A Cataract is a clouding of the lens in the eye leading to a decrease in vision. It can affect one or both eyes. Often it develops slowly. Symptoms may include faded colors, blurry vision, halos around light, trouble with bright lights, and trouble seeing at night. This may result in trouble driving, reading, or recognizing faces. Poor vision may also result in an increased risk of falling and depression. Cataracts are the cause of half of blindness and 33% of visual impairment worldwide. Cataracts are most commonly due to aging, but may also occur due to trauma, radiation exposure, be present from birth, or occur following eye surgery for other problems.
Signs & Symptoms- Signs and symptoms vary depending on the type of cataract, though considerable overlap occurs. People with nuclear sclerotic or brunescent cataracts often notice a reduction of vision. Those with posterior subcapsular cataracts usually complain of glare as their major symptom. The severity of cataract formation, assuming no other eye disease is present, is judged primarily by a visual acuity test. The appropriateness of surgery depends on a patient’s particular functional and visual needs and other risk factors, all of which may vary widely.
Age– Age is the most common cause. Lens proteins denature and degrade over time, and this process is accelerated by diseases such as diabetes mellitus and hypertension. Environmental factors, including toxins, radiation, and ultraviolet light, have cumulative effects, which are worsened by the loss of protective and restorative mechanisms due to alterations in gene expression and chemical processes within the eye.
Trauma- Blunt trauma causes swelling, thickening, and whitening of the lens fibers. While the swelling normally resolves with time, the white color may remain. In severe blunt trauma, or injuries which penetrate the eye, the capsule in which the lens sits can be damaged. This allows fluid from other parts of the eye to rapidly enter the lens leading to swelling and then whitening, obstructing light from reaching the retina at the back of the eye. Cataracts may develop in 0.7 to 8.0% of cases following electrical injuries.
Radiation- Ultraviolet light, specifically UVB, has been shown to cause cataracts, and some evidence indicates sunglasses worn at an early age can slow its development in later life. Microwave radiation has also been found to cause cataracts. The mechanism is unclear, but it may include changes in heat-sensitive enzymes that normally protect cell proteins in the lens. Another possible mechanism is direct damage to the lens from pressure waves induced in the aqueous humor. Cataracts have been associated with ionizing radiation such as X-rays. The addition of damage to the DNA of the lens cells has been considered. Finally, electric and heat injuries denature and whiten the lens as a result of direct protein coagulation. This same process makes the clear albumin of an egg become white and opaque after cooking. Cataracts of this type are often seen in glassblowers and furnace workers. Lasers of sufficient power output are known to damage the eyes and skin.
Genetics- The genetic component is strong in the development of cataracts, most commonly through mechanisms that protect and maintain the lens. The presence of cataracts in childhood or early life can occasionally be due to a particular syndrome. Examples of chromosome abnormalities associated with cataracts include deletion syndrome (part of chromosome gets deleted), cri-du-chat syndrome (rare genetic disorder due to missing part of chromosome), Down syndrome (presence of third copy of chromosome), Patau’s syndrome (chromosomal abnormality), trisomy 18 (Edward’s syndrome) and Turner’s syndrome (female misses all or part of X chromosome), and in the case of neurofibromatosis type 2 (an inherited disease), juvenile cataract on one or both sides may be noted. Examples of single-gene disorder include Alport’s syndrome, Conradi’s syndrome, myotonic dystrophy, and oculocerebrorenal syndrome or Lowe syndrome.
Skin Diseases- The skin and the lens have the same embryological origin and can be affected by similar diseases. Those with atopic dermatitis (inflammation of skin) and eczema occasionally develop shield ulcers cataracts. Ichthyosis (scaly skin) is an autosomal recessive disorder associated with cuneiform cataracts and nuclear sclerosis. Basal-cell nevus and pemphigus have similar associations.
Drug Use- Cigarette smoking & consumption of alcohol has been shown to double the rate of nuclear sclerotic cataracts and triple the rate of posterior subcapsular cataracts. Evidence is conflicting over the effect of alcohol. Some surveys have shown a link, but others which followed patients over longer terms have not.
Medications- Some drugs, such as corticosteroids (steroid hormones) can induce cataract development. People with schizophrenia (abnormal social disorder) often have risk factors for lens opacities (such as diabetes, hypertension, and poor nutrition) but antipsychotic medications (psychiatric medicines) are unlikely to contribute to cataract formation. Miotics (construction of excessive pupil) and triparanol may increase the risk.
