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The Special Sense Organs and Their Disorders
Published in Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss, Understanding Medical Terms, 2020
Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss
Gonioscopy is the examination of the angle of the anterior chamber with a gonioscope (lens) or a contact prism lens and beam illumination from a slit lamp. This procedure is used to detect retinal or optic nerve disease. Applanation tonometry is used to measure intraocular pressure in millimeters of mercury (mmHg). If diagnosis is still in doubt, provocative procedures such as a water drinking test, darkroom test, or mydriatic tests are employed. Other diagnostic procedures may include gross visual fields and basic motor exam, fluorescent angioscopy (examination of the capillary vessels), slit lamp examination, keratometry, ophthalmodynamometry, needle oculo-electromyography, electro-oculography (EOG), and retinoscopy.
Cornea
Published in Mostafa Khalil, Omar Kouli, The Duke Elder Exam of Ophthalmology, 2019
Mostafa Khalil, Omar Kouli, Rizwan Malik
Video keratography (corneal topography): Essential to pick up early keratoconus. Very useful for monitoring and has replaced keratometry. It shows an asymmetrical ‘bow-tie’ pattern in early disease and progresses into a steep cone that is displaced off the visual axis.
The Procedure
Published in John William Yee, The Neurological Treatment for Nearsightedness and Related Vision Problems, 2019
If you have a keratometer, measure the horizontal and vertical curvature of the cornea. The k readings are expressed in diopters. (Refer to the Addendum for more information on taking a k reading.) If you do not have a keratometer, the patient can request a k reading from an eye care specialist. The measurement does not necessarily have to be taken by a private optometrist. It can also be taken by an optician or an optometrist at a retail optical outlet such as Costco or Walmart.
Vecto-keratometry: determination of anterior corneal astigmatism in manual keratometers using power vectors
Published in Expert Review of Medical Devices, 2023
Raquel Salvador-Roger, Rosa Vila-Andrés, Vicente Micó, José J. Esteve-Taboada
Two different manual keratometers have been used along the study, one for each sample: Sample 1 was evaluated with a Helmholtz’s keratometer OM-4 (Topcon, Japan) and Sample 2 was evaluated with a Javal’s keratometer KJ-1000 (Indo, Spain). Before starting the study, both keratometers were calibrated and their repeatability was confirmed [26] using a stainless-steel sphere whose theoretical radius was estimated as half its diameter measured by a three-dimensional measuring machine MORA 0171.20.18.5 (MORA Metrology GmbH, Germany). Knowing the obtained radius for the calibration sphere, 8.02 ± 0.01 mm, we could set the initial error of both keratometers in other to compare the results under the same initial conditions. Values for the two samples were assessed using conventional keratometry and vecto-keratometry, so two consecutive measures were performed for each subject by the same examiner in the same session. Artificial tears were not used under any circumstances; thus, patients were constantly advised to blink.
Non-genetic risk factors for keratoconus
Published in Clinical and Experimental Optometry, 2023
Minji Song, Qing Yi Fang, Ishith Seth, Paul N Baird, Mark D Daniell, Srujana Sahebjada
On the other hand, susceptible patients who wear contact lens along with other risk factors that involve ocular trauma such as Down’s syndrome, Leber’s congenital amaurosis, atopy and significant history of eye rubbing, may cause keratoconus.19 Additionally, contact lens wear can lead to bulging of the central cornea and flatter keratometry readings compared to non-contact lens wear subjects. Corneal hypoxia has also been reported due to contact lens wear, especially hard polymethylmethacrylate lenses, but the association between the two is unclear and thus warrants further exploration as an area of research. In a similar vein, Barr et al.18 found that contact lens wear increases the risk of incident corneal scarring by almost 3 times over no contact lens wear.
The Evolution of Diagnostics for Keratoconus: From Ophthalmometry to Biomechanics
Published in Seminars in Ophthalmology, 2023
Akhil Bevara, Pravin K Vaddavalli
In 1880, Antonio Placido14 introduced the principle of Placido ring-based videokeratoscopes, which use concentric rings of light and a digital camera to capture the reflection of the rings on the corneal surface, and the data is then processed using algorithms to illustrate the topography of the anterior corneal surface. These devices incorporate features of both the keratometer and a photokeratoscope. Rabinowitz and co-workers have described various patterns and indices for early detection of keratoconus using videokeratography.15–18 Inferior steepening with asymmetric bowtie with a skewed radial axis (AB/SRAX) pattern was found in nearly 100% of patients with early keratoconus but only 0.5% of the normal population.19 Additionally, it was shown that 50% of eyes with an AB/SRAX pattern in the normal fellow eye of unilateral keratoconus ultimately progress to keratoconus, proving that this pattern could be a marker for forme fruste keratoconus (FFKC).18,20 A few indices, including I-S value, the SRAX index and KISA% index, were also introduced to improve the detection of keratoconus.15,16,18 However, none of these indices has proven to be 100% accurate in differentiating normal corneas from those that had early keratoconus.