Resource Centre

Below is a list of frequently asked questions concerning how the eye works, eye conditions, cataracts, parts of the eye and more.

What is the eye’s function?
How does the eye work?
What is the cornea?
What is the iris?
What is the lens?
What is the pupil?
What is the retina?
What are other important parts of the eye?
What is accommodation and why does the eye need to be able to do it?
How does the eye protect itself?
What is visual phototransduction?
What is age-related macular degeneration?
What is aniridia?
What is aphakia?
What is astigmatism?
What is blepharitis?
What are cataracts?
What is conjunctivitis?
What is corneal abrasion?
What is corneal edema?
What is a corneal ulcer?
What is cystoid macular edema?
What is diabetic retinopathy?
What is diplopia?
What is glaucoma?
What is hyperopia?
What are hypertropia and hypotropia?
What is hyphema?
What is hypotony?
What is keratoconus?
What is Marfan’s syndrome?
What is myopia?
What is posterior capsular opacification?
What is posterior vitreous detachment?
What is recurrent corneal abrasion?
What is red eye?
What is retinal detachment?
What is uveitis?
What is a contact lens?
Who can wear contact lenses?
What is the difference between an ophthalmologist, an optometrist and an optician?
What are hard contact lenses?
What are soft contact lenses?
What are rigid gas permeable contact lenses?
What are silicone hydrogel contact lenses?
What’s the difference between tinted and coloured contact lenses?
Are there contact lenses available that will block ultraviolet light?
What are toric contact lenses?
What are bifocal contact lenses?
What is the process of contact lens insertion?
What is the process of contact lens removal?
How do I know which contact lens solution is best to use?
What is daily cleaning solution?
What is saline rinsing solution?
What are protein removers and enzymatic cleaners?
What is disinfecting solution?
What is a wetting/soaking solution?
What is multipurpose solution or all-in-one solution?
Is it ok to use tap water or saliva to clean or soak my contact lenses?
Am I allowed to swim whilst wearing contact lenses?
Am I allowed to sleep with my contact lenses in?
Is it ok to participate in sporting activities whilst I am wearing contact lenses?
How do I know when to replace my contact lenses?
Am I allowed to use eye drops when my eyes get dry whilst I’m wearing contact lenses?
Can a contact lens get lost behind my eye?
Are contact lenses painful?
I have had refractive laser surgery - can I wear contact lenses?

What is the eye’s function?

The eye is an organ of the body, which respond to changes in light. It contains structures that allow it to focus light and send messages to the brain, to be perceived as images.

How does the eye work?

Light rays reflecting off an object, enter our eye and pass through different structures, such as the cornea and the lens. These parts of the eye refract the light so that the light rays converge onto the fovea of the retina. The retina then turns this image into a series of electrical impulses, which are sent to the brain via the optic nerve. Once the brain receives the impulses, it can transform them into the image that we see. For more detailed information about how the eye works, please see link.

What is the cornea?

The cornea is the part of the eye that covers the iris and the pupil. It acts as a lens and is the first of three mechanisms that the eye uses to refract light onto the retina. For more information, please see link.

What is the iris?

The iris is the coloured muscle around the pupil, which regulates the amount of light entering the eye. For more information, please see link.

What is the lens?

The lens is a transparent, flexible structure, which refracts light passing through the eye onto the retina. It changes shape depending on the distance away of the object the eye is focusing on. For more information, please see link.

What is the pupil?

The pupil is the hole in the centre of the iris that allows light to pass through into the eye. For more information, please see link.

What is the retina?

The retina is a layer of light-sensitive nerve cells that convert the image from the lens into electrical signals. For more information, please see link.

What are other important parts of the eye?

For information about other parts of the eye not described on this page, and much more detailed descriptions about the structures on the FAQ section, please follow this link.

What is accommodation and why does the eye need to be able to do it?

