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Amblyopia

Amblyopia

Definition

Amblyopia refers to diminished vision in either one or both eyes, for which no cause can be discovered upon examination of the eye. Amblyopia is the medical term used when the vision in one of the eyes is reduced because the eye and the brain are not working together properly. The eye itself looks normal, but it is not being used normally because the brain is favoring the other eye. This condition is also sometimes called lazy eye.

Description

Lazy eye is a common non-medical term used to describe amblyopia because the eye with poorer vision does not seem to be doing its job of seeing. Amblyopia is the most common cause of impaired vision in childhood. It affects approximately two or three out of every 100 children. Vision is a combination of the clarity of the images of the eyes (visual acuity) and the processing of those images by the brain. If the images produced by the two eyes are substantially different, the brain may not be able to fuse the images. Instead of seeing two different images or double vision (diplopia), the brain suppresses the blurrier image. This suppression can lead to amblyopia. During the first few years of life, preferring one eye over the other may lead to poor visual development in the blurrier eye. Unless it is treated successfully in early childhood, amblyopia usually persists into adulthood and is the most frequent cause of monocular (one eye) visual impairment among children.

Demographics

The prevalence of amblyopia is difficult to assess, with estimates ranging from 1.0 to 3.5 percent in healthy children to 4.0 to 5.3 percent in children with other vision problems. It is seen in similar numbers in both sexes and in all races.

Causes and symptoms

Amblyopia may be caused by any condition that adversely affects normal visual development or use of the eyes. All babies are born with poor eyesight. As babies grow, however, their eyesight usually progresses. Good eyesight needs a clear, focused image that is the same in both eyes. If the image is not clear in one eye, or if the image is not the same in both eyes, the vision pathways will not develop as they should. In fact, the pathways may actually worsen. Anything that blurs the vision or causes the eyes to be crossed during childhood may cause amblyopia. Some of the major causes of amblyopia are as follows:

  • Strabismus . A misalignment of the eyes is the most common cause of functional amblyopia. The two eyes are looking in two different directions at the same time. The eyes may turn in, out, up, or down. Strabismus may be diagnosed at birth, or it may develop later in childhood. The brain is sent two different images and this creates confusion. Images from the misaligned or "crossed" eye are turned off to avoid double vision.
  • Anisometropia. A difference of refractive states exists between the two eyes (in other words, a difference in prescription between the two eyes). For example, one eye may be more nearsighted than the other eye, or one eye may be farsighted and the other eye nearsighted. Because the brain cannot fuse the two images, the brain suppresses the blurrier image, causing the eye to become amblyopic.
  • Cataract. Clouding of the lens of the eye causes the image to be blurrier than the other eye. The brain prefers the clearer image, and the eye with the cataract may become amblyopic.
  • Ptosis. If light cannot enter the eye because of the drooping lid, the eye is essentially going unused, which can lead to amblyopia. However, ptosis is rarely related to the development of amblyopia, unless the droopy eyelid completely obscures the pupil.

Barring the presence of strabismus or ptosis, children may or may not show signs of amblyopia. Children may position their heads at an angle while trying to favor the eye with normal vision. They may have difficulty seeing or reaching for things when approached from the side of the amblyopic eye. Parents should see if one side of approach is preferred by the child or infant. If an infant's good eye is covered, the child may cry.

When to call the doctor

Parents should call the doctor if their child demonstrates any signs associated with amblyopia, including the appearance of crossed eyes, lazy eye, a drooping eyelid, difficulty seeing, or if the child seems to favor one side of approach over the other. However, since children do not always show symptoms of amblyopia, it is important to get their eyes examined at or before the age of three and no later than age five, while the disorder is more easily treated.

Diagnosis

It is not easy to recognize amblyopia. A child may not be aware of having one strong eye and one weak eye. Unless the child has a misaligned eye or other obvious abnormality, there is often no way for parents to tell that something is wrong. Because children with outwardly normal eyes may have amblyopia, it is important to have regular vision screenings performed for all children. While there is some disagreement regarding the age children should have their first vision examination, their eyes can, in actuality, be examined at any age, even on the first day of life.

