of strabismus in primary and secondary positions, at near and distance fixation. The measuring range can easily be extended to larger angles of strabismus.

Computational principles in Purkinje I and IV reflection pattern evaluation for the assessment of ocular alignment

PURPOSE

To develop a standardized reasoning for the evaluation of Purkinje I and IV Reflection Pattern data in primary, secondary, and tertiary positions of gaze in the diagnosis of strabismus with a mathematical approach. To demonstrate the applicability of certain mathematical relations and the appropriate graphic representation of computed ocular alignment data.

METHODS

Starting from the known Reflection Pattern Evaluation formulae, equations were derived that allowed for the computation of the relative and absolute positions of the optical and visual axes of both eyes from original data in binocular and monocular fixation. These equations were simplified for clinical use.

RESULTS

The authors obtained a set of equations that could be applied to the objective, quantitative analysis of eye alignment in screening for microtropia, in concomitant and incomitant diagnoses of strabismus in primary and nonprimary positions.

CONCLUSIONS

Purkinje I and IV Reflection Pattern Evaluation can be extended to the diagnosis of strabismus in nonprimary positions with sufficient clinical accuracy. The newly presented principles and equations serve as a basis for a convenient graphic representation of Purkinje I and IV Reflection Pattern data. These principles of evaluation may be applied to any data dealing with ocular alignment, independently of the method.

[Computer-assisted measurement of ocular misalignment in infants and young children using the digital Purkinje reflection pattern procedure]

A digital image recording and processing system is presented that allows a quick diagnosis of microstrabismus in non-cooperative children. It is thus particularly suited for screening purposes.

METHOD

The Purkinje Reflection Pattern Evaluation (RPE) method is used: three small flashes are used to produce the desired Purkinje images. Two horizontal rows of the three 1st Purkinje images (anterior corneal reflections) and of the three 4th Purkinje images (posterior crystalline lens reflections) stemming from the three light sources form the characteristic Purkinje image reflection pattern. Each eye's position is calculated from the shift between the upper and lower rows of reflections by means of two simple formulae. From the angles obtained in binocular fixation and monocular fixation the manifest angle of strabismus corresponding to the angle measured in the simultaneous prism-and-cover test is computed. The measurement is performed at a fixation distance of 50 cm under natural viewing conditions. To obtain a picture one only has to get the child's attention for a short moment. The primary position is triggered with the fixation light, which is operated by a switch.

APPARATUS

The digital image recording is done with a hand-held device comprising two miniaturized video cameras, three photo flashes and a fixation light that is operated manually. An IBM-compatible PC equipped with a hard disk and two frame grabbers was adapted for the storage and processing of the pictures. The pictures are evaluated interactively in a few minutes on the workstation's monitor immediately after the measurement. To this end specially designed menu-driven software was implemented.

RESULTS

Examples of the measuring procedure and clinical results in infants with microtropic highlight the potential of the system as a screening apparatus and for the exact measurement of small and large squint angles. Usually even 1-year-old children can cooperate well enough to get good-quality pictures in binocular fixation. The new digital system allows easy and rapid application of the Purkinje Reflection Pattern Evaluation method since the time-consuming photographic film processing and evaluation are no longer necessary. For the first time small angles of strabismus under 5 degrees (10 PD) can be measured with a precision of less than 1 degree (2 PD) under clinical conditions in non-cooperative children.

Objective measurement of small angles of strabismus in infants and children with photographic reflection pattern evaluation

A new photographic method for the precise measurement of the angle of squint in children and infants is presented. The apparatus consists of a reflex camera with three horizontally aligned flashes and a small fixation light. The subjects are photographed while fixating binocularly or monocularly in the primary or secondary position. Six reflections can be seen on the photograph of each pupil. These are the first and fourth Purkinje images of each light source. From the reflection patterns, the squint angle or the angle kappa or alpha can be computed using a simple formula. A vertical angle of strabismus may be calculated from the same photograph using the same principle. Results from orthotropic and strabismic adults and from children are evaluated to establish reference values. Cooperation from the children is generally very good. The accuracy of the new method is between between 2 and 4.5 prism diopters (between 1 degree and 2.5 degrees), depending on the measuring strategy.

