The majority of people seeking eye care will do so because of refractive error. Correction of such errors by external lenses (glasses) or lenses placed over the cornea (contact lenses) is the central function of the Refraction Service.
For special needs patients, particularly the very young, elderly or infirm, Queens Eye Center provides "portable autorefraction." This modern instrumentation allows the doctor to obtain good measurement of refractive error without need for the more typical but cumbersome and lengthy refraction exam.
For patients with certain types of insurance, refraction can be followed by on-site dispensing of glasses or contact lenses. Those choosing contact lenses will be fitted accurately and will obtain appropriate education in the safe use of contacts and in general eye care.
Eye conditions characterized by refractive error include myopia (nearsightedness), hyperopia (farsightedness), astigmatism and presbyopia. These disorders of the eye are routinely corrected with glasses or contact lenses, and now, with refractive procedures such as LASIK and PRK, intracorneal rings, CK for hyperopia, and even intraocular lens implants (implantable contact lenses).
Myopia, or nearsightedness, is the condition of the eye in which images are formed in front of the retina, resulting in a blurred image. This occurs when the eye is relatively too long or the refractive powers of the cornea and lens of the eye are relatively too strong. Myopia usually begins in childhood, and progressively worsens until adulthood.
Hyperopia, or farsightedness, occurs when images are formed behind the retina, resulting in a blurred image. This is due to an eye that is relatively too short, or the refractive powers of the cornea and lens of the eye are relatively too weak. Depending on the degree of farsightedness and the age of the individual, some farsighted people may see clearly at both distance and near through the process of accommodation, or focusing of the lens in the eye. This may cause significant eyestrain, however, and the abilities are gradually lost with age.
Astigmatism is the presence of a cornea that is not "perfectly" round. The cornea in astigmatism is sometimes referred to as having a football shape. This means that the cornea is steeper in one meridian, and flatter in the opposite meridian 180 degrees away. This results in two images being formed, but to the affected individual, the image is simply blurry. Astigmatism of some degree is present in approximately 30 to 40% of individuals who wear glasses or contact lenses.
Astigmatism indicates that vision is distorted by a variation in the curvature of the cornea. In other words, the cornea has a different curvature in one meridian as compared to the opposite meridian 180 degrees away. When the two meridians of curvature are exactly 180 degrees apart, the condition is known as regular astigmatism. Significant amounts of regular astigmatism occur in about 30 to 40 percent of patients who wear prescription glasses or contact lenses. Regular astigmatism may be corrected with cylinder in eyeglasses, toric soft contact lenses, or rigid gas-permeable contact lenses.
Irregular astigmatism is present when the different meridians of curvature of the cornea are not 180 degrees apart or the cornea takes on multiple meridians of curvature. This condition may be thought of as a bumpy surface. The visual result of irregular astigmatism is distortion of vision that may not correct well even with glasses or contact lenses. Irregular astigmatism frequently occurs with the following conditions: keratoconus, corneal scarring, pressure on the cornea from lid masses such as chalazia, and corneal warpage associated with contact lens wear.
In infancy and childhood the natural lens of the eye is soft and pliable and is easily altered in shape by the ciliary muscles of the eye through a process called accommodation. Throughout life the lens of the eye gradually hardens, becomes less pliable, and progressively increases its resistance to change in shape. This leads to greater difficulty in focusing near. By approximately 45 years of age, most people require reading correction, assuming their vision is corrected for distance. This condition is known as presbyopia.