Accommodation is the ability of the eye to focus on objects over a range of distances. It is needed so that the point of convergence is always on the retina independent of how for an object is away from the eye. The lens is the part of the eye that allows accommodation to happen. For more information, please see link.

How does the eye protect itself?

The eye has a series of structures that prevent dust, foreign objects and too much bright light from entering the eye. These parts of the eye include eyelids, eyelashes and tears. For more information, please see link.

What is visual phototransduction?

Visual phototransduction is the process in which photoreceptors (e.g. rods and cones) transform light into electrical signals on the retina. The process of visual phototransduction and more information about photoreceptors can be found by following this link.

What is age-related macular degeneration?

AMD is a disease that affects the macula (the central part of the retina). It causes a gradual loss in vision as the cells of the macula become damaged. For more information about AMD, the causes, symptoms and treatment, please see link.

What is aniridia?

Aniridia is a condition in which the iris is very underdeveloped. This can cause a loss in vision as well as other conditions, for example, cataracts and glaucoma. For more detailed information about aniridia, please see link.

What is aphakia?

Aphakia is a condition where the eye lacks the lens. This can result in an overexposure of UV light and a loss of accommodation. For more information about aphakia, including causes, symptoms and treatment, please see here.

What is astigmatism?

Astigmatism occurs when the cornea is irregularly shaped. There is another, less common form of astigmatism – lenticular astigmatism, which occurs when the lens is irregularly shaped. Astigmatism causes light rays to converge at two points on the retina instead of just one. Contact lenses can help to correct astigmatism. For more information about, please see here.

What is blepharitis?

Blepharitis is a condition in which the eyelids can become inflamed. Blepharitis is often associated with other conditions of the body such as eye conditions or skin conditions. For the causes, symptoms and treatment of blepharitis, please see here.

What are cataracts?

A cataract is a condition, which occurs when the lens of the eye becomes cloudy. There are four different types of cataracts and the treatment is called cataract surgery. For more information on causes and risk factors, symptoms, different types, detection, who is affected, treatment, cataract surgery and prevention of cataracts, please follow this link.

What is conjunctivitis?

Conjunctivitis is a condition that is also referred to as pink eye. It is where the conjunctiva becomes inflamed when blood vessels in the membrane become irritated and enlarge. For more information on conjunctivitis, including the causes, symptoms and treatment, please see here.

What is corneal abrasion?

Corneal abrasion occurs when the cornea is damaged due to minor trauma. The damage can be caused due to a scratch, scrape or a foreign body embedding itself in the eye. For more information on corneal abrasion, please see here.

What is corneal edema?

Corneal edema is a condition in which the inside layer of the cornea has been damaged and fluid accumulates within it, causing the cornea to swell. For the causes, symptoms and treatment of corneal edema please follow this link.

What is a corneal ulcer?

A corneal ulcer is the inflammation of the outer layer of the cornea, this condition is also called acanthamoeba keratitis. For more information about corneal ulcers, please see here.

What is cystoid macular edema?

Cystoid macular edema is the condition in which fluid-filled cystoids appear on the macular (the central part of the retina). These cystoids cause swelling. For information about the causes, symptoms and treatment of cystoid macular edema please see here.

What is diabetic retinopathy?

Diabetic retinopathy occurs in two stages, the first is when blood vessels in the retina swell and leak fluid and the second stage is when new blood vessels grow on the surface. For more detailed information about diabetic retinopathy, please see here.

What is diplopia?

Diplopia is a condition in which a single object is perceived as two images, it is also known as double vision. For more information about diplopia, including the causes, symptoms and treatment, please see here.

What is glaucoma?

Glaucoma is a condition that occurs when the intraocular pressure of the eye increases. This can cause vision loss due to damage to the optic nerve. For more detailed information about glaucoma, please see here.

What is hyperopia?

Hyperopia is a condition where light coming into the eye forms images behind the retina instead of on it. It is also known as far-sightedness and can be corrected by contact lenses. For the causes, symptoms and treatment of hyperopia please follow this link.