Some people recommend that children have their vision checked by their pediatrician, family physician, ophthalmologist, or optometrist at or before six months of age. Others recommend testing by at least the child's fourth birthday. There may be a critical period in the development of vision, and amblyopia may not be treatable after age eight or nine. The earlier amblyopia is found, the better chance there is for a positive outcome. Most physicians test vision as part of a child's medical examination. If there is any sign of an eye problem, they may refer a child to an eye specialist.

There are objective methods, such as retinoscopy, by which to measure the refractive status of the eyes. This form of examination can help diagnose anisometropia. In retinoscopy, a hand-held instrument is used to shine a light in the child's (or infant's) eyes. While the doctor uses hand-held lenses, he can obtain a rough prescription. Visual acuity can be determined using a variety of methods. Many different eye charts are available (e.g. tumbling E, pictures, or letters). In amblyopia, single letters are easier to recognize than when a whole line is shown. This is referred to as the "crowding effect" and helps in diagnosing amblyopia. Neutral density filters may also be held over the eye to aid in the diagnosis. Sometimes visual fields to determine defects in the area of vision will be performed. Color vision testing may also be done. Again, it must be emphasized that amblyopia is a diagnosis of exclusion. Various medical problems can also cause a decrease in vision. An examination of the eyes and visual system is very important when there is an unexplained decrease in vision.

Treatment

Amblyopia treatment is most effective when done early in the child's life, usually before age seven. It is important that any anisometropia and refractive problems be treated initially, because sometimes amblyopia can be resolved with glasses alone.

The next step is to make the child use the eye with the reduced vision (weaker eye). As of 2004, there are two ways to do this:

  • Patching. An opaque, adhesive patch is worn over the stronger eye for weeks to months. This therapy forces the child to use the eye with amblyopia. Patching stimulates vision in the weaker eye and aids the section of the brain that manages vision to develop more completely. Patching may be part-time or full-time. Studies in the early 2000s have shown that less time patching the eye may be as effective as more. In the case of moderate amblyopia, two hours of daily patching for four months gave the same benefit as six hours of daily patching for the same period of time. Compliance with the patching regimen was also improved with the shorter daily patching time. The treatment plan should be discussed with the doctor to determine how long the patch should be worn. When the child is wearing the patch, prescribed eye exercises may force the amblyopic eye to focus and work. This is called vision therapy or vision training. Even after the child's vision has been restored in the weak eye, part-time patching may be required over a period of years to maintain the improvement.
  • Atropine. This therapy is generally reserved for children who will not wear a patch or where compliance may be an issue. A drop of a drug called atropine is placed in the stronger eye once a day to temporarily blur the vision so that the child will prefer to use the eye with amblyopia. Treatment with atropine also stimulates vision in the weaker eye and helps the part of the brain that manages vision to develop more fully.

Prognosis

The younger the child, the better the chance for improvement with occlusion and vision therapy. Success in the treatment of amblyopia also depends on the amblyopia's severity, its specific type, and the child's compliance with treatment. It is important to diagnose and treat amblyopia early because significant vision loss can occur if it is left untreated. The best outcomes result from early diagnosis and treatment.

Prevention

Early recognition and treatment of amblyopia in children can help to prevent permanent visual deficits. All children should have a complete eye examination at least once between age three and five to avoid the risk of allowing unsuspected amblyopia to go beyond the age where it can be treated successfully.

Nutritional concerns

There are some rarer forms of amblyopia caused by various nutritional deficiencies. In these cases, the doctor recommends the proper diet and perhaps supplementation in order to resolve the problem.

Parental concerns

It is vital that parents bring their child for an eye exam sometime between the ages of three and five to prevent amblyopia from becoming untreatable.

KEY TERMS

Anisometropia An eye condition in which there is an inequality of vision between the two eyes. There may be unequal amounts of nearsightedness, farsightedness, or astigmatism, so that one eye will be in focus while the other will not.

Cataract A condition in which the lens of the eye turns cloudy and interferes with vision.

Occulsion therapy A type of treatment for amblyopia in which the good eye is patched for a period of time, thus forcing the use of the weaker eye.

Visual acuity Sharpness or clearness of vision.

