Cataracts are the primary cause of blindness worldwide. Cataractsare the clouding of the lens. The lens is transparent and isimportant for the focusing of a sharp image on the retina. There areseveral different types of cataracts. Congenital cataracts arepresent at birth, and will be the focus of this paper. An eyedisease causes secondary cataracts. Traumatic cataracts are causedby an injury. Finally, senile cataracts are caused by old age andare the most common form of cataracts.
Cataracts can be unilateral, meaning in one eye or bilateral, inboth eyes. Congenital cataracts may be partial affecting part of thelens, or complete affecting the whole lens. If they are partial andnot dense enough to interfere with light transmission, congenitalcataracts 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 usuallydetects the cataracts in the newborn nursery immediately after birth.
Unilateral infantile cataracts that are central, dense, and largerthan 2mm in diameter will cause permanent damage if not treatedwithin the first 2 months of life (Vaughan, 1989). On the otherhand, 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. Thesurgery is called phacoemulsification. In this procedure, ultrasoundvibrations of up to 40,000 cycles per second are made by a hollowtube-like instrument. It is inserted and the vibrations break up thelens into little pieces. The pieces are then sucked out through thetube (Golstein, 1999). The lens replacement/correction may be doneone of two ways. An intraocular lens is a plastic lens insertedwhere the real lens used to be. Aphakic contact lens correction isusing contact lens to improve the images to the retina. I found thatan intraocular lens might be a better choice compared to glasses orcontact lens because the latter two tend to enlarge the image. Thebrain can not combine the two images if one of them is enlarged andthe other is of normal size (Goldstein, 1999). Finally, I found thatmost treatments end with occlusion therapy. This therapy is likeusing a patch to cover the bad eye(s). Usually, 6 to 8 hours per daywere prescribed. Age differences accounted for different waking andsleeping hours. This therapy corresponds to 90% of waking hoursduring the first months of life and gradually declines to 50% ofwaking hours by age 2 or 3 (Birch, 1996). Occlusion therapy usuallywas terminated by the ages between 6 and 9 years old.
Congenital cataracts may be associated with many different thingsduring the pregnancy or birth of a child. One of these associationsinclude maternal rubella during the first trimester of pregnancy(Vaughan, 1989). Others say that congenital cataracts are associatedwith low birth weight, central nervous system abnormalities, mentalretardation, convulsions, cerebral palsy, genetics and heredity (Veterans', 1986).
Congenital cataracts may worsen as a result of trauma. The traumaof the lens means penetrating injury to the lens of the affected eye. Congenital cataracts may also worsen by therapeutic radiation. Thisis when you have medical treatment by irradiation to the person withgamma rays, x-rays, alpha particles or beta particles (Veterans',1986).
Majorities of people believe that congenital cataracts developgenetically. Many doctors and psychologists are using mice tounderstand the development of these cataracts. There are two mainadvantages to using mice as models for human congenital cataracts. One advantage is that the mice are easy to breed in large littersthat provide statistically significant data (Sidjanin, 1997). Asecond advantage is that the mouse genome is well characterized withmany mouse -to- human homologies (Sidjanin, 1996). This method ofusing mice, provides for predicting the location of human diseasegenes based on the basis of their location in the mouse genome.
Sidjanin, Grimes, Pretsch and their colleauges are using mice justas described above. They have found a mutation called the Coc mutation on the mouse genome. They have found that this mutationcauses one of the most common types of congenital cataracts. Theyare called autosomal dominant congenital cataracts. This isolationand characterization of the mouse Coc gene will allow us to isolatethe homologous human gene (Sidjanin, 1997).
Another group of scientists are using mice for genetic researchwith congenital cataracts. Norose, Clark, and their colleaugestested for SPARC in mice (Norose, 1998). SPARC is a major componentof remodeling tissues and figures prominently in morphogenesis,development, injury, and repair (Norose, 1998). SPARC has been shownto inhibit the cell cycle, prevent cell adhesion, and inactivatecellular responses to certain growth factors (Norose, 1998). SPARC-null mice developed early onset cataracts by 1.5 and 3.5 monthsof age. This age of 1.5 months is equivalent to the age of youngchildren, in humans (Norose, 1998). By 8 months, the wild mice didnot develop cataracts at all. This study provides strong evidencethat the SPARC gene is essential to the normal development andmaintenance of transparent lens cells by the development of earlyonset of cataracts in the SPARC-null mice (Norose, 1998). Therefore,these results indicates that a similar disease could be manifested inhumans with a defective SPARC gene (Norose, 1998).
