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What is Refractive Error?

By definition a refractive error is an abnormality of the eye where the light rays do not converge on the Retina. Due to this a person has blurred image of objects and hence a subnormal eyesight.

There are three main types of Refractive Errors

• Hypermetropia
• Myopia
• Astigmatism

Hypermetropia

In Hypermetropia the image forms behind the retina. Hence if the object is beyond a particular distance, it is visible little more clearly, than if the object is near the eye. A person who crosses the age of 40yrs needs glasses, particularly for reading and near work. This is called Presb.

Another variety of hypermetropia is called Presbyopia. A person who crosses the age of 40yrs needs glasses, particularly for reading and near work. This is called Presbyopic error. This is because after this age the muscles controlling the ability to focus for near start becoming weak.

Children who have this kind of error need to diagnosed very early, otherwise they can loose there eyesight and this can have an effect on there school performance.

Three options are available to treat hypermetropia

• Glasses
• Contact lenses
• Refractive surgery

Refractive surgery is done in various ways. Lasik involves surgery on the Cornea. Similarly Conductive Keratoplasty is a new technique to treat Presbyopic type of refractive error. It is still not very popular, but will be in vogue in future. Prelex is a combination surgery involving surgery on the cornea and implantation of special type of lenses inside the eye.

Myopia

In Myopia the light rays fall in front of the retina. Hence a person with this defect will have better near vision than for distance. Generally the cause of this error is an abnormally long eyeball, but this error could also be due to abnormal shape of cornea. Heredity is one of the strong factors for myopia.

A person who develops myopia late in life is due to cataracts and this is temporary. A person who has myopia of high degree, has a chance of developing break in the retina, which can lead to loss of eyesight. Hence such persons are advised to undergo a very simple screening test of the retina, and if any such defects are noticed the they need to be treated at the earliest(by laser).

Three options are available to treat myopia

• Glasses
• Contact lenses
• Refractive surgery

Two types of Refractive surgeries are done for treating Myopia. Lasik is the commonest refractive surgery done anywhere in the world. A corneal flap of a particular thickness is taken(slice of cornea). This flap remains attached to the cornea at one end. Laser is then done on the exposed bed of the cornea and the flap is repositioned back. Phakic lens implantation is one more option for person with very high myopia (more than – 10). A specially designed lens is implanted inside the eye, without removing the original lens.

Astigmatism

In Astigmatism, some part of light rays fall on the retina, while some part do not. Hence the image seen by persons with this kind of error is abnormal in shape or elongated. Astigmatism can of the Hypermetropic or Myopic type or sometimes it could be a combination of both.

Three options are available to treat Astigmatism

• Glasses(Cylindrical lenses)
• Contact lenses(Toric)
• Refractive surgery

Contact Lenses

Contact lenses are worn on the cornea as an alternative to glasses. The main advantage of contact lenses is that it eliminates any artificially induced restriction in vision due to spectacle. Contact lenses ,therefore give near natural vision to a person having refractive errors. It also adds to the personality of a person.

Contact lenses are of two types

• Hard/Semisoft
• Soft

The Hard/Semisoft type of contact lenses are the older variety of lenses. The only advantage of this type of lens is, that they are durable and long lasting. However they are uncomfortable to wear and often not easily tolerated.

Soft Contact lenses are the most preferred type of lenses. They are more comfortable to wear and more suitable to eyes.

There are 4 types of soft lenses

• Soft lenses for spherical type of numbers:- Here lenses are of the yearly duration, quarterly duration or monthly use
• Toric soft lenses:- These are lenses used by persons having astigmatism(Cylindrical power)
• Multifocal lenses:- These lenses are used by people who need glasses for reading and distance both
• Coloured lenses:= Lenses of various colors are available for cosmetic purpose

Care to be taken while using soft contact lenses

While learning to use soft lenses for the first time, always do all movements very slowly. Do not rush into learning to wear or remove lense from the eye. Sometimes it can lead to injury to the eye if proper instructions from the doctor are not followed. Always wash hands and dry them before wearing and removing lenses. Do not wash soft lenses with water. Use the contact lens cleaning solution only to clean the lens. Do not sleep with the lens in the eye. Change the contact lens solution every 2-3 days. Keep the contact lens container clean. Do not use any kind of cosmetics or eye drops when wearing the lens.