Resources

BOOKS

Barber, Anne. Infant and Toddler Strabismus and Amblyopia, Vol. 41, No. 2: Behavioral Aspects of Vision Care. Santa Ana, CA: Optometric Extension Program Foundation, 2000.

Fielder, Alistair, et al. Amblyopia: A Multidisciplinary Approach. Kent, UK: ElsevierHealth Sciences Division, 2002.

Pratt-Johnson, John A., et al. Management of Strabismus and Amblyopia: A Practical Guide. New York: Thieme Medical Publishers, 2000.

PERIODICALS

Dutton, Gordon N., and Marie Cleary. "Should We Be Screening for and Treating Amblyopia? Evidence Shows Some Benefit." British Medical Journal 327, no. 7426 (November 29, 2003): 124244.

Finn, Robert. "Less Patching Fine for Amblyopia in Young Children: Two Studies." Family Practice News 34, no. 9 (May 1, 2004): 7071.

ORGANIZATIONS

American Association for Pediatric Ophthalmology and Strabismus. PO Box 193832, San Francisco, CA 941193832. Web site: <www.aapos.org>.

National Eye Institute. 31 Center Drive MSC 2510, Bethesda, MD 208922510. Web site: <www.nei.nih.gov>.

Prevent Blindness America. 500 E. Remington Road, Schaumburg, IL 60173. Web site: <www.preventblindness.org>.

WEB SITES

"Amblyopia." National Eye Institute, June 2004. Available online at <www.nei.nih.gov/health/amblyopia> (October 16, 2004).

Deanna M. Swartout-Corbeil, RN Lorraine Steefel, RN

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Lazy Eye

Lazy eye

Definition

Lazy eye, or amblyopia, is an eye condition in which disuse causes reduced vision in an otherwise healthy eye. The affected eye is called the lazy eye. This vision defect occurs in 23% of American children. If not corrected before age eight, amblyopia will cause significant loss of stereoscopic vision, the ability to perceive three-dimensional depth.

Description

In some children, one eye functions better than the other. When a child begins to depend on the stronger eye, the weaker eye can become progressively weaker. Eventually, the weaker eye grows "lazy" from disuse. If left untreated beyond the early child-development years (from birth to seven years old), vision in the affected eye will be underdeveloped due to lack of use.

The impairment of vision in the lazy eye occurs in three phases. In the first (suspension) phase, the brain turns the weaker eye on and off. In the second (suppression) phase, the brain turns off the lazy eye indefinitely. At this point, the eye still has usable vision and can function well if the other eye is covered. In the last (amblyopia) phase, which occurs after age seven, the eye loses all the sensitivity that is essential for good vision because it has not been used for so long.

Lazy eye is a visual problem with potentially serious consequences. If left untreated, the affected child may have permanent loss of vision in the lazy eye. Because of loss of vision in one eye, these children cannot see three-dimensional images very wellall images appear flat. They also have problems with depth perception. This has serious consequences in their future ability to work in professions that require good vision in both eyes. Affected children also have increased risk of blindness should something happen to the good eye.

Causes & symptoms

The following are probable causes of lazy eye:

  • Strabismus, or misalignment of a child's eyes (crossed eyes). This is the most frequent cause of lazy eye. Approximately half of all children with crossed eyes will develop a lazy eye. In children with crossed eyes, the images do not coordinate, thus confusing the brain. Therefore, the brain will suppress the image that comes from one eye and predominantly use the image from the stronger eye.
  • Anisometropia (unequal refractive power). In this case, there is difference in image quality between the two eyes because one eye is severely nearsighted or farsighted. In other words, one eye focuses better than the other. The brain will mostly use the clearer image from the good eye. The other eye will become underdeveloped due to neglect.
  • Congenital cataract. The lazy eye can not see well because its lens is already cloudy at birth.
  • Ptosis (drooping eyelid). Vision in the lazy eye is blocked or impaired by the drooping eyelid.
  • Corneal scarring. The image quality of the affected eye is poor due to scarring in the cornea.

The following are risk factors for amblyopia:

  • rubella (German measles ) or other infections in the mother during pregnancy
  • premature birth
  • other family members with vision problems in childhood

Lazy eye may not present obvious symptoms. For this reason, it is important for small children to have regular eye examinations.

