Question about corneal haze

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Question about corneal haze

Postby Kean » Tue Nov 14, 2006 10:19 pm

I have been trying to understand why haze would form in surface ablation and I still have a lot of questions. For instance

1. LASIK trick our system that our eyes are not injured, thus pretty much eliminated chances of corneal haze. Surface ablation like PRK could cause haze because our system knows that our eyes have been scarred/injured/operated, and haze could form through the healing process. Epi-Lasik creates a thin epithelium flap which was repositioned after photo-ablation. I don't understand why didn't this tricked the system that the eyes are not scared/injured/operated as in Lasik?

2. Tying back to the above question, why is it that surface ablation has a higher risk of haze for eyes with prescription higher than 6.0D? I ask because Lasik does not have corneal haze problem especially for eyes > 6.0D. Both methods ablate the same about of cornea tissue, the difference seems to be the depth of which the ablation happens. If Epi-Lasik has a higher risk for corneal haze for eyes > 6.0D because it ablates deeper, then it does not make much sense since Lasik ablates even deeper than Epi-Lasik. If someone could explain, that will be great.

3. Can someone translate this in layman's term?
"In animal models, it has been shown that this process is probably initiated by keratocyte apoptosis and the subsequent over-proliferation of cells. Collagen type IV alpha 3 is also an important factor in the development of corneal haze after PRK. Mitomycin-C is an antibiotic with anti-metabolite effects that inhibit the proliferation of keratocytes, but it has no effect on normal epithelial cells of the cornea."

3a. Is Cytokines one of the Collagen type IV alpha 3 mentioned above?

Is it true that haze was form when cytokines perform the healing in our eyes?

4. Vitamin C helps reduce chance of corneal haze. Does anyone know of a published paper/study/link available on the net that I can read? Or do you know the success rate of correlating supplemental Vitamin C to corneal haze reduction? Thanks.

5. I have also read that prescribed topical steroids post-op, three times per day for one month seemed to work very well. Is this a common practice? If not, do you know what's the name of the topical steroid?

6a. Mitomycin C (MMC) to control haze, could someone list the advantages and disadvantages? MMC seems to be toxic, but at that diluted level of 0.02, it is safe right?

6b. I have read using MMC post-operation for patient with corneal haze. Initially I thought there's no option for corneal haze post operation, but seems like MMC is an option right? One study that I read says MMC is safe (without adverse effects) and quite effective (85% though in low population study) in treating eyes with severe corneal haze after surgery.

6c. MMC for high myopia patient intra-operation. In one study of 28 patients with high myopia and PRK, all patients didn't have haze problem 6 months after surgery (though haze did appear initially 1mth and 3mths after surgery). In another study, all 40 patients didn't have haze after PRK with MMC intra-operation, compared to non MCC PRK with lots of haze problem. So with high myopia, seems like MMC with surface ablation
technique is the way to go. Comments especially if you know of any bad reasons why that should not will be great.

7. Ultraviolet (UV). I've also read that if eyes are not exposed to UV, it reduces the chance of developing corneal haze. Anyone have seen a link with study done on this? I don't mind covering one side of my eyes for 3-5 days if it helps. Comments are very welcomed.

Sorry for the all these questions. If anyone can provide info even to one of the question, please do so. I appreciate any info that you are willing to share. Also thanks for this site to allow us to discuss or ask questions. Thanks so much!
Kean
 
Posts: 10
Joined: Thu Nov 09, 2006 10:14 pm

Re: Question about corneal haze

Postby LasikExpert » Wed Nov 15, 2006 4:18 am

Kean wrote:1. LASIK trick our system that our eyes are not injured, thus pretty much eliminated chances of corneal haze. Surface ablation like PRK could cause haze because our system knows that our eyes have been scarred/injured/operated, and haze could form through the healing process. Epi-Lasik creates a thin epithelium flap which was repositioned after photo-ablation. I don't understand why didn't this tricked the system that the eyes are not scared/injured/operated as in Lasik?


PRK, LASEK, and Epi-Lasik all mortally wound the epithelium. If the epithelium is removed, a wound response will transpire. If the epithelium is not removed and the Lasik flap and laser ablation is below Bowman’s layer, then the wound response is muted.

Kean wrote:2. Tying back to the above question, why is it that surface ablation has a higher risk of haze for eyes with prescription higher than 6.0D? I ask because Lasik does not have corneal haze problem especially for eyes > 6.0D. Both methods ablate the same about of cornea tissue, the difference seems to be the depth of which the ablation happens. If Epi-Lasik has a higher risk for corneal haze for eyes > 6.0D because it ablates deeper, then it does not make much sense since Lasik ablates even deeper than Epi-Lasik. If someone could explain, that will be great.


