Multi-position eye movement detection system

A device that records saccadic eye movements in any X-Y position is presented in this paper. Eye movements are recorded using infrared optoelectronics mounted on hemispherical shaped eyepieces, which in turn are mounted on goggles styled after an ophthalmologist's test frames. A computer controlled, wall mounted light bank facilitates targeting for eye movements. Output from the device is sent to a PC type computer and stored in the hard disk using a data acquisition board. The user interface is Windows based and the output from the goggles are represented as a trace map of plotted points. This output can also be saved or printed for future analysis and reference. The device is designed with reference to standard ISO design methodology, and subject safety and final product usage have been reviewed following ISO analysis procedures. Accuracy in tracking of eye movements is maintained by utilizing a twenty-four channel detection system, hemispherically mounted and lensed optoelectronics to reduce cross-talk due to incident light, and signal processing that attenuates incident light as well as ambient light. Also, a reset feature is included to maintain equal baseline control. An automatic switching device is included in the test frame to allow the device to "warm up," assuring that equal IR power is delivered for each subject tested. The IR units in the goggles are also modular in case replacement is required.

Initial 67th Combat Support Hospital Optometry Services in Taszar, Hungary, during Operation Joint Endeavor

BACKGROUND

Existing U.S. Army personnel and equipment authorization documents do not recognize the need for optometry services at deployed combat support hospitals (CSHs). The specific hospital tasked with the mission of supporting Operation Joint Endeavor from a support base in Taszar, Hungary, did not have any documentation authorizing the assignment of ophthalmology assets. Current Army doctrine stipulates the presence of an area support medical battalion, with assigned optometry assets, to deploy and operate near a CSH. However, in the winter of 1995, when Operation Joint Endeavor began, there were no area support medical battalions staffed in Europe, and none deployed to the Taszar support base. Therefore, the 67th CSH's mission to provide comprehensive inpatient and outpatient care on a contingency basis to all personnel in the area of operations did not have a doctrinal means of supporting an eye care requirement.

OBJECTIVE

To meet this eye care shortfall between doctrinal policy and actual operational needs or requirements, the optometry staff of the 67th CSH scavenged two optometry field sets from old Operation Desert Storm war stock and deployed with the main body of hospital personnel to Taszar, Hungary, on December 18, 1995. In doing so, the Table of Organization and Equipment was thus supplemented with extra equipment and personnel, beyond doctrinal guidelines, to accomplish the assigned mission.

METHOD

This report is a prospectively gathered summary of the eye care provided from December 18, 1995, to September 15, 1996.

RESULTS

A total of 1,471 patients were examined and treated, averaging 7 patients per day. Less than half of the case load was medical in nature, with the remaining being refractive in nature or for periodic examination. The most common pathologies seen were soft contact lens complications, non-contact lens corneal pathology, conjunctivitis (bacterial, viral, and adenoviral), and ocular trauma (foreign bodies, chemical splashes, blunt injury). Refractive cases during the entire deployment involved primarily myopes requiring increased correction. However, close to half of the refractive cases in the first month involved habitually uncorrected low hyperopes and early presbyopes.

CONCLUSIONS

Based on the productivity presented by the case load demand of this CSH's area medical support mission, an eye care need was clearly met, adding to the overall mission success of the 67th CSH.

Design of a pressurization chamber for recordings of retinal blood flow in the "in vivo eyecup" preparation in the rat

One major goal in our laboratory is development of an "in vivo eyecup" preparation in the rat. This preparation, which involves removal of the cornea and lens, maintains the normal vascular supply of the retina while allowing introduction of pharmacological agents into the medium that bathes this organ. Since we are interested in measuring retinal blood flow, it is sometimes necessary to repressurize the eye to maintain normal perfusion pressure across the retinal vasculature. The goal of this project was to develop a mechanism that allows repressurization of the in vivo eyecup after removal of the front of the eye. The basic design of this chamber consists of an eye ring to mechanically stabilize the eye and a pressurization chamber that attaches to this eye ring. The eye ring is connected to a base via a double hinged arm and can be locked in place. The pressurization chamber is attached to the top of this ring and sealed using an O-ring with a pressure fit. The top of the pressure chamber is composed of a clear polymer, allowing for photic stimulation of the retina, as well as introduction of laser light for blood flow determination. The pressure within the chamber is regulated by an elevated fluid-filled reservoir.

Guided knives

A new type of knife that enables a surgeon to easily create tunnel-shaped incisions with a prescribed depth has been developed. The knife features an incision guide, the arm of which extends just beyond the tip of the blade. The space between the blade and the arm can be set at the desired width. By moving the knife as if sliding the arm across the corneal or scleral surface, the blade can move to a certain depth from the surface. The guided knife enables even novice surgeons to easily make a self-sealing incision during cataract surgery. In addition, the innovative nature of this device seems to be applicable to many other surgeries that require a partial-thickness incision.