Iatrogenic- Nearly every person who undergoes a vitrectomy — without ever having had cataract surgery — will experience progression of nuclear sclerosis at 6-months and 12-month after the operation. This may be because the native vitreous humor is significantly different from the solutions used to replace the vitreous (vitreous substitutes), such as BSS Plus. This may also be because the native vitreous humour contains ascorbic acid which helps neutralize oxidative damage to the lens and because traditional vitreous substitutes do not contain ascorbic acid. As such, for phakic patients requiring a vitrectomy it is becoming increasingly common for ophthalmologists to offer the vitrectomy with a combined prophylactic cataract surgeryprocedure to prophylactically prevent cataract formation.
Apart from these there are many factors or diseases which cause cataract such as-
- Prolonged use of corticosteroid medications
- Medicines used to reduce cholesterol
- Previous eye injury or inflammation
- Previous eye surgery
- Hormone replacement therapy
- High myopia
- Family history
Treatment- Cataract removal can be performed at any stage and no longer requires ripening of the lens. Surgery is usually ‘outpatient’ and performed using local anesthesia. Almost all patients can achieve all good vision after surgery.
Phacoemulsification or Phaco is the most widely used cataract surgery. This procedure uses ultrasonic energy to emulsify the cataract lens. Phacoemulsification typically comprises six steps:
Anaesthetic – The eye is numbed with either a subtenon injection around the eye or using simple eye drops.
Corneal incision – Two cuts are made through the clear cornea to allow insertion of instruments into the eye.
Capsulorhexis – A needle or small pair of forceps is used to create a circular hole in the capsule in which the lens sits.
Phacoemulsification – A handheld probe is used to break up and emulsify the lens into liquid using the energy of ultrasound waves. The resulting ’emulsion’ is sucked away.
Irrigation and Aspiration – The cortex, which is the soft outer layer of the cataract, is aspirated or sucked away. Fluid removed is continually replaced with a saline solution to prevent collapse of the structure of the anterior chamber (the front part of the eye).
Lens insertion – A plastic, foldable lens is inserted into the capsular bag that formerly contained the natural lens. Some surgeons also inject an antibiotic into the eye to reduce the risk of infection. The final step is to inject salt water into the corneal wounds to cause the area to swell and seal the incision.
Extracapsular Cataract Extraction (ECCE) consists of removing the lens manually, but leaving the majority of the capsule intact. The lens is expressed through a 10- to 12-mm incision which is closed with sutures at the end of surgery. ECCE is less frequently performed than phacoemulsification, but can be useful when dealing with very hard cataracts or other situations where emulsification is problematic. Manual Small Incision Cataract Surgery (MSICS) has evolved from ECCE. In MSICS, the lens is removed through a self-sealing scleral tunnel wound in the sclera which, ideally, is watertight and does not require suturing. Although “small”, the incision is still markedly larger than the portal in phacoemulsion. Microincision Cataract Surgery (MICS) is an approach to cataract surgery through incision less than 1.8 mm with the purpose of reducing surgical invasiveness, improving at the same time surgical outcomes. Phacoemulsification requires expensive instrumentation which may not be available at all centres, whereas manual. Small Incision Cataract Surgery (SICS) requires only a minimum addition to the standard cataract surgery instrument armamentarium. Capsulorrhexis is mandatory for phacoemulsification, whereas manual SICS can be comfortably done with the envelope capsulotomy skills acquired previously.
Post-operative Care- The postoperative recovery period (after removing the cataract) is usually short. The patient is usually admitted only on the day of surgery, but is advised to move cautiously and avoid straining or heavy lifting for about a month. The eye is usually patched on the day of surgery and use of an eye shield at night is often suggested for several days after surgery. In all types of surgery, the cataractous lens is removed and replaced with an artificial lens, known as an Intraocular Lens (IOL), which stays in the eye permanently. Intraocular lenses are usually Monofocal correcting for either distance or near vision. Multifocal lenses may be implanted to improve near and distance vision simultaneously.
