This finding is not completely understood. One hypothesis is that changes in the hormonal milieu at menopause somehow increase the risk of lens opacity among women. Evidence in favor of this theory includes a decreased risk of nuclear sclerosis among current users of estrogen replacement therapy 19 20 21 and a protective effect of younger age at menarche and older age at menopause against nuclear and cortical opacities, respectively.
The most prevalent form of cataract in this African population was NSC. This differs from the preponderance of CC, which has been reported for African-derived populations in Barbados 4 and Maryland. Several different types of explanations may be considered for this. One possibility is grader error, or artifact, in the assessment of CC. The fact that all grading for this study was carried out at the slit lamp, without a permanent photographic record, does not permit review of the grading.
However, all grading was performed by a single ophthalmologist RRB , after a period of standardization with one of the original designers of the grading system SKW.
At the end of the training period, reliability testing was carried out using a set of photographs that were graded separately by the two investigators. Good agreement in the grading of photographs does not preclude the possibility of error resulting from uncontrolled factors in a field setting.
For example, inadequate dilation of the pupil could result in an underestimate of the prevalence of CC, because it is often seen primarily at the equator of the lens. In grading of the right eye, subjects The age-adjusted proportion of persons with CC among those with adequate dilation 7. It does not seem likely that inadequate pupillary dilation could explain the low prevalence of CC in this population. Alternatively, the lower observed prevalence of CC in our study may have resulted from differences in cataract grading systems, especially if the WHO System categorizes less severe opacities as 0.
This definition of CC may be compared with the WHO System definition of grade 1 or higher, that is, an opacity occupying one eighth or more of the circumference of the lens. However, it is certainly possible to imagine a wedge-shaped opacity that covers an area slightly greater than standard CI and yet occupies less than one eighth of the circumference. In summary, some eyes graded as having CC in the Barbados study e.
In comparing our results with those of African-American participants in the Salisbury Eye Evaluation SEE Project 5 in Salisbury, Maryland, it does not appear that differences in grading systems can explain the observed difference in prevalence of CC.
Thus, it does not appear that the lower prevalence of CC observed in Tanzania compared with Barbados and Maryland can be explained completely in terms of differences between grading systems. A final reason for the apparent differences in CC prevalence between our African population and African-derived populations in Barbados and Maryland may relate to differences between the populations themselves.
A higher incidence of cataract extraction in Tanzania could theoretically lead to lower observed prevalence of CC. This is well below the prevalence reported for Barbados 4 and Maryland. Another obvious difference between these populations is that of age.
The Tanzanian population mean age, Age adjustment applying the Barbados prevalence rates for CC only considering opacities greater than standard CII as discussed above to the Kongwa population gives an age- and gender-adjusted prevalence for CC of Age adjustment in which prevalence rates for the present study were applied to the SEE population structure gives a prevalence of CC of In summary, it would seem that the major reason for higher observed prevalence of cortical cataract in Salisbury, Maryland, versus the present study was the pronounced difference in age between the two populations.
The difference between Barbados and the present study was partly due to age and partly due to differences in grading systems, where very early cortical opacities were classified in this population as not present. Another aspect of the different patterns of opacity seen in the Tanzanian population appears to be a higher than expected prevalence of NSC.
Analyses similar to those presented above were carried out for NSC. This comparison can be made directly, in that the cutoff for significant NSC between these two studies was of comparable severity. Although the definition of NSC used in the Kongwa Eye Project KEP was more severe than that in the Barbados study, it is interesting to note that the adjusted prevalence obtained by applying the KEP prevalence rates to the Barbados population structure, One reason for the somewhat higher age-adjusted prevalence of NSC in Kongwa than in Salisbury and Barbados may well be the greater availability of cataract surgery, with the prevalence of bilateral pseudophakia among African-Americans in Salisbury being 4.
Smoking, a well-described risk factor for NSC, 24 25 26 27 is not at all widely practiced in the Kongwa region. Although there is much conflicting evidence, the preponderance of epidemiologic studies suggest that reduced intake of antioxidant substances such as vitamins A, C, and E may increase risk for NSC.
Another difference that must be considered between the populations in Tanzania, Barbados, and Maryland is ethnic. The people of central Tanzania were not included in the slave trade to the New World to the same extent as the West African ancestors of participants in the Barbados and Salisbury studies.
Although most Tanzanians share a common ancestry with present inhabitants of West Africa, 29 some ethnic differences across Africa do exist and may underlie the apparent differences in prevalence of the different types of cataract.
Further work on the excess of nuclear opacity in this East African population may be warranted. As rates of cataract surgery were lower in this population than any for which cataract prevalence has been previously reported using a standardized system, our data provide new evidence that PSC prevalence is low not simply because of rapid progression to visual disability and cataract extraction.
The relative frequency of cataract types observed in this Tanzanian population, with NSC more prevalent than CC, is actually more similar to that reported in several studies for white populations. Differences in the prevalence rates of the different types of age-related lens opacity are of more than theoretical interest.
The degree of visual disability associated with the different types of cataract has been reported to vary, with PSC and NSC in particular being more likely to result in vision loss requiring cataract surgery. Commercial relationships policy: N. The publication costs of this article were defrayed in part by page charge payment.
