Laurie Gallaway

Cataracts are the primary cause of blindness worldwide. Cataracts are the clouding of the lens. The lens is transparent and is important for the focusing of a sharp image on the retina. There are several different types of cataracts. Congenital cataracts are present at birth, and will be the focus of this paper. An eye disease causes secondary cataracts. Traumatic cataracts are caused by an injury. Finally, senile cataracts are caused by old age and are the most common form of cataracts.

Cataracts can be unilateral, meaning in one eye or bilateral, in both eyes. Congenital cataracts may be partial affecting part of the lens, or complete affecting the whole lens. If they are partial and not dense enough to interfere with light transmission, congenital cataracts are quite common and often visually insignificant (Vaughan, 1989). Dense central congenital cataracts require surgery. They cause a significant loss visually and must be detected early. A parent usually can not detect these cataracts. The doctor usually detects the cataracts in the newborn nursery immediately after birth.

Unilateral infantile cataracts that are central, dense, and larger than 2mm in diameter will cause permanent damage if not treated within the first 2 months of life (Vaughan, 1989). On the other hand, symmetric bilateral cataracts demand less urgent treatment (Vaughan, 1989).

The main treatment is surgery, followed by lens replacement / correction, and usually completed with occlusion therapy. The surgery is called phacoemulsification. In this procedure, ultrasound vibrations of up to 40,000 cycles per second are made by a hollow tube-like instrument. It is inserted and the vibrations break up the lens into little pieces. The pieces are then sucked out through the tube (Golstein, 1999). The lens replacement/correction may be done one of two ways. An intraocular lens is a plastic lens inserted where the real lens used to be. Aphakic contact lens correction is using contact lens to improve the images to the retina. I found that an intraocular lens might be a better choice compared to glasses or contact lens because the latter two tend to enlarge the image. The brain can not combine the two images if one of them is enlarged and the other is of normal size (Goldstein, 1999). Finally, I found that most treatments end with occlusion therapy. This therapy is like using a patch to cover the bad eye(s). Usually, 6 to 8 hours per day were prescribed. Age differences accounted for different waking and sleeping hours. This therapy corresponds to 90% of waking hours during the first months of life and gradually declines to 50% of waking hours by age 2 or 3 (Birch, 1996). Occlusion therapy usually was terminated by the ages between 6 and 9 years old.

Congenital cataracts may be associated with many different things during the pregnancy or birth of a child. One of these associations include maternal rubella during the first trimester of pregnancy (Vaughan, 1989). Others say that congenital cataracts are associated with low birth weight, central nervous system abnormalities, mental retardation, convulsions, cerebral palsy, genetics and heredity (Veterans', 1986).

Congenital cataracts may worsen as a result of trauma. The trauma of the lens means penetrating injury to the lens of the affected eye. Congenital cataracts may also worsen by therapeutic radiation. This is when you have medical treatment by irradiation to the person with gamma rays, x-rays, alpha particles or beta particles (Veterans', 1986).

Majorities of people believe that congenital cataracts develop genetically. Many doctors and psychologists are using mice to understand the development of these cataracts. There are two main advantages to using mice as models for human congenital cataracts. One advantage is that the mice are easy to breed in large litters that provide statistically significant data (Sidjanin, 1997). A second advantage is that the mouse genome is well characterized with many mouse -to- human homologies (Sidjanin, 1996). This method of using mice, provides for predicting the location of human disease genes based on the basis of their location in the mouse genome.

Sidjanin, Grimes, Pretsch and their colleauges are using mice just as described above. They have found a mutation called the Coc mutation on the mouse genome. They have found that this mutation causes one of the most common types of congenital cataracts. They are called autosomal dominant congenital cataracts. This isolation and characterization of the mouse Coc gene will allow us to isolate the homologous human gene (Sidjanin, 1997).

Another group of scientists are using mice for genetic research with congenital cataracts. Norose, Clark, and their colleauges tested for SPARC in mice (Norose, 1998). SPARC is a major component of remodeling tissues and figures prominently in morphogenesis, development, injury, and repair (Norose, 1998). SPARC has been shown to inhibit the cell cycle, prevent cell adhesion, and inactivate cellular responses to certain growth factors (Norose, 1998). SPARC-null mice developed early onset cataracts by 1.5 and 3.5 months of age. This age of 1.5 months is equivalent to the age of young children, in humans (Norose, 1998). By 8 months, the wild mice did not develop cataracts at all. This study provides strong evidence that the SPARC gene is essential to the normal development and maintenance of transparent lens cells by the development of early onset of cataracts in the SPARC-null mice (Norose, 1998). Therefore, these results indicates that a similar disease could be manifested in humans with a defective SPARC gene (Norose, 1998).

