Blurred vision in dim light

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Blurred vision in dim light

Postby victor65 » Fri Mar 30, 2007 7:45 am

Dear Doctor Glenn, in the first place I would like to thank you for the precious information you provided to patients who have undergone a delicate operation such as refractive surgery. I am now writing to illustrate my case: on the 12th of December 2006 I underwent Lasik, suffering from myopia (dx: sph. -6.50 cyl. -1.00, sx sph. -7.75 cyl. -1.00). Before the operation, I already used to suffer from a moderate dry-eye syndrome, but after the operation this has worsened remarkably. My eye-specialist has therefore made the decision to insert punctual plugs. Now soreness has diminished, and the visual correction is quite good, in spite of a slight continued astigmatism. However, there still remain visual troubles that are particularly evident in dim light, with blurring and vanishing contours, especially in the case of bright objects. Night vision is very good, without halos or starbursts, comparable to the one I had before the operation, when I used to wear contact lenses. Do you think that my difficulties can be related to dry-eye syndrome or rather to the difference between optical zone (6 millimeter) and max diameter of my enlarged pupil (6,5 millimeter)?
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Postby LasikExpert » Fri Mar 30, 2007 4:18 pm

Thank you for the compliment, but I am not a doctor.

If I understand your situation correctly, at night when your pupils would be at their largest, your vision is "very good, without halos or starbursts". In dim light when your pupils would be somewhat constricted you have "blurring and vanishing contours, especially in the case of bright objects".

It is important to remember that not all light entering the eye reaches inside and is "seen". The iris (colored portion of eye) expands and constricts the pupil, blocking and allowing light to enter the eye. In bright light when the pupil is smallest, light passing through the outer edges of the cornea is blocked. If the outer edge of the cornea is irregular, the irregularity would not produce poor vision quality because light passing through the irregularity would not reach inside the eye.

It your case it would appear that you have an irregularity at the mid-periphery of the cornea. With your pupils moderately dilated, light passing through the mid-periphery irregularity reaches inside the eye and is seen. Because of the size of your pupils and the size of the irregularity, the percentage of light reaching inside the eye that is made irregular is elevated enough to cause a degradation in vision quality. Let's say (just an example) that 20% of the light entering your eye with moderate pupil dilation is irregular. For you, this is enough to produce poor vision.

When your pupils become large, the light from the outer edge of the cornea seems to be well focused. The well focused light in the center with the addition of the well focused light at the edge creates a smaller percentage of irregular light from the mid-periphery. Let's say that with the outer edge of well focused light, the total percentage of irregular light is 5%. For you, this is enough to produce good vision.

This situation could be exasperated if your pupils become oval or decentered with dilation.

Because your vision is improved with full natural dilation, your problem is not because your optical ablation zone is 6.0mm and your pupil size is 6.5mm. Lasik pupil size issues are not that simple in the first place, and your improved vision in very dark environments disproves this assumption.

At three months postop your healing should be progressed, but not completed. If you read our article about Lasik flap healing, you will see that this stage is when the adhesive protein that bonds or "glues" the flap to the underlying bed is being produced. The symptoms you describe may occur if there exists a gap between the flap and the underlying bed. Dry eyes can delay healing, so your stage of flap healing may be a bit behind schedule.

Dry cause their own problems. A dry spot at the mid-periphery is certainly enough to cause the symptoms you describe.

You may have some residual astigmatism or irregular astigmatism. If this irregularity is in the mid-periphery you could have the symptoms you describe.

Least likely, but possible, is that the laser ablation created an area of poor correction in the mid-periphery.

Until the dry eye and healing issues are resolved it will be impossible to know what will be your final outcome. You are more than three months postop, but improvement may continue.
Glenn Hagele
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Postby victor65 » Mon Apr 02, 2007 9:08 am

LasikExpert wrote:Thank you for the compliment, but I am not a doctor.

Well, then we confer you a degree "honoris cause" on the field, for your high skills and professional merits :-)

LasikExpert wrote:If I understand your situation correctly, at night when your pupils would be at their largest, your vision is "very good, without halos or starbursts". In dim light when your pupils would be somewhat constricted you have "blurring and vanishing contours, especially in the case of bright objects".

Right. This problem is more evident in the early morning (just awaken) and when I’m tired, as in the evening.


LasikExpert wrote:… The well focused light in the center with the addition of the well focused light at the edge creates a smaller percentage of irregular light from the mid-periphery. Let's say that with the outer edge of well focused light, the total percentage of irregular light is 5%. For you, this is enough to produce good vision.


