- ANATOMY AND FUNCTIONING OF THE EYE
- COMMON EYE AILMENTS
- DRY EYE
- DIABETIC EYE DISEASE
ANATOMY AND FUNCTIONING OF THE EYE
We usually take vision for granted. However the process of how your eye sees and perceives objects is a complex and fascinating process. One can compare it to the functioning of a camera.
Cornea is the clear front surface of the eye. Light is focused primarily by the cornea. This acts like a camera lens.
Iris:- controls the amount of light reaching the back of the eye by automatically adjusting the size of the pupil. One can say it acts like the diaphragm of a camera.
Lens - The Lens is located behind the pupil and it helps the eye focus automatically on near and approaching objects like an autofocus camera through a process called accommodation.
Pupil acts like an aperture of a camera. It is the round dark center of the eye which regulates the amount of the light the retina receives.
The light focused by the cornea and the lens and limited by the iris and pupil reaches the retina. It is a sensory membrane that lines the eye and receives the images and converts it into signals that reach the brain through the optic nerve. The optic nerve then transmits these signals to the visual cortex. The visual cortex is a part of the brain that controls our sense of sight.
Refractive errors are optical imperfections that prevent the eye from properly focusing light, causing blurred vision.
The common refractive errors are myopia, hypermetropia and presbyopia.
- Visual Fatigue
- Squinting in order to focus on the object
- Prescription of Eye Glasses or contact lenses
- Intraocular surgery/Refractive Surgery
Myopia or nearsightedness is a condition when close objects appear clearly but distant objects appear blurry. Instead of the image falling on the retina, it falls infront of the retina due to the eyeball being a little long. This makes distant objects look blurry. This problem may also occur if the cornea is too curved or the lens is too thick for the length of the eyeball.
Hypermetropia or farsightedness is a condition when distant objects appear clearly but near objects appear blurry. Some people may not notice any problems with their vision, especially when they are young. In this condition the image forms behind the retina since the eyeball is too short. An abnormal shape of the cornea or lens may also be a reason.
In astigmatism, light does not fall evenly on the retina. It occurs when light is bent differently depending on where it strikes the cornea and passes through the eyeball. In a normal eye, the degree of roundness in a curve in a cornea is similar in all areas. In an eye with astigmatism, the cornea is unevenly rounded which cause images to be blurry. Multiple focus points occur either behind or infront of the retina.
As people age, the natural lens gradually hardens due to which it is not able to focus light. The muscle fibres around the lens become weaker, which makes it difficult for it to focus light on the retina. The eye finds it harder to focus on close up objects. The image is formed behind the retina just like hypermetropia.
Cataracts are normal clouding of the eye's natural lens which leads to decrease in vision.The lens is mostly made up of protein and water. With age, the protein tends to clump together and starts to cloud a small area of the lens thus affecting vision. The cataract gradually grows bigger and surgery is the only way to treat it. Most of the cataract cases are common after age 60. However, there have been some instances of people getting cataracts in their 50's. The cataracts when small do not affect vision . It grows bigger gradually over time into a mature cataract. Hence detection of the cataract at an early stage is important. Cataracts are the most common eye disease prevalent in the world today.
Patients with diabetes, regular smokers and alcohol drinkers and those whose eyes are exposed for a prolonged time in UV Light are at a risk of having a cataract.
- Having blurry vision
- Seeing double
- Being extra sensitive to light
- Difficulty in night vision
- Seeing bright colours as faded
- Seeing halos when looking at bright lights.
DIABETIC SNOWFLAKE CATARACT
DIABETIC SNOWFLAKE CATARACT
- A subcapsular cataract occurs at the back of the lens. People with diabetes or those taking high doses of steroid medications have a greater risk of developing a subcapsular cataract.
- A nuclear cataract forms deep in the central zone (nucleus) of the lens. Nuclear cataracts usually are associated with aging.
- A cortical cataract is characterized by white, wedge-like opacities that start in the periphery of the lens and work their way to the center in a spoke-like fashion. This type of cataract occurs in the lens cortex, which is the part of the lens that surrounds the central nucleus.
Treatment of cataract involves cataract surgery where the cloudy lens is replaced with an artificial intraocular lens(IOL). The success rate of cataract surgery in general around the world is high. In complicated cases when the patient has multiple diseases such as diabetes and /or glaucoma, the skill and experience of the surgeon is what is important.
Surgery is not performed on both eyes at a time. They are usually operated upon 4 weeks apart.
Before the Surgery
Some tests are done a week or two before the date of surgery. These tests involve measuring the curve of the cornea and the size and shape of the eye. This helps us choose the appropriate IOL.
