Blurred Vision Due To Blood Glucose Level

[Mr_Pot]

Blurred vision is a common symptom of changes in blood glucose level. As I understand it the lens is changed in focal length by a minute change in the curvature of the eyeball. It takes some time, maybe a few weeks, for the brain to adjust to focussing with a new power of lens. The part I don't understand, despite research, is how the glucose level affects the shape of the eyeball. Most explanations gloss over this although there is some mention of osmosis, which seems reasonable, but how does water flow into the eye and where from? Perhaps @Dark Horse or someone else has knowledge of how it works.

 

[Jaylee]

Blurred vision is a common symptom of changes in blood glucose level. As I understand it the lens is changed in focal length by a minute change in the curvature of the eyeball. It takes some time, maybe a few weeks, for the brain to adjust to focussing with a new power of lens. The part I don't understand, despite research, is how the glucose level affects the shape of the eyeball. Most explanations gloss over this although there is some mention of osmosis, which seems reasonable, but how does water flow into the eye and where from? Perhaps @Dark Horse or someone else has knowledge of how it works.

Hi,

It's not the shape as i understand..? More like distortion or changing light refraction due sugar manifesting & causing a "coating" in lubricating moisture on the lens?? (At a rough guess. Don't shoot me.)

I'm glad you tagged in @Dark Horse

 

[In Response]

It was explained to me as sugar in tears having a different focal length to salty tears and the lens adjusting shape for the different focal length

 

[Mr_Pot]

It was explained to me as sugar in tears having a different focal length to salty tears and the lense adjusting shape for the different focal length

I don't think that sounds plausible. Tears are a very thin film of even thickness so wouldn't have a focal length, like looking through the glass of a window.

 

[sgm14]

but how does water flow into the eye and where from

Are you sure it is water? I'm not an expert, but I understood that one of the causes was damage to the tiny blood vessels which meant that there was leakage into the eye fluid and I assumed that leakage was blood which contained lots of glucose.

Also, I think that there is not just one single issue.

The way it was explained to me (by my optician who was probably dumbing it down for me) was that the sugar molecules are quite large and too many of them cause damage to the very tiny blood vessels in the eye and so blood and glucose leaked into the central eye fluid . The high glucose level changed the refractive index of my eye fluid which caused initial blurriness. Then as more glucose molecules entered the eye, some got stuck at the back/edges of my eye and when my blood sugars started to decline these gradually detached from the edges and moved back into the eye fluid causing things to get even worse for a short time until the glucose was drained away and my vision went back to normal.

What you mention, is I think another later stage - where more and and more blood vessels get damaged and can't drain the excess fluid and the centre of the eye begins to swell. (I don't think I was affected by this and this wasn't mentioned to me by my optician, so is my own description.)

 

[Mr_Pot]

Are you sure it is water? I'm not an expert, but I understood that one of the causes was damage to the tiny blood vessels which meant that there was leakage into the eye fluid and I assumed that leakage was blood which contained lots of glucose.

Also, I think that there is not just one single issue.

The way it was explained to me (by my optician who was probably dumbing it down for me) was that the sugar molecules are quite large and too many of them cause damage to the very tiny blood vessels in the eye and so blood and glucose leaked into the central eye fluid . The high glucose level changed the refractive index of my eye fluid which caused initial blurriness. Then as more glucose molecules entered the eye, some got stuck at the back/edges of my eye and when my blood sugars started to decline these gradually detached from the edges and moved back into the eye fluid causing things to get even worse for a short time until the glucose was drained away and my vision went back to normal.

What you mention, is I think another later stage - where more and and more blood vessels get damaged and can't drain the excess fluid and the centre of the eye begins to swell. (I don't think I was affected by this and this wasn't mentioned to me by my optician, so is my own description.)

What I was referring to was the temporary blurred vision which occurs in many people when their blood sugar changes, typically when they start on a low carb diet. I believe this is concerned with the lens at the front of the eye. What you are describing is retinopathy which is damage to the retina at the back of the eye and involves the tiny blood vessels as you say. The temporary blurred vision can occur without retinopathy so I think it is a separate thing.