What are hypertropia and hypotropia?

Both of these conditions are due to differences in intraocular muscles and are a form of strabismus where one eye has deviated in comparison to the other. In hypertropia, one eye has deviated higher than normal and in hypotropia, one eye has deviated lower than normal. For more information on hypertropia and hypotropia, please see here.

What is hyphema?

Hyphema is a condition that occurs when blood collects in the anterior chamber of the eye. This is because blood vessels in the iris have leaked into the aqueous fluid. For the causes, symptoms and treatment of hyphema please follow this link.

What is hypotony?

Hypotony is the opposite of glaucoma and is a condition in which the eye has a low intraocular pressure. It can cause decreased vision. For more information about hypotony, please click here.

What is keratoconus?

Keratoconus occurs when the corneal tissue starts to thin and the pressure of the eye causes it to bulge outwards, creating a conical shaped cornea instead of a rounded one. For more detailed information concerning keratoconus, please click here.

What is Marfan’s syndrome?

Marfan’s syndrome is characterised by an elongation of the eye, this causes very high myopia (near-sightedness). Marfan’s syndrome can also cause a decreased level of vision due to the lens moving upwards and outwards. For more information concerning Marfan’s syndrome, please follow this link.

What is myopia?

Myopia is a condition in which light rays converge before the retina instead of directly on it. This condition is also called far-sightedness and can be corrected by contact lenses. For the causes, symptoms and treatment of myopia, please see here.

What is posterior capsular opacification?

Posterior capsular opacification is a condition in which lens cells grow over the back of an intraocular lens that has been implanted during cataract surgery. For more information concerning posterior capsular opacification, please follow this link.

What is posterior vitreous detachment?

Posterior vitreous detachment is a condition, which occurs when the vitreous humour shrinks and therefore, detaches from the retina. For the causes, symptoms and treatment of posterior vitreous detachment please see here.

What is recurrent corneal abrasion?

Recurrent corneal abrasion is a condition in which epithelial cells on the cornea adhere poorly to the basement membrane and become displaced easily. For more detailed information concerning recurrent corneal abrasion, please follow this link.

What is red eye?

Red eye is a condition, which occurs when a blood vessel under the conjunctiva breaks and bleeds, this causes the sclera to turn red. This condition is also called a subconjunctival haemorrhage. For more information concerning it, please see here.

What is retinal detachment?

Retinal detachment is a condition that occurs when the retina’s sensory layer peels away from the support layer. This means that the brain cannot construct a precise image from the signals sent by the damaged retina. For the causes, symptoms and treatment of retinal detachment, please follow this link.

What is uveitis?

Uveitis is a condition that refers to any inflammation of the iris, the ciliary body or the choroid, all of which make up the uvea. For more detailed information concerning uveitis, please see here.

What is a contact lens?

A contact lens is a medical device that can be used in replacement of eyeglasses. They are inserted into the eye and rest on the cornea. Corrective contact lenses are used to improve visual refraction problems as they refract the light so that it focuses on the retina. Cosmetic contact lenses are used to enhance or change the appearance of the eye.

Who can wear contact lenses?

Due to the many contact lenses available, most people can now wear contact lenses. It is best to talk it through with your eyecare professional, or parents if you are a teenager, first though.

What is the difference between an ophthalmologist, an optometrist and an optician?

An ophthalmologist is a medical graduate who has studied all aspects of medicine but chosen to specialise in a particular area of ophthalmology. They can diagnose conditions and perform treatments and surgery. An optometrist is an eye care specialist who can examine and diagnose eye conditions, however, they cannot perform surgery. An optician is trained in making eyeglasses and contact lenses, as prescribed by the ophthalmologist or optometrist, however they are not trained in diagnosing or prescribing treatment for eye conditions.

What are hard contact lenses?

