As summer gives way to autumn, many of us notice the change in light before we notice the change in temperature. The days gradually become shorter and the sun sits lower in the sky, particularly during the morning and late afternoon.
For some people, this simply means reaching for their sunglasses more often. For others, however, the lower autumn sun can expose changes in the quality of their vision that may previously have gone unnoticed.
Glare when driving towards the sun, difficulty distinguishing objects against bright backgrounds, halos around lights or finding yourself increasingly uncomfortable in bright conditions can all be signs that the eye is not handling light as effectively as it once did.
As an ophthalmologist, one of the important distinctions I make with patients is between how clearly you can see and the quality of the vision you experience in everyday life. Someone may still perform reasonably well when reading letters from an eye chart in a controlled examination room, yet experience considerable difficulty when driving into low sunlight or facing headlights after dark.
Understanding why this happens can help us recognise when glare is simply an environmental inconvenience and when it may be telling us something about our eyes.
Why Can the Autumn Sun Cause So Much Glare?
During the summer months, the sun tends to travel higher across the sky. As we move into autumn and winter, its path becomes progressively lower.
This means sunlight is more likely to enter our eyes at a relatively direct angle, particularly during morning and evening journeys. For drivers, the effect can be especially noticeable when the sun is positioned close to the horizon and directly ahead.
The problem is not simply that the sunlight is bright.
For good vision, light entering the eye needs to travel through the cornea and the natural lens before being focused accurately onto the retina at the back of the eye. The quality of these optical structures therefore influences how effectively we cope with challenging lighting conditions.
When light is scattered within the eye rather than being transmitted and focused cleanly, glare becomes more noticeable.
What Is Glare?
We often use the word “glare” to describe any situation in which light feels excessively bright. From an ophthalmic perspective, however, glare can have a more specific effect on visual performance.
A bright source of light can reduce the contrast between an object and its surroundings, making the object more difficult to distinguish. This is sometimes described as disability glare.
Imagine driving towards a low sun and trying to see a pedestrian, cyclist, road marking or vehicle against the brightness ahead. The object may still be there and your eyesight may otherwise be good, but scattered light can effectively create a veil over the visual scene and reduce your ability to distinguish detail.
This is why assessing vision is about more than simply asking how small a line of letters someone can read.
Good Eyesight Does Not Always Mean Good Quality of Vision
A standard visual acuity test is extremely useful. It tells us how well the eye can resolve fine detail under controlled conditions.
But everyday vision rarely takes place under controlled conditions.
We need to see in bright sunshine, dim rooms, rain, changing light, against low-contrast backgrounds and while facing headlights at night. Our visual system is constantly adapting to different environments.
A person can therefore have relatively good visual acuity on an eye chart while still experiencing problems with contrast sensitivity, glare or night vision.
This distinction becomes particularly important when assessing cataracts.
“An eye chart tells us how clearly someone can resolve detail under controlled conditions. It doesn’t always tell us how well they see when faced with glare, low contrast or headlights at night.”
Mr Gurjeet Jutley, Consultant Ophthalmologist
Why Cataracts Can Make Glare More Noticeable
Inside each eye is a natural crystalline lens. In a healthy younger eye, this lens is normally transparent, allowing light to pass through and focus onto the retina.
A cataract develops when the natural lens becomes progressively less transparent.
Although cataracts are commonly associated with blurred or cloudy vision, the effect on vision can be more subtle in their earlier stages. Changes within the lens can cause incoming light to scatter before it reaches the retina.
Instead of light being focused cleanly, some of it spreads across the retinal image. This can reduce contrast and make bright sources of light disproportionately troublesome.
As a result, someone developing a cataract may begin to notice:
- increased glare from sunlight;
- halos around headlights or streetlights;
- difficulty driving at night;
- colours appearing less vivid;
- difficulty seeing objects against bright backgrounds; or
- needing more light for reading while paradoxically finding very bright light uncomfortable.
Importantly, these symptoms do not always develop at the same rate as a reduction in visual acuity.
A patient may therefore say, “I can still see quite well,” while also explaining that driving towards the sun or driving after dark has become increasingly difficult.