ETA: Also, if it was blood that leaked into the fluid in the eye wouldn't there be a pink cast to your vision?

 

[JoKalsbeek]

Blurred vision is a common symptom of changes in blood glucose level. As I understand it the lens is changed in focal length by a minute change in the curvature of the eyeball. It takes some time, maybe a few weeks, for the brain to adjust to focussing with a new power of lens. The part I don't understand, despite research, is how the glucose level affects the shape of the eyeball. Most explanations gloss over this although there is some mention of osmosis, which seems reasonable, but how does water flow into the eye and where from? Perhaps @Dark Horse or someone else has knowledge of how it works.

https://www.optometrists.org/genera...e-eyes/why-does-diabetes-cause-blurry-vision/ Does this help? (US site, so their numbers)


"Hyperglycemia
High blood sugar levels can cause fluid to move in and out of parts of your eye, and can often lead to swelling of the eye’s lens. The lens is responsible for focusing light onto the retina at the back of your eye.

When the lens swells, the shape of the lens is affected, consequently affecting your ability to see clearly.

When blurry vision is a result of hyperglycemia, clear vision will typically return when blood sugar levels fall within a normal range— usually between 70-130 mg/dL before meals, and less than 180 mg/dL one to two hours after meals."

 

[Mr_Pot]

High blood sugar levels can cause fluid to move in and out of parts of your eye, and can often lead to swelling of the eye’s lens.

This is a typical explanation but they never seem to be more specific. In and out of which parts of the eye? What fluid? Where does it come from?

 

[JoKalsbeek]

This is a typical explanation but they never seem to be more specific. In and out of which parts of the eye? What fluid? Where does it come from?

I'd guess the same sort of fluid that fills a busted knee, but don't pin me down on that, it's just an assumption.

 

[Jaylee]

This is a typical explanation but they never seem to be more specific. In and out of which parts of the eye? What fluid? Where does it come from?

To some degree, the principle kinda reminds me of "screenwash" on a car. The eyelids loosely being like the wipers..

I found this.. which may help? https://www.otsuka.co.jp/en/health-and-illness/dry-eye/functions-of-tears/

 

[Mr_Pot]

One thing I have discovered which might have a bearing on it, is that 70% of the focusing of the eye is done by the cornea and 30% by the lens. The lens and the main part of the eyeball seem to be sealed but the cornea is continuously filled with fluid (the aqueous humor) by the ciliary body behind it.
I would still like to find out how this works from someone who really knows but I think it is more likely to be happening in the cornea. At least the cornea has fluid flowing into it, which no doubt contains glucose and if that changed its shape for some reason it would certainly change focus.
Incidentally I also found out that the cornea is responsible for short sightedness, long sightedness and astigmatism. Presbyopia, the need for reading glasses after the age of 45 or so, is due to hardening of the lens.

 

[Dark Horse]

Blurred vision is a common symptom of changes in blood glucose level. As I understand it the lens is changed in focal length by a minute change in the curvature of the eyeball. It takes some time, maybe a few weeks, for the brain to adjust to focussing with a new power of lens. The part I don't understand, despite research, is how the glucose level affects the shape of the eyeball. Most explanations gloss over this although there is some mention of osmosis, which seems reasonable, but how does water flow into the eye and where from? Perhaps @Dark Horse or someone else has knowledge of how it works.

It's not the brain adjusting to a different focus, it's actual changes in the focussing power of the eye which can take a few weeks to stabilise after blood glusoce levels have been normalised.