Cataract patients may be asked to skip dinner the night before the surgery and breakfast on the day of the surgery.
During the surgery
On the day of the surgery, drops are put into the patients eye to dilate the pupil. The area around the eye is washed and cleaned.
The surgery is painless and the patient may not even need anaesthesia. The surgeon may perform the surgery by only putting drops in the patients eyes. However, all operations involve an anaesthetist on standby who will make the decision based on the patient's health history. Usually the patient stays awake for the duration of the operation and the area around the eye is numbed with an anaesthetic.
After the surgery
After the surgery, a patch will be placed on the patient's operated eye. Itching and mild discomfort will be there for a day after the surgery. T The eye may be sensitive to light and touch. The patient should avoid rubbing or pressing on his/her eye. Some fluid discharge may be present. After a day or two, the discomfort will disappear.
After about a week or two after surgery, eyedrops are generally prescribed to accelerate healing and decrease the risk of infection. Eyeshield glasses or dark glasses are prescribed to protect the operated eye. The patient may have to wear them for a week or two.
Activities such as lifting heavy objects and bending from the waist should be avoided for a while. Light household chores, climbing up and down the stairs can be done.
Possible complications after surgery
Problems after surgery are rare but can occur in some cases.
- double vision
- high or low eye pressure
- loss of vision
If these symptoms occur, the patient should seek medical help promptly in order to treat them successfully.
At times the eye tissue that encloses the IOL may become cloudy which may lead to blurred vision. This condition is called an after cataract. This may develop months or years after surgery.
This is treated by laser treatment called YAG laser capsulotomy. The laser is used to make a tiny hole in the eye tissue behind the lens to let light pass through. It is painless and does not result in high pressure or other such complications. Drops maybe given to lower eye pressure before or after the procedure.
Healing after a cataract surgery takes time as the operated eye needs time to adjust to brightness, especially if the other eye has a cataract. The patient may need new pair of glasses with or without power. He or she may opt for contact lenses if needed. Initially colors may seem to be very bright since the IOL lens is clear whereas the natural lens has a yellowish/brownish tint.
People after the age of 60 should have a comprehensive dilated eye exam every 2 years to detect possible eye conditions such as glaucoma and age related macular degeneration.
What is Glaucoma?
The condition called Glaucoma is a group of conditions that can damage the eye's optic nerve and result in vision loss and blindness. This is the most common eye disease after cataracts in the world. This is a condition which needs to be detected and treated early.
High eye pressure can damage the optic nerve. Fluid flows from in and out of the front portion of the eye called the anterior chamber to nourish the nearby tissues. There is an open angle at the point where the cornea and iris meet. This is the point at which the fluid leaves the chamber. When the fluid reaches the angle, it flows through a spongy meshwork just like a drain. In an eye with open angle glaucoma, the fluid passes through the meshwork too slowly. This leads to a build up of fluid which results in high eye pressure which may damage the optic nerve. This is why controlling pressure inside the eye is important.
Patients with a risk of glaucoma are advised to check their blood pressure as well as it may be a risk for optic nerve damage.
However not every patient with high eye pressure will develop glaucoma. Some people can tolerate higher pressure than others. Whether one gets glaucoma depends on the pressure the optic nerve can tolerate without being damaged. This level of pressure is different for every person. This is why a comprehensive dilated eye examination should be done from time to time.
One can develop glaucoma even without an increase in eye pressure which is called low tension or normal tension glaucoma.
A comprehensive dilated eye exam can reveal risk factors such as high pressure, abnormal optic nerve anatomy and thickness of cornea. Eye drops can reduce the risk of glaucoma by half.
Who are at a risk of getting glaucoma?
People over the age of 60 and people who have a family history of glaucoma.
At first glaucoma has no symptoms. Vision stays normal and it causes no pain. It can develop in one or both eyes. However without treatment, there may be loss in peripheral vision. It may get worse over time as the patient will develop tunnel vision.
Detection of Glaucoma
Glaucoma is detected through various means
- Visual Acuity test - This is a regular eye chart test where patient's vision is checked from various distances.
- Visual Field Test -It measures peripheral or side vision.
- Dilated Eye Exam -After the pupil is dilated or eye is widened due to drops, a special magnifying lens is used to examine retina and optic nerve to check signs of damage.
- Tonometry - A tonometer is used to measure pressure inside the eye. Numbing drops may be used.
- Pachymetry - A pachymeter measures the thickness of the cornea.
Glaucoma can be prevented and its effect reduced but it cannot be cured. Vision lost from glaucoma cannot be restored.
