Hollow Eyes & Orange Eyes: Handicap or blemish?

When the first shrimp with orange eyes appeared in internet forums, the interest in these animals was logically huge, because in contrast to the otherwise rather black eye colors, this new color was literally a new glow in the shrimp sky, also these shrimp behaved "somehow" differently than their representatives with normal eyes. However, a slight suspicion that the animals might be blind also attracted attention, and not least the statement became louder that such shrimp should not even be bred further, if they would lose one of their senses. It was not until 2018 that a study of the animals by C. Logemann was able to bring light into the darkness, which was examined in more detail scientifically by M. Kirchbeck in 2019.

How did the Orange Eyes originate in the first place?

Completely to the origin can be traced back the first appearance of the strange eye color today probably only with difficulty. Presumably, the first tiger shrimp, in which this phenomenon occurred, but from the Asian region and may have aroused enormous interest, as they have slowly spilled between 2011 and 2013 to Europe and were further bred. As with most mutations, the complex genetic variability of orange eye color was still considered erratic and random. In the meantime, shrimp stocks with OE, as Orange Eyes are also known, are more or less heritable and exhibit less split inheritance than they did a few years ago  

It was noticeable that OE initially appeared only in blue, red and black tiger shrimp or in animals with tiger genetics. In the course of time, however, also Neocaridina and also C. hodgarti were encountered with light eyes and the assumption of pure breeding variants was disproved by secured wild stocks with OE, which probably laid the milestone in terms of eye color. But why are the eyes different in color? According to the first assumptions it should be a lack of rhodopsin, which is a visual pigment in the photoreceptors of shrimps. This, in turn, would probably promote the visual impairment.

Comparison of both studies

A different behavior, especially the erection of the antennae, but also a lack of escape reflex in some places, brought the strange animals into focus and raised the concerned question of a handicap. Carsten Logemann from the shrimp house conducted a survey of keepers with these and normal-eyed blue tiger shr imp in advance, the evaluation of which, however, convinced him less, whereupon he set up various experiments and conducted a rough behavioristic study with blue tiger shrimp OE (BTOE). The animals in question, normal-eyed tiger shrimp in the control group for comparison, were placed in photocuvettes and exposed to various stimuli including light and movement to find out differences in their behavior.

Carsten came to the conclusion that "tigers OE recognize differences between light and dark and also point their antennae in the direction from which the shadow comes. However, they cannot perceive movements without shadows, in contrast to *normal* tigers, which apparently can see very well with their compound eyes." He concludes that the OE tiger shrimp must be either blind, or at least severely vision-impaired, but is convinced that they cope with this handicap in captivity just as well as their black-eyed representatives.

Melanie Kirchbeck, on the other hand, in a histological and comparative study(Kirchbeck, et. al., 2019) found that the eyes of OE and normal tigers alike had all the necessary features required for vision, i.e., lamina, medulla, rhabdome and lobula, respectively, medulla externalis, m. internalis and m. terminalis, as well as the crystal body. Compared to animals that live predominantly in the dark and rely rather less on their visual properties, neurophilic lamina and crystal body are usually rather weak to absent, but this was not the case in the OE.

A shrimp eye has so-called ommatidia, i.e. several "single eyes", which are arranged in a cone shape. Depending on the incident light, there is a differently well-developed pigment layer between them - the melamine, which serves to shield strong light conditions, so that the shrimp can still see "sharply" and is not blinded. The absence of this intraommatidial pigment in the OE tigers was conspicuous, although individual functionless remnants of it were noticeable in the study.

Thus, animals with Orange Eyes do not have the natural light protection in the eyes like other shrimp. This therefore results in glare when they are exposed to a strong light source. Although the overall image is still recognizable to them, they lack the ability to see it sharply. Conversely, however, they are able to see better at dusk and in the dark, because the residual light has a better effect on all the individual eyes and enables sharper vision. M. Kirchbeck therefore came to the conclusion that OE shrimps do have a visual problem, but that this can be positively influenced in the aquarium by dimmed aquarium lighting .

Hollow Eyes- eerily interesting eyes

Shrimp with the so-called "Hollow Eyes" have not been in the hobby that long and probably made their first appearance in 2020. Their strange-looking eyes are striking, appearing downright sunken, and are therefore referred to as "hollow eyes", which simply means "sunken". Unlike OE shrimp, however, animals with these eyes are not likely to have poor eyesight, and so far there are no obvious similarities between these two phenomena. The Hollow Eyes are also a gimmick of mother nature, which is based on a genetic mutation and currently only occurs in Crystal Red Ghost Shrimp. The eye feature intensifies with age.

Hollow eyes" also exist in human medicine, but in humans they are called enophtalmia and refer to the symptom of sunken eyeballs (the so-called enophtalmus), which can be due to a variety of causes. This is defined as the retraction of the orbita along with its contents into the orbital cavity. Due to the missing fat cushion, the corpus adiposum orbitae, which is usually found behind the orbit, the re-bearing of the eye is also reduced. This means that the eye can thus be moved backwards without any problems and can retract into the orbit together with all accompanying structures. Hollow eyes" are not actively treated, rather the triggering causes are treated.

So far, there are no study results available on whether shrimps with Hollow Eyes would be limited in any way in their vision or their quality of life. However, their creepy looking eyes are an interesting mutation, even though they are still divisive.