Cataract Surgery After LASIK: the Issues
If you have a history of LASIK and are now preparing for cataract surgery, you should be aware of how prior LASIK interacts with cataract surgery. Understanding how LASIK affects cataract surgery will allow you make informed decisions about your refractive goals, and correctly set your expectations.
The post-LASIK cornea is different than the natural cornea in a two important ways. LASIK for nearsightedness makes the curvature of the central cornea less steep than it was before. Rather than the smooth parabolic curve of the natural cornea, the post-LASIK cornea has more of a box shape. It is steeper in the periphery and flatter centrally.
This has a number of consequences.
1. The cornea is still nearsighted in the periphery, where the LASIK did not take place.
This can become evident to you as glare and halos that are more prominent when your pupil is dilated, for example in the dark.
2. Dry eye may be a bigger issue for you.
Your tear film does not protect the cornea as well as it did before LASIK. The interaction of the inner eyelid to the anterior cornea is slightly altered; the tear film breaks up a little faster. Some of the corneal nerves that tell the eye to make tears were cut during LASIK and may not have completely regenerated. Add to this the fact that cataract surgery itself will mildly stress the cornea, and the postoperative drops have the side effect of causing dry eye. Postmenopausal women are especially prone to dry eye.
3. Your refraction may take longer to stabilize after cataract surgery.
LASIK made the cornea flatter centrally by shaving tissue away. Your cornea is thinner than it was before LASIK. Imagine a balloon that is slightly thinner in one place. When you squeeze the balloon, this area may stick out a bit- it behaves differently than the rest of the balloon. Similarly, the thin post-LASIK cornea may undergo small fluctuations for an extended period of time after cataract surgery, causing the focus of the eye to shift. Post-LASIK patients can require two to three months before their vision stabilizes after cataract surgery. Patients who have not had LASIK may experience stable vision within a week or two of surgery.
4. LASIK makes it harder to predict where your eye is going to focus after cataract surgery.
Current technology allows surgeons to accurately predict the focus of the eye after cataract surgery. If you have had prior LASIK, where your eye focuses after cataract surgery is less predictable. There are two reasons for this. First, the flat post-LASIK central cornea is mathematically more complex than the natural cornea. Even modern corneal topographers have a difficult time predicting the total refractive power of the more complex post LASIK cornea. Second, the thinner post LASIK cornea may settle after cataract surgery into a slightly different curvature than predicted before surgery, resulting in a focus that is closer in or further out than you desired.
5. LASIK makes it harder to predict how much surgery will improve your vision. Some of the side effects of LASIK- glare, halos, and loss of contrast- are identical to some of the symptoms of cataract. It can be hard for your surgeon to tell you if these symptoms are coming from your cataract, or from LASIK. Side effects of LASIK will not be improved by cataract surgery.
What can you do about this? Plenty. Read the post “Cataract Surgery After LASIK: the Solutions."