Lazy Eye(Amblyopia)

Amblyopia causes more visual loss in the under 40 group than all the injuries and diseases combined in this age group. If not detected and treated early in life, amblyopia can cause loss of vision and depth perception. Improvements are possible at any age with proper treatment, but early detection and treatment offer the best outcome. Comprehensive vision screenings are needed for infants and pre-school children. An eye exam by a pediatrician or the 20/20 eye chart screening is not adequate for the detection of amblyopia (and other visual conditions).

Amblyopia, commonly known as lazy eye, is the eye condition noted by reduced vision not correctable by glasses or contact lenses and is not due to any eye disease. The brain, for some reason, does not fully acknowledge the images seen by the amblyopic eye. This almost always affects only one eye but may manifest with reduction of vision in both eyes. It is estimated that 3% of children under six have some form of amblyopia.

Causes of Lazy Eye

Anything that interferes with clear vision in either eye during the critical period(birth to 6 years of age) can cause amblyopia. The most common causes of amblyopia are constant strabismus(constant turn of one eye), anisometropia(different vision/prescriptions in each eye), and/or blockage of an eye due to cataract, trauma, lid droop, etc.

Amblyopia is a neurologically active process. In other words, the loss of vision takes place in the brain. If one eye sees clearly and the other sees a blur, the brain can inhibit(block, ignore, suppress) the eye with the blur. The brain can also suppress one eye to avoid double vision. The inhibition process(suppression) can result in a permanent decrease in the vision in the blurry eye that can not be corrected with glasses, lenses, or lasik surgery.

Detection and diagnosis of Lazy Eye

An eye exam by a pediatrician or the 20/20 eye chart screening is not adequate for the detection of amblyopia(and other visual conditions). The most important diagnostic tools are the special visual acuity tests other than the 20/20 letter charts currently used by schools, pediatricians and eye doctors. Examination with cycloplegic drops can be necessary to detect this condition in the young.

Since amblyopia usually occurs in one eye only, many parents and children are unaware of the condition. Many children go undiagnosed until they have their eyes examined at the eye doctor’s office at a later age. Comprehensive vision evaluations are highly recommended for infants and pre-school children.

Treatment of Lazy Eye

• Early detection of factors causing amblyopia is most effective means of treating Amblyopia.
• Screening of child before he/she starts school by an ophthalmologist is absolutely a must.
• If the child has refractive errors in any of his/her eyes, then it has to be worn from a very early age.
• Special exercises with one eye patched for a specified period of time is the most & only effective treatment for improving a amblyopic childs eyesight.

Remember

If the squint is large it can be a cosmetic problem when the child grows up. However, another important complication is amblyopia. This means that vision can be gradually affected if the squinting eye is left untreated. As mentioned above, even in very minor squints, if the two eyes are not exactly straight they cannot focus on the same point. This confuses the brain as two images are seen at the same time causing double vision. The weaker image then tends to be ignored by the brain. This weaker eye then gradually loses its power(just like if you never use one arm it will become wasted and weak). This loss in vision takes years to develop but is irreversible. Therefore even very slight squints in children should be treated.

The aim of the treatment is to get the weaker squinting eye trained up. If the cause of the squint is due to one eye being more long-sighted then wearing glasses to correct this may do the trick. Sometimes wearing a patch on the good eye to train up the weaker eye is advised for part of each day. Eye muscle exercises are sometimes tried. If the squint is large and the above measures do not seem to be helping, then an operation is sometimes performed to correct the squint. Treatments are usually under the supervision of Orthoptists who are specially trained people who deal with all aspects of squint and work in close co-operation with eye surgeons.

Squint Eye

Squint is the term used when the eyes are not exactly straight. When looking at an object, normal eyes will look exactly in the same direction. This is required for the light to fall on exactly the same parts of the two retinas(the backs of the eyes). If a squint is present the two eyes cannot focus on exactly the same point.