Misalignment of flexible iris hook retractors for small pupil cataract surgery: effects on pupil circumference

A graphical method was used to assess the effect on pupil shape and circumference of various flexible iris hook malpositions. Results confirmed that all hook malpositions necessitate increased pupil stretching to create space to perform a capsulorhexis of a given diameter. This method also confirmed that the addition of a fifth hook to create a pentagonal pupil reduces pupil stretching by 17%. A simple method of marking the limbus before hook insertion to ensure equidistant hook separation and thus minimize pupil stretching is suggested.

Evaluation of the Zeiss retinal vessel analyser

AIM

To investigate the reproducibility and sensitivity of the Zeiss retinal vessel analyser, a new method for the online determination of retinal vessel diameters in healthy subjects.

METHODS

Two model drugs were administered, a peripheral vasoconstrictor (the alpha receptor agonist phenylephrine) and a peripheral vasodilator (the nitric oxide donor sodium nitroprusside) in stepwise increasing doses. Nine healthy young subjects were studied in a placebo controlled double masked three way crossover design. Subjects received intravenous infusions of either placebo or stepwise increasing doses of phenylephrine (0.5, 1, or 2 microg/kg/min) or sodium nitroprusside (0.5, 1, or 2 microg/kg/min). Retinal vessel diameters were measured with the new Zeiss retinal vessel analyser. Retinal leucocyte velocity, flow, and density were measured with the blue field entoptic technique. The reproducibility of measurements was assessed with coefficients of variation and intraclass correlation coefficients.

RESULTS

Placebo and phenylephrine did not influence retinal haemodynamics, although the alpha receptor antagonist significantly increased blood pressure. Sodium nitroprusside induced a significant increase in retinal venous and arterial diameters (p<0.001 each), leucocyte density (p=0.001), and leucocyte flow (p=0.024) despite lowering blood pressure to a significant degree. For venous and arterial vessel size measurements short term coefficients of variation were 1.3% and 2.6% and intraclass correlation coefficients were 0.98 and 0.96, respectively. The sensitivity was between 3% and 5% for retinal veins and 5% and 7% for retinal arteries.

CONCLUSIONS

These data indicate that the Zeiss retinal vessel analyser is an accurate system for the assessment of retinal diameters in healthy subjects. In addition, nitric oxide appears to have a strong influence on retinal vascular tone.

A new BB forceps

Retained intraocular BBs are difficult to remove. According to manufacturers' specifications, BBs have a spherical diameter of 4.5 mm and a copper plate covering a steel core. They have only moderate magnetic properties because of the copper plate cover and they are too large to be grasped by almost all intraocular forceps and, therefore, present a problem when they are retained in the eye after injury. Arch Ophthalmol. 2000;118:1574-1575

Repeated measures of horizontal heterophoria

PURPOSE

To assess repeatability, horizontal heterophoria measurements were taken from 31 subjects on five occasions, each between 1 and 4 weeks apart.

METHOD

Distance heterophoria was measured using a Maddox Rod, and near heterophoria was measured using a Maddox Wing. In addition, near measurements were repeated with a +3.00 D lens in front of each eye to place the targets at optical infinity. In each case, the standard deviation of the five values was taken as a metric of the test variability.

RESULTS

On average, the variability of the Maddox Rod was half of the Maddox Wing, both with and without the lenses.

CONCLUSION

This consistency suggests that the difference reflects the test conditions rather than optical differences in the target position.

Microbiological investigations to validate the preparation of corneal transplants

The globe and cornea are colonized by microorganisms and cannot be removed as sterile products. Antiseptic measures and storage of the cornea in medium containing antibiotics lead to an obvious reduction of the microbial flora. Unfortunately there is the possibility of secondary microbial contamination during the preparation. Large amounts of bacteria or resistant bacteria can ruin attempts to reduce the microbial flora. To validate the whole process of preparation we investigated the contamination of removed globes, environment, materials, instruments and media for each sequence of operation and eliminated sources of contamination. Recommendations are given to ensure a virtually sterile product at the end of preparation.

A fully automated remote refraction system

Traditional methods of performing refractions depend on a trained refractionist being present with the subject and conducting an interactive form of subjective testing. A fully automated refraction system was installed in 13 optical dispensaries and after 15 months the patient and statistical information was gathered. The data from all operators were consistent and suggested a lack of operator effect on the refraction results. The mean of the SD of subjective sphere measurements was 0.2, or slightly less than a quarter dioptre, which would be an acceptable level of accuracy for ordering corrective lenses. The present study suggests an absence of operator influence on the results of the refractions and a degree of consistency and accuracy compatible with the prescription of lenses.

