Eye see you (:

Some colour blindness tests

2008-03-10T19:51:00.002+08:00

Here is a type of test carried out to see if a person is colourblind.

What numbers can you see in the following images?

Answers: 29, 25, 6, 45, 8, 56

Did you see all of the numbers above? If you do, congratulations! Your vision is normal! If not, you should consult a doctor for a more detailed analysis.

Fun Optical Illusions!

2008-03-06T21:53:00.000+08:00

Fun Optical Illusions!

Primrose's field

This amazing illusion to the right was created by Akiyoshi Kitaoka. It already looks quite 'wavy', but try scrolling down slowly while concentrating on the image. You should see the picture 'waving' in an incredible way.

Wheel of Fun
Focus on the dot in the centre and then move your head towards and away from the monitor. You should see the circles rotate spookily!Sakura
Try scrolling down slowly while focusing on the middle of the picture. It looks like it's moving!

Flickering Fog
Based on an illusion byAkiyoshi Kitaoka. Stare intently at the red dot in the center of the left block for about a couple of minutes.Once you've done this, look over to the center of the right block. It should act weird - by fading out and 'flickering'. If you move your head closer and further from the monitor (while focusing on the center), you should see some interesting effects too.
Done By: Yee Herng

Colour Blindness

2008-03-06T17:46:00.001+08:00

Types of colour blindness:

Red-green hereditary photoreceptor disorders [most common]

- Result from partial or complete loss of function in one or more of the different cone systems.
- The most frequent forms of human colour blindness result from problems with either the middle or long wavelength sensitive cone systems, and involve difficulties in discriminating reds, yellows and greens from one another. This is collectively referred to as "red-green colour blindness". However, this term is an over-simplification and is somewhat misleading.
- Other forms of colour blindness are much more rare. They include problems in differentiating blues from yellow, and the rarest forms of all, complete colour blindness or monochromacy, where one cannot distinguish any colour from grey, as in a black-and-white movie or photography.

Acquired colour blindness through damage to the eye, nerves or brain

- Unlike genetic disorders, acquired colour blindness may only occur in a portion of the visual field but maintain normal colour vision elsewhere
- Some forms are reversible
- Transient colour blindness, for migraine sufferers [very rare]

Classification of colour deficiencies

Colours of the rainbow as viewed by a person with no colour vision deficiencies

Colours of the rainbow as viewed by a person with protanopia

Colours of the rainbow as viewed by a person with deuteranopia

Colours of the rainbow as viewed by a person with tritanopia

Colour vision deficiencies can be classified:[as mentioned earlier].

- Acquired
- Inherited

Monochromacy:

- Also known as "total colour blindness".
- The lack of ability of distinguish colours
- Caused by cone defect or absence
- Occurs when two or all three of the cone pigments are missing and colour and lightness vision is reduced to one dimension.

Rod monochromacy:

- Rare, non-progressive inability to distinguish any colours as a result of absent or non-functioning retinal cones
- Associated with
- Light sensitivity [photophobia]
- Involuntary eye oscillations [nystagmus]
- Poor vision

Cone monochromacy:

- A rare, total colour blindness
- Accompanied by relatively normal vision, electroretinogram and electrooculogram

Dichromacy:

- A moderately severe colour vision defect
- One of the three basic colour mechanisms is absent or not functioning
- Hereditary
- Gender-linked - affects only males
- Occurs when one of the cone pigments is missing and colour is reduced to two dimensions

Protanopia:

- Severe type of colour vision deficiency caused by the complete absence of red retinal photoreceptors
- A form of dichromatism in which red appears dark
- Hereditary
- Gender-linked - occurs in 1% of all males

Deuteranopia:

- Colour vision deficiency in which the green retinal photoreceptors are absent, moderately affecting red-green hue discrimination
- A form of dichromatism in which there are only two types of cone pigments present
- Hereditary
- Gender-linked - present in 1% of all males

Tritanopia:

- Exceeding rare colour vision disturbance
- Only two cone pigments present
- A total absence of blue retinal receptors
- Anomalus trichromacy
- Common type of inherited colour vision deficiency
- Occurs when one of the three cone pigments is altered in its spectral sensitivity
- Results in an impairment, rather than a loss, of trichronmacy [normal three-dimensional colour vision]

