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  2. A-scan ultrasound biometry - Wikipedia

    en.wikipedia.org/wiki/A-scan_ultrasound_biometry

    A-scan ultrasound biometry. A-scan ultrasound biometry, commonly referred to as an A-scan (short for Amplitude scan ), is a routine type of diagnostic test used in optometry or ophthalmology. The A-scan provides data on the length of the eye, which is a major determinant in common sight disorders. The most common use of the A-scan is to ...

  3. Corneal topography - Wikipedia

    en.wikipedia.org/wiki/Corneal_topography

    A corneal topogram of an eye affected by keratoconus. Blue shows the flattest areas, and red the steepest. Corneal topography, also known as photokeratoscopy or videokeratography, is a non-invasive medical imaging technique for mapping the anterior curvature of the cornea, the outer structure of the eye. Since the cornea is normally responsible ...

  4. List of instruments used in ophthalmology - Wikipedia

    en.wikipedia.org/wiki/List_of_instruments_used...

    Contact lenses. to correct refractive errors of the eye; a little invasive. Phoropter. used in refraction testing. Tonometers. used to determine the intraoccular pressure (IOP) - useful in glaucoma; video link for various types of tonometers. Speculum: to keep the eyes open during any operation. Universal eye speculum.

  5. Jackson cross cylinder - Wikipedia

    en.wikipedia.org/wiki/Jackson_cross_cylinder

    Astigmatism. Based on. circle of confusion. The Jackson cross cylinder ( JCC) is an instrument used by ophthalmologists, orthoptists and optometrists in their routine eye examination, particularly in determination of corrective lens power in patients with astigmatism. It is also used for testing near point of the eye.

  6. Astigmatism - Wikipedia

    en.wikipedia.org/wiki/Astigmatism

    Mixed astigmatism – focal lines are on both sides of the retina (straddling the retina). Throughout the eye. Astigmatism, whether it is regular or irregular, is caused by some combination of external (corneal surface) and internal (posterior corneal surface, human lens, fluids, retina, and eye-brain interface) optical properties.

  7. Pinhole occluder - Wikipedia

    en.wikipedia.org/wiki/Pinhole_occluder

    A pinhole occluder is an opaque disk with one or more small holes through it, used by ophthalmologists, orthoptists and optometrists to test visual acuity. The occluder is a simple way to focus light, as in a pinhole camera, temporarily removing the effects of refractive errors such as myopia. Because light passes only through the center of the ...

  8. Amsler grid - Wikipedia

    en.wikipedia.org/wiki/Amsler_grid

    Test of. Central visual field. The Amsler grid, used since 1945, is a grid of horizontal and vertical lines used to monitor a person's central visual field. The grid was developed by Marc Amsler, a Swiss ophthalmologist. It is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the ...

  9. Aberrations of the eye - Wikipedia

    en.wikipedia.org/wiki/Aberrations_of_the_eye

    Spherical aberration is the cause of night myopia and is commonly increased after myopic LASIK and surface ablation. It results in halos around point images. Spherical aberration exacerbates myopia in low light (night myopia). In brighter conditions, the pupil constricts, blocking the more peripheral rays and minimizing the effect of spherical ...

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