We all know about the dangers of the sun’s ultraviolet (UV) radiation, but many of us tend to forget to protect our eyes. Your sun behaviour today will determine your chances of developing eye diseases such as cataracts, cancers and macular degeneration later in life.
Types of UV
The visible light spectrum extends from 380 to 750 nanometres (nm). Invisible UV radiation extends beyond the violet end of the spectrum, in the shorter wavelengths of 100 to 400nm. It is important to note that part of the UV radiation spectrum actually overlaps with the visible light spectrum between 380 to 400nm. This is the high energy visible light spectrum and also has the potential to harm our eyes.
UVA – Key Facts
- Accounts for 95% of UV radiation exposure
- It does not make the skin red
- Responsible for many of the sun-related aging processes
- Penetrates deep, generating free radicals and destroys Vitamin A
- Causes mutation of the deep skin cells (basal cell keratinocytes)
- Linked to Macular Degeneration and skin cancers
- Passes through window glass (buildings and cars)
It is not uncommon for professional drivers, such as truck drivers, to have visibly more damage to one side of the face.
UVB – Key Facts
- Levels of UVB vary according to altitude and time of day
- Causes direct damage to a cell DNA
- Causes sun tan and sunburn
- Damages collagen
- Destroys Vitamin A
- Largely responsible for skin cancers including melanomas
- Plays a role in Vitamin D production, 5-30 minutes twice a week is all we require!
UVC – Key Facts
- Very little reaches the surface of the earth
- Only penetrates the highest levels in the atmosphere
- Ionising radiation, so it kills living cells fast.
Skin Cancers in Eyes
We all know about skin cancers, but we still aren’t taking action. When we venture outdoors, we still don’t always use SPF sunscreen, wear a hat or wear sunglasses! With 90% of all skin cancers occurring above the neck, a significant proportion of sun-related skin cancers occur in or around the eyes.
As an eye health professional, these cases are some of the saddest, as they almost never have a good outcome for the patient. It is alarming how many patients I am seeing with skin cancers around or in the eyes.
Skin cancers around or in the eyes are always referred to a specialist eye surgeon.
It’s terrible to see the results of surgery and even more horrific to learn that a patient has been given only 3 months to live when they are in their 30’s with a young family, with their whole life ahead of them.
Effects of UV on the Eye?
The front parts of the eye including the cornea and the crystalline lens block almost all UV light from reaching the retina. Some UVA reaches the retina and these are the wavelengths closest to the visible light spectrum. Remember, while the front parts of the eye do help to protect the retina at the back of the eye, they pay the price and accumulate the damage. This damage can present in different ways, with the most common being Pterygium and Cataracts.
Pterygium or “Surfer’s Eye” is a change to the surface of the eye in an area called the Limbus. That’s the junction between the coloured part of the eye and the white of the eye and is where a pterygium may form. A phenomenon known as the “corneal peripheral light focusing effect” focuses light and UV radiation onto the limbal stem cells which are believed to drive the formation of pterygia. Typically, the light originates from the side, above and below the eye and is focused towards the side of the eye closest to the nose.
Importantly, spectacles or sunglasses may mimic this phenomenon with UV light coming from the side or even behind the wearer. What’s more, is that indirect or peripheral light does not cause the pupil to constrict as much as it would with direct light. This exposes the internal lens of the eye to more damaging UV radiation which leads to cataract formation.
As the internal crystalline lens of the eye absorbs UV radiation its structure changes to form a cataract over time. Cataracts are covered in another post here.
Peak UV exposure for the eyes
Peak UV exposure of the skin occurs between 10 am and 2 pm, with the summer months being the highest risk. This is not the same for the eyes with their peak in UV exposure occurring between 8 am-10 am and 2 pm-4 pm, all year round. This is due to the lower angle of the sun and the increased amount of scattered and reflected UV radiation reaching the eye.
More UV radiation reaches the eye through scattering by clouds or reflection from surfaces such as the ground.
Peak expoure for eyes is 8 am-10 am and 2 pm-4 pm, all year round. Children are also half as likely to wear eye protection for UV radiation than parents!
Direct and Indirect UV
50% of all your eye’s UV exposure is known to originate from indirect exposure. This includes reflection off surrounding surfaces including water, snow, buildings, roadways and also the back of sunglasses lenses.
Commonly prescribed medications such as Doxycycline, anti-depressants, CNS stimulants, anticholinergics and even some pain killers and antihistamines can have side effects that cause the pupil to open wider, allowing more indirect UV light to enter the eye. Indirect exposure even occurs when you adopt avoidance behaviours such as turning away from bright visual light or the sun. In fact, on average, around 7% of our total UV exposure occurs when we are indoors or in a car, behind glass.
The Right Type of Lens for your Eyes
Modern spectacle and sunglass lenses can provide multiple layers of UV protection. Unfortunately, there are a lot of lenses out there that do not provide UV protection.
High quality plastic lenses often include a 100% UV blocker, while lower quality standard lenses provide little protection. Tinting on its own does not ensure 100% UV protection either.
Plastic lenses can have a clear or tinted UV absorbing factor applied. Photochromatic lenses and high index lens materials automatically include this property but not all tinted sunglass lenses include this property.
Back surface anti-reflective treatments
Since the back surface of a lens has the potential to reflect up to 90% of the light from the side or behind the wearer, it is important to prevent this form of indirect UV exposure. A specific UV absorbing back surface treatment is applied to all good quality lenses.
Polarising filters help to make your vision more comfortable by blocking out glare that makes you squint. Unless polarised lenses have a UV blocker included, polarised lenses do not necessarily block 100% of UV radiation.
Wear Good Quality Sunglasses
When it comes to protecting your eyes from UV rays, there is no substitute for wearing good quality sunglasses while outdoors in conjunction with a hat and sunscreen around the eyes. Remember, the eye is affected by both direct UV radiation and indirect UV radiation from the side, behind and below the eye.
Make sure your sunglasses include as many of the following 5 components for maximum protection and the long term health of your eyes:
- Polarising filter
- 100% UV absorbing lens treatment, right up to 400nm
- High quality plastic lens material of 1.53 index or higher
- Good quality UV specific back surface anti-reflective lens treatment
- A wrap around, close fitting frame style
For more information on how to protect your eyes properly from the sun or to have your eyes checked for early signs of sun damage make an appointment to see an Optometrist at Noosa Optical or call us on 07-5447-3711.