Cataract induction in an arthropod reveals how lens crystallins contribute to the formation of ‘biological glass’

Summary Lenses are vital components of eyes, crafted through the precise arrangement of proteins to achieve transparency and focusing power, and placed appropriately within the eye for the retina to receive sharp, focused images. Maintaining these states is challenging due to substantial post-embryonic eye and lens growth. Here, we gain insights into required processes by exploring consequences of silencing Lens3, a key lens protein, during growth in Thermonectus marmoratus sunburst diving beetle larvae. We show that lens3RNAi leads to opaque aggregates reminiscent of vertebrate lens ‘cataracts,’ causing the projection of degraded images which impact behaviour in low light. Our findings uncover how complex biological lenses are constructed and further support that visual input is inconsequential for coordinated eye growth in this clade. We highlight the utility of this insect as a tractable model system to investigate the aetiology of lens cataracts and refractive errors in a sophisticated camera-type eye. Highlights ● Crystallin protein knockdown induces central cataracts in an insect camera-type eye ● Cataractous lenses project blurry images but have unchanged focal length ● Result: ing image degradation impacts behaviour in challenging low light conditions ● Contrary to vertebrates, blurry vision does not affect refractive state