Diagnosis

Diagnosis of amblyopia is often made during visual screening during routine infant check-ups and in the preschool years (aged three to five). Premature babies need to have more frequent eye exams during early childhood to prevent this and other vision problems. A new photoscreening instrument that has been recently introduced appears to significantly increase the accuracy of diagnosis of these eye problems.

Treatment

The following alternative methods may complement conventional treatment of lazy eye. However, they are not replacements for conventional treatments. Because their effectiveness is not proven, parents should consult their child's ophthalmologist about the appropriate use of these methods (if any) in their child's overall eye treatment program.

Orthoptics (eye exercises)

Eye exercises can be helpful. Orthoptic exercises are designed to help the eyes move together and assist the fusing of the two images seen by the eyes. It can help correct faulty vision habit due to misalignment of the eyes and can teach the child to use both eyes effectively and comfortably. This form of therapy can be used before or after eye-realignment surgery to improve results.

Vision therapy

Vision training is a form of physical therapy for the brain and the eyes. It is a more extensive form of eye exercise and requires more frequent visits.

Acupuncture

One study shows that acupuncture treatment may be effective in treating anisometropia, a condition in which one eye focuses much better than the other. Acupuncture can reduce the differences in refractive powers between the eyes so that both eyes can have similar image quality. This helps reduce the amblyopia problem. However, its long-term effectiveness remains unknown.

Allopathic treatment

In order to treat lazy eye, the doctor has to identify and treat underlying causes. Depending on these underlying causes, the doctor may recommend surgical or nonsurgical treatments, as discussed below.

Refractive error correction

If both eyes need vision correction, children are given prescription glasses for better focus and to prevent misalignment of the eyes.

Forcing the use of the lazy eye

In many children with amblyopia, only one eye has a focusing problem or weak muscles. In order to force the affected eye to work, the doctor will cover the strong eye with a patch for most of the day for at least several weeks. Sometimes, this treatment requires as long as a year. The eye patch forces the lazy eye to work and thus, strengthens its vision and its muscles. This is the most common method used to treat lazy eye. To prevent the strong eye from becoming weaken due to disuse, the child is allowed to remove the patch so that he can see with the good eye for at least a few hours each day.

Another way to force the lazy eye to work harder is to use eye drops or ointment to blur the vision in the strong eye so that the child has to use the lazy eye to see. This method is not often used because it is associated with more adverse effects.

Surgical treatments

If the problem is caused by imbalances of the eye muscles and is not treatable with nonsurgical methods, the eye muscles can be realigned surgically to help the eyes coordinate better. Sometimes more than one surgery is required for the correction. Eye patch, glasses, or orthoptic exercises may be necessary following surgery to help the child use both eyes effectively. Long-term follow-up of surgical treatment indicates that it is highly effective in correcting the problem.

In patients whose amblyopia is caused by a congenital cataract in one eye, the cloudy lens is surgically removed and replaced by an intraocular lens. However, after surgeryeven with eye glasses or contact lensesthis eye will still have poorer image quality than the good eye. Thus, the risk for amblyopia remains high. Therefore, nonsurgical treatment for lazy eye is often started after cataract surgery.

For a child whose vision is affected by a drooping eyelid, ptosis surgery is needed.

Expected results

With early diagnosis and treatment, children with amblyopia are expected to restore the sight in the lazy eye. However, if left untreated, the weak eye never develops adequate vision and the person may become functionally blind in that eye.

Prevention

Most cases of lazy eye are congenital, occurring since birth. However, if diagnosed early, vision loss in the affected eye can be prevented.

Resources

BOOKS

"Crossed Eyes." In Reader's Digest Guide to Medical Cures and Treatments. New York: Reader's Digest Association, 1996.

PERIODICALS

Broderick, Peter. "Pediatric Vision Screening for the Family Physician." American Family Physician 58, no. 3 (September 1, 1998): 691700+. <http://www.aafp.org/afp/980901ap/broderic.html>.

Mills, Monte D. "The Eye in Childhood." American Family Physician 60, no. 3 (September 1, 1999): 90718. <http://www.aafp.org/afp/990901ap/907.html>.

