Tag: Astigmatism

Contact Lens Prescriptions

Karen Griffith

A contact lens is a medical device, like a breast implant or a hearing aid. Contacts can be worn to correct vision as well as for cosmetic or therapeutic reasons. In the United States, all contact lenses require a current prescription. A contact lens prescription generally expires on a yearly basis. This is to ensure that the eyes are healthy enough to support contact lens wear and that the current contact lenses are still the most appropriate. Dr. Griffith

An eye examination is necessary to determine the suitability of contact lenses and also to determine the size, parameters and limitations of the eye. This typically includes a refraction to determine the proper power to see clearly, keratometry to measure the shape and size of the cornea and a thorough health assessment of the eye.

Conditions that may complicate contact lens wear include dry eye, irregular and high astigmatism and eyelid irregularities.

Vision Screening Vs. Vision Exam

Karen Griffith

The department of motor vehicles, the school nurse and the pediatrician use vision screening to identify vision problems. Screening usually involves standing a given distance from a lettered chart, covering one eye and reading down the chart to the smallest letter possible.

SNELLEN

A vision screening is intended to help identify children with eye or vision problems that threaten sight or impair their ability to develop and learn normally. However, vision screenings are a limited process and cannot be used to diagnose an eye or vision problem, but rather to indicate a potential need for further evaluation.

Screenings are typically designed to detect problems with distance vision, and that is important for children socially and physically, but myopia represents the least risk for reading and learning. A myopic child is more likely to notice that the board is blurry and move to the front of the classroom. Hyperopia on the other hand, makes it more difficult to see things close up and astigmatism effects vision at all distances. Children with uncorrected hyperopia and astigmatism will have more difficulty reading and writing and may not even be aware that the difficulty is due to his or her vision. These are the children that may complain of headaches, avoid reading and school related tasks.
A vision screening test identifies some vision problems, but can miss disorders that have a profound effect on a child’s ability to succeed in school.

During a comprehensive eye examination an optometrist can identify, diagnose and prescribe treatment.

Astigmatism

admin

Most astigmatism is caused by the shape of the cornea. The cornea is the outer most surface of the eye. It is the clear structure that first bends light (refracts). Instead of being spherical with a single curvature, it has two curvatures that result in the light focusing in two different locations within the eye. Ideally, the light focuses at one point on the retina. (emmetropia). If the eye is myopic (nearsighted) the light focuses in front of the retina. If the eye is hyperopic, far-sighted, the light focuses behind the retina. If the eye is astigmatic, the light focuses in two different places, one focus can be on the retina and one in front of or behind the retina.

Astigmatism is not a disease, it is a refractive condition. A common example optometrists use to describe astigmatism is the difference between a basketball and a football. A basketball is round, and has only one curve for the entire ball. You can think of that curve as a lens power. A football on the other hand has two curves. This is like an eye that has two powers or an astigmatism.

Like other refractive errors, astigmatism can be corrected with glasses, contact lenses or refractive surgery.

 

 

Reliability of Vision Screenings

admin

     The department of motor vehicles, the school nurse and the pediatrician use vision screening to identify vision problems. Screening usually involves standing a given distance from a lettered chart, covering one eye and reading down the chart to the smallest letter possible.
     According to a recent study in Australia, researchers found that results for detecting myopia in 12 -13 year olds was nearly 98%. Good news for the nearsighted, but not so good for the tweens with astigmatism or hyperopia. Only half of the hyperopic children were identified by the vision screening and 25% of the kids with astigmatism were missed.
Screenings are best designed to detect problems with distance vision, and that is important for children socially and physically, but myopia represents the least risk for reading and learning. A myopic child is more likely to notice that the board is blurry and move to the front of the classroom. Hyperopia on the other hand, makes it more difficult to see things close up and astigmatism effects vision at all distances. Children with uncorrected hyperopia and astigmatism will have more difficulty reading and writing and may not even be aware that the difficulty is due to his or her vision. These are the children that may complain of headaches, avoid reading and school related tasks.
     A vision screening test identifies some vision problems, but can miss disorders that have a profound effect on a child’s ability to succeed in school.