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The cornea is the eye’s outermost layer. It is the clear, dome-shaped surface that covers the front of the eye. Although the cornea is clear and seems to lack substance, it is actually a highly organized group of cells and proteins. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection. Instead, the cornea receives its nourishment from the tears and aqueous humor (a fluid in the anterior portion of the eye) that fills the chamber behind it. The cornea must remain transparent to refract light properly, and the presence of even the tiniest blood vessels can interfere with this process. To see well, all layers of the cornea must be free of any cloudy or opaque areas.
Structure- The corneal tissue is arranged in five basic layers, each having an important function. These five layers are:-
Epithelium- The epithelium is the cornea’s outermost region, comprising about 10 percent of the tissue’s thickness. The epithelium functions primarily to: (1) block the passage of foreign material, such as dust, water, and bacteria, into the eye and other layers of the cornea; and (2) provide a smooth surface that absorbs oxygen and cell nutrients from tears, then distributes these nutrients to the rest of the cornea. The epithelium is filled with thousands of tiny nerve endings that make the cornea extremely sensitive to pain when rubbed or scratched. The part of the epithelium that serves as the foundation on which the epithelial cells anchor and organize themselves is called the basement membrane.
Bowman’s Layer- Lying directly below the basement membrane of the epithelium is a transparent sheet of tissue known as Bowman’s layer. It is composed of strong layered protein fibers called collagen. Once injured, Bowman’s layer can form a scar as it heals. If these scars are large and centrally located, some vision loss can occur.
Stroma- Beneath Bowman’s layer is the stroma, which comprises about 90 percent of the cornea’s thickness. It consists primarily of water (78 percent) and collagen (16 percent), and does not contain any blood vessels. Collagen gives the cornea its strength, elasticity, and form. The collagen’s unique shape, arrangement, and spacing are essential in producing the cornea’s light-conducting transparency.
Descemet’s Membrane- Under the stroma is Descemet’s membrane, a thin but strong sheet of tissue that serves as a protective barrier against infection and injuries. Descemet’s membrane is composed of collagen fibers (different from those of the stroma) and is made by the endothelial cells that lie below it. Descemet’s membrane is regenerated readily after injury.
Endothelium- The endothelium is the extremely thin, innermost layer of the cornea. Endothelial cells are essential in keeping the cornea clear. Normally, fluid leaks slowly from inside the eye into the middle corneal layer (stroma). The endothelium’s primary task is to pump this excess fluid out of the stroma. Without this pumping action, the stroma would swell with water, become hazy, and ultimately opaque. In a healthy eye, a perfect balance is maintained between the fluid moving into the cornea and fluid being pumped out of the cornea. Once endothelium cells are destroyed by disease or trauma, they are lost forever. If too many endothelial cells are destroyed, corneal edema and blindness ensue, with corneal transplantation the only available therapy.
Function – Because the cornea is as smooth and clear as glass, but is strong and durable, it helps the eye in two ways:
1. It helps to shield the rest of the eye from germs, dust, and other harmful matter. The cornea shares this protective task with the eyelids, the eye socket, tears, and the white part of the eye (sclera).
2. The cornea acts as the eye’s outermost lens. It functions like a window that controls and focuses the entry of light into the eye. The cornea contributes between 65-75 percent of the eye’s total focusing power.
When light strikes the cornea, it bends–or refracts–the incoming light onto the lens. The lens further refocuses that light onto the retina. For you to see clearly, light rays must be focused by the cornea and lens to fall precisely on the retina. The retina converts the light rays into impulses that are sent through the optic nerve to the brain, which interprets them as images.
Disease & Disorders- Some diseases and disorders of the cornea are:-
a) Allergies- Allergies affecting the eye are fairly common. The most common allergies are those related to pollen, particularly when the weather is warm and dry. Symptoms can include redness, itching, tearing, burning, stinging, and watery discharge
b) Conjunctivitis (Pink Eye)- This term describes a group of diseases that cause swelling, itching, burning, and redness of the conjunctiva, the protective membrane that lines the eyelids and covers exposed areas of the sclera, or white of the eye. Conjunctivitis can spread from one person to another. Conjunctivitis can be caused by a bacterial or viral infection, allergy, environmental irritants, a contact lens product, eye drops, or eye ointments. At its onset, conjunctivitis is usually painless and does not harm vision. The infection will clear in most cases without requiring medical care. But for some forms of conjunctivitis, treatment will be needed.