Types

The severity can vary. Some squints are very marked and obvious. Some only become noticeable when the child is tired. Some are quite small and are only discovered by a proper examination.

The cause can vary. Sometimes they are due to muscle or nerve problems of the eye. Sometimes eye diseases cause a squint. However, the majority are due to one eye being more longsighted than the other. In this common situation one eye has to strain more than the other to see clearly and this can lead to a squint.

The direction can vary. Most are convergent i.e. the squinting eye tends to look inwards. However, the squinting eye can be divergent(looking outward) or looking up or down.

Broadly Squint is divided in 2 types:

• Incommitant(where the degree of squint varies in different directions)
• Commitent(where the squint in all directions of gaze remains the same)

The Incommitent squint is mainly due to paralysis of one or muscles of the eye.

The Commitent type has multiple reasons. It is broadly classified as

• Exotropia(eyes move out)
• Esotropia(Eyes move inwards)
• Vertical squints(misalignment of eyes in vertical direction)

Exotropia

Exotropia is the outward deviation(turn) of an eye. The deviation may occur while fixating(looking at) distant objects, near objects or both. Fortunately, most exotropia is intermittent and this means that the eye deviation or turn occurs only some of the time. As long as the eyes are straight some of the time, the brain will develop some normal functioning of the eyes(stereoscopic depth perception). Since the brain and eyes work properly some of the time, time is on your side.

Treatment for intermittent exotropia does not have to occur immediately. As a matter of fact, early surgery has the potential of disturbing the ability of the brain for fusion in the future and can cause a permanent reduction in vision (Amblyopia).

When the turn occurs during distance viewing the major problem is cosmetic. The child might be accused of daydreaming or not paying attention. The parents will often notice the turn and then they bring their child to the eye doctor who might not find it. This is because the turn usually occurs during times of inattention, fatigue, or distance viewing not during the anxiety-provoking eye examination. These children often close their eye in bright sunlight.

If the squint is constant and is causing disruption of the ability of stereopsis(three dimensional vision) then corrective muscle surgery is the only tretment.

Esotropia

Esotropia can be divided into various categories each requiring a different treatment plan, each having a different prognosis.

Types of Esotropia

There are following 4 types of Esotropia:

• Congenital Esotropia
• Infantile Esotropia
• Accommodative Esotropia
• Partially Accommodative Esotropia

Congenital and Infantile Esotropia

Congenital means from birth and, using this strict definition, most infants are born with eyes that are not aligned at birth. Only 23% of infants are born with straight eyes. In the majority of cases, one eye or the other actually turns outward during the neonatal period. Within the first three months the eyes gradually come into more consistent alignment as coordination of the two eyes together as a team develops.

It is common for infants to appear as if they have Esotropia, or inward turn of the eyes, because the bridge of the nose is not fully developed. This false or simulated appearance of an inward turning is known as Epicanthus. As the infant grows, and the bridge narrows so that more of the white of the eyes(Sclera) is visible on the inner side, the eyes will appear more normal.

True Congenital Esotropia is an inward turn of a large amount, and is present in very few children, but the infant will not grow out of this turn. True Infantile Esotropia usually appears between the ages of 2 and 4 months.

The baby with Infantile Esotropia usually cross fixates, which means that he or she uses either eye to look in the opposite direction. The right eye is used to look toward the left side, and the left eye is used to look toward the right side. By definition, they alternate which eye they are looking with. It is more difficult to help this type of Strabismus with non-surgical methods, such as vision therapy and/or glasses. Sometimes, clear tape applied to the inner third of each lens(Occlusion) can reduce the tendency to turn inward. Prisms may aid alignment if the turn is not too large.

Some children who develop Strabismus, in which coordination between the two eyes is poor, also have a typical gross motor development patterns. They typically skip the crawling stage with bilateral movements, and go right from creeping to standing. The interplay between gross motor, particularly balance systems(Cerebellar and Vestibular) and Binocular Systems(motor control of the two eyes) is evident in the large number of young children with Cerebral Palsy who have Strabismus.

