# Eyesight in monitor lizards



## Smittiferous (Jul 19, 2016)

Does anybody know where I can find some references to monitor vision, and how good it is? I can't find a great deal on Google. Also curious to know how susceptible they are to visual defects, be it developed over time or from birth/hatching. My mertens has what appears to be best described as coloboma in both eyes, (and has had these odd eyes from day one) and doesn't seem to respond to visual cues, After sitting and watching him for a long period I observed him climbing to the top of obstacles in his enclosure, reach the top, and continue trying to climb thin air multiple times while staring straight up. I can even place my hands right in his face or all around his head and he doesn't bat an eyelid, so to speak. If he smells me, or if there's physical contact, it's on for young and old. 

Out of interest, he hasn't eaten a single feeder fish in his tank. The person I purchased him from claims that feeder fish were his primary diet.

From the day I brought him home:





The other eye is far less pronounced in the images I have, but looks more severe now when I looked at him today.


----------



## pinefamily (Jul 20, 2016)

Do his eyes change when he has a food response? All of our monitors get what we call "food eyes" when they show a food response.
Never heard anything about eye defects before, sorry.


----------



## Smittiferous (Jul 20, 2016)

I've never seen him eat. When offered food, he either hisses or ignores it completely, only to snap it up from wherever I deposit it shortly afterwards, when I'm not looking of course.


----------



## pinefamily (Jul 20, 2016)

Put a hand near our guys' heads, and they pull their heads away hissing and carrying on.

- - - Updated - - -

I checked the reptile diseases book we have, but there's nothing in there about what you've described. The closest thing is blocked tear ducts, but that usually shows as swelling around the eye.


----------



## pythoninfinite (Jul 20, 2016)

There looks to be some damage to the iris. Do the pupils contract and expand in the normal fashion when light intensity changes? Monitors usually have excellent vision, and rely on both vision and scent when foraging. The fact that it won't feed while you are watching would seem to indicate that it is visually aware of your presence.

Jamie


----------



## BredliFreak (Jul 20, 2016)

Not to mention they have a third eye/ocelli on the top of their head. Ever wondered why they are so hard to photograph or catch? They can see you from a mile away!


----------



## Smittiferous (Jul 20, 2016)

[MENTION=38465]pinefamily[/MENTION] I can place my hands a centimetre from his face, even his eyes, and I get absolutely no response at all.
[MENTION=41820]pythoninfinite[/MENTION] I haven't observed them doing so. He doesn't seem to focus on anything at all, or watch me the way the other monitors usually would. I don't know how good their hearing supposedly is, but if he is in his hide all I have to do is breathe in the next room and he hisses up a storm while in his hide. It's really bizarre, most of the time he seems completely oblivious to me unless I touch him or he smells my hand. Auditory cues send him hissing but usually only when he is in his hide.


----------



## Evil_Birdy (Jul 20, 2016)

BredliFreak said:


> Not to mention they have a third eye/ocelli on the top of their head. Ever wondered why they are so hard to photograph or catch? They can see you from a mile away!



I thought it was only tuataras that had a third eye, which is part of what separates them from Squamata (aka lizards). Even then it is covered with skin and used (we think) to set sleep and seasonal patterns. This is just what I can remember from my biology textbook. 

Smittiferous sorry I have no idea what might be wrong with your mertens, all I can suggest is that if you think it is serious enough and if it concerns you, take him to an exotics vet.


----------



## BredliFreak (Jul 20, 2016)

Evil_Birdy said:


> I thought it was only tuataras that had a third eye, which is part of what separates them from Squamata (aka lizards). Even then it is covered with skin and used (we think) to set sleep and seasonal patterns. This is just what I can remember from my biology textbook.
> 
> Smittiferous sorry I have no idea what might be wrong with your mertens, all I can suggest is that if you think it is serious enough and if it concerns you, take him to an exotics vet.



Nope, iguanas, skinks and monitors all have them. I think beardies might too but I'm no dragon expert. Have a look at your ackies head (or blueys if you have one) and you might see it, but it can be hard to spot.


----------



## Stompsy (Jul 20, 2016)

I believe Bearded Dragons also have them as I remember reading about it a few months ago. 


