Swinging light test for assessment of direct and indirect pupillary light reflexes
This testing technique is the most effective way to assess both the direct and indirect pupillary light reflexes in companion animal species.
Testing is best performed in a darkened environment. The gaze of the observer always follows the light stimulus (i.e do not try and light stimulate the right eye and look at the left eye, it is too difficult). The swinging light test is performed by having the dog or cat facing you. Light is shone into the right eye for a few seconds and the direct pupillary light reflex (PLR) is assessed. The light is then moved across the bridge of the nose and stimulates the left eye. When the light first reaches the left eye, the pupil in that eye is in the indirect PLR state. As you continue to stimulate the left eye, the pupil will respond to constrict a bit more intensely as the reflex converts to the direct PLR. Next move the light across the bridge of the nose and stimulate the right eye. As before, first you will see the indirect PLR, then the direct PLR in the right eye. This can be repeated several times until you form a pattern of how the patient is responding.
This is a normal dog however there is some adrenaline affect on the pupil responsiveness in the left eye, hence the variation in the pupil diameter during the testing.
Monocular indirect ophthalmoscopy
This video demonstrates the monocular indirect ophthalmoscopy technique. This is a great technique to provide you with a wide view of the fundus.
Hold a bright light source next to your eye and attain the fundus reflection at arm’s length from the patient. This if often easier if you close one eye. Keep the little finger of the hand holding the lens on the patient to stabilise this hand. Rotate the indirect ophthalmoscopy lens into the field of view. The lens should be the appropriate focal distance from the patient’s eye and parallel to the plane of the iris. If you lose the image, remove the lens from your field of view, re-align and then bring the lens back into position.
Direct ophthalmoscopy
Direct ophthalmoscopy provides you with a narrow view of the fundus, useful for closely examining areas of interest. Use the white, large circular light on your direct ophthalmoscope head, with the lens set at 0 or -1. Start at arm’s length away from the patient to align the optic axis (fundus reflection). Follow the fundus reflection in until you are close to the eye and can observe the fundus structures.
Distant direct ophthalmoscopy
This technique is useful for assessing clarity of the visual axis. Anything which blocks the visual axis will show up as a dark shadow, from mucous on the cornea, to a cataract, to a lesion in the posterior segment of the globe or anything in between. You can then use the rest of your ophthalmic examination to locate the cause of the shadow and decide whether or not it is a pathologic lesion. This technique is particularly useful in differentiating nuclear sclerosis (transparent) from cataracts (opaque).
Use the white, large circular light and your direct ophthalmoscope head, with the lens set at 0 or -1. Stand arm’s length away from the patient and assess the fundus reflex as it retroilluminates the visual axis.
