A C T A O P H T H A L M O L O G I C A V O L . 5 7 1 9 7 9

From the Department o\ OPhthnlniology (Head: Salnie Vannas), University of Helsinki

A SIMPLE METHOD FOR SCREENING OF CHILDREN WITH STRABISMUS, ANISOMETROPIA OR AMETROPIA BY

SIMULTANEOUS PHOTOGRAPHY OF THE CORNEAL AND THE FUNDUS REFLEXES

BY

KARl KAAKINEN

A simple screening method for detecting strabismus, anisometropia and ametropia in young children by simultaneous photography of the corneal and fundus reflexes with a conventional camera and flashlight is pre- sented. The method is the photographic application of the von Briickner Durchleuchtung test and static skiascopy. The objective document from the external part of the eyes and the face is obtained at the same time. Model photographs with certain gaze deviation angles are presented with the method.

Key words: strabismus - von Briickner Durchleuchtung test - static skia- scopy - fundus reflex - corneal reflex - photography screening of vision defects and eye disorders in young children - flashlight - flickering fixa- tion light (LED) - simple documentation.

It is important for the prevention of amblyopia to make a strabismus diagnosis as early as possible in childhood (for example, Pigassou (1977)).

Ingram (1977) pondered the problem of screening children for visual de- fects. In his opinion, the methods used today are still time-consuming and expensive. Especially straight-eyed amblyopes with anisometropic refractive errors require determination of refraction in early childhood. Unfortunately, examinations at this age can often be very difficult, even impossible, because of fear or some other lack of co-operation on the part of the child. Even the cover test can be very difficult to perform when the subject is under three

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Received June 6, 1978.

Acta ophthal. 5 7 . 2

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years. There is no simple and quick screening method to detect this kind of visual defect.

Von Bruckner (1962, 1965) presented the Durchleuchtung test in which the corneal reflexes according to the Hirschberg test and the fundus reflexes and pupillary reactions are also examined with an ophthalmoscope from a distance of one metre. The strabismus or aniscmetrcpia can be diagnosed from the asymmetry of these reflexes without touching the child. It seemed possible, therefore, to make the documented von Briickner Durchleuchtung test by using a conventional camera with a flashlight instead of an ophthalmoscope. All that is required is for the child to look a t the camera for the brief moment when the corneal and fundus reflexes are photographed. The photographs can be later analysed by an ophthalmologist for corneal or fundus reflex asym- metry, indicative of strabismus or anisometropia. In addition, the fundus re- flex photographs could provide information on possible changes in transparent ocular media. The approximate refractive errors, too, can be estimated from the different appearance of the fundus reflexes (Rosengren 1937, 1948) ac- cording to the static skiascopy.

Maddox (1902) used photography to examine strabismus angles. Later, among others, Graham PC Naylor (1957), Weekers et al. (1963), Joachim & Gilson (1964), Breitenmoser & Wurth (1970) and Jones & Eskridge (1970) photo- graphed the Hirschberg test and determined the stage of the deviation of the eyes from the localisation of the corneal reflexes.

Transparent ocular media are also examined quite frequently by photo- graphy, generally using the Douvas & Allen (1950) principle. This has been applied in practice by Fincham (1955) and many others.

Howland & Howland (1974) presented an apparatus for photorefraction of both eyes with a camera, but I have not found any report in the literature of the use of the combined corneal and fundus reflex photography method for both eyes for diagnosing strabismus and refractive errors simultaneously.

T o discover if this was possible, I constructed a simple photographical equipment for simultaneous documentation of the corneal and fundus reflexes and to test its practicality in diagnosing strabismus and refractive errors.

The first part of this investigation presents primarily the method and some experience gained with its use.

Methods and Material

In principle, it is possible, by using a coaxial flashlight attached to the ob- jective of the camera, to photograph simultaneously the corneal and fundus reflex when the patient fixes his gaze on the camera objective.

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F i g . 1. The pocket flashlight Sunpak Gx 1 7 in front of the Canon objective FD 100 mm 1:2.8 S. S. C. The red flickering fixation light (LED) is in the middle, under the flash unit. On the right is the oscillation circuit box of the flicker system with a switch-on

coupler. This was usually mounted in the back of the camera body.

A standard 35 mm single lcns reflex camera (Canon EF) with an FD 100 mm 1 : z . S S. S. C. Canon lens was used. A weak telephoto lens was chosen, because it is quite small and handy, but still gives enough enlargement from a distance of one metre to detect even slight deviations of the eyes.

A Sunpak Gx 1 7 electronic flash unit was attached in front of the objective in the middle horizontally, with the help of the Canon lens hood BT-55, so that the distance between the low edge of the flash unit and the lowest outside margin of the lens hood was 42 mm. A piece corresponding to the size of the flash unit was cut from the lens hood, so that the flash unit was firmly attached by the hood.

A commercial, red, round flickering LED 2.5 mm in diameter was attached as a fixation light to the middle of the anterior low edge of the flash unit.

