Handheld fixation device

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Figure 1
The handheld fixation lamp

Purpose: Presentation of a new handheld fixation device

Method: In the direct method of the fundus examination of the patients with bad compliance I urge the eye for fixation by an optically placed at infinity red flashing ledlamp that I put directly in front of the fellow eye

Key words: fixation device, fundus examination

Summary: The author presents a new hand-held gaze-fixation device which has proved invaluable in the fundus examination of patients with bad compliance.

In such cases it is possible to make the eye under examination involuntarily fixate, with the use of a red flashing LED-lamp held directly in front of the fellow eye. The lamp lightsource of which is optically located at infinity.

The good cooperation between the examiner and the patient is essential in most medical examination procedures. In many cases difficulties in cooperation can be overcome with the help of a good resource. In this way further intervention (e.g. general anaesthesia) in order to set up a more precise diagnosis can be avoided, that might be expensive or means a certain risk for the patient or claims more staff. This is even more so in the case of children. Numerous ophthalmological examinations necessitate that the examined person should be able to fixate to a given point permanently. In the fundus examination quite often it brings also a problem up: the unability of the sustained concentration of the patients. For example in the direct ophthalmoscopy people with bad compliance the concern is, that the object showed by the examiner to the patient aimed to grip the interest for getting a fixed eye position or to aim for the following of the eye to a given gaze position, is covered by the examiner’s head.

Methods

For the distance cover test the patient needs to fixate ordinarily a continuous light source or movable object, for the near cover test he or she needs to fixate a small picture, a point of a pencil or optotyp (1,2). There are more complicated equipments that work with electrical amenable, movable figures, light emissing or that give sound. Sometimes the examiner uses slide projector (1).

Lang (1) made a suggestion for a special fixation device for the distance cover test to complete to the former ones that worked on continuous light. He achieved more effective concentration of the attention by a music box maintained with changing color flashing light.

The new device

Figure 2
A child helds the device in his hand in front of his right eye. The red ligth of the LED-lamp at the moment of the flash glints on the cornea. During that time the doctor examines the left eye of the patient.

The device designed by myself in most of all cases can eliminate „the lap” mentioned in the introduction. The new device is a led-lamp (Figure 1) which works with an inner power source (accumulator) giving a flashing, red light („Bunny Eye”) with low intensity, that with the help of its little size we may it place directly in front of the either eye (Figure 2).

Thus the attention of examined person can be aroused and drawn to a certain point, so the other eye can be examined making good use of the synkinesis of the two eyes.

This fixation lamp is a pencil-like roll a little longer and thicker (lenght 215mm, diameter17mm). The light comes from an aperture in the upper third of the device (Figure1). The ligth source gives the picture as it would be projected from a distance, as the divergent rays optically are made parallel. With this help the so-colled „instrument convergence” or „proximal convergence” (3) may be decreased significantly.

The intensity of the light is reduced so much, that for its effect no afterimage is created, but the „pulse” of the led-lamp provides sufficient preference over the continuous and sharp light of the ophthalmoscope used for examination of the other eye. So the eye will pay attention to the slight flashing light rather than the sharp still one. The physiological basis of this common experience is that the threshold of the stimulus of the eye arised by the effect of the continuous light presenting a monotone stimulus, thus the sight will dislike that. So it is easier to pay attention to a flashing light rather than a continuous one’s.

The end of the device getting closer to the eye is rounded, thus the device itself can be held by the child examined without any risk of damage or harm. Giving the device in the hand of the children we encourage them to participate in the examination. But of course the lamp can also be held by the doctor, assistant or the joint person of the child. (For in-patents we can carry the direct ophthalmoscopy out so that the device may lean on the edge of the orbita, and thus we urge the patient to fixate.) The device can be hung in the examined patient’s neck with the help of a ribbon thus avoiding dropping it.

Discussion

Recently world-wide scale the indirect binocular ophthalmoscopy increasingly gains ground for the fundus examination. However in spite of the doubtless advantage (wider field of view) of the indirect method because of the disadvantages (too high intensity of the illumination, inverted virtual image of the retina, claim of the additional plus lens, smaller magnification, more expensive price) the indirect ophthalmoscopy probably will not displace the direct method from the everyday practice for a long time.

 

Conclusion

As for the resolution of the mentioned in the introductory problem (the fixation target is covered by the examiner’s head) of the direct ophthalmoscopy I did not find any data in the literature, I’d like to recommend this new device designed by myself and used with success more than one year for all who principally deals with the children or with the patients with bad compliance, or with in-patients, for those colleagues who deal with fundus examination or deal with the examination of eyemovement. The lamp worked on slight intensity allows too of an approximate assessment for the visual acuity of a child who can not speak. It may be useful for the representatives of the associate professions as for the optometrists or for paediatricians.

 

References

1. Lang J.: Fixationseinrichtungen für den Abdecktest. Klin. Mbl. Augenheilk 1975; 167: 308-311.

2. Noorden G.K. von, Helveston E.M.: Strabismus: A Decision Making Approach. I st ed., Mosby Co.
    St. Louis, 1994; p.1.

3. Noorden G. K. von, Campos E. C.: Binocular Vision and Ocular Motility. Theory and Management of Strabismus. VI th ed. Mosby Co. London, 2001; p. 98.