Effects of artefacts on scanning laser polarimetry of retinal nerve fibre layer thickness measurement

AIMS

To investigate the effects of artefacts on scanning laser polarimetry of the retinal nerve fibre layer.

METHODS

Six eyes of six normal volunteers and an artificial nerve fibre layer were examined using the nerve fibre analyser II. The retinal nerve fibre layer thickness (RNFLT) was measured in each of four 90 degree quadrants, superior (S), temporal (T), inferior (I), and nasal (N), at 1.5 disc diameters from the disc margin. Study 1: Measurement in normal eyes. The amount of maximum error in RNFLT measurements was investigated as follows: (1) the intensity setting of the laser beam was changed to be as weak as possible or to be as strong as possible; (2) the intentional offsets of the laser beam axis in relation to the pupil were made in four directions; (3) the eye was rotated by shifting the head 45 or 90 degrees; (4) the right eye was measured by moving it to the left eye position on the head rest. Study 2: Measurements on an artificial nerve fibre layer. The birefringence measurements were confirmed with a plastic disc, which has a radial arrangement of birefringence. The plastic disc with black paper was fixed at the right eye position or the left eye position on the head rest. The retardation of the laser beam by the plastic disc on the black paper was measured. The retardation of the plastic disc was checked by an automatic birefringence evaluation system (ABR-10A, Uniopt Co, Ltd, Shizuoka).

RESULTS

Study 1: The effects of the rotated eye and the measurement of the opposite eye position were significant. The eyes rotated 90 degrees showed quite a different pattern in which the thicker and thinner locations of the RNFLT are switched. The nasal RNFLT of the baseline and the 90 degree rotated eye are 41.9 (SD 6.0) microm and 122.5 (11.2) microm, respectively (p<0.0001, Scheffe multiple comparison test). Study 2: The uniform retardation of the plastic disc was observed with the ABR-10A. The NFA detects the retardation of the plastic disc which the retardation map showed as a double humped pattern.

CONCLUSIONS

Study 2 indicated that the amount of corneal compensation was not small. The cause of significant influences by the rotated eyes and right eyes measurement in left eye position were thought to be incorrect corneal compensation. To increase the diagnostic ability of SLP, an improved compensation of the cornea is thought to be important.

Collaborative telemedicine between optometry and ophthalmology: an initiative from the University of Houston

The University of Houston College of Optometry (UHCO) has developed a strong Telemedicine Optometry/Ophthalmology program. Patient care, clinical teaching and research benefit from utilizing Telemedicine technology. This initiative between Optometry and Ophthalmology is at the forefront of eyecare! Presented here: clinical teaching opportunities via tele-education including retinal, uveitic, neuro-ophthalmic disorders and glaucoma. Seminars introduce students to this technology and enhance their clinical experience through exposure to eye pathologies often related to systemic diseases. UHCO's affiliated clinics include multidisciplinary centers staffed by optometrists: the Frost Eye Clinic (HIV multidisciplinary care), Good Neighbor Health Clinic and Rusk School Health Promotion Project (indigent multidisciplinary care). These centers can converse on line with eyecare professionals. Large sites interested in low vision/visual rehabilitation include: The Institute for Rehabilitation and Research (TIRR), the Social Security Hospital (Lima, Peru), the Matagorda General Hospital and the Quentin Mease Hospital. These sites, do offer quality care but require visual rehabilitation programs provided by UHCO. These sites also provide exposure to pathology for the students. A residency program trains optometrists in Telemedicine. The research program focuses on optics and imaging necessary to diagnose glaucoma, diabetic retinopathy, and neuro-ophthalmic disorders through Telemedicine. UHCO supports the advancement of standards in tele-eyecare.

ByOPHTEL: a Bavarian project for rapid telemedical exchange of knowledge, files and skills between practitioners and hospitals in eye care

ByOPHTEL, part of the Bavarian initiative Bayern Online, derived its name from the European project OPHTEL, to which it is closely linked and which, in Bavaria, is more or less worked out and performed by identical persons and institutions. It provides a group of 7 practitioners in and around the city of Munich with the possibility of exchanging general ophthalmologic knowledge as well as patient-related information with anyone in the group, or with the related ophthalmologic, internal, resp. scientific centers at the TU Munich and the GSF Neuherberg. Connections are routinely performed in the asynchronous or in the synchronous mode, and all partners participate in the scientific projects Knowledge Based Information System, Glaucoma Monitor, and Diabetic Retinopathy Monitor--as well as in the enhancement of a trustful patient-physician relationship ("second opinion") and a closer cooperation in out-patient and in-patient ophthalmical surgery and medical treatment.

