Bifocal is additional power in the lens. It has an additional measurement listed on the prescription as "add" to show the strength of the lens. The type of lenses used in eyeglasses depends on the type of vision problem, and may include:.
Concave lenses. These are thinnest in the center. The numerical prescription in diopters is always marked with a minus - symbol. These lenses are used to correct nearsightedness myopia. Convex lenses. These lenses are thickest in the center, like a magnifying glass. They are used to correct farsightedness hyperopia. Cylindrical lenses. These curve more in one direction than in the other. They are used to correct astigmatism. If your child is old enough, let them play an active role in choosing their own glasses.
Think about the features below when buying eyeglasses for children:. Ear pieces that wrap around the ear cable temples are advised for children under 4 years. Straps may also be advised to hold the glasses in place. About 45 million Americans wear contact lenses. About 9 out of 10 people who wear contact lenses use soft lenses.
In general, there are 2 types of contact lenses:. A contact lens prescription includes more information than an eyeglass prescription. Special measurements are taken of the curvature of the eye.
In addition, your child's healthcare provider will determine if their eyes are too dry for contact lenses. The provider will also see if there are any corneal problems that may prevent your child from wearing contact lenses. They can develop secondary to trauma, medical treatment iatrogenic causes, or spontaneously. The area of damage causes a migration of lens epithelial cells into the area and subsequent transformation of the cells into myofibroblasts in a process known as fibrous metaplasia.
This results in an opacity on the anterior surface of the lens beneath the anterior capsule. Electron micrographs of the anterior lens epithelial cells in anterior subcapsular cataract. BM, basement membrane. From Font, R.
In one of the first studies on ASC, 5 lenses with ASC were examined by light and electron microscopy and confirmed the ability of the lens epithelium to undergo transformation to a fibrous plaque. The lens epithelial cells lost their normal cuboidal shape and elongated into a more spindle-shaped cell Fig. These cells were found frequently to be in contact with one another, resulting in the fibrous plaque known as ASC.
This process can be broken down into two phases: a proliferative and a degenerative phase. The proliferative phase was most evident near the periphery of the plaque, showing numerous spindle-shaped cells and mitotically active cells. It is followed by a degenerative phase, which results in an almost structure-less hyaline mass with fewer spindle-shaped cells. Although the cause of ASC is varied, an association between ASC and the formation of synechiae after trauma or inflammation has been hypothesized.
The synechiae would form between the posterior iris and anterior lens capsule, resulting in a stagnation of aqueous humor and accumulation of toxic metabolites that could produce a toxic effect on anterior lens epithelium. Direct injury to the head or eye can cause significant mechanical disruption and lead to cataract formation. A Vossius ring can occur if the insult caused the posterior iris pigment epithelium to imprint on the lens capsule. The pigment deposition may abate and resolve completely with time.
Severe blunt injury can cause stellate lenticular opacities in the cortex and capsule. Such insult can lead to lens epithelium dysfunction, resulting in a significant edematous response to the superficial cortical lens.
Vacuole pockets can then become trapped permanently within the lamellar zone, becoming integrated within the lenticular fibers while new layer are elaborated over the lesion. Alternatively, blunt trauma can also cause cataract formation within all the lenticular layers, leading to a diffuse fibrous metaplasia Fig. Other forms of trauma that can lead to cataract formation include exposure to radiation, infrared, extreme heat and electrical injury.
Traumatic cataract. Extensive anterior fibrous metaplasia arrows displaying prominent collagen staining blue in a traumatic cataract Trichrome stain, X Several pharmacological agents have been shown to cause cataract formation. Long term corticosteroid therapy and anabolic steroid use are among the most common agents associated with cataract formation, particularly posterior subcapsular cataract.