Protanomaly:

- Mild colour vision defect
- An altered spectral sensitivity of red retinal receptors [closer to green receptor response] resulting in poor red-green hue discrimation
- Hereditary
- Gender-linked - present in 1% of all males
- Often passed from mother to child

Deuteranomaly:

- Caused by a similar shift in the green retinal receptors
- The most common type of colour vision deficiency
- Affects red-green hue discrimation in 5% of all males
- Hereditary
- Gender-linked

Tritanomaly:

- Rare
- Hereditary
- Colour vision deficiency affecting blue-yellow hue discrimation

Done by: Wen Yi

Introduction to colour blindness

2008-03-05T20:06:00.001+08:00

Introduction to colour blindness

What is it?
- The inability to spot the differences in some of the colours that can be spotted by other people.

Causes of colour blindness
- Often caused by genes
- But other possible causes are damage to the eye, nerve or brain.

Trivia facts about colour blindness
- Colour blindness is sometimes referred to as “Daltonism”, due to John Dalton’s work on his own colour blindness. However, this term is now used to describe a type of colour blindness known as “deuteranopia”.
- Colour blindness is classified as a disability.
- Colour blind people can have an advantage over people with normal colour vision in certain situations.
- Some studies show that colour blind individuals are better at seeing through certain camouflages. *Monochromats may have a minor advantage in dark vision, but only in the first five and a half minutes of dark adaptation.

The following is an 1895 illustration of normal vision and various kinds of color blindness.

*Refer here for more information on monochromats.

Background information
Color Blindness affects both men and women. The normal human retina contains two kinds of light cells: the rod cells (active in low light) and the cone cells (active in normal daylight).

Normally, there are three kinds of cones, each containing a different pigment. The cones are activated when the pigments absorb light. The absorption spectra of the cones differ; one is maximally sensitive to short wavelengths, one to medium wavelengths, and the third to long wavelengths (their peak sensitivities are in the blue, yellowish-green, and yellow regions of the spectrum, respectively).

The absorption spectra of all three systems cover much of the visible spectrum, so it is not entirely accurate to refer to them as "blue", "green" and "red" receptors, especially because the "red" receptor actually has its peak sensitivity in the yellow.

The sensitivity of normal color vision actually depends on the overlap between the absorption spectra of the three systems: different colors are recognized when the different types of cone are stimulated to different extents. Red light, for example, stimulates the long wavelength cones much more than either of the others, and reducing wavelength causes the other two cone systems to be increasingly stimulated, causing a gradual change in hue.

Done by: Wen Yi

Myopia and Hyperopia

2008-03-05T14:21:00.000+08:00

For more information, click here for a clear overview of myopia and hyperopia.
The site includes surgical treatments such as LASIK and PRK and is in swf format (a flash animation).

2008-03-04T22:20:00.001+08:00

CORNEAL TRANSPLANTATION

I will be talking about corneal transplantation. Corneal transplantation is also known as corneal grafting, which is a surgical procedure where a damaged or diseased cornea is replaced by donated corneal tissue which has been removed from a recently deceased individual having no known diseases which might affect the viability of the donated tissue.

The first cornea transplant was performed in 1905, by Eduard Zirm, making it one of the first types of transplant surgery successfully performed.

Corneal transplantations are done to improve visual acuity by replacing the opaque host tissue by clear healthy donor tissue; to preserve corneal anatomy and integrity in patients with stromal thinning and descemetoceles, or to reconstruct the anatomy of the eye; to remove inflamed corneal tissue unresponsive to antibiotics or anti-virals treatments and to improve the appearance of patients with corneal scars that have given a whitish or opaque hue to the cornea.

On the day of the surgery, the patient is given a brief physical examination by the surgical team and is taken to the operating room and given anesthesia.

With anesthesia induced, the surgical team prepares the eye to be operated on. An eyelid speculum is placed to keep the lids open, and some lubrication is placed on the eye to prevent drying. A metal ring is then stitched to the sclera, which will provide a base for a trephine.

A trephine is then placed over the cornea and is used by the surgeon to cut the host cornea. The trephine is then removed and the surgeon cuts a circular graft from the donor cornea. Once this is done, the surgeon returns to the patient's eye and removes the host cornea.

The donor cornea is then brought into the surgical field and maneuvered into place with forceps.