Corresponding author: Nathan Congdon, Wilmer , N. Wolfe Street, Baltimore, MD T able 1. View Table. Prevalence No. Prevalence Prevalence of Cortical Cataract 40—49 2. T able 2. T able 3. The model is for both right and left eyes, with SEs having been corrected for the correlation between eyes.
The outcome variable for vision is Logmar, or negative log of best-corrected acuity; thus, a negative beta-coefficient indicates that the factor in question is protective, whereas a positive value indicates an association with worse vision.
The authors thank M. Cristina Leske for her generosity in making available data from the Barbados Eye Study for purposes of comparison with the results of the present study.
Global data on blindness. Cataracts are not always caused by age, however. They can be brought on by injuries to the eye, medical conditions such as diabetes, eye surgeries or other eye conditions. The use of steroids may hasten the progression of cataracts. Though relatively uncommon, children are sometimes born with congenital cataracts or develop them during childhood.
Thankfully, regardless of their cause, cataracts can be treated surgically with a high degree of success. Interestingly enough, not all cataracts are the same.
Each type of cataract forms in a specific portion of the lens with varying physical effects and progression patterns. Posterior Subcapsular Cataracts PSC form in the back of the lens, aside the capsule which holds the lens in place. As the cataract develops, it will increasingly obstruct the path of light and cause glare.
This type of cataract is commonly found in patients who have had eye trauma or surgery, who have had elevated blood sugar levels, or who have been treated with steroids. However, a PSC cataract can form in perfectly normal eyes who do not meet any of these criteria. Occasionally, PSC cataracts will be present in children and even infants. The progression of a PSC cataract is typically more rapid than other forms of cataract.
It may become visually significant over the course of months or years, but can happen as quickly as weeks and even days. If left untreated, posterior subcapsular cataracts may result in significant impairment of vision and can progress to the point of blindness. Nuclear cataracts affect the center of the lens, also known as the nucleus. With this type of cataract, the lens gradually hardens and turns densely yellow or brown over time.
In general, nuclear cataracts cause more significant impairment on distance vision than near vision. As a nuclear cataract reaches advanced stages, it can make it difficult for the patient to distinguish between different shades of color. Many patients are able to delay cataract surgery with effective reading glasses and eyeglasses, wearing anti-glare sunglasses, and taking precautions such as avoiding night driving.
Visual function is determined by asking the patient how they are limited in function by their vision and by measuring their visual acuity with and without spectacle correction.
In patients complaining of glare, brightness acuity is tested by asking a patient to read the eye chart while shining a bright light at the patient from the side. There are also other instruments which can mimic glare. These simulate the oncoming headlights of night driving and can reveal functional impairment.
A comprehensive dilated eye exam is performed on all patients when possible. Specific attention is paid to several factors impacting surgical planning including the severity of the cataract, the size of the dilated pupil smaller pupils increase the complication rate , the clarity, thickness and health of the cornea, stability of the lens, depth of the anterior chamber, and health of the optic nerve and retina. In order to get the best possible visual outcomes, several preoperative measurements are necessary to determine the power of the IOL implant.
A careful refraction of both eyes, especially if planning on operating on only one eye, is needed to avoid dissimilar refractive errors postoperatively, as this can be disturbing to patients. To determine the IOL power needed, measurements of the axial length of the eye, the corneal refractive power, and the anterior chamber depth are taken. Additional tests that can be helpful in select cases include corneal topography and endothelial cell counts.
No medical treatment has been show to be effective in the treatment or prevention of cataracts, although this is an active area of research. To slow the development of cataracts it is generally recommended that patients eat a balanced diet, prevent excessive exposure to UV radiation by using good quality UV blocking sunglasses, avoiding injuries by using protective eyewear, and if diabetic closely control blood sugar levels.
Other approaches to temporarily improve visual function include careful refraction to get the best-corrected vision, pharmacological dilation, increased lighting and the use of magnifiers for near work.
Cataract surgery is one of the most common surgical procedures performed around the world and has a very high success rate. The most common type of cataract surgery in the United States utilizes ultrasound energy to break the cataract into particles small enough to aspirate through a handpiece. This technique is referred to as phacoemulsification. Other techniques include manual extracapsular cataract extraction ECCE in which the entire nucleus of the cataract is removed from the eye in one piece after extracting it from the capsular bag.
While ECCE traditionally involved a large incision that required multiple sutures, a newer techinique known by many names such as manual small incision cataract surgery or small incision ECCE allows for manual extraction without the need for any sutures. The goal in modern cataract surgery is not only the removal of the cataract, but also the replacement of the cataract with an intraocular lens IOL.
The IOL is typically placed during the cataract surgery, and may be placed in the capsular bag as a posterior chamber lens PCIOL , in the ciliary sulcus, as a sulcus lens, or in the anterior chamber anterior to the iris as an anterior chamber lens ACIOL.
There are multiple types of IOLs that may be used in modern cataract surgery, including monofocal, multifocal, accomodative, and astigmatism-correcting lenses. The goal of all IOLs is to improve vision and limit dependency upon spectacles or contact lenses. This procedure still relies upon the cataract surgeon to remove lens material in a manner similar to phacoemulsification, but it replaces several manual steps of the procedure with a more automated laser mechanism.
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Original article contributed by :. Brad H. Feldman, M. All contributors:. Patel, M. Assigned editor:. ICD - Section Preferred Practice Patterns. American Academy of Ophthalmology.
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