c) Corneal Infections- Sometimes the cornea is damaged after a foreign object has entered the tissue, such as from a poke in the eye. At other times, bacteria or fungi from a contaminated contact lens can pass into the cornea. Situations like these can cause painful inflammation and corneal infections called Keratitis. These infections can reduce visual clarity, produce corneal discharges, and perhaps erode the cornea. Corneal infections can also lead to corneal scarring, which can impair vision and may require a corneal transplant.
d) Dry Eye- The continuous production and drainage of tears is important to the eye’s health. Tears keep the eye moist, help wounds heal, and protect against eye infection. In people with dry eye, the eye produces fewer or less quality tears and is unable to keep its surface lubricated and comfortable. As we age, the eyes usually produce fewer tears. Also, in some cases, the lipid and mucin layers produced by the eye are of such poor quality that tears cannot remain in the eye long enough to keep the eye sufficiently lubricated.
e) Fuchs’ Dystrophy- Fuchs’ dystrophy is a slowly progressing disease that usually affects both eyes and is slightly more common in women than in men. Although doctors can often see early signs of Fuchs’ dystrophy in people in their 30s and 40s, the disease rarely affects vision until people reach their 50s and 60s. Fuchs’ dystrophy occurs when endothelial cells gradually deteriorate without any apparent reason. As more endothelial cells are lost over the years, the endothelium becomes less efficient at pumping water out of the stroma. This causes the cornea to swell and distort vision. Eventually, the epithelium also takes on water, resulting in pain and severe visual impairment.
f) Corneal Dystrophies- A corneal dystrophy is a condition in which one or more parts of the cornea lose their normal clarity due to a buildup of cloudy material. There are over 20 corneal dystrophies that affect all parts of the cornea. Corneal dystrophies affect vision in widely differing ways. Some cause severe visual impairment, while a few cause no vision problems and are discovered during a routine eye examination. Other dystrophies may cause repeated episodes of pain without leading to permanent loss of vision.
g) Herpes Zoster (Shingles)- This infection is produced by the varicella-zoster virus, the same virus that causes chickenpox. After an initial outbreak of chickenpox (often during childhood), the virus remains inactive within the nerve cells of the central nervous system. But in some people, the varicella-zoster virus will reactivate at another time in their lives. When this occurs, the virus travels down long nerve fibers and infects some part of the body, producing a blistering rash (shingles), fever, painful inflammations of the affected nerve fibers, and a general feeling of sluggishness. Varicella-zoster virus may travel to the head and neck, perhaps involving an eye, part of the nose, cheek, and forehead. In about 40 percent of those with shingles in these areas, the virus infects the cornea.
h) Iridocorneal Endothelial Syndrome- More common in women and usually diagnosed between ages 30-50, iridocorneal endothelial (ICE) syndrome has three main features: (1) visible changes in the iris, the colored part of the eye that regulates the amount of light entering the eye; (2) swelling of the cornea; and (3) the development of glaucoma, a disease that can cause severe vision loss when normal fluid inside the eye cannot drain properly. ICE is usually present in only one eye.ICE syndrome is actually a grouping of three closely linked conditions: iris nevus (or Cogan-Reese) syndrome; Chandler’s syndrome; and essential (progressive) iris atrophy (hence the acronym ICE).
i) Keratoconus- This disorder–a progressive thinning of the cornea–is the most common corneal dystrophy in the U.S., affecting one in every 2,000 Americans. It is more prevalent in teenagers and adults in their 20s. Keratoconus arises when the middle of the cornea thins and gradually bulges outward, forming a rounded cone shape. This abnormal curvature changes the cornea’s refractive power, producing moderate to severe distortion (astigmatism) and blurriness (nearsightedness) of vision. Keratoconus may also cause swelling and a sight-impairing scarring of the tissue.
j) Lattice Dystrophy- Lattice dystrophy gets its name from an accumulation of amyloid deposits, or abnormal protein fibers, throughout the middle and anterior stroma. During an eye examination, the doctor sees these deposits in the stroma as clear, comma-shaped overlapping dots and branching filaments, creating a lattice effect. Over time, the lattice lines will grow opaque and involve more of the stroma. They will also gradually converge, giving the cornea a cloudiness that may also reduce vision. In some people, these abnormal protein fibers can accumulate under the cornea’s outer layer–the epithelium. This can cause erosion of the epithelium. This condition is known as recurrent epithelial erosion. These erosions: (1) alter the cornea’s normal curvature, resulting in temporary vision problems; and (2) expose the nerves that line the cornea, causing severe pain. Even the involuntary act of blinking can be painful.