Once in place, the surgeon will fasten the cornea to the eye. The surgeon finishes up by reforming the anterior chamber with a sterile solution injected by a canula, then testing that it's watertight by placing a dye on the wound exterior.

With the metal ring removed and antibiotic eyedrops placed, the eye is patched, and the patient is taken to a recovery area while the effects of the anesthesia wear off. The patient typically goes home following this and sees the doctor the following day for the first post operative appointment.

Hyperopia [3]

2008-03-04T13:57:00.001+08:00

Hyperopia

swf file taken from allaboutvision.com & requires flash player to view

-XiuLi

Hyperopia [2]

2008-03-03T23:53:00.000+08:00

Signs and symptoms of hyperopia
• general eye discomfort or a headache after prolonged interval of doing close tasks, such as reading, writing or drawing
• eyestrain, including burning eyes, aching in or around the eyes, and, rarely, a headache
• squinting of eyes to see near objects clearer

Treatment of hyperopia
People with hyperopia often squint when working with objects up close. This allows them to see better as a different amount of light is refracted. Like treatments for myopia, treatments for hyperopia are designed to refract a correct amount of light into the eyes through either corrective lenses or reshaping of the cornea through surgical and non-surgical methods.

Like myopia, spectacles, contact lenses, and refractive surgery are the primary options to correct the refraction error of hyperopia.

Similarly, eyeglasses and contacts are usually the first treatment people use for hyperopia.
However, the inconveniences of using spectacles and contacts have lead to the search for other treatments.
Depending on the degree of the patient's myopia and his/her age, other techniques may be used. Laser assisted in situ keratomileusis, or LASIK Eye Surgery, is the most popular surgery used to treat hyperopia.

• In this procedure the shape of the cornea is measured and changed to fix the degree of myopia using a laser.

An alternative to LASIK, Conductive Keratoplasty, CK for short, uses the same concept of reshaping the cornea but uses different procedures and caters to patients who are over 40 and have hyperopia in the range from +0.75 to +3.00 diopters.

For patients who have extreme myopia or hyperopia, there's a new treatment, Phakic Intraocular Lenses that can be used to correct high degrees of hyperopia and is also a promising option for patients with hyperopia who also suffer from presbyopia.

• uses an implantation of lens much like a contact lens inside the eye to allow better light refraction
• correct the refractive error without removing the natural lens

-XiuLi

Trachoma

2008-03-03T18:13:00.001+08:00

Trachoma
Trachoma (Ancient Greek: "rough eye") is an infectious eye disease, unlike cataracts which are mainly caused by exposure to radiation.

Globally, 84 million people suffer from active infection and nearly 8 million people are visually impaired as a result of this disease. However, few people have heard of trachoma. It is often overlooked as a priority for public-health intervention because it is not fatal. In rural communities, people live in overcrowded conditions with limited access to water and health care. In some communities, the disease is so common that blindness from trachoma is simply accepted as a fact of life. Yet trachoma is treatable, and the suffering it causes is avoidable.

Those who are infected by trachoma do not instantly go blind. The disease manifests gradually. Children may not notice its effects until adulthood, when scarring from repeated infections causes the eyelashes to turn inward and scratch the cornea, leading slowly to complete blindness.

Causes
Trachoma is caused by the bacterium Chlamydia trachomatis and it is spread by direct contact with eye, nose, and throat secretions from affected individuals, or contact with inanimate objects such as towels or washcloths that have had similar contact with these secretions. The bacteria can be spread easily on an infected person's hands or clothing, or may be carried by pests that were in contact with the discharge of an infected person. Children are most susceptible to infection, but the effects are often not felt until adulthood.

Because trachoma is transmitted through close personal contact, it tends to occur in clusters, often infecting entire families and communities. Women are up to three times more likely than men to be blinded by the disease.

Symptoms
The bacteria Chlamydia trachomatis has an incubation period of 5 to 12 days, after which the affected individual experiences symptoms of conjunctivitis, or irritation similar to "red eye".
Further symptoms include:

Eye discharge

Swollen eyelids

Trichiasis (turned-in eyelashes)

Swelling of lymph nodes in front of the ears

Corneal scarring

Further ear, nose and throat complications.

