Here is a list of headgear in the game (does not include the new artifact helmet added in p6).

Agree with it.

Personally, I think this corruption should be reworked entirely.
I have no idea in what book a single eye is better (as in more perceptive) than two eyes - single eye takes away depth perception and would literally make archery impossible.
If anything, this corruption should take away at least 5-6 points of perception.
As a compensation, a bigger eye also has more light coming in, hence this corruption could maybe grant vision in the dark or extend effective view range by 2 tiles.

I don't think you entirely understand the "Perception" stat. In this case, the issue is that you think depth perception is the only important facet.

The one larger eye would presumably be able to take in more information, and with only one eye for the brain to process, presumably the brain would be able to pick out finer details. Furthermore, depth perception is still possible with only one eye - it's just more difficult, requiring head movement in order to enhance the very slight depth perception that a single eye can still achieve.

As for the idea that it would harm archery, that's somewhat debatable. On the one hand, loss of regular depth perception would certainly make judging distance harder. On the other, having just one eye and the brain being wired for that one eye would allow them to better judge in terms of aiming (sight-line-wise).

This is plain wrong. Evolution proved that two eyes offer a better solution than a single one.
You underestimate the importance of depth perception, to which all humanoid beings in the game are used (except cyclops).
Suddenly getting your eyes merged would be a shock to the brain, it would require relearning a lot of stuff.
Depth perception is of course not the only important element, there's more.
With two eyes you have a much wider field of vision than with single eye. You can use perception from the corner of each eye to notice things otherwise impossible to notice with a single eye.
Also I can't imagine moving your head around each time you want to gauge distance.
As for processing information from eyes - the brain has two hemispheres and thus having two eyes is a natural way of things to achieve the most effective use of resources.
The brain only uses a fraction of its computing power to analyze signals from the eyes; having a single eye would not improve that situation at all.
As for aiming with a single eye, you can already achieve the same by closing eyelids. You disable one eye for the purpose of having a uniform vision of the target, but you still use two eyes to assess distance and perceive more targets in combat as well as estimate movement vectors.
To sum it all up:

With eyes merged, you trade depth perception, field of vision and peripheral vision for what? More light coming into a larger eye? That's one hell of a trade off.
My conclusion is that this corruption wasn't well thought-through.
In fact, the bonuses it grants are quite ridiculous.

I used to run a painting crew. In the crew there was one guy with only one eye. He could not paint straight with a brush and used to make a mess by touching his brush all over the show.

My deduction is that he had no clue where his hand and the surface was with relation to each other.

This is where your argument falls apart. This is a fantasy setting. It's magic causing the merging of the eyes - it seems reasonable to assume that the same magic is also adapting the PC's brain to suit the corruption, much as how growing antennae by corruption results in appendages that are useful, and growing a total of 12 eyes doesn't leave the PC with 10 eyes lacking the necessary nerve connections to use them.

A bigger eye wouldn't likely collect a whole lot more light in what has been established to be magical darkness, but it would be able to collect more information due to being higher resolution (just like a more expensive camera). This allows the PC to perceive finer details, at the expense of depth perception... and you don't lose all depth perception with one eye. Not only do you still have slight depth perception with one eye due to the fact that the pupil isn't infinitesimal, but you also perceive depth in the same way that we all perceive depth when we look at something like this: http://27.media.tumblr.com/tumblr_lh...p4fro1_500.gif

Let's be honest, using evolution to justify things in ADoM is just a little bit silly, given the nature of the game.

I think what I was trying to say is that the Pe is probably fine, but there should be a penalty to DV and to-hit. The DV penalty is perhaps already the case, I cannot exactly remember all the effects of this corruption.

Depth perception with one eye is mostly just memory at work.

It's not silly at all. We have basic biological and physical constants present in the game.
Characters need to eat and have variable metabolism. We have gravity and all objects in the game have mass.
Stuff is heavier or lighter and depending on strength (and a bunch of other things), different amounts can be carried.
There are different states of matter - solid, liquid, gas.
There is light and darkness, so there are photons and electromagnetic radiation in this world.
Magic is nice and fine, to justify things like fire/frost/lightning bolts, invisibility, teleportation and flying but we need some point of reference.