If the inward turn of the eye is constant, and of a large amount, surgery may be indicated. Both the parent and surgeon have to be committed to multiple procedures to obtain perfect alignment. Improved alignment may look better cosmetically, but it does not necessarily enable the brain to utilize information from both eyes together. Stereopsis, or two-eyed depth perception, is often poor following surgical treatment. The best chance for visual success occurs when the surgeon works with an Optometrist who is comfortable in prescribing glasses and exercises to encourage perfect alignment of the eyes with proper fusion. This model of cooperative care is similar to the relationship between the orthopedic surgeon and physical therapist.

If Amblyopia is present(poorer vision in the turned eye), therapy including patching is often required so that the turned eye develops the capacity to see as well as the better eye. It is best to do this before surgery.

The chance of developing Binocular Vision with surgery alone diminishes with age. Older children with Infantile Esotropia may need both surgical intervention and vision therapy. Smaller turns may only require vision therapy. Getting the eyes to work together requires a lot of time and effort, but is usually worth it.

Accomodative Esotropia

If excessive inward turning of an eye is first noted around 2 years of age, it may be due to difficulty integrating the focusing(accommodative) system with the eye alignment(binocular) system. Normally when we look across the room or beyond, our eyes are parallel, or straight. However, when we look at things up close, two things happen. We need to converge more(aim both eyes inward at the same time) and we have to input more focus, or accommodate to keep things clear. Children have large amounts of focusing power, and sometimes in getting things clear, inward turning or Esotropia results. If the inward turning only occurs up close, as when playing with small objects, making eye contact, coloring, looking at picture books and so forth, the child may just need glasses for near activities to reduce or eliminate the esotropia.

However, if a child is significantly farsighted(Hyperopia), an inward turn of the eye may even occur when focusing to look further away, such as television. If the amount of turn is greater at near than far, your optometrist may prescribe a multifocal lens. For children this could be a traditional bifocal with a line, or a form of no-line bifocal or progressive lens. Your optometrist will review with you which is the best option for your child. In addition, vision therapy may be of benefit. This condition should never be treated with surgery.

When the eyes are aligned by corrective lenses sometimes the eyes spontaneously begin to work together. Other times, they need help. Remember, the habit of suppressing or turning off one eye or the other was probably developed over a number of years. The eyes have to be trained to work together again and suppression must be eliminated in order to restore normal eye teaming, depth perception, and stereopsis. The eye doctor might have to patch an eye that was suppressed or turned off and/or employ vision therapy.

Intermittent turns usually do not require long term treatment. Vision Therapy may be necessary to improve the muscle coordination and eventually eliminate the bifocal.

Patients with Accommodative Esotropia should never have eye muscle surgery to eliminate the need for glasses. If they do, they will have significant focusing problems when they get older. In the future, these patients might be excellent candidates for refractive surgery(Hyperopic LASIX) or contact lenses. This should be coordinated with the developmental Optometrist and LASIK surgeon.

Partially Accommodative Esotropia

In some instances, part of the inward turn is due to basic Esotropia, and an additional amount due to the effect of accommodation. Glasses may reduce the amount of eye turn, but it is not totally compensated. Initially, the eye doctor may prescribe prism to compensate for the amount of turn. Office-based Vision Therapy is usually needed. Surgery remains an option to address the non-accommodative portion of the Esotropia. Remember that surgery alone rarely enables a patient to learn how to use both eyes together as a team, and usually leaves the patient with poor Stereopsis. Because vision is a learned process, some form of therapy is often helpful in learning new binocular vision patterns, or restoring normal pathways that have been lost or underutilized. Binocular vision occurs in the visual centers of the brain, not in the eye muscles.

Hypertropia

Upward deviation of the eye is usually due to a paresis of one of the muscles that either elevate or depress the eye. Most of the time it is due to one specific muscle known as the Superior Oblique. The paresis may be congenital(born with it) or acquired. Most of the time, palsy of the superior oblique is congenital but may present itself later in life. For one reason or another the fusion system breaks down and the deviation becomes manifest. An inexperienced doctor may send this patient out for extensive neurological testing including MRI. There are tell tale signs that tell the sophisticated doctor that the turn has been there a long time and one does not have to worry about it such as a head tilt being present in old pictures, etc.