Prevention/Treatments
Although trachoma was eliminated from much of the developed world in the last century, this disease persists in many communities without adequate access to water and sanitation. Trachoma keeps families shackled within a cycle of poverty, as the disease and its long-term effects are passed from one generation to the next.

The World Health Organization (WHO) has set a goal of eliminating blinding trachoma as a public health concern by 2020. National governments in collaboration with numerous non-profit organizations implement trachoma control programs using the WHO-recommended SAFE strategy, which includes:

Surgery to correct advanced stages of the disease

Antibiotics to treat active infection, using Zithromax

Facial cleanliness to reduce disease transmission

Environmental change to increase access to clean water and improved sanitation.

Effects
If not treated properly with oral antibiotics, the symptoms may escalate and cause blindness, which is the result of ulceration and consequent scarring of the cornea. Surgery may also be necessary to fix eyelid deformities.

Picture of the day:

Nerve signals travel from each eye along the optic nerve and other nerve fibers (called the visual pathway) to the back of the brain, where vision is sensed and interpreted. at the optic chiasm (in front of the pituitary gland), the optic nerve from each eye divides, and half of the nerve fibers cross to the other side to the back of the brain. Thus, the right side of the brain receives information through both optic nerves for the left field of vision, and vice versa. The middle of these fields of vision overlaps. It is seen by both eyes (called binocular vision).

An object is seen from slightly different angles by each eye so the information the brain receives from each eye is different, although it overlaps. The brain integrates the information to produce a complete picture.

Done By: Yee Herng

Hyperopia

2008-03-02T13:38:00.000+08:00

The opposite defect of myopia is hyperopia.

What is hyperopia?
• also known as hypermetropia or as farsightedness or longsightedness
• a common vision condition in which you can see objects in the distance clearly, but objects nearby may be blurry
• with mild farsightedness, one may see clearly objects that are closer
• with severe farsightedness, one can see clearly only objects a great distance away
• in extreme cases, one can’t even focus on objects at any distance

Causes of hyperopia?
• caused when the cornea is too flat (curved too little) or when the eye is too short

How or why hyperopia happens?
simply put, the light entering the eyes is not focused correctly, focused behind the retina rather than directly on the retina
• refractive defect of the eye causes collimated light to produce image focus behind the retina

Note: Hyperopia is often confused with presbyopia. People suffering from presbyopia will also experience blurry near vision and good far vision. However, these are two different eye conditions brought about by different causes.
___________________________________________________________________

Presbyopia is an eye condition that will happen to some degree to everyone some time in life. It in inevitable and there is no cure for presbyopia although there are a lot of procedures to help correct presbyopia to allow improved near vision.

It occurs because of a reduced accommodative amplitude which is brought about by natural aging changes with the crystalline lens. As we age, the lens of the eyes becomes rigid, loses its flexibility, and thus its ability to focus as well, causing presbyopia.

-XiuLi

Myopia [3]

2008-03-01T13:00:00.009+08:00

Myopia

swf file taken from allaboutvision.com & requires flash player to view

-XiuLi

Myopia

2008-02-29T23:09:00.002+08:00

Myopia -introduction

" Myopia is becoming very common. In Singapore, the rate of myopia amongst school kids has increased from about 25% just 30 years ago to about 75%. "

What is myopia?
• many different types i.e. pathological myopia, secondary myopia, pseudomyopia, nocturnal myopia and the most common simple myopia
___________________________________________________________________

Simple myopia
• also called nearsightedness or short sightedness
• a vision condition in which near objects are seen clearly but distant objects do not come into proper focus, appearing blurred

Causes of simple myopia?
• caused by a natural change in shape of the eyeball that makes it egg-shaped rather than round
• if the eyeball is too long or the cornea has too much curvature (too steep)

How or why simple myopia happens?
simply put, the light entering the eyes is not focused correctly, focused in front of the retina rather than directly on the retina
• light focused on the vitreous humour inside the eye rather than on the retina at the back of the eye
• refractive defect of the eye causes collimated light to produce image focus in front of the retina when accommodation is relaxed
___________________________________________________________________

Nocturnal myopia
• also known as twilight myopia or night myopia
• a condition in which the eye has a great difficulty seeing in low illumination areas although daytime vision is normal
___________________________________________________________________

