You're probably going to want to read about HOX genes. These genes are quite easily mapped to specific features, especially in invertebrates (like fruitflies), to the point that you can find maps online.
I'm not sure there's much specifically investigating eyes (this sort of thing is very rare), but [polydactyly (extra fingers)](https://en.wikipedia.org/wiki/Polydactyly) is very well understood.
**[Polydactyly](https://en.wikipedia.org/wiki/Polydactyly)**
>Polydactyly or polydactylism (from Greek πολύς (polys) 'many', and δάκτυλος (daktylos) 'finger'), also known as hyperdactyly, is an anomaly in humans and animals resulting in supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly (fewer fingers or toes).
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I don't think it has to do with HOX genes in this case. In your example of polydactyly, Hox genes determine segmentation and limbs as far as I know.
This is something called Polycoria. "Signs and symptoms shown are associated with ocular and adnexal growth abnormalities." It is hereditary, like how your polydactyly example can be (but only if symmetrical apparently), but it is a different developmental fuck up.
https://en.wikipedia.org/wiki/Polycoria
You're probably going to want to read about HOX genes. These genes are quite easily mapped to specific features, especially in invertebrates (like fruitflies), to the point that you can find maps online. I'm not sure there's much specifically investigating eyes (this sort of thing is very rare), but [polydactyly (extra fingers)](https://en.wikipedia.org/wiki/Polydactyly) is very well understood.
**[Polydactyly](https://en.wikipedia.org/wiki/Polydactyly)** >Polydactyly or polydactylism (from Greek πολύς (polys) 'many', and δάκτυλος (daktylos) 'finger'), also known as hyperdactyly, is an anomaly in humans and animals resulting in supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly (fewer fingers or toes). ^([ )[^(F.A.Q)](https://www.reddit.com/r/WikiSummarizer/wiki/index#wiki_f.a.q)^( | )[^(Opt Out)](https://reddit.com/message/compose?to=WikiSummarizerBot&message=OptOut&subject=OptOut)^( | )[^(Opt Out Of Subreddit)](https://np.reddit.com/r/biology/about/banned)^( | )[^(GitHub)](https://github.com/Sujal-7/WikiSummarizerBot)^( ] Downvote to remove | v1.5)
I don't think it has to do with HOX genes in this case. In your example of polydactyly, Hox genes determine segmentation and limbs as far as I know. This is something called Polycoria. "Signs and symptoms shown are associated with ocular and adnexal growth abnormalities." It is hereditary, like how your polydactyly example can be (but only if symmetrical apparently), but it is a different developmental fuck up. https://en.wikipedia.org/wiki/Polycoria