A new digital optic disc stereo camera: intraobserver and interobserver repeatability of optic disc measurements

AIMS

To investigate the intraobserver and interobserver repeatability of optic disc measurement using a new digital optic disc stereo camera.

METHODS

112 consecutive new patients presenting to a glaucoma service had dilated optic disc photography performed using a new digital stereo camera (Discam, Marcher Enterprises Ltd, Hereford). The images were analysed by two masked observers using a stereo viewer and computer simulated stereopsis. Vertical and horizontal cup:disc ratios (CDR), cup area:disc area, and cup circumference:disc circumference were computed. Intraobserver and interobserver repeatability analyses were performed. Intraclass correlation coefficients (ICC) and 95% tolerance for change (TC) were computed.

RESULTS

220 optic discs were photographed, of which 196 were suitable for analysis (10 were of poor image quality and 14 had anomalous discs). Mean age of patients was 65 years, 60 were male and 48 female. For intraobserver measurements of: horizontal CDR, ICC = 0.94, TC = 0.11 (15% of range); vertical CDR, ICC = 0.92, TC = 0.14 (16% of range); cup area:disc area, ICC = 0.95, TC = 0.10 (13% of range), and cup circumference:disc circumference, ICC = 0.95, TC = 0.09 (14% of range). For interobserver measurements of: horizontal CDR, ICC = 0.89, TC = 0.14 (19% of range); vertical CDR, ICC = 0.90, TC = 0.14 (16% of range); cup area:disc area, ICC = 0.92, TC = 0.13 (16% of range), and cup circumference:disc circumference, ICC = 0.90, TC = 0.12 (17% of range). Systematic bias between observers was within acceptable limits.

CONCLUSIONS

Digital stereo disc photography and analysis provide repeatable measures of optic disc variables. The results compare favourably with ophthalmoscopic and stereophotographic methods of assessment of the optic disc.

The Night Vision Threshold Test (NVTT): a simple instrument for testing dark adaptation in young children

It is estimated that 41 per cent of the population aged under 5 in the developing world has an inadequate vitamin A dietary intake resulting in increased morbidity and mortality. Half a million children go blind each year as a result of vitamin A deficiency. Thirteen and a half million have night blindness, the first sign of vitamin A deficiency. Unfortunately, there is no simple, sensitive and inexpensive means to identify the child who has marginal levels of vitamin A and thus institute means to prevent their development of severe deficiency. A low cost, simple, easy-to-use instrument designed to detect a young child's ability to adapt to darkness was tested in children admitted to the Mwanamugimu Nutrition Unit at Makerere Medical School in Kampala, Uganda. Despite the severe degree of malnutrition found in these children, Night Vision Threshold Test results and serum retinol levels were related (r = 0.41, p < 0.05). Further efficacy trials for this instrument are planned at community sites in Nepal.

[In vivo measurement of ocular circulation with the laser speckle method--development of apparatus and application in ophthalmological research]

