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.

[Computer-assisted measurement of ocular misalignment in infants and young children using the digital Purkinje reflection pattern procedure]. / Computergestützte Messung von Augenfehlstellungen bei Säuglingen und Kleinkindern mit Hilfe des digitalen Purkinje-Reflexmuster-Verfahrens.

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.

[A new photographic method for measuring squint angles in infants and small children]. / Eine neue photographische Methode zur Messung von Schielwinkeln bei Säuglingen und kleinen Kindern.

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.

[Quantifying retinal capillary circulation using the scanning laser ophthalmoscope]. / Zur Quantifizierung der retinalen Kapillardurchblutung mit Hilfe des Scanning-Laser-Ophthalmoskops.

The quantitative picture analysis of video fluorescein angiograms allows one to evaluate retinal hemodynamics. However, this method does not permit us to quantify the retinal capillary perfusion. Now, for the first time, we are able to quantify capillary bloodflow directly and objectively by means of scanning laser ophthalmoscopy. Even the measurement of the bloodflow velocity in all capillaries is now possible. Using digital frame-to-frame picture analysis of digital recordings, bloodflow velocities can be measured on the basis of the movement of dye boluses.

Diagnostic image workstations for PACS.

Image workstations will be the 'window' to the complex infrastructure of a PACS with its intertwined image modalities (image sources, image data bases and image processing devices) and data processing modalities (patient data bases, departmental and hospital information systems). They will serve for user-to-system dialogues, image display and local processing of data as well as images. Their hardware and software structures have to be optimized towards an efficient throughput and processing of image data.