Sent from my iPhone using Tapatalk


----------



## GBWhite (Jul 20, 2016)

Hi Smittiferous,

As Jamie has alluded monitors have excellent eye sight.

I've done a little digging around and from what you describe and from the photo I'd be inclined to believe that your lizard is blind or at least suffering from presbyopia, which is difficulty in seeing things up close.

I think you might be spot on with your suspicion regarding coloboma of the iris. The black notch at the bottom of the iris is a good indicator of the condition. It can be congenital and can be inherited or a result of environmental conditions during incubation.

All the same if it's feeding well and appears in good condition I can't see it having a serious long term effect on its health.

Cheers,

George.


----------



## pinefamily (Jul 20, 2016)

Beardies definitely have the "third eye".

It's odd your Mertens only hisses at sounds when he's in his hide.


----------



## Evil_Birdy (Jul 20, 2016)

BredliFreak said:


> Nope, iguanas, skinks and monitors all have them. I think beardies might too but I'm no dragon expert. Have a look at your ackies head (or blueys if you have one) and you might see it, but it can be hard to spot.


Very, very interesting. I'm definitely going to have a look, although my ackies head is about the size of my thumbnail, so I'm not sure if I'll have any luck. I do indeed have a blue tongue, who is sizeably larger and will probably have something more visible. I have never noticed it before, although I have never even looked. What am I even looking for? Is it just like a small bump?


----------



## GBWhite (Jul 20, 2016)

BredliFreak said:


> Not to mention they have a third eye/ocelli on the top of their head. Ever wondered why they are so hard to photograph or catch? They can see you from a mile away!



Hi BF,

It's actually referred to as a parietal eye in reptiles. It is also present in amphibians and some species of fish. It is not used for vision it is basically a patch of light sensitive cells that are used as a compass to calibrate the sun and assist with thermoregulation. It is also believed to assist with the absorption of UV as well as determining light/dark cycles (photoperiod).

In Tuatara the parietal eye does have a cornea, lens and retina and is connected to the brain by a degenerated nerve, again it is not used for visual identification. It is visible in hatchlings but is covered by scales after a few months. 

George


----------



## BredliFreak (Jul 20, 2016)

well in blueys there should be an indentation on one of their head scales and you should see a dot but ackies are harder, I haven't held one in a while but I remember it kind of looking like the selfie camera on an iPhone/iPad


----------



## Smittiferous (Jul 20, 2016)

[MENTION=39076]GBWhite[/MENTION] He has no issue feeding, I don't believe he has ever refused one. I am one hundred percent certain I have never seen his eyes adjust their focus, ever. He moves his eyeballs around, but doesn't appear to alter his focus on whatever direction he's "looking". Sometimes (as in the example I cited earlier, with him attempting to continue climbing into thin air) he acts well, blind, but he doesn't seem to have any apparent difficulty navigating in general, and by saying that I mean I've never seen him walk into anything, and he swims/crawls around objects. I guess it's possible he may be using his tongue (whether inadvertently or deliberately, which I guess would be kind of interesting and cool) as a kind of blind cane. He seems to be able to navigate up my arm without issue, for example. 

I have an appointment booked for him with Shane Simpson tomorrow night, see what he says regarding it. It'd be good to get a definitive answer if possible. 

I'm curious, could this deformity in his eyes make his eyesight more sensitive or susceptible to damage from intense light? I have contacted the person I got him from, who expressed surprise when I told him about this. Reckons the little guy didn't exhibit anything like this, would hunt fish from his water trough and generally acted like a normal monitor. Could it be that once he was transferred into an enclosure with spot lamps and a compact UV (as opposed to a fluorescent tube and simple radiant heat) that the more intense lighting did damage?


----------



## BredliFreak (Jul 21, 2016)

GBWhite said:


> Hi BF,
> 
> It's actually referred to as a parietal eye in reptiles. It is also present in amphibians and some species of fish. It is not used for vision it is basically a patch of light sensitive cells that are used as a compass to calibrate the sun and assist with thermoregulation. It is also believed to assist with the absorption of UV as well as determining light/dark cycles (photoperiod).
> 
> ...



