Eye Health Central

Corneal Neovascularisation

The Optician said I had blood vessels growing in my eye!

The Optician said I had blood vessels growing in my eye!

Corneal Neovascularisation

It is not uncommon to be told during a contact lens checkup at your Opticians, that you have 'blood vessels' growing in your eye, caused by excessive contact lens wear. It is a condition called corneal vascularisation.

Despite its prevalence in the contact lens community, chances are you’ve never heard of corneal neovascularisation (CNV). Unfortunately, the first time most contacts-wearers learn about CNV is after they’ve been diagnosed with the condition by their Optometrist. Left untreated, CNV could have disastrous effects on your vision. So, if you wear contact lenses every day, it’s a good idea to learn the warning signs of CNV to be proactive about your eye health.

In this post, we’ll teach you everything you need to know about this potentially blinding disorder. After going over exactly what CNV is, we’ll share a few potential treatment strategies and preventative measures you could discuss with your optometrist.  

What Is Corneal Neovascularisation?

Even if you have no medical training, you might’ve already guessed what CNV refers to by considering its name. As Matrix fans should already know, “neo” refers to “new.” “Vascularisation” thus suggests the “new things” appearing are blood vessels. And since there’s “corneal” in the front of the name, it’s not all that difficult to guess where these new blood vessels are growing!

This condition has been known to Optometrists since the 1920's, when it was first noted in a wearers of large solid contact lenses called scleral lenses. Today is is more commonly found in soft lens wearers.

Since contact lenses cover the corneas, a large chunk of that air supply is reduced during the day. The scientific name for oxygen deprivation in the cornea is known as corneal hypoxia and, if this occurs regularly enough,  it frequently results in CNV. As the corneas start to swell due to a lack of oxygen, they try to pull nutrients from surrounding structures, which results in these new blood vessels. 

Simply put: if your eyes are often red when you wear contact lenses, it’s a clear warning sign your eyes are in distress. Without prompt treatment, CNV could gradually develop and these blood vessels could grow over your pupils and cause partial or complete blindness. This is a condition which ideally needs detection early, and needs active management when detected.

Common CNV Risk Factors

The greatest risk factor for developing CNV is wearing contact lenses for extended periods of time - and especially sleeping overnight in contact lenses that are not designed for this purpose. No matter how long you’re lenses are approved for use, it’s always a good idea to take them out once and awhile to (literally) give your eyes a breather. Obviously, you must always throw away lenses as soon as they’ve passed their expiration date to avoid CNV and other eye conditions. 

Other factors that predispose towards this complication include using dirty or degraded lenses or low water content lenses - especially thick ones and tight lenses which trap debris. 

It’s especially important to take out your lenses before going to sleep every night. Closing your eyelids is bad enough for your corneas, but wearing contact lenses reduces the supply of oxygen significantly while you sleep. People who frequently wear ordinary (non continuous wear) contact lenses to sleep are at a higher risk of developing CNV.

The only contact lenses approved for overnight wear are ortho-k gas permeable lenses and /contact-lenses/continuous-wear. All other contact lenses need to be removed before bedtime.   

Although a lack of oxygen is the primary cause of CNV, sometimes infections, protein deposits, or improperly fitting lenses could trigger this disorder. So, practising good contact lens hygiene and regularly visiting your optometrist is essential for avoiding CNV. 

Improperly fitting lenses could also cause corneal issues, so getting your eyes properly measured every year is a great strategy against CNV. You should also consider wearing UV-protecting sunglasses whenever you’re outside to keep the sun’s rays from harming your corneas.

If you have a bad habit of keeping your contact lenses on while you sleep, then you need to discuss a solution with your optometrist. Typically, the individual will be fitted with silicone lenses, something like 1 Day Acuvue Trueye, which will discourage hypoxic (low oxygen) conditions from arising and so prevent any further vascularization. This particular lens alows virtually 100% of oxygen to be transmitted to your cornea and will often be prescribed, not as an overnight lens, but as a daily wear lens that will help with the condition.

Over time, the vessels can drain of blood and become what are known as 'ghost vessels'. Over several years even these can regress and clear. The condition will need careful management by your Optometrist.

Can I nap in my Contact lenses?

There is no evidence that having a nap in your contact lenses will cause any harm to your eyes. Nevertheless, if you frequently nap with your contact lenses in, it would be a good idea to wear lenses that contain silicone, as these lenses allow a good supply of oxygen to your eyes.

Does CNV Cause Eye Pain? 

A major problem with CNV is that it usually presents no obvious warning signs. While you might experience some eye discomfort and light sensitivity, the warning signs aren’t generally severe and could easily be brushed off as dry eye syndrome. Even if you see the red blood vessels protruding around your eyes, you might mistakenly think your eyes are just bloodshot due to stress. 

Since CNV is so hard to detect in the early stages, it’s crucial for contact lens users to see their optometrist at least once per year for vision checkups. Only an eye specialist can detect the early warning signs of CNV and put you on an actionable treatment plan.


Author: John Dreyer Optometrist Bsc(Hons), MCOPTOM, DipCLP
Created: 24 Apr 2015, Last modified: 10 Feb 2020