SIGHT CONDITIONS
1. What are 2020 Vision, Short-sightedness, Long-sightedness Presbyopia and Astigmatism?
2020 Vision
This is also known as perfect sight where no prescription is required in order to see things clearly and comfortably. The fraction 20/20 is understood as follows: the bottom half represents the distance in feet at which a perfect sighted person is able to see clearly a target seen by another at 20 feet. So if you are perfect sighted you will see at 20 feet exactly what another perfect sighted person will see at 20 feet. However, if you have trouble seeing things in the distance, you might see at 20 feet what a perfect sighted person sees at 40 feet. So this means your vision is measured as 20/40.
Assuming you have perfect sight then when you are looking at something in the distance, light from the object will focus on your retinas very precisely. When seeing something close-up the focusing is blurred very momentarily, but this is unnoticeable because your eye has an automatic refocusing ability that makes the target clear. This refocusing ability is called 'Accommodation' and it works by making the natural lens of the eye fatter, or more convex in shape. As we get older we lose more and more of this ability, which is why things close-up start to blur after about 45 years of plodding on the planet.
Short-sightedness means that the light focuses in front of your retinas or 'too short' and long-sightedness means it focuses 'behind' or 'too long'.
Assuming you have perfect sight then when you are looking at something in the distance, light from the object will focus on your retinas very precisely. When seeing something close-up the focusing is blurred very momentarily, but this is unnoticeable because your eye has an automatic refocusing ability that makes the target clear. This refocusing ability is called 'Accommodation' and it works by making the natural lens of the eye fatter, or more convex in shape. As we get older we lose more and more of this ability, which is why things close-up start to blur after about 45 years of plodding on the planet.
Short-sightedness means that the light focuses in front of your retinas or 'too short' and long-sightedness means it focuses 'behind' or 'too long'.
Short-sightedness
Also known as Near-sight or Myopia, short-sighted individuals have trouble seeing things in the distance whilst anything close-up is clearer. This occurs because light from the objects being viewed focuses in front of the retina and not on it. It is believed that this mostly happens as a result of the eyeball being slightly too long. The scientific term for this is Axial Myopia.Long-sightedness
Also known as Far-sight or Hyperopia, long-sighted individuals have difficulty with anything close-up whilst their general distance vision is not as bad. Light from objects viewed will theoretically focus behind the retina and not on it. However because the eye is able to naturally fatten the lens and cause light to bend more, this error in focus is overcome, which explains why distance vision is generally pretty good. When the same individual tries to look at something up close, much more effort is required, as light from a near object will fall much further back behind the retina. Vision at near is therefore worse.Presbyopia
As our eyes grow older the ability to focus clearly on anything close-up starts to diminish. This occurs because we lose our ability to accommodate or make the lens of the eye fatter in shape. One popular way of explaining how this happens likens the natural lens of the eye to a pillow with feathers inside. The lens contains many fibres (feathers) which grow throughout life in the same way that hair and skin continues to grow. This is not surprising considering that these tissues all come from the same founding cells. When the lens is younger and has fewer fibres it is more flexible and can change its shape more easily just as a pillow with fewer feathers can. When the lens is older and has many more fibres this flexibility is obviously lost which causes the near vision to blur.Astigmatism
Often the eye is shaped like an egg or rugby ball. This is what we call astigmatism and it is quite a normal condition which most of us have to some degree. Like an egg, two main areas of curvature are found: one is flatter and the other is steeper. This causes the light to focus in two different positions such that the steeper or more curved area focuses further forward and the less curved or flatter further back. The effect on vision is to distort shapes so similarly shaped characters become confused. The letter G may be confused with a C and the number 2 may be mistaken for the letter Z.2. What is the difference between a squint and astigmatism?
A squint is when one eye is turned either up, down, in or out relative to the other eye.
The term 'lazy eye' is sometimes used when the turn is not detected at an early age and left uncorrected.
It is essential that any parents noting a turn in their child's eye have them assessed by an optometrist or eye doctor as soon as possible.
The sooner it is treated the better the prognosis for use of this eye in later years.
By the time the child has reached 9 years of age, it may already be too late.
Squints are sometimes confused with Astigmatism. Astigmatism is a condition where the shape of the eye is like an egg, whilst a squint refers to a turn in the eye.
Squints are sometimes confused with Astigmatism. Astigmatism is a condition where the shape of the eye is like an egg, whilst a squint refers to a turn in the eye.
3. Why do we become more “long-sighted” as we grow older?
This is due to a progressive change that occurs within the natural lens of the eye and is called presbyopia.
Although similar to long-sightedness in its effect, these two conditions are not identical.
4. My close-up vision is not as good as it used to be - is this normal?
Yes - this change in your near vision focus happens to everyone and is called presbyopia.
The effect of presbyopia is similar to that of longsightedness, but they are not the same.
5. I see black spots floating around in my vision especially when the sun is out - what are these and should I be worried?
These are called floaters. As the eye ages, more of these are seen and they are due to the changes in the vitreous jelly of the eye.