We have developed an apparatus utilizing laser speckle phenomenon which can measure the peripheral circulation in the iris, choroid, retina and optic nerve head (ONH) and blood velocity through retinal vessels in the living eye non-invasively and quantitatively. A blue-component argon laser (wavelength 488 nm) was used for measurement of peripheral circulation in the retina and a diode laser (wavelength 808 nm) for measurements of peripheral circulation in the iris, posterior choroid and ONH, and measurement of centerline blood velocity through retinal vessels. A fundus camera (TRC-WT 3, Topcon) was equipped with a laser source and an image sensor where the speckle pattern from the fundus appears, and the data were analyzed with a personal computer to give a normalized blur (NB) value or a square blur rate (SBR) value, both quantitative indices of blood velocity. The NB value, whose computation requires much less time, was adopted to evaluate peripheral circulation because of non-linear correlation between the NB and actual blood velocity in the range above 20 mm/sec. The SBR value, whose computation requires a longer time, was adopted for measurement of blood velocity through retinal vessels. Measurement field in the living eye was 1.06 x 1.06 mm at its maximum and reproducibility index of the in vivo measurement in the rabbit iris, choroid, retina, and ONH was approximately 10%. When blood flow was changed by intraocular pressure (IOP) change in rabbit eyes, NB values obtained from the iris, choroid, and retina showed a significant correlation with the blood flow simultaneously determined with the colored microsphere technique in the same eye, and the NB obtained from the ONH also correlated with the blood flow determined with the H2 gas clearance method. Stepwise reduction in the ocular perfusion pressure (OPP) by stepwise increment of IOP resulted in proportional reduction in the iris- and choroid-NB. On the other hand, the retina- or ONH-NB remained almost unaltered at OPP levels above 50 mmHg, and decreased along with OPP at levels less than 50 mmHg. By monitoring NB values for 2 hours, presence or absence of autoregulatory mechanism against OPP change in the choroidal and ONH circulation was studied in rabbits. Throughout the experimental period of 2 hours, the choroidal NB was changed along with the OPP change, suggesting absence of blood flow autoregulation in this tissue. In the ONH, however, the NB returned to the baseline after its transient increase or decrease when the OPP was continuously increased or decreased, showing the presence of an autoregulatory mechanism in the ONH circulation. However, the time course of the NB resumption depended on the extent of OPP change. These results indicated that the laser speckle method can be useful in investigating the autoregulatory mechanism and processes of peripheral circulation in ocular tissues. Unilateral instillation of drugs with vasodilative activity (ifenprodil, betaxolol or nipradilol) in rabbit eyes significantly increased ONH and/or choroidal circulation. The extent in change in the ONH and/or choroidal circulation correlated with the number of doses, but not with the extent of IOP reduction, which suggested that the observed effects were attributable to the drug which penetrated locally. Intravenous administration of a Ca(2+)-antagonist (nicardipine, nilvadipine or pranidipine) significantly increased choroidal or retinal circulation in rabbits. The ONH circulation, however, was not affected by nicardipine, but affected by nilvadipine or pranidipine. Given the same effect on the ONH circulation, systemic hypotensive effect was stronger in pranidipine than in nilvadipine, which suggested that nilvadipine can be used in patients with ocular circulatory insufficiency. A modification of the laser speckle apparatus used for animal experiments was devised so that the NB or SBR values could be measured in human eyes every 0.12 sec on a real-time basis. (ABSTRACT TRUN

[Recent development of endoscope system in ophthalmology]

The new ophthalmic laser microendoscope are widely used in a variety of clinical settings up-to-date. In this paper, we will describe the technical characteristics, recent development and prospectie evaluation of the microendoscope system.

Anomaloscope examination: scotopization (the luminance fall)

PURPOSE

The evaluation of a criterion for the detection of pathologic scotopization in routine anomaloscope examination.

METHODS

Fifty congenital protan subjects, 50 congenital deutan subjects, 30 autosomal recessive congenital achromats, and 25 (44 eyes) acquired type I red-green defective subjects were selected. The anomaloscope examination was according to the Linksz procedure. The luminance fall was calculated as the slope quotient SQ: Y units luminance fall per X units width of the matching range.

RESULTS

The mean SQ was -0.01 for congenital deutan subjects, -0.40 for congenital protan subjects and -1.30 for congenital achromats. There was no overlap between the three groups. Pathologic scotopization was found in 98% of the eyes presenting with an acquired type I colour vision defect.

CONCLUSION

Calculation of the slope quotient SQ is helpful for the detection of pathologic scotopization in acquired colour vision deficiency.

High frequency (20 MHz) ultrasonic devices: advantages and applications

OBJECTIVE

This paper investigates the problems, advantages and potential applications of 20 MHz ultrasonic devices.

METHOD

Aqueous gel and a thin appropriate membrane to enclose the front tip were used with 20 MHz probes without obvious decrease in resolution and sensitivity compared to the results obtained without a membrane and this considerably facilitates their routine use.

RESULTS

Many applications with linear scanning were evaluated in dermatology, ophthalmology (investigations of the anterior chamber of the eye, checking of corneal grafts), stomatology (detection and evaluation of periodontal disease) and in the field of measurement of very low velocities in small vessels by means of a duplex probe comprising two 20 MHz transducers: an imaging transducer and an inclined blood flow measurement transducer. Velocity profiles (velocities less than 0.50 mm/s) were measured in 100-300 microm diameter vessels using a cross-correlation method.

CONCLUSION

The use of 20 MHz frequency limits resolution but we have shown that this frequency allows the development of easy to handle probes.

Endoscopy of the lacrimal system

BACKGROUND/AIM

Until recently, diagnosis of disorders of the lacrimal system has depended on digital dacryocystography and on clinical examinations such as the fluorescein dye test, lacrimal probing, and irrigation. The lacrimal system and its mucous membranes can now be viewed directly with a lacrimal endoscope. While the first endoscopes were rigid and limited by poor picture quality in axial illuminations, the new generation of endoscopes are a great leap forward for new diagnostic and therapeutic approaches.

