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Physiology and pathophysiology of the pupil light reflex

Karolína Skorkovská M.D., Ph.D.
Image Karolína Skorkovská

My field of interest is pupil research. I work as an ophthalmologist and so I am interested particularly in the physiology and pathophysiology of the pupil light reflex. My research work takes place at the Pupil Lab of the Centre for Ophthalmology in Tübingen (Germany), under the supervision of professors Barbara and Helmut Wilhelm. My studies were supported by the Marie-Curie-Training Site "Fighting Blindness" of the European Union and by the Jung Stiftung.

 In my experiments I mostly use the method of pupil perimetry (campimetry). It allows an objective examination of the visual field by analyzing the pupil light reactions (PLR) to focal light stimuli presented within the 30° visual field. Pupillary constrictions are registered by an infrared video camera. A visual field defect is characterized by a reduced or totally absent PLR.

An objective evaluation of the visual field by means of pupil campimetry can be a great advantage either in patients who are not able to perform standard automated perimetry or in cases suspected of simulation. Our own study provided evidence that pupil campimetry is applicable for differentiating between retinal dystrophy and functional concentric visual field loss, which is the most common feigned visual field defect (Fig.1) [1].

Figure 1: Pupillomotor field in a patient with retinitis pigmentosa and the corresponding 30° visual field in Goldmann perimeter (right eye). The red column represents the mean value of pupil light response in mm at each tested location in the visual field. The pupil reaction is present only within the preserved visual field
figure 1

It seems that the pupil is not only controlled subcortically, but the retrogeniculate visual pathway or even the visual cortex seems to be involved in the PLR. However, this assumption has not been generally accepted yet and the anatomy of the pupillary pathway is still waiting for its review. With my experiments I provided further evidence to support this data. I have examined many patients with retrogeniculate damage of the visual pathway by means of pupil campimetry and showed that it is indeed possible to demonstrate visual field defects due to retrogeniculate lesions very well (Fig 2a, b) [2].

Figure 2a: Visual field of both eyes in a patient with a retrogeniculate lesion of the visual pathway and a homonymous visual field defect
Figure 2b: In the pupil field of the right eye the pupil reaction in the region corresponding to the visual field defect is reduced or totally absent

Another issue that I am interested in are the “pupillomotor receptive fields”. I have examined the PLR in healthy persons at different locations in the visual field with stimuli increasing in size. Results of this study suggest that pupillomotor receptive fields exist within the pupillary pathway. They show larger diameters than the retinal receptive fields but respect the summation rules valid for the retinal receptive fields (unpublished results).

Recently we became interested in the possibilities of pupillography in the diagnosis of glaucoma. We showed that it is possible to detect significant differences between the PLR of glaucoma patients and healthy subjects by means of pupil campimetry. On the other hand, in this particular study, the sensitivity of the method fell short of being ideal for screening purposes [3]. Nevertheless, pupillary tests offer a new approach in glaucoma diagnosis and their application should be further investigated.

Pupil research is an interesting field in ophthalmology. It offers many possibilities also for future research and I hope to be able to contribute to it.

References

  1. Skorkovská K, Lüdtke H, Wilhelm H, Wilhelm B.
    Pupil campimetry in patients with retinitis pigmentosa and functional visual field loss.
    Graefes Arch Clin Exp Ophthalmol. 2009;247(6):847-53
  2. Skorkovská K, Wilhelm H, Lüdtke H, Wilhelm B.
    How sensitive is pupil campimetry in hemifield loss?
    Graefes Arch Clin Exp Ophthalmol. 2009;247(7):947-53
  3. Skorkovská K, Kelbsch C, Wilhelm H, Wilhelm B.
    Glaucoma screening by means of pupil campimetry.
    2011; www.pupil-colloquium.org

Karolína Skorkovská M.D., Ph.D.

St. Ann University Hospital

Department of Ophthalmology

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