Pseudomyopia
• the blurring of distance vision brought along by the spasm of the ciliary muscle
• common in young adults

Causes of pseudomyopia?
• differs from simplel myopia in that the focusing of light in front of the retina is due to transient spasm of the ciliary muscle which causes an increase in the refractive power of the eye
• classically occurs after change in visual requirements, such as students preparing for an exam, or a change in occupation
• can only be caused by diseases such as uncontrolled diabetes, Myasthenia gravis and nervous system disorders

-XiuLi

Cataracts

2008-02-29T17:59:00.005+08:00

Cataracts
A cataract is an opacity that develops in the crystalline lens of the eye or in its envelope. Early in the development of age-related cataract, the power of the crystalline lens may be increased, causing near-sightedness (myopia), and the gradual opacification of the lens may reduce the perception of blue colours. Cataracts progress slowly to cause vision loss and are potentially blinding if untreated.

Cataract is derived from the Latin cataracta meaning "waterfall". Cataracts are the leading cause of blindness in the world. In the United States, age-related lenticular changes have been reported in 42% of those between the ages of 52 to 64, 60% of those between the ages 65 and 74, and 91% of those between the ages of 75 and 85.

Causes

Cataracts usually develop without any apparent cause; however, they can result from injury to the eye, prolonged exposure to certain drugs (such as corticosteroids) or to x-rays (such as with radiation therapy to the eye), inflammatory and infectious eye diseases, and as a complication of diseases such as diabetes. They are usually a result of denaturation of lens proteins.

Cataracts also seem to be more common in people with dark eyes, those who have had prolonged exposure to direct sunlight, those with poor nutrition, and smokers. People who have had a cataract in one eye are more likely to develop one later in the other eye. Sometimes cataracts can develop in both eyes at the same time. Babies can be born with them (congenital cataracts) and children can also develop cataracts, usually as a result of injury or illness.

Cataracts may also be produced by eye injury or physical trauma. A study among Icelandair pilots showed commercial airline pilots as three times more likely to develop cataracts than people with non-flying jobs. This is due to the excessive exposure to radiation coming from outer space. Cataracts are also common in people exposed to infrared or microwave radiation, such as glassblowers.

Cataracts may be partial or complete, stationary or progressive, and hard or soft. Cataracts are also classified by their location, e.g. posterior and anterior [common (senile) cataract is related to aging].

This is a summary of the different main types of cataracts:

1. Secondary cataract. Cataracts can form after surgery for other eye problems, such as glaucoma. Cataracts also can develop in people who have other health problems, such as diabetes. Cataracts are sometimes linked to steroid use.
2. Traumatic cataract. Cataracts can develop after an eye injury, sometimes years later.
3. Congenital cataract. Some babies are born with cataracts or develop them in childhood, often in both eyes. These cataracts may be so small that they do not affect vision. If they do, the lenses may need to be removed.
4. Radiation cataract. Cataracts can develop after exposure to some types of radiation.

5. Age-related cataract. Most cataracts are related to aging. Cataracts are very common in older people.

How Cataracts Affect Vision

On the left, a normal lens receives light and focuses it on the retina. On the right, a cataract blocks some light from reaching the lens and distorts the light being focused on the retina.

How a person with cataract sees the world

Symptoms
The following symptoms can also be a sign of other eye problems such as myopia. If you have any of these symptoms, be sure to check with your eye care professional.

Cloudy or blurry vision.
Colors seem faded.
Glare. Headlights, lamps, or sunlight may appear too bright. A halo may appear around lights.
Poor night vision.
Double vision or multiple images in one eye. (This symptom may clear as the cataract gets larger.)
Frequent prescription changes in your eyeglasses or contact lenses.

Prevention
Although cataracts have no scientifically proven prevention, it is sometimes said that wearing ultraviolet-protecting sunglasses may slow the development of cataracts. Regular intake of antioxidants (such as vitamin A, C and E) is theoretically helpful, but taking them as a supplement has been shown to have no benefit.

Treatment
The most effective and common treatment is to surgically remove the cloudy lens. There are two types of surgery that can be used to remove cataracts: extracapsular cataract extraction (ECCE) and intracapsular cataract extraction (ICCE).

Extra-capsular (ECCE) surgery consists of removing the lens but leaving the majority of the lens capsule intact. High frequency sound waves are sometimes used to break up the lens before extraction.