Hard contact lenses, made from the plastic PMMA, were the first type of lenses to be introduced. Although they do still exist, they are not normally used as they are uncomfortable to wear and do not allow oxygen to pass through to the cornea easily which causes many other problems for the wearer.

What are soft contact lenses?

Soft contact lenses are made from a type of plastic called hydrogels, which are hydrophilic (water-loving). This uptake of water allows oxygen to pass through the lens and into the eye. Soft contact lenses can very from 30% water content to 80% water content and this means they are flexible to varying degrees. This property of soft lenses also allows them to be more comfortable and easier to insert and remove.

What are rigid gas permeable contact lenses?

Rigid gas permeable contact lenses are not as pliable as soft lenses, but not as inflexible as hard contact lenses. This property stems from the incorporation of silicone into the plastic. Silicone makes the lens much more flexible, whilst allowing oxygen to permeate through. Although slightly harder to get used to than soft lenses, RGP’s are much more durable and easier to clean.

What are silicone hydrogel contact lenses?

Silicone hydrogel contact lenses are the newest invention and can allow much greater amounts of oxygen to pass into the eye than any other contact lens. This is because the lenses are made of hydrogels (like in soft contacts), which take up water and allow oxygen to pass through and they also contain silicone (like in RGP contacts) that, again, takes up oxygen. This property allows silicone hydrogel contact lenses to be worn for around 30 days at a time, including during the night.

What’s the difference between tinted and coloured contact lenses?

Tinted contact lenses are used to enhance the eyes natural colour, for example, they can make light coloured eyes more vivid or slightly darker in colour. However, tinted lenses will have no effect on dark coloured eyes. Coloured lenses are used to completely change the colour of an eye, or to make the pupil and iris a different shape. Some contact lenses have a handling tint, which does not affect the colour of the eye but is used to help see the lens when it is out of the eye.

Are there contact lenses available that will block ultraviolet light?

Some lenses now do exist that contain ultraviolet light blockers, which are a certain chemical that absorbs the harmful rays. However, these should not be used as a replacement for sunglasses, just as an extra safety addition, as the contact lens does not cover the whole of the eye.

What are toric contact lenses?

The function of toric contact lenses is to correct the eye condition of astigmatism, which is characterised by an irregularly shaped cornea. The toric lens has a different shaped base curve that normal so to correct the uneven cornea.

What are bifocal contact lenses?

Bifocal contact lenses are used to correct presbyopia and they do this by having two parts to the lens. The upper part is used for seeing objects in the distance and the lower part has a different focusing power and is used for near-distance tasks.

What is the process of contact lens insertion?

Firstly, your hands should have been cleaned with soap and dried with a lint-free towel. Then you should check that the lens is undamaged and not inside out (only for soft lenses). Before you insert the lens, rinse it with saline solution and balance it on your fingertip, place a drop of saline solution on the lens and insert into your eye. Repeat this process with the other contact lens. For more detailed steps and information containing the differences of this process for soft and gas permeable lenses then please follow this link.

What is the process of contact lens removal?

As with insertion, make sure you hands are clean and dry using soap and a lint-free towel. Fill the lens case with either disinfecting solution or wetting/soaking solution depending on which type of lens you have. When the lens has been removed, place a drop of cleaning solution on the surface and rub the lens between your thumb and index finger, gently but firmly, for 30 seconds. Rinse the lens with saline solution and put it in the solution-filled case. Repeat for the other lens and store overnight.

How do I know which contact lens solution is best to use?

Your eyecare professional should recommend the solutions that you will need to use for your specific contact lenses. If you wish to change solutions, then always discuss the options with them first.

What is daily cleaning solution?

Daily cleaning solution is used with both soft and gas permeable lenses. It is used to loosen debris and remove deposits and secretions that have formed on the lens. For more information, please see here.

What is saline rinsing solution?

