Giving invertebrates an eye exam: an ophthalmoscope that utilizes the autofluorescence of photoreceptors.

One of the most important functional features of eyes is focusing light, as both nearsightedness and farsightedness have major functional implications. Accordingly, refractive errors are frequently assessed in vertebrates, but not in the very small invertebrate eyes. We describe a micro-ophthalmoscope that takes advantage of autofluorescent properties of invertebrate photoreceptors and test the device on the relatively well-understood eyes of jumping spiders and flies. In each case, our measurements confirmed previous findings with a greater degree of accuracy. For example, we could precisely resolve the layering of the anterior median eyes and could map out the extensive retina of the anterior lateral eyes of the spider. Measurements also confirmed that fly ommatidia are focused into infinity, but showed that their focal plane is situated slightly below the receptor surface. In contrast to other approaches, this device does not rely on reflective tapeta and allows for precise optical assessment of diverse invertebrate eyes.