Early diagnosis and treatment is important as it can delay progression of the disease.
Medicines in the form of eyedrops or pills are prescribed to lower eye pressure. Conventional surgery and trabeculoplasty are also done when required by the eye surgeon.
What is Dry Eye?
Dry Eye happens when the eye does not produce tears properly, or the tears are not of the correct consistency or when it evaporates quickly. This condition may also lead to inflammation of the surface of the eye. If dry eye is left untreated, dry eyes can lead to pain, ulcers or scars on the cornea. Reading or watching a computer screen for an extended period of time is a difficult task for dry eye patients. Some types of Dry Eye are Aqueous Tear Deficient Dry Eye and Evaporative Tear deficiency dry eye. Aqueous Tear deficient dry eye happens when lacrimal glands fail to produce enough of the watery component of tears to maintain a healthy surface. Evaporative dry eye results from inflammation of the meiobian glands located in the eyelids. The meiobian glands produce the lipid or oily part of tears that slows evaporation and keeps the tears stable.
Dry Eyes can be linked with -
- inflammation of the surface of the eye, the lacrimal gland or the conjunctiva.
- any disease which alters the components of tears.
- an increase in the surface of the eye such as thyroid disease when the eyes protrude forward.
- cosmetic surgery where the eyes are opened too widely.
- stinging or burning of the eye
- sandy or a gritty feeling as if something is in the eye
- production of excess tears followed by very dry eye periods
- stringy discharge from the eye
- pain and redness in the eye
- heavy eyelids
- episodes of blurred vision
- inability to cry when under stress
- decreased tolerance of activities which require constant visual attention like reading or working on a PC.
- uncomfortable contact lenses
Causes of Dry Eye -
- Infrequent blinking especially while staring at computer or video screens.
- dry eye may result as a side effect of some medications such as antihistamines, nasal decongestants, birth control pills,tranquilizers and certain blood pressure medicines.
- Skin diseases on or around the eyelids can result in dry eye.
- Diseases of the glands in the eyelids such as meibomian gland dysfunction.
- Can occur in pregnant women.
- Allergies can be linked to dry eyes.
- It can be a symptom of chronic inflammation of the conjunctiva which is the membrane lining the eyelid and covering the front part of the eye or the lacrimal gland.
- Dry eyes can be associated with immune system disorders such as Sjogren's syndrome,lupus and rheumatoid arthritis. These diseases can lead to inflammation and dryness of the eyes, mouth and other mucous membranes.
- Loss of sensation in the cornea from long term contact lens wear can lead to dry eye.
- Dry Eyes can develop after refractive surgery like LASIK. Here dry eye symptoms may last from 3-6 months.
Depending on the causes of dry eye, the patient is accordingly treated. The priority is to check the underlying cause of dry eye such as lacrimal and meibomian gland dysfunction. Hence the underlying disease needs to be treated first. Cyclosporine which is an anti inflammatory medicine in the form of eye drops or ointment is the only prescription drug available to treat dry eye. It decreases corneal damage, increases basic tear production and reduces symptoms of dry eye. If contact lens wear is the cause, another type of contact lens maybe recommended. The patient may have to reduce the number of hours he/she wears the contact lens. In some cases, if the dry eye is severe, he/she may have to stop wearing contact lenses. In some cases lacrimal plugs or punctual plugs can be inserted painlessly in order to plug the drainage holes which are small circular openings at the inner corners of the eyelids where tears drain from the eye into the nose. The plugs are a temporary measure and is made of silicon or collagen. Supplements such as Omega -3 fatty acids may decrease the symptoms of irritation.
Conjunctivitis also known as Pink Eye happens when the conjunctiva gets inflamed. Conjunctiva is the thin, clear tissue which covers the inside of the eyelid and the white part of the eye called sclera. Due to the inflammation, blood vessels are more visible which gives the eye a pink or reddish appearance. The eye is usually painful, itchy and has a burning sensation. The eyes have a discharge that form a sticky crust during sleep. Conjunctivitis is also contagious and can happen to anyone who comes in contact with the infected person through touch. Allergic conjunctivitis is not contagious.
- Swelling of the conjunctiva
- Foreign body sensation in the eye
- Sensitivity to bright light
- Enlargement or tenderness in the lymph node infront of the ear. The enlargement feels like a small lump.