The Defect Fluorite Phase in the ZrO2-PrO1.5 System and Its Relationship to the Structure of Pyrochlore

A detailed transmission electron microscope and X-ray powder diffraction study has been made of the so-called 'defect fluorite' phase field in the ZrO2-PrO1.5 system and of its close relationship to the pyrochlore solid solution field in the same system. Even for the lowest possible PrO1.5 content within the 'defect fluorite' phase field, it is clear that the sharp Bragg reflections characteristic of the underlying fluorite average structure are accompanied by some of the 'satellite reflections' characteristic of the pyrochlore solid solution field. As the PrO1.5 content increases, these satellite reflections increase systematically in intensity as well as sharpening very considerably. It is shown that this 'defect fluorite' phase field cannot be adequately described either in terms of random point defects within an average fluorite-type matrix or in terms of a diphasic texture of pyrochlore domains embedded coherently into a fluorite matrix, but must be regarded as enuinely intermediate between these two end-member structures and of commensurately modulated fluorite type. A group theoretical approach is used to propose a model for the structural deviation from the underlying fluorite average structure.

[A new photographic method for measuring squint angles in infants and small children]

A new photographic method for measuring squint angles in children and infants is presented. A photographic picture is taken from the subject, using a camera with the three flashes bulle. One flashbulle is placed vertically over the lens, two other flashbulles are placed symmetrically in an angle of 10 degrees beside the middle flash. Six reflections can be seen on the photographic picture in each pupil. (1. and 4. Purkinje Sanson Images of each light source.) The horizontal distance of two reflections is determined by the distance of the flashguns. If the reflection lines in both eyes are symmetrical, there is no squint. If there is a shift, it can be measured on the slide and by using a simple formula the squint angle can be calculated. The accuracy of the method is between 2 and 3 degrees.

New Sivapithecus humeri from Pakistan and the relationship of Sivapithecus and Pongo

New humeri of two species of the Miocene hominoid Sivapithecus are described from near Chinji in Pakistan from between approximately 9 and 11 Myr ago. Sivapithecus, a middle and late Miocene hominoid from Turkey and Indo-Pakistan, is overall unlike any living hominoid, although facial-palatal similarities to the extant orangoutan, Pongo, have been used to support a hypothesis of close relationship. Living hominoids have postcranial similarities assumed to be shared derived, among them features of the proximal humerus. However, the new Sivapithecus proximal humeri differ from those of living hominoids, supporting an alternative hypothesis in which Sivapithecus and Pongo are not closely related. It is not clear how to choose between these incompatible hypotheses.

High resolution electron microscopy of nonstoichiometric apatite crystals

The application of high resolution electron microscopy, computer image processing, and image simulation techniques to the investigation of synthetic nonstoichiometric apatites has provided new details of apatite crystal growth mechanisms. Under certain precipitation conditions, calcium-deficient apatites with distinct octacalcium phosphate (OCP)-apatite intergrowths have been observed. Apatite crystals with unit-cell thick overgrowths of OCP on their surfaces confirmed the stepwise hydrolysis crystal growth mechanism initially proposed by Brown (Nature 196:1048-1050). However, many crystals also contained a central two-dimensional OCP inclusion one to two unit cells thick, embedded in an apatite matrix. Similar planar defects have been observed in dental enamel, dentin, and bone crystals. We have developed a modified version of Brown's stepwise OCP hydrolysis apatite crystal growth mechanism to explain the formation of crystals with OCP central planar defects. The mechanism involves the nucleation of an OCP seed that grows until it reaches a critical size, rh, before OCP hydrolysis occurs. Apatite subsequently grows epitaxially on the OCP seed, thereby embedding it in the center of an apatite crystal. Apatite growth is facilitated by partial screw dislocations emanating from the planar defect.

Oxygen ordering and twinning in YBa2Cu3O7-x

Direct structure images of the YBa2Cu3O7-x high Tc superconducting ceramic (also called the 1-2-3 compound) at 1.7 A resolution have been obtained for the [100] and [001] orientations. It was found that for the purposes of studying oxygen ordering in this compound it is better to use lattice images of lower resolution. The oxygen ordering was studied via the measurement of the bending of (100) and (110) lattice planes on crossing the (110) twin boundaries in crystals oriented in the [001] zone. Significant variations were found in the b/a ratios, owning to a variation in oxygen ordering, between different crystal grains, and between different regions in the same grain. For the three different 1-2-3 samples studied, the average b/a ratio was 1.016, the same value as was found in neutron diffraction studies. The twin boundaries in the orthorhombic 1-2-3 phase are sharp and planar. It seems likely that the transformation from the high-temperature tetragonal phase to the lower-temperature orthorhombic phase is martensitic in nature. A new phase has been discovered on some of the twin boundaries. The new phase can be indexed as tetragonal with a = 7.5 +/- 0.2 A, and c = 6.8 +/- 0.2 A. It is possible that the new phase is stabilized by the stress which occurs at the twin boundaries.