METHODS

132 patients ranging in age from 8 months to 73 years with nasolacrimal obstruction were referred to the lacrimal department. Diagnostic lacrimal imaging utilising various small calibre endoscopes less than 0.5 mm in external diameter was performed. The endoscopes are coupled to specially designed lacrimal probes as well as a CCD camera and a video recorder. The imaging was performed during standard lacrimal probing and irrigation in an outpatient clinic setting in 120 of 132 patients

RESULTS

All patients reported the pain of endoscopy as being similar to that of standard lacrimal probing and irrigation. No adverse effects such as bleeding or lacrimal perforation were noted. Endoscopic manipulation was not too difficult and the picture quality, depth of focus, and illumination were satisfactory in all cases. The most common site of stenosis was the nasolacrimal duct (59 patients), followed by the lacrimal sac (39 patients) and the canaliculi (34 patients). In 25 patients, partial obstruction, rather than complete stenosis, was visualised as a narrow lumen, which widened during irrigation. In 14 of 28 patients, obstruction was due to canalicular submucosal folds and was removed with laser. In addition, the colour and consistency of the lining mucosa correlated with type of obstruction. Normal mucosa is smooth and light pink in colour. Inflammatory changes manifest as thickened and reddish grey mucosa. More complete stenosis is shown as fibrotic plaques with grey white inelastic membranes.

CONCLUSION

Lacrimal endoscopy is a new, non-invasive method used to view directly and localise obstructions precisely. It allows differentiation between inflammatory, partial, and complete stenosis. Endoscopy enables one to choose the appropriate surgical therapy for patients. Patients tolerated the procedure well without any adverse reactions or effects. While it may not replace standard probing and irrigation, this technique is an extremely useful adjunct in determining the proper surgical modality, ease, and tolerance of the endoscopic manipulation by patients, and obtaining sharp and clear images of the nasolacrimal outflow system anatomy and pathology. Differentiation of various types of obstruction by precise location and severity can be achieved.

A new device for ocular surgical training on enucleated eyes

OBJECTIVE

To develop a reliable inexpensive device for teaching ocular surgical procedures and practicing experimental techniques on enucleated eyes.

DESIGN

Teaching device trial.

PARTICIPANTS

Thirty enucleated porcine eyes.

METHODS

A Plexiglas ocular bulb holder was secured with its base support to a polyvinylchloride pillar on a modified polystyrene trial head.

MAIN OUTCOME MEASURE

The convenience and reproducibility of both laser and surgical ocular techniques performed with this new device were evaluated.

RESULTS

This model allows curvilinear capsulorrhexis and phacoemulsification of porcine lenses through a corneal tunnel incision and insertion of a soft foldable acrylic intraocular lens into the capsular bag. Argon and neodymium:YAG laser iridotomy and retinal argon laser photocoagulation can also be performed with this model.

CONCLUSIONS

This inexpensive device is useful for teaching both surgical and laser ocular procedures.

Real-time rotation vectors

Rotation vectors are a useful way of describing eye position without reference to arbitrary axes of rotation since any eye position can be reached from the reference position by rotation about a single axis. A real-time display of rotation vectors would not only help to acquire more reliable data, but would also widen the range of possible eye movement experiments. We describe a novel PC based data acquisition and analysis system which calculates and displays rotation vectors, velocity vectors and Listing's plane in real-time using voltages obtained from a two field coil system. The system was implemented using LabVIEW and optimised using Code Interface Nodes. Off-line processing can be sped up by varying parameters that indicate the amount of available RAM. During processing Listing's plane data can be rotated horizontally, vertically and torsionally. A computer controlled laser target changes position randomly every half second and so the targets are evenly spread, producing an appropriate range of eye positions which are used to calculate Listing's plane.

Efficacy and safety of infrared warming of the eyelids

PURPOSE

To evaluate our newly developed infrared heater (IRH) and compare it to a broad-spectrum heater (BSH) for warming the eyelids.

MATERIALS AND METHODS

Ten normal subjects were enrolled in this study. All measurements were recorded in a room with temperature 23 degrees C, 40% humidity, and no wind. The IRH is composed of two hard eye patches that have light-emitting diodes (LEDs) emitting near-infrared radiation. We first compared the temperature rises in the cornea, lacrimal gland, and eyelids after warming through closed eyelids with the IRH for 5 and 10 min. Next, we compared warming with the IRH or BSH for 30 min. We then used the IRH for 5 min with the eyes open to confirm its safety. Finally, we determined subjective feeling after warming the eyes.