Causes & Types of Conjunctivitis
Conjunctivitis is generally caused due to bacterial or viral infections. It can also be caused due to allergic reactions or exposure to irritants. Viral conjunctivitis - Adenovirus or Herpesvirus are the most common viruses that cause conjunctivitis but it can also be caused due to other viruses. It can occur along with sore throat, cold and upper respiratory tract infection. Bacterial conjunctivitis - In this case the eye is infected with bacteria such as Staphylococcus Aureus, Streptococcus pneumonia and Haemophilius. Allergic conjunctivitis - it can be caused by allergies to pollen, dust mites, molds and animal dander. Irritants such as contact lens and lens solutions,chlorine in swimming pool, smog or cosmetics can be an underlying cause of conjunctivitis.
Most common cases of conjunctivitis are mild and heal on their own without any prescription treatment. Symptoms can be relieved by artificial tears for dryness and cold packs for inflammation. Viral conjunctivitis usually heals on its own within 7-14 days without any treatment. Antiviral medication can be prescribed by a physician to treat more severe form of conjunctivitis such as herpes simplex virus or varicella-zoster virus. Antibiotics usually does not heal viral conjunctivitis. Bacterial conjunctivitis can be treated with the help of antibiotics which shorten the illness and reduce the spread of infection to others. Medication is usually in the form of antibiotic eyedrops and ointment. These drops should help heal the eye within a few days. Allergic conjunctivitis is usually healed by eliminating or reducing contact with the allergen such as pollen. Allergy medication and certain eye drops can provide relief. Conjunctivitis caused by irritants such as contact lenses clear up after temporarily eliminating the irritant until the problem is resolved.
Steps to prevent and spread conjunctivitis
Viral and bacterial conjunctivitis are highly contagious. However allergic conjunctivitis is not contagious. Following are the steps one should take -
- Washing hands often with soap and water especially after touching the affected person's eyes,hands, linen or clothes. An alcohol based sanitizer will also work.
- The affected person should avoid touching or rubbing his/her eyes. - The discharge as a result of conjunctivitis should be washed several times a day.
- Eyeglasses / Sunglasses should be cleaned
- Towels, blankets and pillowcases should not be shared.
- Likewise eye makeup, face makeup ,make up brushes ,sunglasses should not be shared.
DIABETIC EYE DISEASE
Diabetic Eye disease is a group of eye conditions that can affect people with diabetes. Diabetic Retinopathy involves change to retinal blood vessels that can cause them to bleed or leak fluid thus distorting vision. It is the most common cause of vision loss among people with diabetes. Since retinopathy goes unnoticed until vision loss occurs, people with diabetes should get a comprehensive dilated eye examination done at least once a year. Controlling diabetes by taking medications as prescribed, staying physically active and maintaining a healthy diet can prevent or delay vision loss. Diabetic macular edema (DME) is a consequence of diabetic retinopathy which involves swelling in an area of the retina called the macula. Diabetic eye disease also includes cataract and glaucoma. All forms of diabetic eye disease has the potential to cause vision loss and blindness.
The early stages of diabetic retinopathy have no symptoms. The disease progresses unnoticed until it affects vision. Bleeding from abnormal retinal blood vessels can cause the appearance of "floating spots". These spots sometimes clears on their own. Without prompt treatment, bleeding often recurs, increasing the risk of permanent vision loss. DME can cause blurred vision.
A person with diabetic eye disease would have to undergo a comprehensive dilated eye examination which includes :
- Visual Acuity Testing - The eye chart measures a person's ability to see at various distances.
- Tonometry - this measures eye pressure.
- Pupil dilation - this enables the doctor to examine the retina and optic nerve once the pupil is widened using drops.
- Optical coherence tomography (OCT) - this technique is similar to ultrasound but uses light waves instead of sound waves to capture images of tissue inside the eye.
The dilated exam enables the doctor to -
- Check retina for changes to blood vessels.
- Leaking blood vessels or warning signs of leaky blood vessels such as fatty deposits.
- Swelling of the macula (DME)
- Changes in lens
- Damage to nerve tissue
Anti VEGF therapy - Anti VEGF drugs are injected into the vitreous gel to block a protein called vascular endothelial growth factor which can stimulate abnormal blood vessels to grow and leak fluid. Blocking VEGF can reverse abnormal blood vessel growth and decrease fluid in the retina. Focal/grid macular laser surgery - Here a few to hundreds of small laser burns are made to leaking blood vessels in areas of edema near the macula. Laser burns for DME slow the leakage of fluid thereby reducing swelling in the retina. Proliferative diabetic retinopathy (PDR) is treated with scatter laser surgery, sometimes called panretinal laser surgery or panretinal photocoagulation. This procedure involves making 1000-2000 tiny laser burns in areas of the retina away from the macula. These laser burns are intended to make the abnormal blood vessels shrink. It can preserve central vision but can cause loss of peripheral vision, night vision and colour.