k) Map-Dot-Fingerprint Dystrophy- This dystrophy occurs when the epithelium’s basement membrane develops abnormally (the basement membrane serves as the foundation on which the epithelial cells, which absorb nutrients from tears, anchor and organize themselves). When the basement membrane develops abnormally, the epithelial cells cannot properly adhere to it. This, in turn, causes recurrent epithelial erosions, in which the epithelium’s outermost layer rises slightly, exposing a small gap between the outermost layer and the rest of the cornea. Epithelial erosions can be a chronic problem. They may alter the cornea’s normal curvature, causing periodic blurred vision. They may also expose the nerve endings that line the tissue, resulting in moderate to severe pain lasting as long as several days. Generally, the pain will be worse on awakening in the morning. Other symptoms include sensitivity to light, excessive tearing, and foreign body sensation in the eye.
l) Ocular Herpes- Herpes of the eye, or ocular herpes, is a recurrent viral infection that is caused by the herpes simplex virus and is the most common infectious cause of corneal blindness in the U.S. Previous studies show that once people develop ocular herpes, they have up to a 50 percent chance of having a recurrence. This second flare-up could come weeks or even years after the initial occurrence. Ocular herpes can produce a painful sore on the eyelid or surface of the eye and cause inflammation of the cornea. Prompt treatment with anti-viral drugs helps to stop the herpes virus from multiplying and destroying epithelial cells. However, the infection may spread deeper into the cornea and develop into a more severe infection called stromal keratitis, which causes the body’s immune system to attack and destroy stromal cells. Stromal keratitis is more difficult to treat than less severe ocular herpes infections. Recurrent episodes of stromal keratitis can cause scarring of the cornea, which can lead to loss of vision and possibly blindness.
m) Pterygium – A pterygium is a pinkish, triangular-shaped tissue growth on the cornea. Some pterygia grow slowly throughout a person’s life, while others stop growing after a certain point. A pterygium rarely grows so large that it begins to cover the pupil of the eye. Pterygia are more common in sunny climates and in the 20-40 age group. Scientists do not know what causes pterygia to develop. However, since people who have pterygia usually have spent a significant time outdoors, many doctors believe ultraviolet (UV) light from the sun may be a factor. In areas where sunlight is strong, wearing protective eyeglasses, sunglasses, and/or hats with brims are suggested. While some studies report a higher prevalence of pterygia in men than in women, this may reflect different rates of exposure to UV light.
n) Refractive Errors – About 120 million people in the United States wear eyeglasses or contact lenses to correct nearsightedness, farsightedness, or astigmatism. These vision disorders–called refractive errors– affect the cornea and are the most common of all vision problems in this country. Refractive errors are usually corrected by eyeglasses or contact lenses. Although eyeglasses or contact lenses are safe and effective methods for treating refractive errors, refractive surgeries are becoming an increasingly popular option. Read more about refractive errors.
o) Stevens – Johnson Syndrome. Stevens-Johnson Syndrome (SJS), also called erythema multiforme major, is a disorder of the skin that can also affect the eyes. SJS is characterized by painful, blistery lesions on the skin and the mucous membranes (the thin, moist tissues that line body cavities) of the mouth, throat, genital region, and eyelids. SJS can cause serious eye problems, such as severe conjunctivitis; iritis, an inflammation inside the eye; corneal blisters and erosions; and corneal holes. In some cases, the ocular complications from SJS can be disabling and lead to severe vision loss.
Treatment- A corneal transplant involves replacing a diseased or scarred cornea with a new one. When the cornea becomes cloudy, light cannot penetrate the eye to reach the light-sensitive retina. Poor vision or blindness may result. In corneal transplant surgery, the surgeon removes the central portion of the cloudy cornea and replaces it with a clear cornea, usually donated through an eye bank. A trephine, an instrument like a cookie cutter, is used to remove the cloudy cornea. The surgeon places the new cornea in the opening and sews it with a very fine thread. The thread stays in for months or even years until the eye heals properly (removing the thread is quite simple and can easily be done in an ophthalmologist’s office). Following surgery, eye drops to help promote healing will be needed for several months.