If the Hypertropia is a decompensation of a congenital deviation, then treatment may consist of prism glasses and vision therapy. Our goal is fusion without prismatic glasses. However, often, treatment requires small amount of prism to hold the eyes in comfortable alignment.

Diabetic Eye Disease

Normal Retina

Diabetic Macular Edema

Severe Nonproliferative Diabetic Retinopathy

Vitreous Haemorrhage

Diabetes is a chronic(lifelong) disease in which carbohydrate(Glucose ) metabolism(breakdown ) is abnormal due to insufficient level of Insulin hormone in the body. High glucose blood level is the hallmark of this disease. This causes many secondary effects on all organs and systems in the body.

Diabetic eye disease is one of the vital and potentially dangerous complication 0f diabetes. If it remains undetected and therefore untreated it can cause permanent blindness.

What is Diabetic Eye?

Diabetic eye disease refers to a group of eye problems that people with diabetes may face as a complication of this disease. All can cause severe vision loss or even blindness.

Diabetic eye disease may include:

• Diabetic retinopathy – damage to the blood vessels in the retina.
• Cataract – clouding of the eye lens.
• Glaucoma – increase in fluid pressure inside the eye that leads to optic nerve damage and loss of vision

Most common Diabetic Eye disease

Diabetic retinopathy. This disease is a leading cause of blindness all over the world. It is caused by changes in the blood vessels of the retina. In some people with diabetic retinopathy, retinal blood vessels may swell and leak fluid. In other people, abnormal new blood vessels grow on the surface of the retina. These changes may result in vision loss or blindness.

Symptoms

Often there are none in the early stages of the disease. Vision may not change until the disease becomes severe. Nor is there any pain. Blurred vision may occur when the macula – the part of the retina that provides sharp, central vision – swells from the leaking fluid. This condition is called macular edema. If new vessels have grown on the surface of the retina, they can bleed into the eye, blocking vision. But, even in more advanced cases, the disease may progress a long way without symptoms. That is why regular eye examinations for people with diabetes are so important.

Most likely to be affected

Anyone with diabetes. The longer someone has diabetes, the more likely he/she will get diabetic retinopathy. Between 40-45 percent of those with diagnosed diabetes have some degree of diabetic retinopathy.

Detection

If you have diabetes, you should have your eyes examined at least once a year. Your eyes should be dilated during the exam. That means eyedrops are used to enlarge your pupils. This allows the eye care professional to see more of the inside of your eyes to check for signs of the disease. In some patients special procedures are done to detect changes which could lead to blindness. These are Fundus Photography, Fundus Fluoroscein Angiography(FFA) and Optical Coherence Tomography(OCT). The figure is that of a normal Fundus Angiogram.

Treatment

Your eye care professional may suggest laser surgery in which a strong light beam is aimed onto the retina. Laser surgery and appropriate follow-up care can reduce the risk of blindness by 90 percent. However, laser surgery often cannot restore vision that has already been lost. That is why finding diabetic retinopathy early is the best way to prevent vision loss.

In patients with very advanced diabetic eye disease, surgery is necessary to remove the accumulated blood and clear the scar tissue from inside the eye(Vitrectomy).

Prevention

Diabetic Retinopathy cannot be totally prevented, but your risk can be greatly reduced. The Diabetes Control and Complications Trial (DCCT) showed that better control of blood sugar level slows the onset and progression of retinopathy and lessens the need for laser surgery for severe retinopathy.

The study found that the group that tried to keep their blood sugar levels as close to normal as possible also had much less kidney and nerve disease. This level of blood sugar control may not be best for everyone, including some elderly patients, children under 13, or people with heart disease. So ask your doctor if this program is right for you.

Other Diabetic Eye Diseases

If you have diabetes, you are also at risk for other diabetic eye diseases. Cataracts develop at an earlier age in people with diabetes. Cataracts can usually be treated by surgery.