Many studies have shown that LASEK and Epi-Lasik have the same wound response as PRK. The risk of corneal haze is virtually the same for all surface ablation techniques. Since corneal haze is related to the amount of tissue removed at the surface, surface ablation for more than about 6.00 diopters of correction (or more accurately, more than about 75 microns of tissue removal) has an elevated risk of haze.

Kean wrote:3. Can someone translate this in layman's term?
"In animal models, it has been shown that this process is probably initiated by keratocyte apoptosis and the subsequent over-proliferation of cells. Collagen type IV alpha 3 is also an important factor in the development of corneal haze after PRK. Mitomycin-C is an antibiotic with anti-metabolite effects that inhibit the proliferation of keratocytes, but it has no effect on normal epithelial cells of the cornea."


Laser ablation causes a wound response. The greater the wound, the greater the response. At a certain point, the death and replacement of cells is no longer one-to-one and an excess of cells create the opacities that we call haze. Mitomycin C mutes the wound response pharmacologically.

Kean wrote:3a. Is Cytokines one of the Collagen type IV alpha 3 mentioned above?

Is it true that haze was form when cytokines perform the healing in our eyes?


I’ll leave that one to the scientists.

Kean wrote:4. Vitamin C helps reduce chance of corneal haze. Does anyone know of a published paper/study/link available on the net that I can read? Or do you know the success rate of correlating supplemental Vitamin C to corneal haze reduction? Thanks.


Journal of Refract Surgery, 2003 May-Jun;19(3):338-43. Ascorbate prophylaxis for corneal haze after photorefractive keratectomy, Stojanovic A, Ringvold A, Nitter T.,
Eye Department, University Hospital of North Norway, University of Tromso, SynsLaser Clinic, Tromso, Trondheim, Norway

Kean wrote:5. I have also read that prescribed topical steroids post-op, three times per day for one month seemed to work very well. Is this a common practice? If not, do you know what's the name of the topical steroid?


The use of topical steroids after ocular surgery is common. There are several different manufacturers of topical steroids and each doctor seems to have his or her own preference, depending upon the circumstances.

Kean wrote:6a. Mitomycin C (MMC) to control haze, could someone list the advantages and disadvantages? MMC seems to be toxic, but at that diluted level of 0.02, it is safe right?


At a recent ophthalmology convention several studies were presented on the long term effects of MMC. The study included MMC 0.02 applied for up to two minutes without deleterious long term effects. Today, MMC 0.02 for 12-20 seconds is considered adequate.

Kean wrote:6b. I have read using MMC post-operation for patient with corneal haze. Initially I thought there's no option for corneal haze post operation, but seems like MMC is an option right? One study that I read says MMC is safe (without adverse effects) and quite effective (85% though in low population study) in treating eyes with severe corneal haze after surgery.


MMC is an option for treatment of corneal haze. Removal of hazed tissue with an eximer laser is another option, but is only appropriate if the haze is limited to the anterior surface of the cornea.

MMC has been used as an anti-scaring treatment in cosmetic surgery for many years.

Kean wrote:6c. MMC for high myopia patient intra-operation. In one study of 28 patients with high myopia and PRK, all patients didn't have haze problem 6 months after surgery (though haze did appear initially 1mth and 3mths after surgery). In another study, all 40 patients didn't have haze after PRK with MMC intra-operation, compared to non MCC PRK with lots of haze problem. So with high myopia, seems like MMC with surface ablation technique is the way to go. Comments especially if you know of any bad reasons why that should not will be great.


Many doctors have moved from Lasik and IntraLasik to surface ablation techniques because the final outcome has been shown to be better with surface ablation. MMC is used only as required. Vitamin C is an excellent method to reduce the probability of corneal haze with little risk of adverse effect.

Kean wrote:7. Ultraviolet (UV). I've also read that if eyes are not exposed to UV, it reduces the chance of developing corneal haze. Anyone have seen a link with study done on this? I don't mind covering one side of my eyes for 3-5 days if it helps. Comments are very welcomed.


The study cited above references 100% UVA and UVB protection after surface ablation surgery. This is a good practice with or without surgery.
Glenn Hagele
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Thanks very much again Glenn.

Postby Kean » Wed Nov 15, 2006 8:49 pm

Glenn, thanks very much for your time in responding all of my questions. Now I know so much more about corneal haze than I eved had. I would have gone for Epi-Lasik with MMC, however, my large pupil size makes me a bad candidate for any refractory surgery as you've mentioned. Though that was a checkup 5 years ago, I'll do another one to find out once and for all. Again, I sincerely appreciate your time in helping me to understand corneal haze related to surface ablation surgery.
Kean
 
Posts: 10
Joined: Thu Nov 09, 2006 10:14 pm

Postby LasikExpert » Thu Nov 16, 2006 7:15 pm

A tremendous amount of refractive surgery technology and technique has been changed in the last five years. You owe it to yourself to be evaluated.
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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