The vitreous is simply a clear jelly that fills up the internal space of the eyeball between the lens and the retina.
Changes may occur which cause the very fine fibrils contained in the jelly to clump together and become visible as floaters.
As long as these are longstanding and not associated with any flashing lights, they are generally okay and all you would need to do is notify your optometrist and keep a watchful eye on them.
If however you have not seen them before and they have only recently appeared, a thorough check with your optometrist or better still, an ophthalmologist (eye doctor), is advised.
Floaters are most easily seen against a white or bright background.
This is why they are more visible in the sunshine, against white walls or whilst flying and looking out at the clouds.
Sometimes floaters are an indication of retinal tears and possible detachment of the retina.
Although this does not happen all that often it is wiser to be safe rather than sorry so if in doubt, please find out!.
6. Sometimes I see flashing lights, my vision goes 'watery' and I get a headache. Is this an eye problem?
No. You have probably experienced a migraine attack.
Your GP would be the best person to advise you on what to do.
Flashing lights that seem fairly constant are more serious as this may indicate a problem with your retina.
Fairly urgent assessment of your eyes is then required and you should see an ophthalmologist(eye doctor) as soon as possible.
7. What is a cataract?
A cataract refers to any cloudiness within the natural lens of the eye.
Most often, this is age-related, but accelerated risk of cataract is now caused by over-exposure to ultra-violet light. This is worsened by the fact that the Ozone Layer is constantly thinning. Our advice is to take care when in the sun and always don a hat and a good pair of UV-blocking sunglasses. Ask your optometrist for more information.
If you develop or are developing a cataract, don't worry unnecessarily. The sky does not fall down even though it might be slightly smeary to look at. A simple operation can be performed by an ophthalmologist (eye doctor) whereby the cataractous lens of the eye is removed and replaced by a new implant. You will probably be sent home the same day!
If you develop or are developing a cataract, don't worry unnecessarily. The sky does not fall down even though it might be slightly smeary to look at. A simple operation can be performed by an ophthalmologist (eye doctor) whereby the cataractous lens of the eye is removed and replaced by a new implant. You will probably be sent home the same day!
8. What is glaucoma?
There are two types of adult-onset glaucoma and both refer to an increased abnormal pressure within the eyeball.
The rarer form is when an acute attack occurs.
Symptoms include a painful, red eye and possible light sensitivity and nausea.
The most common form of Glaucoma is the preventable chronic type.
Sight is adversely affected if it is not picked up early, the long-term effect being progressively worsening tunnel vision. It is essential to have your eyes screened for glaucoma once you are over the age of 40 years as the relative risk increases from this point. Other factors increasing the risk of glaucoma are diabetes, high levels of short-sightedness, Afro-Caribbean descent, age and family history.
9. At the start of spring I can't wear my contact lenses comfortably as my eyes itch - why is this?
You are probably suffering from an eye allergy.
Spring often brings about more sneezing and increased pollen counts along with all the daffodils.
Certain susceptible individuals will experience a reaction in the eyes and an allergic conjunctivitis results.
The itching is usually confined to the upper and/or lower lids and possibly the corner of the eye closest to your nose.
If you wear contact lenses, the best thing to do is switch to spectacles for the duration of the allergy and buy a small supply of daily disposable lenses so that you can use them for a few hours out in the evening if you are desperate. Daily disposables would be the best lens type if your allergies are fairly chronic and you refuse to wear glasses.
For relief from the itching certain anti-histamine containing drops can be bought from your local pharmacy. Most cannot be used in conjunction with contact lenses. Other types of drops can be used over a sustained period of time to strengthen the membranes of the cells that cause the symptoms of allergy. These drops have a longer-term effect and are called mast-cell stabilisers. The active ingredient is usually sodium cromoglycate. Ask your optometrist or pharmacist for more information.
If you wear contact lenses, the best thing to do is switch to spectacles for the duration of the allergy and buy a small supply of daily disposable lenses so that you can use them for a few hours out in the evening if you are desperate. Daily disposables would be the best lens type if your allergies are fairly chronic and you refuse to wear glasses.
For relief from the itching certain anti-histamine containing drops can be bought from your local pharmacy. Most cannot be used in conjunction with contact lenses. Other types of drops can be used over a sustained period of time to strengthen the membranes of the cells that cause the symptoms of allergy. These drops have a longer-term effect and are called mast-cell stabilisers. The active ingredient is usually sodium cromoglycate. Ask your optometrist or pharmacist for more information.
10. Why is it more difficult for me to see at night?
When it gets dark, our pupils dilate and this makes everyone more short-sighted.
This is usually why night-time vision is worse than during the day even if you are wearing your up-to-date prescription.
Should you be driving at night, more care should be taken on the roads, as oncoming headlamp glare can be quite distracting.
Any prescription found for general use should obviously be worn in these conditions.
Some inherited conditions of the eye like retinitis pigmentosa also cause problems with night vision.
You would be advised to seek an ophthalmologist's opinion if this is the case.