Glaucoma may also become a problem. A person with diabetes is nearly twice as likely to get glaucoma as other adults. And, as with diabetic retinopathy, the longer you have had diabetes, the greater your risk of getting glaucoma. Glaucoma may be treated with medications, laser, or other forms of surgery.

Current Research

Much research is being done to learn more about diabetic eye disease. This research should provide better ways to detect and treat diabetic eye disease and prevent blindness in more people with diabetes.

Protection of vision

Finding and treating the disease early, before it causes vision loss or blindness, is the best way to control diabetic eye disease. So, if you have diabetes, make sure you get a dilated eye examination at least once a year.

In a nutshell

Diabetes is a disease that can cause very serious health problems. If you have diabetes:

• Know your ABCs-A1C (blood glucose), blood pressure (BP), and cholesterol numbers.
• Take your medicines as prescribed by your doctor.
• Monitor your blood sugar daily.
• Reach and stay at a healthy weight.
• Get regular physical activity.
• Quit smoking.

What is Glaucoma?

What is Cataract?

What is Dry Eye?

Dry Eye(also called dry eye syndrome) is a very common condition. Dry eye occurs when people do not have either enough tears, or the correct composition of tears, on the surface of their eyes to lubricate the eyes and keep them comfortable.

The diagram shows the tear film and its layers along with the location of the glands responsible for the secretion of the components of the film onto the surface of the eye. The outer, oily layer of the tear film is produced by the meibomian glands in the eyelids and reduces evaporation of the tears. The thick, middle, watery layer is made by the lacrimal gland above the upper eyelid and washes away irritants. The inner, mucus layer is secreted by the goblet cells in the conjunctiva of the eyelids and helps the tear film stick to the cornea.

The prevalence of Dry Eye increases with age, so that it is extremely common in older people of both sexes. The condition affects 2 – 3 times more women than men.

Symptoms

If you have dry eye, your eyes can feel persistently gritty, itchy, burning, and painful. These sensations often worsten as the day goes on. Stringy mucus may appear in or around the eyes. You will know if you have dry eye. The condition does not require sophisticated diagnosis. Patients with the most severe disease are at increased risk of developing corneal infection, scarring or ulceration. These conditions can cause permanent vision loss, so it is important to seek professional help if you have severe symptoms of dry eye.

Dry eye syndrome is not a frequent cause of blindness; however, it is still an important public health problem. One reason for this is that it is so common. In fact, visits for dry eye syndrome are one of the leading reasons for patients to seek eye care. This is because its symptoms are very bothersome and lead to a decreased quality of life, reduced work capacity, and poor psychological health. Furthermore, dry eye syndrome is associated with a decreased ability to perform activities that require visual attention, such as reading and driving a car.

Severe dry eye is sometimes caused by Sjögren’s syndrome, which is a chronic, multi-organ, autoimmune disorder that also results in dry mouth and often arthritis.You should be under a doctor’s frequent care if you have Sjögren’s.

Diagnosis

Some very simple tests are used to diagnose dry eye. Schirmmer test is one of them. Here a filter paper strip of a particular length is kept In the lower lid space and its wetting is measured. Staining of the Cornea and Conjunctiva with special dye like Fluoroscein and Rose Bengal are some of the other ways to diagnose dry eye.

Computer Vision Syndrome

People who work on computers or any kind of video display unit for very long hours, tend to develop symptoms of dry eye.

Some simple measures can help in relieving these symptoms, like working at a comfortable distance from the monitor, blinking frequently(average of 20 times in a minute), no staring at the monitor, keeping the brightness and contrast levels of the monitor to a comfortable level, taking intermittent rest during working hours, no sitting in front of an air draft ( a/c., fan), keeping the monitor at a slightly lower level than the eye, keeping yourself well hydrated, maintaining a comfortable posture.

Prevention is better than cure

Anything that may cause dryness, such as an overly warm room, hair dryers, smoke or wind should be avoided by any person with dry eye. A humidifier in heated rooms may help. If wearing contact lenses increases your discomfort, wear spectacle eye-glasses instead. Some people with dry eye complain of scratchy eyes when they wake up. This symptom can be treated by using an artificial tear ointment at bedtime. There is some evidence that, in older women, hormone replacement therapy makes dry eye worse. If you are using HRT, talk to your doctor about this. And seek help if symptoms occur frequently or interfere with your functioning; it is important to see an ophthalmolist or optometrist to rule out corneal injury or infection.

