November 7, 2021 | Lasik

What Causes Blood In Eye After Lasik?

By Barrett Eubanks, M.D.

What Causes Blood In Eye After Lasik?

Most people after lasik have clear vision but also nice clear white eyes. But there are some people that can have bleeding or blood in the eye after lasik. Did something go wrong with the lasik procedure? This bleeding is also called a subconjunctival hemorrhage and fortunately it doesn't cause any issues after lasik. But let's see where it comes from, how it heals and what can be done about it.

Let's start at the conjunctiva

The white part of the eye contains two principal layers. The bottom layer is the firm structural part of eye, called the sclera and on top of the sclera is a thin flexible layer called the conjunctiva. The sclera is opaque and white. The conjunctiva is actually somewhat transparent. Between the conjunctiva is an empty space (with some fibrous tissue called Tenon's capsule). The conjunctiva can move relatively freely over the surface of the sclera. This free movement allows us to look around with ease without the conjunctiva limiting any movement.

Underneath and within the conjunctiva are tiny little blood vessels. These blood vessels supply red blood cells with nutrients to the conjunctiva and white blood cells to fight off infections. But just like any other blood vessels on the body, these blood vessels can break. When these blood vessels break, the blood spreads out in the empty space between the conjunctiva and the sclera. This is called a subconjunctival hemorrhage (which translates to bleeding below the conjunctiva). This is very similar to a bruise anywhere else on the body, the one key difference on the eye is that the conjunctiva is a transparent structure. Because you can see through the conjunctiva, you can see the bright red blood.

Enter lasik

Lasik for the most part doesn't involve the conjunctiva. The lasik flap is created on the cornea; all the laser energy is applied to the cornea. In general, lasik is a pretty atraumatic process.

The exception is during the step which creates the lasik flap. To create a lasik flap, a femtosecond laser creates sequential microscopic pockets of air in the 3D shape of a flap. In order to ensure that each of these pockets are next to each other, the laser has to make sure the eye doesn't move in the process. The way this is achieved is by actually suctioning onto the surface of the eye. Thus, if the eye moves around, the laser moves around with the eye.

The laser suction ring surrounds the cornea and suctions onto the conjunctiva. As the suction ring squeezes onto the conjunctiva, it can squeeze some of the tiny blood vessels in the conjunctiva. Occasionally this squeezing can cause some of those blood vessels to break and create a subconjunctival hemorrhage; bleeding on the eye. note: sometimes even in a ring pattern from the suction ring.

Are subconjunctival hemorrhages a problem?

While they may look really really bad, subconjunctival hemorrhages don't cause any extra issues with the eye or the healing process after lasik. Similar to how a bruise goes away over time, the same happens to a subconjunctival hemorrhage. It just takes some time to completely go away. The blood and red eye can take upwards of two weeks (and rarely more) for it to disappear. The more bleeding you have, the longer it will take for it to go away. Gradually the blood will break down and be cleaned and recycled out by the blood vessels.

The subconjunctival hemorrhage will NOT affect how your vision heals up from lasik. It will not change the final outcome of your vision or how quickly you heal up. It just affects the short-term look of the eye (but it does give you an opportunity to brag about your lasik when people ask about it).

Can the bleeding be prevented?

Lasik surgeons not only want to get the best possible vision after lasik, they also want to create the best experience possible. Although subconjunctival hemorrhages after lasik are harmless, they just don't look nice; and something that doesn't look nice affects the overall experience after lasik. So many lasik surgeons use some eye drops to attempt to prevent this bleeding as much as possible.

By reducing blood vessels in the conjunctiva, we can reduce the chance that the suction ring squeezes a blood vessel and causes it to pop. While we can't actually remove blood vessels, one thing that we can do is use certain eye drops to cause those blood vessels to constrict. A constricted blood vessel carries much less blood and is stronger and less likely to break from the force of the suction ring. If a constricted blood vessel does break, much less blood will leak out and the body's own clotting mechanism prevents creating a large subconjunctival hemorrhage.

There are a few types of eye drops which can be used to help constrict those subconjunctival blood vessels. These eye drops actually are repurposed from other uses such as treating glaucoma or allergies. It just happens that these eye drops are also a great way to reduce the blood vessels under the conjunctiva. These eye drops aren't perfect, however. A medication powerful enough to cause a lot of blood vessel constriction is also powerful enough to dilate the eye. And we don't want to perform lasik on a dilated eye (the eye tracker built into lasik lasers relies on having a normal undilated eye for the best results). But these eye drops do a pretty good job for most people.

As you get all your eye drops prior to lasik, included in all your sets of drops may more than likely be one of these drops to help prevent blood in the eye after lasik. After-all, even though this bleeding won't cause any issues, it's still nice to have perfectly clear white eyes after lasik.

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