If you subject everything to magic and the fantasy nature of the gameworld then the only thing you achieve is chaos, because of lack of rules that affect things.
I realize magical world can explain and justify a lot of flexibility in game mechanics but some things need to be consistent and a single larger eye being better than two smaller ones for the purpose of measuring one's overall perception is very, very far from consistency.

Research shows that this is completely untrue. Larger eye simply means the tissue is composed of larger cells, the scale remains the same.
Elephants have significantly larger eyes than humans, yet it is known they do not perceive more than us, perhaps even less.
Predatory birds have significantly smaller eyes than bipedal beings yet their vision acuity is far superior, as is their prediction of movement and depth perception.
I can cite relevant work in this regard but I don't think it is necessary.
You say that you don't lose all depth perception having a single eye, but this again is untrue.
You do lose ALL depth perception. You make up for it solely with past experience of perceiving the world with two eyes.

There are humans that have been born without sight - specific group of them have their nerve endings but due to genetic issues, the eyes themselves have not developed properly.
Modern medicine managed to build artificial eyes for several of them, one per person. It has been discovered that they are completely unable to function in three dimensional environment using their single artificial eye.
Without depth perception and no previous experience, it is impossible.
Conclusion is simple - there are only drawbacks (and severe ones) to having a single larger eye versus two separate ones. Magic or not.

In real life, yes. But this larger eye is a magical creation, by the forces of chaos, and the eye itself is composed of the cells from two normal eyes, and therefore the total number of cells has increased.

EDIT: Also, regarding single-eye depth perception: http://www.scientificamerican.com/po...53f8a716af422/ http://theness.com/neurologicablog/i...th-perception/ - basically, there are a lot of ways that our brains get depth information from our vision. Everything from logical deduction (A is clearly in front of B, because A covers part of B), through physical cues like parallax (binocular vision or moving your head from side to side), to the subtle hints (like the effect of changing your eye's focal point, or the apparent blueness of things in the farther distance). Losing binocular vision does impede depth perception, but it doesn't totally eliminate it.

Short way of putting it: If you're going to use science to argue your point, at least get the science right.

Well apparently there are conflicting opinions even among scientists. We may very well both be right.

Again, all of the above stem from experience. You need to have basic knowledge about optics, otherwise you won't know what is it that you're seeing.

It doesn't eliminate it only because of past experience with three-dimensional perception. Without that experience, it wouldn't be possible.

http://scienceblogs.com/cognitivedai...n-whose-visio/
This is about having sight restored to both eyes after many years of being blind.
We're talking about months necessary to get used to perceiving world with eyes and still it's not as well developed after that time as it would have been if that person could see from the day she was born.
How much more difficult it would have been with just one eye, is subject of speculation.

http://www.losteye.com/depthper.htm
Honorable mention goes to this. There is a sentence that clearly states that during fast-paced activities, having a single eye and trying to move your head around to allow the brain to generate a three-dimensional image of an object is impossible because everything takes place so fast.
Arguably, that is what combat is in ADoM. Fast, dynamic, leaves little room for handicaps. This supports the idea that single eye is inferior to dual vision in virtually every respect.

Which also means that the skull would not accommodate such a large eye and you could barely move it at all. You'd have to move your entire head instead.
There is no mention of elongated skull and increase of frontal facial cavities, so I assume eyes merge but the facial bone structure remains the same. Conclusion?
You can't move your merged eye at all. This should directly translate to in-game 50% reduction in view range and -8 or -10 to perception attribute.
How it can possibly increase perception, is a mystery to me.

Having stiff muscles is also a result of chaos and magic at work, yet nobody argues this is a terrible corruption to have.
It is however consistent, as stiffness in muscles prevents them from flexing fast enough and adjusting to all the requirements of dungeon exploration.
Thus, cost of movement dramatically increases as less efficient muscle mass requires significantly more energy to perform the same work.
Such a consistency is nowhere to be seen in case of merged eyes.

I can't believe it took me this long to think about the possiblity that this might refer to the single eye being like a "third eye" located in the middle of the forehead, which would then make the headgear bit make perfect sense. If this is the case, then this bug would definitely be a feature after all...