Treatment

The first line of treatment is usually eye drops that act as artificial tears and give some temporary relief. These solutions and ointments give some temporary relief, but do little to arrest or reverse any damaging conditions. Many brands are available without a prescription. For mild cases, try several to find the one you like best. The preservatives in some eye drops can irritate the eye. Preservative-free artificial tears may be required. Researchers are trying to develop better artificial tears, especially ones that are formulated to normalize the electrolyte balance while lubricating the ocular surface. One promising new treatment now in clinical trials is the use of eye drops containing andogen.

For more severe cases of dry eye, in which the cornea is inflamed, anti-inflammatory agents are sometimes prescribed. Topical steroids(in eye drops) are safe for short-term use, to combat inflammation, but can cause side-effects when used for a long time. A current research area is how to actively suppress inflammatory mechanisms, rather than just passively lubricate the surface of the eye. Tears drain out of each eye, and into the nose, through a small channel. Your ophthalmologist may decide to close these channels either temporarily or permanently, to keep the tear film on the surface for a longer time. For some forms of dry eye, tiny plugs can keep tears on the eye surface by slowing the rate of drainage from the eye; this procedure is called Punctal Occlusion.

Anatomy of the eye

Structure of the eye ball: This is the cross-section(side view) of the eye. The eye works like the camera, transmitting light and images to the brain.

Tear apparatus of the eye: Tears are formed in the Lacrimal Glands and the Accessory Lacrimal Glands. They are drained via the Lacrimal Ducts, at the nasal side of the eye, into the Nasolacrimal duct, which opens into the nose. That is why any eyedrops applied to the eye come into the nose and throat. Sometimes the Nasolacrimal duct may get blocked and it may then need to be openned surgically.

Cross-section of the eyelid: The tarsal plate is like a backbone of the eyelid. It gives strength and flexibility to the eye lid. The muscles in the lid are attached to this structure. The Meibomian Glands are like sweat glands. It secretes a fatty substance which helps in maintaining the surface tension of the tears. A blockage of these glands leads to a condition called Chalazion.

Cross-section of the Cornea: Cornea is the front transparent layer of the eye. It is a multi layered structure. The tears also form a thin layer on top of the cornea and protect and nourish it. A deficiency of tears can cause Dry eye. Shape of the Cornea is altered with LASER in Refractive Surgery(Surgery for correcting spectacle numbers). Any opacity or injury to this structure can cause permanent opacity and hence loss of vision.

Division of the eye: The eye is divided in two main parts. The front or Anterior Segment. This has a water like fluid called Aqueous Humor.The back part or Posterior Segment has a thick jelly like substance called Vitreous Humor.

Anterior Segment of the eye: It also has 2 sub-sections divided by the Iris. The Iris is like the shutter of camera. It controls the amount of light coming in the eye. The Aqueous Humor enters the chamber from the Ciliary Body and passes through the hole in the Iris called the Pupil, to exit in the angle between the Iris and Cornea. Any obstruction in the circulation of this fluid leads to rise in the eye pressure and can then cause a condition called Glaucoma.

Lens of the eye: When this becomes opaque, it is called Cataract. Surgery is the only treatment for Cataract.

Front view of the Retina: Retina is inner layer of the eye which when stimulated by light sends signal to brain and we perceive an image. The retina may get detached from the inner layer and is then put in its place by surgery. Diseases like Diabetes, High Blood pressure, old age, high myopia, etc can also damage the retina and can cause permanent loss of vision.

Cross-section of the Retina: Retina is made up of 10 layers. Signal from here are carried by the Optic Nerve to the brain via the visual pathway. The Optic Nerve can be affected in many disease, like Glaucoma and Alcohol abuse.

Eye Muscles: They control the eye movement. Any imbalance in the tone of these muscles can lead to Squint. Sometimes surgery is necessary to restore the proper balance.