Intra-capsular (ICCE) surgery removes the entire lens of the eye, including the lens capsule, but is rarely performed in modern practice. In either of the surgeries, the cataractous lens is removed and replaced with a plastic lens which stays in the eye permanently.

Picture of the day:
The internal structure of the eye. Click 'Introduction' on the navigations to find out more about our eye! (:

Done By: Yee Herng

Myopia [2]

2008-02-28T23:16:00.004+08:00

Signs and symptoms of myopia
• headaches caused by eyestrains
• squinting of eyes to see far objects clearer
• persistent squinting
• sitting only short distances from television, movie screen or whiteboard
• holding of books very closely while reading
• unawareness of distant objects

Treatment of myopia
People with myopia usually are able to see a little better by squinting. This is caused by the different amount of light refracted into the eyes. All treatments for myopia have this same goal. Spectables, contacts and different surgeries all have the goal of correcting this refraction error.

Spectacles, contact lenses, and refractive surgery are the primary options to correct the refraction error of myopia.

Eyeglasses and contacts are usually the first treatment people use for myopia.
However, the inconveniences of using spectacles and contacts have lead to the search for other treatments.
Depending on the degree of the patient's myopia, other techniques may be used. Laser assisted in situ keratomileusis, or LASIK Eye Surgery, is the most popular surgery used to treat myopia.

• In this procedure the shape of the cornea is measured and changed to fix the degree of myopia using a laser.

An alternative to LASIK, Photorefractive Keratectomy, PRK for short, uses the same concept of reshaping the cornea but uses different procedures.

For non-surgical treatments (except glasses and contacts), there are Orthokeratology and Corneal Ring Segments.
People with lower degrees of myopia are better suited for these techniques.

• Orthokeratology uses RGP contact lenses to gradually and temporarily reshape the curvature of the cornea.
• Corneal ring segments are small polymer plastic materials that are implanted into the cornea to reshape it for corrected vision.

-XiuLi

Blindness - Loss of vision

2008-02-28T15:33:00.002+08:00

Blindness - Loss of vision

Definition
Blindness is the condition of a lack of vision or the inability to see. It may also refer to a loss of vision that cannot be corrected with glasses or contact lenses.

Partial blindness means you have very limited vision. Complete blindness means you cannot see anything and do not see light. People with vision worse than 20/200 are considered legally blind in the United States.

Causes
Blindness has many causes. The leading causes of chronic blindness include cataract, glaucoma, age-related macular degeneration, corneal opacities, diabetic retinopathy, trachoma, and eye conditions in children (e.g. caused by vitamin A deficiency).

Age-related blindness is increasing throughout the world, as is blindness due to uncontrolled diabetes. On the other hand, blindness caused by infection is decreasing, as a result of public health action. Three-quarters of all blindness can be prevented or treated.

Most visual impairment is caused by disease and malnutrition. According to WHO estimates in 2002, the most common causes of blindness around the world are: cataracts (47.8%), glaucoma (12.3%), uveitis - inflammation involving the interior of the eye (10.2%), age-related macular degeneration (AMD) (8.7%), corneal opacity (5.1%), diabetic retinopathy - damage to the retina (4.8%), and trachoma - infectious eye disease (3.6%).

Other causes include:
- Blocked blood vessels
- Complications of premature birth (retrolental fibroplasia - abnormal blood vessel development in the retina in a premature infant)
- Complications of eye surgery
- Lazy eye
- Optic neuritis (inflammation of the optic nerve)
- Stroke
- Tay-Sachs disease (deadly disease passed down through families that causes damage to the nervous system)
- Retinitis pigmentosa (an eye disease which causes damage to the retina. Causes problems with night vision and peripheral vision.)
- Retinoblastoma (cancer of the retina, affects children under age of 6)
- Lead poisoning
- Optic glioma (tumors that grow in various parts of the brain)

I will focus on two different causes of blindness - Cataracts and Trachoma in the later posts.

Pictures of the day:

The world looks different to an insect because of the compound nature of its eyes and also because they are more sensitive to different wavelengths of light than our eyes are. For example some insects can see UV rays. Features of plants that are invisible to our eyes are apparent to insects because the patterns of the features are visible in the UV rays.

Done by: Yee Herng