If you have congenital cataracts, you must receive treatmentearly. Early treatment is associated with better acuity. Birch andStager experimented with 45 children between the ages of 5 to 8 yearsof age. All of the children were diagnosed with dense unilateralcongenital cataracts between the ages of 1 to 10 days of age. Thechildren received surgery, aphakic lens correction, and occlusiontherapy. Birch and Stager found that a bilinear model fit better forthe time frame of these dense unilateral congenital cataracts whencompared to a linear model. The bilinear model states that thereexists an early window of time during which treatment is maximallyeffective, followed by declining success (Birch, 1996). The linearmodel states there is a gradual worsening of prognosis with delay oftreatment from the time of birth (Birch, 1996). Therefore, Birch andStager believe that children should receive treatment within a 6-weektime frame after birth to increase acuity.
Birch and Stager also did another experiment with Leffler andWeakley. In this study, they purpose that dense unilateralcongenital cataracts not only compromises visual development throughvisual deprivation, but they also cause interocular competition. Children with dense bilateral congenital cataracts primarily containvisual deprivation alone. Birch and Stager and their colleges wantedto determine whether early treatments (< 8 weeks of age) minimizesnot only the grating acuity deficits, but also the unequalcompetition during the immediate post treatment period. They alsotested for contrast sensitivity deficits (Birch, 1998).
Birch and Stager tested 29 children between the ages of 6 to 8years, each with a history of dense unilateral and bilateralcongenital cataracts (more than 5mm in diameter). There were twotreatment groups. One group had treatment between 1 to 8 weeks oflife, and the second group had treatments between 12 and30 weeks. The parents of the children were told by an ophthalmologist when theywere 1 to 10 days old. Parents refusing surgery until the child wasolder caused delayed treatments (Birch, 1998). All of the childrenhad surgery, aphalic contact lens correction, and occlusion therapy(Birch, 1998). The results of this study found that grating acuityand contrast sensitivity deficits were similar of both unilateral andbilateral congenital cataracts for the treatment of 1 to 8 weeks ofage (Birch, 1998). For the 12 to 30-week treatment group, theunilateral cataract children had a significantly larger gratingacuity and contrast sensitivity deficits, than did the bilateralcataracts did (Birch, 1998). Therefore, only visual deprivation isactive as an amblyogenic factor during the first weeks of life(Birch, 1998).
Lewis, Maurer, and Brent studied the same types of cataracts asthe above experiment. They researched how various treatments affectacuity. They compared patients' monocluar acuity with that ofchildren with no history of eye disorders (Lewis, 1995). Theresearchers used either optokinetic nystagmus (OKN), perferentiallooking (PL), or both to measure the grating acuity of the childrentested (Lewis, 1995). OKN acuity of the treated eyes did not improvewith age and was abnormal by 12 months of age. PL acuity increasedwith age, especially with the bilateral patients. Therefore, thedeficits in the grating acuity are apparent earlier in OKN acuitythan in the PL acuity (Lewis, 1995).
In conclusion, the main topics I researched discussed genetics andthe deficits of acuity. If we know that congenital cataracts aregenetic, can research be done to test for ways to decrease the chanceof inheriting the cataracts? Perhaps a certain type of food or drinkthat the mother could take during her pregnancy to decrease thechances of her child having to receive surgery immediately afterbirth. I suppose that the surgery does not hurt the baby, thereforeyou want to receive treatment immediately instead of waiting untilthe child gets older. It might increase the risk of losing acuityand contrast sensitivity if you wait too long. The child couldpossibly even go blind resulting from putting treatment off.
Birch, Eileen E., Stager, David R., (1996). The Critical Periodfor 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 MinimizesUnequal Competition. Investagative Ophthalmology and Visual Science,37 (11), 1560-1565.
Goldstein, Bruce E., (1999). Sensation and Perception. PacificGrove, CA. 523-524.
Lewis, Terri L., Maurer, Daphne., Brent, Henry P., (1995). Development of Grating Acuity in Children Treated for Unilateral orBilateral Congenital Cataract. Investigative Ophthalmology andVisual 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) onMouse 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.