Both pieces of information are important when assessing the functional effect of a cataract.
Why Driving Can Highlight Changes in Your Vision
Driving places considerable demands on the visual system.
It requires us to identify detail quickly, judge distances, detect movement, distinguish objects with relatively little contrast and continually adapt to changing levels of illumination.
Autumn can make these demands particularly apparent.
As daylight hours shorten, morning and evening journeys increasingly coincide with sunrise or sunset. Drivers may encounter intense low-angle sunlight during one part of their journey and relatively dim conditions during another.
Later in the season, more journeys also take place after dark, introducing another common source of glare: oncoming headlights.
For someone with developing cataracts, the combination of low sunlight, reduced contrast and headlights can make driving significantly less comfortable even when daytime vision under normal conditions remains relatively good.
This is one reason why changes in driving confidence can sometimes be an important clue when discussing a patient’s vision.
Is All Sensitivity to Bright Light Caused by Cataracts?
No.
Finding bright sunlight uncomfortable does not automatically mean that you have a cataract.
Glare and light sensitivity can occur for many reasons. Dry eye disease, problems with the corneal surface, uncorrected refractive error and certain retinal or ocular conditions can all influence the way we experience light.
Some people are also naturally more sensitive to bright conditions than others.
What matters is recognising a change from what is normal for you.
If glare has recently become more troublesome, appears substantially worse in one eye, is accompanied by blurred vision or halos, or is beginning to interfere with activities such as driving, it is sensible to have your eyes examined.
An ophthalmic assessment can help establish whether cataracts or another eye condition may be contributing.
Sunglasses Can Help – But Choose Them for Protection, Not Just Darkness
Good-quality sunglasses can make low autumn sunlight considerably more comfortable.
However, the darkness of the lens is not in itself an indication of how effectively sunglasses protect your eyes from ultraviolet radiation.
Look for sunglasses providing appropriate UVA and UVB protection, ideally labelled UV400. A well-fitting pair can reduce discomfort from bright sunlight while also protecting the eyes from unnecessary UV exposure.
For driving, keeping the windscreen clean inside and out can also make a surprising difference. Dirt, condensation and fine surface marks can scatter light and exaggerate glare, particularly when the sun is low.
If you require prescription glasses for driving, ensuring that the prescription remains appropriate is equally important.
These measures can improve comfort, but persistent or increasing glare should not simply be masked indefinitely if there has been a noticeable change in vision.
When Should You Have Your Eyes Checked?
An occasional struggle with very bright sunlight is common and does not necessarily indicate an eye problem.
I would, however, recommend arranging an eye examination if you notice that:
your vision has become increasingly blurred or hazy; glare is noticeably worse than it used to be; headlights are surrounded by halos; colours appear less vivid; one eye seems to cope with bright light differently from the other; or your vision is beginning to affect your confidence when driving.
A comprehensive assessment allows us to examine the health of the eye and determine whether cataracts, refractive changes, dry eye or another condition may be contributing.
Any sudden deterioration in vision, new severe eye pain, marked redness, flashes of light, a sudden increase in floaters or a shadow or curtain across the vision should be assessed promptly rather than attributed to seasonal glare.
Looking Beyond the Eye Chart
As we move into autumn, changes in daylight can make us more aware of aspects of our vision that are easy to overlook during the rest of the year.
For some people, glare from a low sun is simply an inconvenience. For others, it can reveal a reduction in contrast sensitivity or changes within the eye that deserve further investigation.
This is particularly relevant with cataracts because the decision to investigate or treat a cataract should not be based solely on a number on an eye chart. We also need to understand how vision is affecting the individual’s everyday life.
If you can still read clearly but increasingly avoid driving at night, struggle with oncoming headlights or find low sunlight makes it difficult to see the road ahead, those experiences matter.
Gurjeet Jutley is a Consultant Ophthalmologist specialising in cataract and glaucoma care. If you have noticed changes in your vision, increasing glare or difficulties with your everyday sight, an ophthalmic consultation can help identify the cause and discuss the most appropriate options for your individual circumstances.