Receiving a pterygium diagnosis from your eye doctor can be alarming, particularly if you weren’t aware of the presence of any such thing before you walked into the clinic. A pterygium is a triangular growth from the white sclera of the eye over the transparent cornea, driven by exposure to UV radiation and irritants like wind and dust. Fortunately, it is benign and not cancerous but it can still cause a few problems if left unattended.

Can a Pterygium Cause Blindness?

Theoretically, a pterygium could cause blindness but on a scale of «you’d have to be astronomically unlucky to experience pterygium-induced blindness» to «imminently sight-threatening», the likelihood falls closer to the former end of the scale.

It may help to first define blindness, because this term is often used quite loosely among the general public. In the medical world, total blindness is defined as having no perception of light – you could be standing on the street in broad daylight and see only darkness. Legal blindness is defined as having vision worse than 20/200 despite optimal correction with glasses or contact lenses (with 20/20 vision being considered the standard of «normal» vision; 20/200 is therefore 10 times worse than normal). Then there is also the concept of vision impairment, which describes poor vision that may or may not reach the definition of legal blindness but is enough to interfere with daily function such as reading or driving.

With these definitions in mind, a pterygium is never going to cause total blindness. It is also extremely unlikely – especially in Western society – that it will even cause legal blindness or any form of permanent visual impairment. In developing nations with limited access to ophthalmology care, there may be a higher chance of a pterygium progressing to the stage of causing severe interference with vision, but in the USA we are fortunate to have the option of undertaking pterygium surgery before it even gets close to that point. This is not to say, however, that a pterygium can’t mess with your vision.

How Does Pterygium Affect Vision?

The cornea is the transparent dome of tissue over the colored iris. It’s transparent for a reason, namely for light to pass through freely. But then comes along a pterygium, a decidedly non-transparent, fleshy growth of tissue with bright red blood vessels, creeping over the cornea.

An early or small pterygium won’t cause any visual disturbances. In fact, you may not have realized you have a pterygium at all (cue close inspection in the mirror). However, as a pterygium progresses, becoming thicker or approaching the center of your cornea, it may start to cause some vision problems.

Astigmatism

Astigmatism is a form of refractive error. In most cases, it develops from an irregular cornea, even without a pterygium. As light passes through the curved cornea, it bends (or refracts). But if the cornea doesn’t have a uniform curve across its surface, some light rays will bend more than others. If these light rays don’t come to a sharp focused point on the retina, you will perceive that as blur.

Other symptoms of astigmatism can include:

Difficulty driving at night because oncoming car headlights or streetlamps appear smeared out or streaky
Slanting or distortion of lines and edges that should be straight
Eyestrain and headaches with reading

A pterygium is known to induce astigmatism by disturbing the curvature of the cornea. Sometimes this can be corrected with eyeglasses but the degree of astigmatism may change as the pterygium progresses.

Dry Eye and Irritation

The tear film is a microscopic layer of water, lipids, mucins, immune system components, and other substances that covers the surface of the eyeball. Any disruption to this tear film – short evaporation time, increased osmolarity (salt content), thin lipid layer, poor spreading across the surface of the eye with each blink – can lead to dry eye disease, inflammation, and irritation.

A pterygium is a disruption to the smooth surface of the cornea. It doesn’t have to be huge and thick, but the fact that it is there is already a disturbance, which can destabilize the tear film and contribute to inflammation. Not all pterygia will cause dry eye issues, but as we learnt in July for National Dry Eye Awareness Month, pterygium and dry eye are linked. Even if you don’t identify your eyes as feeling dry per se, dry eye disease symptoms also include:

Blurry vision that fluctuates with blinking
Stinging, burning
A gritty sensation of something being stuck in your eye
Red eyes
Paradoxically, watering, as your dry eyes overcompensate with tear production

Blurry Vision

If the pterygium is allowed to grow so far over the cornea that it covers the pupil, we have a problem. The pupil is the hole in the center of your iris, and is the little portal where light passes through to reach the retina at the very back of the eyeball. If this hole is covered by something opaque like a pterygium, naturally, light cannot get through very well. The extent and exact area of pupil that the pterygium covers will determine how much your vision is impacted.

As mentioned earlier, it is highly unlikely for a pterygium to get to this point, at least among developed nations such as the US. The vast majority of pterygia will have been managed through pterygium surgery before its triangular point can creep over the pupil.

So, can a pterygium cause complete blindness? No. Can it still upset your vision somehow? Yes. Can you do something about it if it bothers you? Certainly – that’s what pterygium surgery is all about, and you can read more about modern pterygium surgery with conjunctival autografting here.