Paysse, Evelyn A., et al. "Detection of Red Reflex Asymmetry by Pediatric Residents Using the Bruckner Reflex Versus the MTI Photoscreener." Pediatrics 108 (October 2001): 997.

ORGANIZATIONS

American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. <http://www.eyenet.org>.

American Association For Pediatric Ophthalmology and Strabismus. c/o Denise De Losada Wilson. P.O. Box 193832, San Francisco, CA 94119-3832. (415) 561-8505. aapos@aao.org. <http://med-aapos.bu.edu>.

National Association for Parents of the Visually Impaired, Inc. P.O. Box 317, Watertown, MA 02471. (800) 562-6265. Fax: (617) 972-7444. <http://www.spedex.com/napvi>.

OTHER

"Congenital Eye Defects." The Merck Manual Online. [cited October 2002]. <http://www.merck.com/pubs/mmanual/section19/chapter261/261i.htm>.

Mai Tran

Rebecca J. Frey, PhD

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Amblyopia

Amblyopia

Definition

Amblyopia is an uncorrectable decrease in vision in one or both eyes with no apparent structural abnormality seen to explain it. It is a diagnosis of exclusion, meaning that when a decrease in vision is detected, other causes must be ruled out. Once no other cause is found, amblyopia is the diagnosis. Generally, a difference of two lines or more (on an eye-chart test of visual acuity) between the two eyes or a best corrected vision of 20/30 or worse would be defined as amblyopia. For example, if someone has 20/20 vision with the right eye and only 20/40 with the left, and the left eye cannot achieve better vision with corrective lenses, the left eye is said to be amblyopic.

Description

Lazy eye is a common non-medical term used to describe amblyopia because the eye with poorer vision doesn't seem to be doing its job of seeing. Amblyopia is the most common cause of impaired vision in children, affecting nearly three out of every 100 people or 2-4% of the population. Vision is a combination of the clarity of the images of the eyes (visual acuity) and the processing of those images by the brain. If the images produced by the two eyes are substantially different, the brain may not be able to fuse the images. Instead of seeing two different images or double vision (diplopia), the brain suppresses the blurrier image. This suppression can lead to amblyopia. During the first few years of life, preferring one eye over the other may lead to poor visual development in the blurrier eye.

Causes and symptoms

Some of the major causes of amblyopia are as follows:

  • Strabismus. A misalignment of the eyes (strabismus) is the most common cause of functional amblyopia. The two eyes are looking in two different directions at the same time. The brain is sent two different images and this causes confusion. Images from the misaligned or "crossed" eye are turned off to avoid double vision.
  • Anisometropia. This is another type of functional amblyopia. In this case, there is a difference of refractive states between the two eyes (in other words, a difference of prescriptions between the two eyes). For example, one eye may be more nearsighted than the other eye, or one eye may be farsighted and the other eye nearsighted. Because the brain cannot fuse the two dissimilar images, the brain will suppress the blurrier image, causing the eye to become amblyopic.
  • Cataract. Clouding of the lens of the eye will cause the image to be blurrier than the other eye. The brain "prefers" the clearer image. The eye with the cataract may become amblyopic.
  • Ptosis. This is the drooping of the upper eyelid. If light cannot enter the eye because of the drooping lid, the eye is essentially not being used. This can lead to amblyopia.
  • Nutrition. A type of organic amblyopia in which nutritional deficiencies or chemical toxicity may result in amblyopia. Alcohol, tobacco, or a deficiency in the B vitamins may result in toxic amblyopia.
  • Heredity. Amblyopia can run in families.

Barring the presence of strabismus or ptosis, children may or may not show signs of amblyopia. Children may hold their heads at an angle while trying to favor the eye with normal vision. They may have trouble seeing or reaching for things when approached from the side of the amblyopic eye. Parents should see if one side of approach is preferred by the child or infant. If an infant's good eye is covered, the child may cry.

Diagnosis

Because children with outwardly normal eyes may have amblyopia, it is important to have regular vision screenings performed for all children. While there is some controversy regarding the age children should have their first vision examination, their eyes can, in actuality, be examined at any age, even at one day of life.