RESULTS

Direct comparison of 5 versus 10 min of warming with the IRH showed no significant differences in temperature rises in the upper eyelid (p = 0.09). The IRH caused significantly more heating (p < 0.05) than did the BSH everywhere except the cornea. The temperatures never rose above 37.7 degrees C for either heater during 30 min or with the IRH with the eyes open for 5 min. The subjects' comfort level rose significantly (p < 0.05) after treatment with the IRH.

CONCLUSIONS

Our study showed the efficacy and safety of warming the eyelids with a newly developed IRH. Only 5 min is necessary to increase ocular temperature and enhance comfort.

Impact resistance of ceramic brackets according to ophthalmic lenses standards

The overall resistance to accidental blows of the many ceramic brackets that are sold today has not been explored. Facing a similar diversity, the eyeglasses industry has chosen to standardize the testing of lenses by subjecting them to the drop of a steel ball. By slightly modifying this test, 10 brands of ceramic brackets were examined. In most cases, the findings coincided with those found by other authors when duplicating debonding. Thus, polycrystalline ceramics with bulkier structures and glazed surfaces were found to be more resistant to impact than the monocrystalline brackets, the loftier real "twins," and the less dense attachments. Protruding tie wings and bases were liabilities, and domed configurations seemed to deflect the blows. Bulkier "single" designs alone did not offer a guarantee of impact resistance when not accompanied by an appropriate microstructure and a smooth surface. The ceramic brackets most resistant to impact were found to be 20/20 by American Orthodontics and Fascination by Dentaurum. Medium resistance was displayed by Lumina by Ormco, Allure III and Allure by GAC, Transcend 2000 and Transcend by Unitek/3M; the last was not as good as the other four. The least resistant were Illusion by Ortho-Organizers, Intrigue by Lancer Orthodontics, and Starfire TMB by "A"-Co. Probably because of its real twin design, the last bracket lends itself to the highest probability for accidental breakage. Although resistance to impact and accidental debonding is desirable from the point of view of treatment, the advantage should be weighted against the chance of enamel fracture. Indeed a weak bracket attached with a soft adhesive may be preferable when the chance of an increased exposure to accidental blows is probable. In such cases, the ceramic may take the brunt of the force, instead of the tooth.

Screening for refractive errors in children: accuracy of the hand held refractor Retinomax to screen for astigmatism

AIMS

To assess the reliability of the hand held automated refractor Retinomax in measuring astigmatism in non-cycloplegic conditions. To assess the accuracy of Retinomax in diagnosing abnormal astigmatism in non-cycloplegic refractive screening of children between 9 and 36 months.

METHODS

Among 1205 children undergoing a non-cycloplegic refractive screening with Retinomax, 299 (25%) had repeated non-cycloplegic measurements, 302 (25%) were refracted under cycloplegia using the same refractor, and 88 (7%) using retinoscopy or an automated on table refractor. The reproducibility of non-cycloplegic cylinder measurement was assessed by comparing the cylindrical power and axis values in the 299 repeated measurements without cycloplegia. The influence of the quick mode on cylinder measurement was analysed by comparing the cylinder and axis value in 93 repeated measurements without cycloplegia where normal mode was used in one measurement and quick mode in the other. Predictive values of the refractive screening were calculated for three different thresholds of manifest astigmatism (> or = 1.5, > or = 1.75, and > or = 2 D) considering as a true positive case an astigmatism > or = 2 D under cycloplegic condition (measured by retinoscopy, on table, or hand held refractor).

RESULTS

The 95% limits of agreement between two repeated manifest cylinder measurements with Retinomax attained levels slightly less than plus or minus 1 D. The 95% limits of agreement for the axis were plus or minus 46 degrees. The comparison of non-cycloplegic measurements in the quick and normal mode showed no significant difference and 95% limits of agreement plus or minus 0.75 D. The mean difference between non-cycloplegic and cycloplegic cylinder values measured by Retinomax reached 0.17 D and was statistically significant. Manifest thresholds of > or = 1.5 D, > or = 1.75 D, > or = 2 D cylinder value diagnosed 2 D of astigmatism under cyclplegia respectively with 71-84%, 59-80%, 51-54% of sensitivity (right eye-left eye) and 90-92%, 95%, 98% of specificity.

CONCLUSION

Without cycloplegia, Retinomax is able to measure cylinder power with the same reproducibility as cycloplegic retinoscopy. No significant difference was found in the cylinder values obtained with the quick and the normal modes. Therefore, the quick mode of measurement is recommended as it is more feasible in children. No difference, which is significant from a screening point of view, exists between the non-cycloplegic and the cycloplegic cylinder value (< 0.25 D). Retinomax diagnoses abnormal astigmatism (> or = 2 D) in a non-cycloplegic refractive screening at preschool ages with 51-84% sensitivity rates and 98-90% specificity rates, depending on the chosen threshold of manifest astigmatism. If 2 D of manifest astigmatism is chosen as a positive test, the positive predictive value of the screening reaches 81-84% and the negative predictive value 91-90% (right eye-left eye).