If you have congenital cataracts, you must receive treatment early. Early treatment is associated with better acuity. Birch and Stager experimented with 45 children between the ages of 5 to 8 years of age. All of the children were diagnosed with dense unilateral congenital cataracts between the ages of 1 to 10 days of age. The children received surgery, aphakic lens correction, and occlusion therapy. Birch and Stager found that a bilinear model fit better for the time frame of these dense unilateral congenital cataracts when compared to a linear model. The bilinear model states that there exists an early window of time during which treatment is maximally effective, followed by declining success (Birch, 1996). The linear model states there is a gradual worsening of prognosis with delay of treatment from the time of birth (Birch, 1996). Therefore, Birch and Stager believe that children should receive treatment within a 6-week time frame after birth to increase acuity.

Birch and Stager also did another experiment with Leffler and Weakley. In this study, they purpose that dense unilateral congenital cataracts not only compromises visual development through visual deprivation, but they also cause interocular competition. Children with dense bilateral congenital cataracts primarily contain visual deprivation alone. Birch and Stager and their colleges wanted to determine whether early treatments (< 8 weeks of age) minimizes not only the grating acuity deficits, but also the unequal competition during the immediate post treatment period. They also tested for contrast sensitivity deficits (Birch, 1998).

Birch and Stager tested 29 children between the ages of 6 to 8 years, each with a history of dense unilateral and bilateral congenital cataracts (more than 5mm in diameter). There were two treatment groups. One group had treatment between 1 to 8 weeks of life, and the second group had treatments between 12 and30 weeks. The parents of the children were told by an ophthalmologist when they were 1 to 10 days old. Parents refusing surgery until the child was older caused delayed treatments (Birch, 1998). All of the children had surgery, aphalic contact lens correction, and occlusion therapy (Birch, 1998). The results of this study found that grating acuity and contrast sensitivity deficits were similar of both unilateral and bilateral congenital cataracts for the treatment of 1 to 8 weeks of age (Birch, 1998). For the 12 to 30-week treatment group, the unilateral cataract children had a significantly larger grating acuity and contrast sensitivity deficits, than did the bilateral cataracts did (Birch, 1998). Therefore, only visual deprivation is active as an amblyogenic factor during the first weeks of life (Birch, 1998).

Lewis, Maurer, and Brent studied the same types of cataracts as the above experiment. They researched how various treatments affect acuity. They compared patients' monocluar acuity with that of children with no history of eye disorders (Lewis, 1995). The researchers used either optokinetic nystagmus (OKN), perferential looking (PL), or both to measure the grating acuity of the children tested (Lewis, 1995). OKN acuity of the treated eyes did not improve with age and was abnormal by 12 months of age. PL acuity increased with age, especially with the bilateral patients. Therefore, the deficits in the grating acuity are apparent earlier in OKN acuity than in the PL acuity (Lewis, 1995).

In conclusion, the main topics I researched discussed genetics and the deficits of acuity. If we know that congenital cataracts are genetic, can research be done to test for ways to decrease the chance of inheriting the cataracts? Perhaps a certain type of food or drink that the mother could take during her pregnancy to decrease the chances of her child having to receive surgery immediately after birth. I suppose that the surgery does not hurt the baby, therefore you want to receive treatment immediately instead of waiting until the child gets older. It might increase the risk of losing acuity and contrast sensitivity if you wait too long. The child could possibly even go blind resulting from putting treatment off.

Birch, Eileen E., Stager, David R., (1996). The Critical Period for Surgical Treatment of Dense Congenital Unilateral Cataract. Investigative Ophthalmology and Visual Science, 37 (8), 1532-1538.

Birch, Eileen E., Stager, David., Leffler, Joel., Weakley, David., (1998). Early Treatment of Congenital Unilateral Cataract Minimizes Unequal Competition. Investagative Ophthalmology and Visual Science, 37 (11), 1560-1565.

Goldstein, Bruce E., (1999). Sensation and Perception. Pacific Grove, CA. 523-524.

Lewis, Terri L., Maurer, Daphne., Brent, Henry P., (1995). Development of Grating Acuity in Children Treated for Unilateral or Bilateral Congenital Cataract. Investigative Ophthalmology and Visual Science, 36 (10), 2080-2093.

Norose, Kazumi., Clark, John I., Syed, Nasreen A., Basu, Amitabha., Heber-Katz, Ellen., Sage, E. Helene., Howe, Chin C., (1998). SPARC Deficiency Leads to Early-Onset Cataractogenesis. Investigative Ophthalmology and Visual Science, 39 (13), 2674-2680.

Sidjanin, Duska J., Grimes, Patricia A., Pretsch, Walter., Neuhauser-Klaus, Angelika., Favor, Jack., Stambolian, Dwight E., (1997). Mapping of the Autosomal Dominant Cataract Mutation (Coc) on Mouse Chromosome 16. Investigative Ophthalmology and Visual Science, 38 (12), 2502-2506.

Vaughan, Daniel., Asbury, Taylor., Tabbara, Khalid F. (1989). General Ophthalmology. East Norwalk, CO: Appleton and Lange. 147, 332.

Internet: Veterans' Entitlements Act 1986. Subsection 196B(2). ICD Codes: 743.30-743.34. Congenital Cataract.