University Eye Hospital Tübingen
Department of Ophthalmology

The aim of this project is to investigate how the reduced pupillary light reflex in the blind hemifield of patients with hemianopia depends on the light intensity of the stimulus. The study will also examine whether retrograde ganglion cell degeneration is present in this group and whether it correlates with the pupillary light reflex, the age of the lesion, or stroke treatment. Furthermore, the study aims to investigate the extent to which visual field defects regress following ischemia and how this correlates with the aforementioned factors. Based on these findings, a reliable CPC protocol for patients with hemianopia due to posterior ischemia will be developed. To this end, patients with hemianopia will be examined initially, as well as 1, 3, 6, 12, and 18 months after the stroke event.

Preliminary work:

• How lesions at different locations along the visual pathway influence pupillary reactions to chromatic stimuli. Kelbsch C, Stingl K, Jung R, Kempf M, Richter P, Strasser T, Peters T, Wilhelm B, Wilhelm H, Tonagel F. Graefes Arch Clin Exp Ophthalmol. 2022 May;260(5):1675-1685. doi: 10.1007/s00417-021-05513-5. Epub 2021 Dec 13. PMID: 34902059 Free PMC article.

The goal is to analyze pupillary escape in patient groups with pathologies of the inner retinal layers or disruptions in the synaptic connections between the inner and outer retina, with the long-term aim of potentially establishing escape as an additional diagnostic pupillographic marker. To this end, patients with X-linked retinoschisis (XLRS) with central involvement, patients with congenital stationary night blindness (CSNB), and patients with retinal arterial occlusion (ZAV/AAV) will be examined.

Preliminary work:

• Central retina plays a decisive role in the suppression of pupillary escape.
  Kelbsch C, Jendritza R, Strasser T, Tonagel F, Richter P, Jung R, Peters T, Wilhelm H, Wilhelm B, Stingl K. Graefes Arch Clin Exp Ophthalmol. 2023 Jun;261(6):1713-1722. doi: 10.1007/s00417-022-05959-1. Epub 2023 Jan 16.

The aim is to distinguish between different types of acute optic neuropathies using pupillography, as well as to differentiate them from healthy individuals, and to investigate “pupillary escape” as a potential marker of dysfunction in the inner retinal layers. To this end, patients with acute optic neuritis (NNO), symptom onset < 2 weeks; patients with acute anterior ischemic optic neuropathy (AION), symptom onset < 2 weeks; and patients with Leber’s hereditary optic neuropathy (LHON) (molecularly confirmed diagnosis) will be examined.

Preliminary work:

• Chromatic pupil campimetry as an objective diagnostic tool for progressive optic neuropathies. Edelmayer MV, Strasser T, Jung R, Sonntag A, Jendritza R, Tonagel F, Peters T, Wilhelm H, Wilhelm B, Kelbsch C. Doc Ophthalmol. 2025 Oct 15. doi: 10.1007/s10633-025-10054-x. Online ahead of print. PMID: 41094347

The PupilPanda project emerged from a series of studies that investigated how perception-based stimuli can be used to study visual function at various physiological levels. The work is based on investigations of the Panda illusion, a visual stimulus that relies on the principle of pulse-width modulation. We were able to demonstrate that the illusion is decoded by the visual system through spatial low-pass filters. This explains why reduced visual resolution can improve the visibility of the embedded panda (Straßer et al., Scientific Reports, 2020). This perceptual property established a direct relationship between the detectability of the illusion and spatial frequency.

Building on this concept, the illusion was initially evaluated as a tool for determining visual acuity. It was found that the detection thresholds systematically vary with spatial frequency and blur. This enables the estimation of functional visual acuity using a perception-based stimulus instead of conventional optotypes (Kelbsch et al., British Journal of Ophthalmology, 2023). These results established the panda illusion as a controllable probe of visual resolution.

In the next step, the paradigm was extended from psychophysics to objective electrophysiology. In the study “Seeing the Panda,” the illusion was embedded in a visual oddball design to elicit both visual evoked potentials (VEP) and P300 responses (Nikolaidou & Strasser, ISCEV 2025 Conference). This approach enabled the simultaneous investigation of early sensory processing and higher-level cognitive evaluation of the stimulus. The results showed that the amplitudes of VEP and P300 covary with optical blur and spatial frequency. This supports the assumption that refractive and cognitive aspects of visual acuity can be captured within a unified neural framework. Following the demonstration of robust cortical effects, the paradigm was extended to pupillography. In the study “Your pupil knows better: Functional Pupillography with the Panda Illusion” (Nikolaidou, Schedel & Strasser, ARVO 2026 Conference), the illusion reliably elicited event-related pupillary responses. Notably, the pupil dilation patterns differed from the reactions recorded via button press. This suggests that autonomic responses follow stimulus-driven perceptual processing even when conscious perception is inconsistent. These results suggest that pupil dynamics offer an additional, objective window into visual processing.