First of all I wish to thank you for your articulated and exhaustive answer. If I understood what you mean to say, it is not the absolute quantity of twisted light that reaches the retina to cause a worsening of the visual quality, but rather the percentage of twisted light in relation to the TOTAL quantity of light that, reaching the retina, is "seen". The distortion of the light that enters the eye could be due to different factors: incomplete recovery of the cornea, presence of dry zones on the corneal surface, a residual astigmatism and/or a lack of correction aside of the laser. Is it right?

LasikExpert wrote:Dry cause their own problems. A dry spot at the mid-periphery is certainly enough to cause the symptoms you describe.

If dryness is the cause of blurry vision, is it normal that, as I said above, this trouble exacerbates in the early morning and in the late evening?
Last edited by victor65 on Tue Apr 03, 2007 1:45 pm, edited 1 time in total.
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Postby LasikExpert » Mon Apr 02, 2007 4:46 pm

victor65 wrote:If I understood what you mean to say, it is not the absolute quantity of twisted light that reaches the retina to cause a worsening of the visual quality, but rather the percentage of twisted light in relation to the TOTAL quantity of light that, reaching the retina, is "seen". The distortion of the light that enters the eye could be due to different factors: incomplete recovery of the cornea, presence of dry zones on the corneal surface, a residual astigmatism and/or a lack of correction aside of the laser. Is it right?


Precisely.

Not every ray of light entering the cornea is perfectly focused, even for someone with 20/20 vision. Some are distorted, but the brain learns to "ignore" this data. If too much of the light is distorted, or if the light is suddenly distorted in a new area, the brain may not be able to ignore. At least for a while. Neural adaptation is the process of the brain learning how to deal with poor data and is very important to human vision.

An example of the brain's ability to ignore is the blind spot. We all have a spot without any vision whatsoever, but we don't "see" the blind spot because our brains have learned to ignore it. Neural adaptation at its best.

victor65 wrote:If dryness is the cause of blurry vision, is it normal that, as I said above, this trouble exacerbates in the early morning and in the late evening?


Many people experience greater dry eye symptoms in the morning and late in the day. A variable dry eye problem could be contributing to your difficulties; however there may be another factor. My response above considered only ambient light and pupil size issues. Now we also understand that you have greater symptoms at different times of day and when you are tired or have just awakened.

Accommodation is the process of the natural lens within the eye changing shape to change the focus of the light entering the eye. As we age we are less able to change the shape of the natural lens. This is called presbyopia and is when reading glasses or bifocals are required. Presbyopia is usually not a problem until after around age 40.

If you are at or near age 40, it may be that presbyopia is starting to limit your ability to focus. Perhaps presbyopia’s effects are worse when you first awaken and/or when you are tired.

In addition to the possibility of presbyopia, your eyes now have a very different range of vision to which they must accommodate since you have changed from being about 7.00 diopters myopic to emmetropic. Your eyes may be having a difficult time dealing with this new range. We have a detailed article about Lasik eye strain that you should read.

What is probably happening is a combination of all these issues, dry eyes, accommodation, pupil size, tiny corneal irregularities that individually may not mean much but in the right combination provide the vision symptoms you describe.

BTW, I am a doctor...sort of. I have an honorary doctorate from the University of San Moritz in London. That is an honorary degree from an unaccredited foreign university. I'm as much a doctor as Capt' Crunch is a maritime genius.
Glenn Hagele
Volunteer Executive Director
USAEyes

Lasik Info &
Lasik Doctor Certification

I am not a doctor.
LasikExpert
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Posts: 3309
Joined: Fri May 12, 2006 6:43 am
Location: California

Postby victor65 » Tue Apr 03, 2007 1:49 pm

LasikExpert wrote:What is probably happening is a combination of all these issues, dry eyes, accommodation, pupil size, tiny corneal irregularities that individually may not mean much but in the right combination provide the vision symptoms you describe.


If these are the cases, do you think time will help?
Many thanks.
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Postby LasikExpert » Tue Apr 03, 2007 4:39 pm

Dry eye can be managed and treated. Rigid gas permeable (RGP) contact lenses can help with surface irregularities. Accommodation difficulties often resolve with the eye learning the new range and limitations. Pupils can be artificially constricted with eye drops. The brain may learn how to "look around" minor optic imperfections.

You have many options and all may contribute to an improvement in vision quality. The most likely contributor to improved vision will be continued healing.
Glenn Hagele
Volunteer Executive Director
USAEyes

Lasik Info &
Lasik Doctor Certification

I am not a doctor.
LasikExpert
Site Admin
 
Posts: 3309
Joined: Fri May 12, 2006 6:43 am
Location: California


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