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An eye examination, commonly known as an eye test, [1] is a series of tests performed to assess vision and ability to focus on and discern objects. [2] It also includes other tests and examinations of the eyes. [2] Eye examinations are primarily performed by an optometrist, ophthalmologist, or an orthoptist.
Subjective Refraction is a technique to determine the combination of lenses that will provide the best corrected visual acuity (BCVA). [1] It is a clinical examination used by orthoptists , optometrists and ophthalmologists to determine a patient's need for refractive correction, in the form of glasses or contact lenses.
By measuring this zone, the autorefractor can determine when a patient's eye properly focuses an image. The instrument changes its magnification until the image comes into focus. The process is repeated in at least three meridians of the eye and the autorefractor calculates the refraction of the eye, sphere, cylinder and axis.
When an eye focuses light correctly on to the retina when viewing distant objects, this is called emmetropia or being emmetropic. This means that the refractive power of the eye matches what is needed to focus parallel rays of light onto the retina. A distant object is defined as an object located beyond 6 meters (20 feet) from the eye.
While moving the streak or spot of light through the pupil across the retina, the examiner observes the relative movement of the reflex or manually places lenses over the eye (using a phoropter or trial frame and trial lenses) to "neutralize" the reflex. [2] Static retinoscopy is a type of retinoscopy used in determining a patient's refractive ...
Refractive surgery can eliminate the need to wear corrective lenses altogether by permanently changing the shape of the eye but, like all elective surgery, comes with both greater risk and expense than the non-invasive options. Various considerations involving eye health, refractive status, and lifestyle determine whether one option may be ...
Diagnosis is by an eye exam. [2] The World Health Organization (WHO) estimates that 80% of visual impairment is either preventable or curable with treatment. [1] This includes cataracts, the infections river blindness and trachoma, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness. [15]
A duochrome test is a test commonly used to refine the final sphere in refraction (undercorrection and overcorrection), which makes use of the longitudinal chromatic aberration of the eye. Because of the chromatic aberration of the eye, the shorter wavelengths (green) are focused in front of the longer red wavelengths.