The flickering mechanism was accomplished with an oscillation circuit. The light was connected to a switch, which was placed at the back of the camera body for easy handling (Fig. 1).

The film material was commercial colour films. The aperture range was adjusted to the Sunpak Gx 1 7 flash units guide number chart for a photography distance of one metre, which was selected as the practical distance for photography. This is the same distmce that is generally used for the von Briickner Durchleuchtung test.

The photography technique and standardisation

To prevent inadvertent movement of the distance scale adjustment of the ob- jective, it was fixed with a piece of adhesive tape a t exactly one metre. Photo- graphy was done by hand without a stand. For focusing, the camera was slowly moved to and fro until the object in the middle of the viewer was sharpest. In repeated experimental measurements focusing in this way a t one metre with the camera's range finder, the greatest possible error was k 2 cm.

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The photography was performed in dim light for reliable focusing. The pupils of the subjects were then larger than in bright light and the flickering fixation light interested the children and tended to make them stare a t it.

Mydriatic drops were not used because the aim was to photograph the physiological situation. With young children, in particular, it was found useful to focus first and then switch on the flicker light just before taking the photo- graph, asking a t the same time what was flickering. This gave both a visual and auditory stimulus to the child to fix his gaze on the light.

Testing the method

1. Summary mcnsurcment of refraction by photography. The usefulness of the method was examined by photographing a Carl Zeiss Jena Optical Demonstra- tion Eye with different refraction errors which were controlled with a streak retinoscope (Fig. 2).

2. Detecting strabismus. T o establish the smallest deviation angle of the eyes that causes the change in intensity or colour of the fundus reflex or that could be seen as shifting of the corneal reflexes in the photographs, an experimental test photo series was made. An emmetropic straight-eyed test subject was photographed when her gaze deviated from the fixation light of the camera by a certain number of degrees (lo-13'). The deviation angles were calculated from a slightly coarse cyclopean eye schema by using trigonometrical tangent func- tions in a right-angled triangle, where both the catheds were known: the greater was the photography distance of one metre and the smaller the meas- ured distance that the test subject was asked to look to the side of the fixation light of the camera.

By calculating trigonometrically, it is possible to determine, by using this kind of cyclopean eye schema instead of the two-eyed natural situation, that the error in 3' gaze deviation is +. 2 min of arc and in the case of 13' k 6 min of arc. This is accurate enough and the cyclopean eye schema can be used be- cause it is easy and practical for making measurements (Fig. 3).

Fig. 2. Refractive error models photographed from the Carl Zeiss Jena Demonstration Eye

(-5.0, 4.0, -3.0, -2.0, k 0 , +2.0, +3.0, +4.0 and +5.0).

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A Simple Method f o r Strabismus

, /'/

RIGHT EYE&*< _ _ _ _ - _ - - - _ 0 -

The photographs were taken twice and found identical. When the gaze de- viated, one eye presented exotropia and the other esotropia. The photographs were compared with an orthophoric photograph where the same test subject gazed into the camera (Fig. 4).

T o make the examination easier, schemas corresponding to a normal strabis- mus situation were made by cutting the photographs in the middle and com- bining the gaze deviations of different degrees with half-face photos in which the test subject was looking straight ahead. This gave artificial photos in which one eye was straight and the other deviating a certain number of degrees (Figs. 5 and 6).

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F i g . 4. Photographed corneal and fundus reflexes when the gaze is deviated to the right lo-13'. Top, the gaze is fixed on the camera (OO).

A Simple Method f o r Strabisnius

Fig . 5 . Artificial left esotropia 3'. Combination of the two photographs. The right eye is fixed on the camera and the left 3' to the right of the camera. The positions of the corneal reflexes are slightly asymmetrical. The different brightness of the fundus

reflexes is quite apparent.

Fig. 6 . Artificial right exotropia 3'. Combination of two photographs as in Fig. 5 .

Moderate asymmetrical corneal and fundus reflexes.

The resolution and quality of the photographs was good. In two different test sessions, phGtographing the Carl Zeiss Demonstration Eye in different refrac- tion errors, the results were identical.

In hyperopia a light crescent was found in the low part of the fundus reflex and in myopia in the upper part of the fundus reflex. Both the hyperopic and the myopic crescents increased in size with the refraction error. This refraction change could not be found when the small pupil of the demonstration eye was used. The crescent appeared in myopia around -3 D. and in hyperopia around +1 diopters.

In the test photos, where the gaze of the test subject was a certain number of degrees off the fixation light of the camera, it could be observed that an angle of just 3' convergent or divergent strabismus can be seen as clear, mode- rate deviation of corneal reflexes, while at a deviation angle of 2' it was somewhat doubtful. It was found that deviation changes of 3' were readily de-

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Fig . 7. A 29-year-old woman with anisometropia and left amblyopia. Straight eyes in the cover test. Refraction in the cycloplegia in the right eye -3.5 comb. cyl. +0.25 ax. 90' and in the left +5.0 comb. cyl. +1.0 ax. 130'. The vision of the right eye with correction 1.6 and of the left 0.15. Anatomically normal eyes. There are symmetrical corneal

reflexes and the hyperopic crescent is visible in the left fundus reflex.