Psychotropic agents, particularly phenothiazine, induce deposition of pigmented material into the anterior lens epithelium in a very distinct axial configuration [14]. Other pharmaceutical agents known to cause lenticular cataracts include miotics, and amiodarone [15]. While age-related changes remains the leading factor for cataract formation, specifically senile cataract, other contributory factors include smoking, systemic disease, excessive exposure to sunlight and the aforementioned pharmacological agents [].
In diabetic patients, cortical and PSCs appear to occur earlier, particularly among patients with poor glycemic control.
Hypocalcemia-induced cataracts usually initiate as small white dot opacities that can coalesce into larger flakes. Smoking, sun exposure and systemic disease management are modifiable risk factors, so taking measures to changes these factors can delay the onset and progression of cataract formation. Phytonutrients, such as xanthophyll carotenoids, lutein and zeaxanthin may play a potential role in limiting or neutralizing light induced oxidative changes within the lens [22].
Currently, there are several ongoing studies evaluating other possible protective agents. Although there is no definitive measure to prevent cataract formation, cataract surgery remains an extremely safe and highly successful intervention. Two videos showing cataract surgical procedures from the anterior and posterior views of the anterior segment of the human eye. Surgery for cataracts has undergone extensive evolution.
Ancient knowledge viewed the cataratous eye as an imbalance of humors that needed displacement to recover vision. Using a needle, the surgeon would proceed to displace the abnormal humor until the crystalline lens dislocated. Modern cataract surgery has undergone significant changes and is now characterized by several steps: corneal incision, continuous curvilinear capsulorrhexis CCC , hydrodissection, phacoemulsification, cortical aspiration, and intraocular lens IOL implantation.
Earlier surgical intervention to remove the entire cataractous lens required a 12 mm incision with subsequent suture closure. However, a small 2. The CCC technique was developed by Gimbel and Neuhann in the s and truly revolutionized the phacoemulsification technique [16]. CCC involves creating a tear in the anterior capsule then continuing the tear in a circular continuous fashion while minimizing shear forces exerted on the zonular fibers.
After creation of the CCC, phacoemulsification is used to fragment and emulsify both the cortical and nuclear material. Originally pioneered by Kelman in , phacoemulsification remains a vital part of cataract surgery [17,18]. The CCC opening is large enough to allow implantation of the entire optic and haptics of an intraocular lens IOL within the remnant lens capsular bag.
The prior use of non-foldable polymethylmethacrylate lenses required a relatively large clear corneal incision for implantation. However, the development of the foldable silicone and acrylic IOLs allowed insertion through a small incision mostly less than 4.
Innovation is constantly improving these steps of cataract surgery, from novel IOLs with unique design to minimize the corneal incision, to use of the femtosecond laser to create an automated corneal incision, CCC and to fragment the nucleus prior to aspiration.
Details of the types of intraocular lenses, that are presently being used in cataract surgery, are presented in the following chapter in webvision by Jason Nguyen, and Liliana Werner. Epidemiology of cataract in childhood: A global perspective. Global prevalence of childhood cataract: a systematic review.
The critical period for surgical treatment of dense congenital bilateral cataracts. The critical period for surgical treatment of dense congenital unilateral cataract.
American Journal of Ophthalmology. Lancet London, England. Early treatment of congenital unilateral cataract minimizes unequal competition. The Beaver Dam Eye Study. Epidemiology of risk factors for age-related cataract.
Survey of Ophthalmology. Human Posterior Subcapsular Cataract. Archives of Ophthalmology. Corticosteroid-induced cataracts. Topical-Corticosteroid-Induced Cataracts.
Annals of Pharmacotherapy. Exposure to Phenothiazine Drugs and Risk of Cataract. Influence of various miotics on cataract formation. British Journal of Ophthalmology. Continuous Curvilinear Capsulorhexis. Phacoemulsification in the Anterior Chamber. The History and Development of Phacoemulsification.
International Ophthalmology Clinics. Journal of Refractive Surgery. Author: Healthwise Staff. This information does not replace the advice of a doctor. Healthwise, Incorporated, disclaims any warranty or liability for your use of this information.
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