Yes,that was the one I was talking about, never knew what it was called though so I called it an ocelli (invert term for basic light-sensing eye). I didn't know it could assist with UV absorption though. You learn something new everyday.


----------



## Sheldoncooper (Jul 21, 2016)

Smittiferous said:


> [MENTION=39076]GBWhite[/MENTION] He has no issue feeding, I don't believe he has ever refused one. I am one hundred percent certain I have never seen his eyes adjust their focus, ever. He moves his eyeballs around, but doesn't appear to alter his focus on whatever direction he's "looking". Sometimes (as in the example I cited earlier, with him attempting to continue climbing into thin air) he acts well, blind, but he doesn't seem to have any apparent difficulty navigating in general, and by saying that I mean I've never seen him walk into anything, and he swims/crawls around objects. I guess it's possible he may be using his tongue (whether inadvertently or deliberately, which I guess would be kind of interesting and cool) as a kind of blind cane. He seems to be able to navigate up my arm without issue, for example.
> 
> I have an appointment booked for him with Shane Simpson tomorrow night, see what he says regarding it. It'd be good to get a definitive answer if possible.
> 
> I'm curious, could this deformity in his eyes make his eyesight more sensitive or susceptible to damage from intense light? I have contacted the person I got him from, who expressed surprise when I told him about this. Reckons the little guy didn't exhibit anything like this, would hunt fish from his water trough and generally acted like a normal monitor. Could it be that once he was transferred into an enclosure with spot lamps and a compact UV (as opposed to a fluorescent tube and simple radiant heat) that the more intense lighting did damage?



I wouldn't think it would be a light issue. If u hold him in a dark room and shine a torch in front of him u should see his eyes dialate.

- - - Updated - - -

I think lighting would only be an issue if the lights were heating from a side angle and not from above


----------



## pinefamily (Jul 21, 2016)

So what did Shane Simpson say about your Mertens eyesight Smittiferous?


----------



## Smittiferous (Jul 21, 2016)

Shane's verdict is, he's blind as a bat. Otherwise perfectly healthy and surprisingly calm for an animal who cannot see what's around him. It was also the first case of coloboma he's seen in a monitor. CBDs apparently present with this relatively frequently, but he'd never seen one in a monitor ever until this evening.


----------



## Sheldoncooper (Jul 22, 2016)

Smittiferous said:


> Shane's verdict is, he's blind as a bat. Otherwise perfectly healthy and surprisingly calm for an animal who cannot see what's around him. It was also the first case of coloboma he's seen in a monitor. CBDs apparently present with this relatively frequently, but he'd never seen one in a monitor ever until this evening.



Does it mean its been blind since birth. Hence u were lied to


----------



## Smittiferous (Jul 22, 2016)

Sheldoncooper said:


> Does it mean its been blind since birth. Hence u were lied to



Most likely blind since birth, but a very small chance he had some vision but it has completely deteriorated by now. 

As for being lied to... That's an uncomfortable possibility. I explained this to Shane, and he suggested that due to being kept in a much smaller enclosure with much less going on (filter pump, spray bar etc which is in his current one) he may have been easily able to use auditory and/or olfactory cues to hunt feeder fish, or that any vision he had may not have completely deteriorated at this time. Also I highly doubt he'd have even remotely close to the amount of attention paid to him, it's possible that simply nobody noticed. He does navigate his enclosure perfectly fine... You really have to pay close attention to notice anything is irregular. 

Either way, he's blind, he's in my care and I have no interest in moving this special case on to another home just because he can't see. If anything it sort of makes him even more unique to me... Not every day you meet a blind monitor after all.


----------



## pinefamily (Jul 22, 2016)

Exactly that. We have reptiles we have bought, knowing there were toes or tail tips missing. But picked them because of colouring or marking or whatever reason at the time. Our leatherback beardie has the tiny end of his tail missing, but when I put my hand into the enclosure, he was the only one to climb onto my hand. So of course he came home with us.


----------



## inkarnate (Jul 23, 2016)

Mine has rediculous vision. I can have the door only open a few cm and peering in and he'll stop what he's doing and watch me.


----------