Fig. 8. A 15-year-old girl with -6.0 myopia in cycloplegia in both eyes. Straight eyes in the cover test and anatomically normal eyes. Symmetrical myopic crescents are visible in both fundus reflexes, and the positions of the corneal reflexes are also symmetrical.

Fig . 9 . A one-year-old boy with an anomaly of the right upper lid retraction and small inter- mittent hypotropia of the right eye. Anatomically normal eyes and refraction t2.0 in both eyes in cycloplegia. The cover test reveals very small right hypotropia and some- times no movement at all. The right hypotropia and lid retraction are very apparent

in the photograph. The brightness of the fundus reflexes are symmetrical.

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A Simple Method f o r Strabismus

F i g . 10. A 10-year-old boy with a very small left esotropia and amblyopia. Refraction in the cycloplegia on the right side +2.0 comb. cyl. +0.5 ax. 90° and on the left t2.5. Ana- tomically normal eyes v. 0. dx. = 1.3 and v. o. sin. = 0.1 with the correction. In the cover test very small left esotropia in which the angle of the deviation with synopto- phore is t2 ' . A moderate asymmetry of the corneal reflexes is apparent in the photo- graph and the fundus reflex of the deviating left eye is lighter than in the right one.

tectable, while 2' changes were demonstrable but somewhat questionable. To determine the asymmetry of the corneal reflexes, a normal millimetre scale was used a t first to measure the distances of the corneal reflexes from the limbus. But this was not practical because even the slightest asymmetry to be measured was a t least as clear by visual examination.

The colour of the fundus reflex became moderately lighter when the eye of the test subject deviated from the straight position 1' medially or laterally. Then the fundus reflex kept roughly as bright except at +11°-130 esodeviation when it became very light coloured.

In test photography sessions, one-year-old children co-operated by looking at the fixation light. Some illustrative strabismus and a straight eyed refrac- tive error cases of different ages are presented in Figs. 7-10.

Discussion

If a one-year-old child can be persuaded to co-operate in dim light by looking a t a flickering fixation light, screening at that age could be possible with the method, which, because of its simplicity, can even be set up by a technician.

Graham & Naylor (1957) found that their eye deviation measurements made by photography differed from the synoptophoric results. Joachim & Gilson (1964) reported that when they were examining by photography, the measure- ments by synoptophore gave overvaluation in convergent strabisnius and under- evaluation in divergent strabismus. These and the studies of Breitenmoser & Wurth (1970) and Jones & Eskridge (1970) give the impression that the devia- tion angle of the eye at the moment of photography can be examined with a

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great degree of accuracy lroni the photograph, which, at the same time, is a permanent document for future reference.

The different size of the kappa angles in the right and left eye of the same person could cause an error in estimating the possibility of strabismus or measuring eye deviations by comparing localisation of the corneal reflexes in the contralateral eves. But this source of error has been shown to be of no im- portance in practice, because photography has revealed that the kappa angles are identical in both eyes of the same person (Weekers et al. 1963).

In principle, the method described here is about as accurate for measuring eye deviations as the methods cited in the foregoing. The procedure and appa- ratus are similar but simpler. Complicated stands that could frighten a child are not needed. The small and handy flickering LED light has shown itself to be a practical way of attracting the attention of small children.

The method makes it possible to photograph, with the conventional camera, corneal and fundus reflexes simultaneously. A mere 1" convergent or divergent deviation of the eyes in experiments made the fundus reflexes moderately lighter than in the straight position. This concurs with the claim of von Briickner (1962), that a deviation of ll/to causes a change in pupillary brightness in the Durchleuchtung test. It seems that this could facilitate the diagnosis of small- angled strabismus cases. According to von Briickner (1962), the dark fundus reflex of the straight eve is reflected from the macula compared with the other parts of the retina which are lighter reflecting. The very light fundus reflex that appeared in +I 1'-13O esodeviation is apparently caused by the bright reflex of the optic disc.

It is clear that the method measures the refraction rather roughly according to the principle of static skiascopy in the line through the camera lens and the light source accordingly in the vertical meridian. Its accuracy is not sufficient for exact refraction measurements and the method is meant mostly for screen- ing, not only to detect strabismus but also straight eyed cases with great aniso- metropic or ametropic refractive errors. T o obtain more accuracy for examining refractive errors, especially hyperopia, cycloplegic medication should be used.

The method has already been applied to a clinical strabismus and refraction material that is to be published later.

Acknowledgments

I am indebted to Docent Veikko Tommila for his critical support and to Paavo Heik- kinen, M. Sc., for the mathematical planning and application.

This study was supported in part by a grant from the Instrumentarium Research Foundation.

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Author’s address: Kari Kaakinen, Kalliokatu 15 B 15, 87100 Kajaani 10, Finland.

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