Some recommend that children have their vision checked by their pediatrician, family physician, ophthalmologist, or optometrist at or before six months of age. Others recommend testing by at least the child's fourth birthday. There may be a "critical period" in the development of vision, and amblyopia may not be treatable after age eight or nine. The earlier amblyopia is found, the better the possible outcome. Most physicians test vision as part of a child's medical examination. If there is any sign of an eye problem, they may refer a child to an eye specialist.

There are objective methods, such as retinoscopy, to measure the refractive status of the eyes. This can help determine anisometropia. In retinoscopy, a handheld instrument is used to shine a light in the child's (or infant's) eyes. Using hand-held lenses, a rough prescription can be obtained. Visual acuity can be determined using a variety of methods. Many different eye charts are available (e.g., tumbling E, pictures, or letters). In amblyopia, single letters are easier to recognize than when a whole line is shown. This is called the "crowding effect" and helps in diagnosing amblyopia. Neutral density filters may also be held over the eye to aid in the diagnosis. Sometimes visual fields to determine defects in the area of vision will be performed. Color vision testing may also be performed. Again, it must be emphasized that amblyopia is a diagnosis of exclusion. Visual or life-threatening problems can also cause a decrease in vision. An examination of the eyes and visual system is very important when there is an unexplained decrease in vision.

Treatment

The primary treatment for amblyopia is occlusion therapy. It is important to alternate patching the good eye (forcing the amblyopic eye to work) and the amblyopic eye. If the good eye is constantly patched, it too may become amblyopic because of disuse. The treatment plan should be discussed with the doctor to fully understand how long the patch will be on. When patched, eye exercises may be prescribed to force the amblyopic eye to focus and work. This is called vision therapy or vision training (eye exercises). Even after vision has been restored in the weak eye, part-time patching may be required over a period of years to maintain the improvement.

KEY TERMS

Anisometropia An eye condition in which there is an inequality of vision between the two eyes. There may be unequal amounts of nearsightedness, farsightedness, or astigmatism, so that one eye will be in focus while the other will not.

Cataract Cloudiness of the eye's natural lens.

Occulsion therapy A type of treatment for amblyopia in which the good eye is patched for a period of time. This forces the weaker eye to be used.

Strabismus A condition in which the eyes are misaligned and point in different directions. One eye may look straight ahead, while the other turns inward, outward, upward, or downward. This is also called crossed-eyes.

Visual acuity Acuity is the acuteness or sharpness of vision.

While patching is necessary to get the amblyopic eye to work, it is just as important to correct the reason for the amblyopia. Glasses may also be worn if there are errors in refraction. Surgery or vision training may be necessary in the case of strabismus. Better nutrition is indicated in some toxic amblyopias. Occasionally, amblyopia is treated by blurring the vision in the good eye with eye drops or lenses to force the child to use the amblyopic eye.

Prognosis

The younger the person, the better the chance for improvement with occlusion and vision therapy. However, treatment may be successful in older childreneven adults. Success in the treatment of amblyopia also depends upon how severe the amblyopia is, the specific type of amblyopia, and patient compliance. It is important to diagnose and treat amblyopia early because significant vision loss can occur if left untreated. The best outcomes result from early diagnosis and treatment.

Prevention

To protect their child's vision, parents must be aware of amblyopia as a potential problem. This awareness may encourage parents to take young children for vision exams early on in lifecertainly before school age. Proper nutrition is important in the avoidance of toxic amblyopia.

Resources

ORGANIZATIONS

American Academy of Ophthalmology. 655 Beach Street, P.O. Box 7424, San Francisco, CA 94120-7424. http://www.eyenet.org.

American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. http://www.aoanet.org.

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amblyopia

amblyopia (am-blee-oh-piă) n. poor sight, not due to any detectable disease of the eyeball or visual system, known colloquially as lazy eye. a. ex anopsia a condition in which factors such as squint (see strabismus), cataract, and other abnormalities of the optics of the eye (see refraction) impair its normal use in early childhood by preventing the formation of a clear image on the retina.

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lazy eye

la·zy eye • n. an eye with poor vision that is mainly caused by underuse, esp. the unused eye in strabismus.

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lazy eye

lazy eye (lay-zi) n. see amblyopia.

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