The real answer to the question 'how do changes in blood glucose cause changes in the focussing of the eye' is that nobody really knows. There are a number of theories which are discussed in this paper:- https://www.researchgate.net/publication/277799230_Refractive_Error_Changes_in_Diabetes_Mellitus

Water enters the eye in the form of aqueous humour which is produced by the ciliary body (basically by extracting it from blood) and leaves via Schlemm's canal. https://www.allaboutvision.com/eye-care/eye-anatomy/aqueous-humor/

 

[Mr_Pot]

It's not the brain adjusting to a different focus, it's actual changes in the focussing power of the eye which can take a few weeks to stabilise after blood glusoce levels have been normalised.

The real answer to the question 'how do changes in blood glucose cause changes in the focussing of the eye' is that nobody really knows. There are a number of theories which are discussed in this paper:- https://www.researchgate.net/publication/277799230_Refractive_Error_Changes_in_Diabetes_Mellitus

Water enters the eye in the form of aqueous humour which is produced by the ciliary body (basically by extracting it from blood) and leaves via Schlemm's canal. https://www.allaboutvision.com/eye-care/eye-anatomy/aqueous-humor/

Thanks for the very useful references, I will study them later. At least I seem to be right about the aqueous humour being involved. As for the brain adjusting, I have "known" that for a long time so I will try to find out where I got that from. I don't know what other mechanism could be involved in adjusting apart from the brain. I have heard that babies adjust to the image being inverted on the retina but that may not be correct either.

 

[Dark Horse]

Thanks for the very useful references, I will study them later. At least I seem to be right about the aqueous humour being involved. As for the brain adjusting, I have "known" that for a long time so I will try to find out where I got that from. I don't know what other mechanism could be involved in adjusting apart from the brain. I have heard that babies adjust to the image being inverted on the retina but that may not be correct either.

It is true that images on the retina are inverted and the brain adjusts to seeing them the right way up. People can be given inverting spectacles where images appear upside down but if they wear them for long enough, the brain adjusts and flips them so images appear the right way up. Then when they take the spectacles off, they will see the images as upside down, as they really are. https://www.theguardian.com/education/2012/nov/12/improbable-research-seeing-upside-down

Yes, I would be interested to see your link but my thoughts are that if the brain could adjust to a different focus, we would never need glasses.

 

[Mr_Pot]

It is true that images on the retina are inverted and the brain adjusts to seeing them the right way up. People can be given inverting spectacles where images appear upside down but if they wear them for long enough, the brain adjusts and flips them so images appear the right way up. Then when they take the spectacles off, they will see the images as upside down, as they really are. https://www.theguardian.com/education/2012/nov/12/improbable-research-seeing-upside-down

Yes, I would be interested to see your link but my thoughts are that if the brain could adjust to a different focus, we would never need glasses.

It seems the theory that the brain adapts (neuroadaption) is well studied as it is critical in cataract surgery where the lens is replaced with an artificial one. You may find the attached article interesting which contains this paragraph..
What about a reshaped cornea? Corneal refractive corrections also require some neuroadaptation. “There may be aberrations created by the corneal refractive surgery that present the patient with a visual percept not encountered before,” said Dr. Maloney. But, he said, “This neuroadaptation usually is quite rapid, much like adjusting to a new spectacle prescription.” Dr. Kershner noted that most refractive surgery patients can neuroadapt, and young patients adapt quickly.
If the cornea were to be changed, not by surgery but by a change of glucose in the aqueous humour, then no doubt a similar adaption could occur. In my mind the remaining question is why a change in glucose changes the cornea, or possibly the lens. Either the refractive index changes or due to osmosis or something the pressure of the aqueous humour changes. Either way it sounds more plausible than the idea that the whole eyeball is affected.