Reflective meniscometry: a non-invasive method to measure tear meniscus curvature

AIMS

To devise a method to measure tear meniscus curvature by a non-invasive specular technique.

METHODS

A photographic system was devised. The system consisted of a camera and an illuminated target with a series of black and white stripes oriented parallel to the axis of the lower tear meniscus. The target was mounted on a flash gun close to the objective of a Brown macrocamera and calibrated using a graduated series of glass capillaries of known diameter, ground down to expose the inner wall. It was then applied to normal human eyes (n = 45) to measure the tear meniscus curvature. A video system was also assessed which provided qualitative online information about the tear meniscus.

RESULTS

Using the photographic system, measured values for capillary radii were in excellent agreement with theoretical calculations (r2 = 0.996, p < 0.0001). The radii of curvature of lower tear menisci in normal human subjects (mean 0.365 (SD 0.153) mm, range 0.128-0.736; n = 45) were similar to those reported in the literature. Both systems demonstrated variations in meniscus shape. The video system provided stable images of human menisci over prolonged periods of time and promises to be useful for the analysis of dynamic changes in meniscus volume.

CONCLUSIONS

Reflective meniscometry is a non-invasive technique providing quantitative information about tear meniscus shape and volume and of potential value in the study of ocular surface disease.

[Modified moisture chamber]

BACKGROUND

Moisture chambers can protect the eye in corneal lubrication or eyelid closure disorders. However, in cases with protrusio bulbi or pronounced chemosis conjunctivae direct damaging contact of the cornea or conjunctiva on the one hand and the inside of the moisture-chamber-bandage on the other hand are possible. Since commercial moisture-chamber-bandages are not available with different internal radii, new methods are necessary to increase the distance between the bandage and the eye.

MATERIAL AND METHODS

A special pressure relieving foam dressing used in the therapy and prophylaxis of decubitus was prepared in such a way that a periocular attachment was enabled and an opening for the eye was left blank. This central opening was covered with a commercial moisture-chamber-bandage. Five test persons and two ventilated patients with protrusio bulbi and manifest lagophthalmus were treated with the modified moisture chamber. The relative humidity within the bandage was measured.

RESULTS

The modified moisture chamber allows an individual adaptation to the periocular shape of the face and rises the level of the monoculus for about 7 mm. The internal relative humidity was for eight hours at 98% in both test persons and patients. All test persons felt more comfortable with the modified moisture chamber on their skin.

CONCLUSIONS

The presented modified moisture chamber is a derivative of the commercial monoculus bandage for patients with sensitive protrusio bulbi.

Magnification characteristics of fundus imaging systems

OBJECTIVE

To compare the magnification properties of 11 different fundus cameras (including 1 stereo fundus camera), a Rodenstock (infrared) scanning laser ophthalmoscope (SLO), the Heidelberg Laser Tomographic Scanner (LTS), and the Heidelberg Retina Tomograph (HRT).

DESIGN

A cross-sectional study of the relationship between the true size of a fundus feature and its photographic-computer image in 14 different fundus imaging devices. This relationship was evaluated for each instrument using a model eye adjusted for axial ametropia between +11 diopter (D) and -14 D. To simulate refractive ametropia, the "crystalline lens" was removed to render the model eye aphakic, and the axial length was adjusted to give aphakic ametropia from emmetropia to +20 D.

MAIN OUTCOME MEASURES

A correction factor (p) was calculated for each instrument, which can be used in calculations for determining true retinal size.

RESULTS

The following were found to be of telecentric construction, Zeiss Oberkochen (WS240 Heidelberg), Zeiss Oberkochen (UK), Zeiss Oberkochen (Cologne), Nikon NF505, Kowa RCXV, SLO prototype (UK), LTS, and the HRT, and each exhibited a constant relationship between p and degree of ametropia of the model eye. The Canon CF6OU, Canon CF6OS, Canon CR4-45NM, Nidek 3-DX, Olympus GRCW, and Carl Zeiss Jena Retinophot were found not to be telecentric and exhibited a linear relationship between p and degree of ametropia of the model eye. For all instruments, p remained unchanged for axial and refractive ametropias of the same degree.

CONCLUSIONS

The study has shown that not all fundus imaging systems are telecentric, so the use of a single magnification correction value may not be appropriate. These findings have important implications for the way in which true retinal size calculations are performed. Examples are given to show how the tabulated values of correction factors can be used for both telecentric and nontelecentric cameras in image size calculations.