In the compound eye of invertebrates such as insects and crustaceans, the pseudopupil appears as a dark spot which moves across the eye as the animal is rotated.[1] This occurs because the ommatidia that one observes "head-on" (along their optical axes) absorb the incident light, while those to one side reflect it.[2] The pseudopupil therefore reveals which ommatidia are aligned with the axis along which the observer is viewing.[2]

The head of a mantis showing the black pseudopupil in its compound eyes
The eye of a mantis shrimp has three regions, each with its own pseudopupil.

Pseudopupil analysis techniqueEdit

The pseudopupil analysis technique is used to study neurodegeneration in insects like Drosophila. An adult Drosophila eye consists of nearly 800 unit ommatidia which are repeated in a symmetrical pattern. Each ommatidium contains 8 photoreceptor cells each of which forms a rhabdomere (7 and 8 rhabdomere are overlapping therefore, only 7 are visible at any given plain focus). Neurodegeneration leads to loss or degradation of photoreceptors.[3] By visualizing and counting the intact rhabdomeres, degradation level can be measured. Thus, analyzing the pseudopupil can permit empirical study of neurodegeneration.


  1. ^ M. F. Land; G. Gibson; J. Horwood; J. Zeil (1999). "Fundamental differences in the optical structure of the eyes of nocturnal and diurnal mosquitoes" (PDF). Journal of Comparative Physiology A. 185 (1): 91–103. doi:10.1007/s003590050369. S2CID 9114187. Archived from the original (PDF) on 2016-03-04. Retrieved 2008-07-27.
  2. ^ a b Jochen Zeil & Maha M. Al-Mutairi (1996). "Variations in the optical properties of the compound eyes of Uca lactea annulipes" (PDF). The Journal of Experimental Biology. 199 (7): 1569–1577. PMID 9319471.
  3. ^ Song, Wan; Smith, Marianne R.; Syed, Adeela; Lukacsovich, Tamas; Barbaro, Brett A.; Purcell, Judith; Bornemann, Doug J.; Burke, John; Marsh, J. Lawrence (2013). Morphometric analysis of Huntington's disease neurodegeneration in Drosophila. Methods in Molecular Biology. Vol. 1017. pp. 41–57. doi:10.1007/978-1-62703-438-8_3. ISBN 978-1-62703-437-1. ISSN 1940-6029. PMID 23719906.