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2. Astigmatism (optical systems) - Wikipedia

   en.wikipedia.org/wiki/Astigmatism_(optical_systems)

   There are a number of tests that are used by ophthalmologists and optometrists during eye examinations to determine the presence of astigmatism and to quantify the amount and axis of the astigmatism. [13] A Snellen chart or other eye chart may initially reveal reduced visual acuity.

3. 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 eye's lens, defects in the shape of the lens ...

4. List of instruments used in ophthalmology - Wikipedia

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

   Spectacles (glasses) to correct refractive errors of the eye; not invasive. 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.

5. Astigmatism - Wikipedia

   en.wikipedia.org/wiki/Astigmatism

   The cause of astigmatism is unclear, although it is believed to be partly related to genetic factors. [3][4] The underlying mechanism involves an irregular curvature of the cornea and protective reaction changes in the lens of the eye, called lens astigmatism, that has the same mechanism as spasm of accommodation. [1][3] Diagnosis is by an eye ...

6. 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), uses an ultrasound instrument for diagnostic testing. [1] A-scan biometry measures the axial length (AL) of the eye prior to cataract surgery in order to assess the refractive power of the intraocular lens that will be implanted.

7. Humphrey visual field analyser - Wikipedia

   en.wikipedia.org/wiki/Humphrey_Visual_Field_Analyser

   Humphrey field analyser (HFA) is a tool for measuring the human visual field that is commonly used by optometrists, orthoptists and ophthalmologists, particularly for detecting monocular visual field. [1] The results of the analyser identify the type of vision defect. Therefore, it provides information regarding the location of any disease ...