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Cataracts and Amblyopia By L. E. Leguire Ph.D., MBA Executive Director Ohio Amblyope Registry The most common reasons for an infant or child to develop amblyopia, commonly known as "lazy eye", include misaligned eyes (strabismus), a difference in refractive error between the eyes (anisometropia) and refractive error, usually hyperopia. Another important reason for an infant or young child to develop amblyopia is because of the presence of a cataract in one or both eyes. Usually, people think of cataracts as only occurring in older adults. Indeed, if you live long enough, most people will develop cataracts in their lifetime. However, infants can be born with cataracts and older children can develop cataracts for numerous reasons. A cataract is a clouding or opacity of the lens of the eye such that light is not refracted (bent) properly to focus on the back of the eye, known as the retina. The main purpose of the lens, which is changeable and flexible (at least until a person is 45 years old or so), is to focus light onto the retina. If light is focused properly by the lens, a sharp image is projected onto the retina and the person will experience clear and sharp vision. If, however, the light is focused in front of the retina, as in myopia, or if the light is focused behind the retina, as in hyperopia, the person will experience blurred vision - a sign that the person needs glasses. With a cataract, light is scattered and cannot be focused onto the retina to create a clear and sharp image. Scattered light caused by a cataract can be very unpleasant and can cause light sensitivity and can even be painful. Patients with a cataract in one eye may intentionally or unintentionally close the affected eye to reduce the light sensitivity and blurred vision. Patients with cataracts may see halos around lights and/or may experience "star-burst" when looking at on-coming car headlights, for example. As cataracts get worse, my mother-in-law would say "as the cataract ripens", visual acuity will start to decrease. When an infant is born with a cataract in one or both eyes, the condition is called "congenital cataract". Congenital cataracts are often "nuclear cataracts" or "polar cataracts", a reference to the location of the cataract in the lens of the eye. A congenital cataract may be large or small and may or may not affect vision depending on its location in the lens. If the congenital cataract is small and not in the center light pathway (visual axis) of the lens, it might not affect vision and there may be no reason to remove the cataract and lens of the eye. Congenital cataracts often do not change in size as the child grows. Often, however, congenital cataracts require immediate medical treatment and surgery. Delaying cataract surgery, even for a few weeks, in a young infant with a dense cataract can lead to a permanent loss of vision due to the rapid development of deep amblyopia that may not respond to treatment. If the cataract develops later in childhood the cataract is called a "developmental cataract". Developmental cataracts are sometimes "lamellar cataracts", specifying the location of the cataract within the lens. Developmental cataracts are not present at birth but form later in childhood. Developmental cataracts do grow in size over time and, depending on size and location, may require surgery to remove the cataract and lens of the eye. If a cataract forms after trauma to the eye, often a penetrating injury to the eye or blunt trauma, it is called a "traumatic cataract". A traumatic cataract may form soon after trauma to the eye and require removal of the lens. Traumatic cataracts can grow very large and encompass the whole or nearly the whole lens requiring immediate surgery particularly in a young child; otherwise, amblyopia may develop. Traumatic cataract can also be associated with the development of closed-angle glaucoma - a very serious and vision threatening condition. Cataract surgery is serious surgery and requires general (whole body) anesthesia. As a consequence, the ophthalmologist, an eye doctor that performs surgery, will not want to perform cataract surgery on an infant or child until the cataract interferes with vision; that is, until the cataract threatens vision. At the same time, however, amblyopia can develop rapidly and become very deep and cause blindness in a very young infant with congenital cataracts. As a consequence, surgery is often performed in the first few months of life if there is a congenital cataract. Indeed, studies have shown that visual outcome is much better in infants with congenital cataracts when cataract surgery is performed before the first 6 - 12 weeks of life than when it is performed later. Children with cataracts pose numerous challenges for the eye doctor. On the one hand, the doctor doesn't want to undertake surgery and general anesthesia on a young infant for fear of serious complications and to avoid the unique challenges posed by such little patients with small eyes. On the other hand, the eye doctor doesn't want to wait too long and have deep amblyopia develop in the infant and thus complicate management of the patient. This is where professional judgment comes to play and the eye doctor knows when surgery is required, particularly if the cataract is large or interferes with light entering the eye. Amblyopia and strabismus (misaligned eyes) are two signs that a cataract is serious enough to have it surgically removed. Also, the presence of nystagmus (repetitive back-and-forth movement of the eyes) in an infant with congenital cataracts is a serious sign of a significant and permanent loss of vision. Children with congenital cataracts who develop nystagmus have, in general, a poor visual outcome even if the cataracts are subsequently removed and proper optical correction provided. Infants with congenital cataracts who develop nystagmus often have a visual acuity of 20/200 - legal blindness. In the last 30 years, much research has been undertaken as to the timing of surgery for congenital cataracts. To prevent the development of amblyopia or strabismus, congenital cataracts are removed as early as possible, often in the first 6 weeks of life. In general, infants who have had cataract surgery performed in the first 6-8 weeks of life do much better, in terms of visual acuity, than infants who had cataract surgery performs after 12 weeks of life. A real problem after cataract surgery is determination of the best way to correct the high refractive error that is present once the natural lens of the eye is removed. Unless good optical correction is provided following cataract surgery, the patient is essentially blind and can see very little after the natural lens of the eye is removed. Without the natural lens, and without proper optical correction, a child may have light perception only, and not be able to see object details. Basically, there are 3 choices for correcting the high refractive error caused by removal of the natural lens of the eye: glasses, contact lens and intraocular lens. Unfortunately, all choices leave a lot to be desired and none are ideal for all patients. Glasses for patients who have had cataract surgery are very thick and heavy. Trying to get an infant to wear thick, heavy glasses poses numerous challenges for the parents. These challenges are amplified if only one eye was operated on and when only one eye needs a thick lens. Contact lenses also pose numerous challenges to the patient and parent. Daily insertion of the contact, cleaning of the contact and trying to avoid the patient from simply rubbing out the contact are just some of the challenges. Also, because the contacts are very high power, they're expensive and a young patient may "go through" numerous contacts over a year period. Also, infants seem to have a knack for swallowing the contact with an anxious parent checking the diapers on a regular basis to retrieve the contact lens. Often, the contact lens simply disappears never to be seen again. In the mean time, when the patient doesn't have the contact on the eye properly, he or she will experience blurred vision and the chance of amblyopia increases dramatically. If you're elderly and require cataract surgery, optical correction simply involves replacing the old cataract lens with an intraocular lens - sort of a contact lens that fits inside the eye. An intraocular lens is very small and lightweight and is inserted inside the eye in the same location or nearly so as the natural lens. Unfortunately, intraocular lenses in infants and young children pose a host of problems. First, because the eye is still growing in childhood, numerous complications can result with cataract surgery and intraocular lens implantation. Cataract surgery in children is more complicated than in adults, because of the small size of the eyes and other surgical considerations. A common complication in children with an intraocular lens is opacification of the visual axis; that is, cells within the eye adhering to the intraocular lens and preventing light from being focused on the retina - equivalent to another "cataract" forming but this time on the intraocular lens. If needed, the intraocular lens can be replaced. Commonly, posterior capsular opacification occurs after cataract extraction, with or without an intraocular lens. This is referred to as an "after cataract". After cataract occurs 3 months to about 2 years after cataract surgery and requires a simple laser surgery called Nd: YAG laser capsulotomy - basically cutting a hole in the capsule to allow clear vision. Probably the most serious complication of an intraocular lens in a child is the development of secondary glaucoma that can lead to blindness in the affected eye(s). Whichever optical correction is undertaken following cataract surgery, regular follow-up and rapid treatment of amblyopia are essential for minimizing vision loss. Ideally, an infant or child who has had cataract surgery is given proper optical correction and is closely managed with regular eye doctor appointments to prevent or treat the development of amblyopia and/or misaligned eyes. Causes of Cataracts Regarding congenital cataracts, most of the time the reason for the cataract(s) is unknown. However, congenital cataracts can run in families, so there is a clear genetic component in some cases. Congenital cataracts are sometimes associated with infections such as congenital herpes simplex and congenital syphilis. Steroid use and exposure to radiation during pregnancy may also cause congenital cataracts. Alcohol and drug use during pregnancy are also associated with congenital cataracts. Numerous syndromes or diseases are also associated with congenital cataracts, including Down's syndrome, Trisomy 13 and Rubella syndrome, among others. Metabolic abnormalities can also lead to cataract formation. Regarding developmental cataracts, much like congenital cataracts, the reason for the cataract(s) is often unknown. Developmental cataracts may be associated with nutritional or metabolic abnormalities, certain genetic diseases (e.g., Trisomy 18) and certain syndromes (e.g., Alport's syndrome, Turner syndrome). Exposure to radiation, extended use of steroids or other drugs are sometimes related to cataract development. Sometimes, the type and location of the cataract provides clues as to the cause of the cataract. Brief Literature Review Zetterstrom and colleagues (Cataract Refract. Surg. 2005 p824-840) review the literature on the management of cataract in children and offer this advice:
Weisberg and colleagues (Ophthalmology, 2005, p1625-1628) undertook a retrospective study in which they reviewed the medical charts of 94 patients who had cataract surgery. They found the following:
Travi and colleagues (J AAPOS 2005, p449-454) undertook a review of the charts of 53 patients who had cataracts initially thought to be too small to justify cataract surgery. Patients were first treated for the amblyopia, which included glasses, patching and atropine (dilating eye drop in the better eye). The patients who failed to improve underwent cataract surgery. Of those who had cataract surgery, 67% showed a 3 line improvement on the eye chart. Also, 25 of 51 patients (49%) had a final visual acuity of 20/40 or better, considered a success. Overall, patients who had undergone cataract surgery had a final visual acuity better than those patients who did not have cataract surgery, although the differences between the surgery and non-surgery groups was not statistically significant. Forbes and Guo (Pediatric Ophthalmol. & Strabismus, 2006, p143-151) reviewed the recent literature on the surgical management of cataracts in children. They report that the success of surgery and long-term management of infants and children with cataracts has improved. They cite progress in getting infants in earlier for cataract surgery, better forms of optical correction including more use of the intraocular lens, and the employment of many surgical techniques in children which were developed for older people with cataracts. One major topic of discussion was the need for early surgery, at or before 6 weeks of age, before the development of binocular vision; that is, before the two eyes start to work together for single vision and depth perception. Ruth and Lambert (J AAPOS 2006, p587-588) presented a case report of an infant with a congenital cataract in one eye. The patient underwent cataract extraction and intraocular lens implantation at 8 weeks of age. The patient ended up with better vision in the eye that had a cataract than in the other "normal" eye. [Note: Sometimes when young infants are occluded for amblyopia; that is, when a patch is placed on the normal eye to force use of the lazy eye, so-called "reverse amblyopia" can occur. Reverse amblyopia is a form of deprivational amblyopia in which amblyopia develops in the normal eye and is caused by patching the normal eye too long. Such reversal of amblyopia occurs in young infants, particularly if parents get too aggressive and patch the patient much longer than the doctor's recommended patching time. Reverse amblyopia can also develop when a parent misses an eye doctor appointment and continues to patch the child the recommended time.] Ledoux and colleagues (J AAPOS, 2007, p218-224) undertook a chart review of 510 pediatric patients who had undergone cataract surgery and primarily received an intraocular lens. After looking over the data the authors reported on the findings from 139 patients. The average age of the patients was about 5 years, so most of the patients had developmental cataracts. Vision was assessed about 4 years later, when the patients were about 9 years old. The results showed that 50% of the patients had a visual acuity of better than 20/30 and 50% had a visual acuity of worse than 20/30. When a child had a cataract in only one eye, the median visual acuity was 20/40 and when the child had a cataract in both eyes the median visual acuity was 20/25. In general, older children had better visual acuity than younger children due mainly to the presence or absence of amblyopia. About 14% of the patients ended up with a visual acuity of 20/200 or worse (legal blindness). Of the 139 children, 18 (13%) required muscle surgery for an eye misalignment and 22 (16%) needed additional intraocular (within the eye) surgery due to problems related to the intraocular lens or related to the cataract extraction.
Figure 1. Close-up photograph of the front of the eye looking through the pupil and observing the lens of the eye with scattered opacities (cataracts). The patient has a strong family history of early cataracts (congenital). Visual acuity was not affected in the patient because the cataracts are small and not in the center light axis of the eye. However, even though visual acuity was 20/20 (i.e., normal), the patient had problems with glare and with seeing halos around lights as well as problems with on-coming headlights from cars.
Terms to Remember Phakic eye (Phakia): An eye with a natural lens in place. A normal eye. Aphakic eye (Aphakia): An eye without the natural lens. Pseudophakic eye (Pseudophakia): An eye that has had the natural lens removed and an intraocular lens implanted in the eye. Lens capsule: A capsule or "bag" which holds the lens of the eye. During cataract surgery, the lens of the eye is removed but the lens capsule remains in place. After cataract: After a cataract is removed, the lens capsule may become opaque or cloudy, mimicking a cataract.
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