DC,MD AND VA LASIK question. Thin Corneas, Large Pupils, LASIK OK?
By Andrew E Holzman, MD FACS on January 27, 2013
Question received. Is it ok to have LASIK with thin corneas and large pupils?
Answer- This question brings up many import ant issues concerning laser vision correction. First and foremost, readers must realize that not everyone is suited for LVC and that we at TLC take the steps of determining your candidacy very seriously. Testing done at our centers in Rockville, Tysons and Charlottesville is state of the art and allows us to determine who should be considered for the procedure. Close to 20% of the patients that we see in our centers are deemed non-candidates, and by being this vigilant and conservative in our approach, it allows us to proceed in a very low risk environment when we are operating on patients deemed excellent candidates.
Having said that, all patients at TLC Tysons, Rockville and Charlottesville undergo testing of their corneal structure with a 3 D pentacam, which images the cornea in multiple views and gives us important information concerning corneal thickness, corneal curvature and strength, and also pupil size. We double check the thickness with an ultrasonic device to make sure that thickness calculation is precise and checked with two independent devices. Pupils are also double checked with a device called the Colvard pupillometer.
Now to answer the question posed, patients need to understand that we practice evidence-based medicine. This means that we use proven techniques that have been proven through peer reviewed studies and have been published in journals. Pupil size was always THOUGHT to be a very important factor in potential for chronic glare in patients. However, over the last decade, multiple studies have shown that is NOT the case. The largest study conducted was done by Dr Schallhorn for the military several years ago. they studied thousands of cases and found that pupil size did not matter in determining the risk of glare. What did matter was the amount of correction attempted, so if the patient has a very high prescription, the risk of glare was higher and vice versa for lower corrections. Pupil size did not matter.
Lets talk about thickness. Many studies have shown that corneal thickness, in and of itself, is not a risk factor for corneal weakness after surgery. This comes as a shock to many Doctors who stick to the belief that no one should have LASIK if the cornea is thinner than 500 microns. However, what is more important is corneal structure and strength, combined with the thickness issue. If a cornea is slightly under 500 microns, let's say 490, and the scans are perfect showing excellent structural integrity, and the prescription of the patient is relatively low, then LASIK is OK! If however the cornea is thin and the patient RX is high, we usually opt for PRK procedures, which are safer and keep us to our conservative guidelines of leaving at least 300 microns of cornea in the corneal bed after surgery.
Technology concerns are also important in this calculation and candidacy question. We use the three best and most recognized lasers in the industry and of course we only employ bladeless , all laser technology. The Intralase laser creates the flap and this is predictable, accurate and allows us to use thin flaps which saves us corneal tissue. This also allows us to treat candidates who may not have been candidates in the past due to the thickness. We then use either the Visx CustomVue or the Wavelight Allegretto laser to fix the vision. Both of these are designed to minimize glare and haloes and to optimize the vision. I look at the aberration maps and determine which of these two excellent devices will optimize the vision for the patient the best. This is a huge advantage for me to have both of these devices as I can truly customize and optimize each and every patient we treat. The Wavelight laser many times will remove less corneal tissue, so we may employ that when we are concerned about thickness issues.
So, LASIK is possible if you have large pupils and thin corneas, BUT it really depends on how thin, what the structural strength of your cornea is, and how high your prescription is. Sometimes we may opt for PRK in this situation and other times the patient is deemed a non-candidate.