Saline solution can be used for either soft lenses or gas permeable lenses and it is used to rinse off any loose particles of debris or dirt after cleaning. Saline solution also helps to aid insertion in the morning. Two other functions of saline solution include, rinsing lens cases and diluting enzymatic cleaner tablets. For more information please follow this link.

What are protein removers and enzymatic cleaners?

Over time, residue from the eye builds of protein deposits, which will irritate the eye and make contact lenses less comfortable to wear. Protein removers and enzymatic cleaners are used to breakdown these deposits to provide clean, comfortable contact lenses. Protein removers are generally in liquid form whereas enzymatic cleaners are in tablet form and have to be diluted with saline solution before use. For more information on these two solutions, please click here.

What is disinfecting solution?

Disinfecting solution is only used with soft contact lenses. This solution is used to soak the contact lenses overnight and whilst doing that, it kills all bacteria so that the lenses are clean and ready to wear in the morning. For more information on disinfecting solution please follow this link.

What is wetting/soaking solution?

Wetting/soaking solution is used with gas permeable lenses and disinfects the lens as well as providing liquid for an easy insertion of the lens into the eye.

What is multipurpose solution or all-in-one solution?

Multipurpose solution is used for soft lenses whereas all-in-one solution is used for gas permeable lenses. These solutions provide an easy alternative to using many bottles of solution in caring for your lenses. Each solution contains a mix of solutions that will help to clean, disinfect and rinse contact lenses. They are helpful as they save time, space and confusion. For more information on multipurpose solution, please click here, for more information on all-in-one solution, please click here.

Is it ok to use tap water or saliva to clean or soak my contact lenses?

No. Saliva and tap water are not sterile and, therefore, can contain many sources of bacteria and dirt, which could get in your eye and cause damage. If possible, always carry around with you a small bottle of solution so that you never get in the situation where you have to consider substitutes.

Am I allowed to swim whilst wearing contact lenses?

Generally, it is advisable not to as firstly, the motion of the water can easily dislodge and remove a contact lens from your eye and secondly, all the bacteria and chemicals in a pool will be absorbed into the lens and transferred into your eye. If you do wish to go swimming with contact lenses in, wear goggles with a very tight fitting seal or wear goggles that have a prescription like glasses.

Am I allowed to sleep with my contact lenses in?

The answer is normally no, however, if you are wearing contact lenses that are made from silicone hydrogel and can be kept in for 30 days then the amount of oxygen reaching your eye makes it safe for you to sleep in them. It will be clearly written on the packet of your lenses whether or not you are allowed to sleep in them but, if in doubt, speak to your eyecare professional.

Is it ok to participate in sporting activities whilst I am wearing contact lenses?

Yes, in fact, contact lenses are the corrective lens recommended by ophthalmologists for people who take part in a lot of sport. This is because they are more convenient as they offer more peripheral vision and do not get steamed up or fall off like glasses.

How do I know when to replace my contact lenses?

The length of time in which you can wear the same contact lenses varies with each type. For example, lenses can be worn for just one day, one week, one month etc. You should always check with your eyecare professional and follow the guidelines on the packet.

Am I allowed to use eye drops when my eyes get dry whilst I’m wearing contact lenses?

You can, but check with your eyecare professional and the instructions for the contact lenses to decide which eye drops you should use. Saline solution can be used for every type, however, for rewetting drops, a specific type of solution will be needed that matches your contact lens.

Can a contact lens get lost behind my eye?

No, this can never happen, as the lens cannot pass through the conjunctiva. The lens may move under an eyelid, but it can easily be manipulated out.

Are contact lenses painful?

Soft contact lenses are not painful at all due to their flexibility, however, RGP contact lenses may feel slightly uncomfortable at first but this feeling will subside once you get used to them.

I have had refractive laser surgery - can I wear contact lenses?

Yes, however, you will require a more specialised lens as the cornea will have changed shape due to the surgery. Speak to your eyecare professional for more information involving your particular case.

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