As to your thought "if the brain could adjust to a different focus, we would never need glasses". I suggest that the adaption by the brain is to know how to control the ciliary muscles. But if only 30% of focussing is done by the lens, then it doesn't have enough range to compensate for big errors in the cornea.

https://www.aao.org/eyenet/article/new-lens-same-brain-importance-of-neuroadaptation

 

[Dark Horse]

It seems the theory that the brain adapts (neuroadaption) is well studied as it is critical in cataract surgery where the lens is replaced with an artificial one. You may find the attached article interesting which contains this paragraph..
What about a reshaped cornea? Corneal refractive corrections also require some neuroadaptation. “There may be aberrations created by the corneal refractive surgery that present the patient with a visual percept not encountered before,” said Dr. Maloney. But, he said, “This neuroadaptation usually is quite rapid, much like adjusting to a new spectacle prescription.” Dr. Kershner noted that most refractive surgery patients can neuroadapt, and young patients adapt quickly.
If the cornea were to be changed, not by surgery but by a change of glucose in the aqueous humour, then no doubt a similar adaption could occur. In my mind the remaining question is why a change in glucose changes the cornea, or possibly the lens. Either the refractive index changes or due to osmosis or something the pressure of the aqueous humour changes. Either way it sounds more plausible than the idea that the whole eyeball is affected.

As to your thought "if the brain could adjust to a different focus, we would never need glasses". I suggest that the adaption by the brain is to know how to control the ciliary muscles. But if only 30% of focussing is done by the lens, then it doesn't have enough range to compensate for big errors in the cornea.

https://www.aao.org/eyenet/article/new-lens-same-brain-importance-of-neuroadaptation

Thanks for the link. As I read it, they are talking about the brain adapting to having both focussed and unfocussed areas on the retina due to the use of multi-focal lenses. I think the adaptation they are talking about is the brain learning to pay attention to the area that is in focus and to ignore the area that is out of focus rather than starting to see out of focus images as being in focus. If an image is unfocussed on the retina, there is a loss of information which the brain can't properly compensate for although it's plausible that someone could get better at interpreting blurred images.

You're right that the cornea is responsible for the majority of refraction of the incoming light (about 2/3rds) and the lens is used to provide accommodation so we can see at both near and far distances. In the old days, cataract surgery involved removal of the lens with no artificial lens to replace it and people who had this became very far-sighted.

Another link you might find interesting is https://webeye.ophth.uiowa.edu/eyeforum/cases/295-refractive-changes-in-diabetes.htm It says:-

• Sudden refractive changes in a diabetic patient are related to changes in osmotic pressure in the lens
• Osmotic changes → swelling or dehydration of the lens → change in the thickness, curvature, and/or refractive index
• Myopic shifts are more commonly reported, but hyperopic shifts have been reported and are thought to be due to changes in refractive index of the lens

The general view is that changes in focussing ability with hypeglycaemia are due to effects on the lens rather than the cornea.

 

[Mr_Pot]

Thanks for the link. As I read it, they are talking about the brain adapting to having both focussed and unfocussed areas on the retina due to the use of multi-focal lenses. I think the adaptation they are talking about is the brain learning to pay attention to the area that is in focus and to ignore the area that is out of focus rather than starting to see out of focus images as being in focus. If an image is unfocussed on the retina, there is a loss of information which the brain can't properly compensate for although it's plausible that someone could get better at interpreting blurred images.

You're right that the cornea is responsible for the majority of refraction of the incoming light (about 2/3rds) and the lens is used to provide accommodation so we can see at both near and far distances. In the old days, cataract surgery involved removal of the lens with no artificial lens to replace it and people who had this became very far-sighted.

Another link you might find interesting is https://webeye.ophth.uiowa.edu/eyeforum/cases/295-refractive-changes-in-diabetes.htm It says:-

• Sudden refractive changes in a diabetic patient are related to changes in osmotic pressure in the lens
• Osmotic changes → swelling or dehydration of the lens → change in the thickness, curvature, and/or refractive index
• Myopic shifts are more commonly reported, but hyperopic shifts have been reported and are thought to be due to changes in refractive index of the lens

The general view is that changes in focussing ability with hypeglycaemia are due to effects on the lens rather than the cornea.

Thanks for the reference. If only all eye exams were that thorough. It seems this is a complex question with, as you said before, a certain amount of "nobody really knows" particularly as the effect can be myopic or hyperopic. It would be interesting to know if post-cataract surgery patients with plastic lenses also exhibit this effect.