The Special Sense Organs and Their Disorders
Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss in Understanding Medical Terms, 2020
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.
Anterior segment OCT
Pablo Artal in Handbook of Visual Optics, 2017
Corneal topography can be revealed by mapping the corneal thickness (pachymetry), surface elevation, or curvature/power mapping (keratometry) and plays an important role in the assessment of keratorefractive surgical procedures, corneal transplantation, or screening the corneal degenerations and dystrophies (e.g., keratoconus). There are several techniques enabling topographic description of the eye (Mejia-Barbosa and Malacara-Hernandez, 2001, Pinero, 2015). Access to volumetric data sets enables mapping the corneal thickness (corneal pachymetry). Several studies have been performed to show reproducibility of OCT pachymetry and agreement with standard instruments (Wirbelauer et al., 2002, Li et al., 2006, 2008, 2010, Pinero et al., 2008). The comparison of corneal pachymetry for normal subject and patient with keratoconus is presented in Figure 4.18 (Karnowski et al., 2011). The maps were calculated from corresponding 3-D data sets after segmentation of corneal interfaces and correction for light refraction.
The Procedure
John William Yee in 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.
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.
Pediatric Keratoconus in A Tertiary Eye Center in Alexandria: A Cross-sectional Study
Published in Ophthalmic Epidemiology, 2022
Shahira Mahmoud, Ahmed El-Massry, Mohamed Bahgat Goweida, Islam Ahmed
A diagnosis of keratoconus was confirmed using a rotating Scheimpflug imaging system (Pentacam, Oculus, Germany) to detect the keratometry value in both the flat (Kf) and Steep (Ks) meridians, the average (AveK) and maximum keratometry (Kmax) values, the central corneal thickness (CCT), the thinnest pachymetry reading, the vertical (Y) and horizontal (x) distances between the corneal apex, the location of thinnest part of the cornea, the corneal volume, and the anterior chamber volume. The topographic cone type was determined as nipple when the cone was central, 5 mm or less in diameter, oval when the cone was mid-peripheral, >5 mm in diameter, and globus when the diameter of the cone was ≥ 75% of the diameter of the cornea.10 Meanwhile, the clinical stage was defined using the Amsler-Krumeich (AK) classification system.11 In cases with corneal hydrops or scarring, eyes were classified as AK stage 4.
Effects of General Anesthesia on Ocular Refraction
Published in Journal of Binocular Vision and Ocular Motility, 2022
Manami Kawai, Hitoshi Ishikawa, Sonoko Tatsui, Shunsuke Kanayama, Ayano Nakazawa, Hiromi Matsuda, Hirotsugu Okamoto, Nobuyuki Shoji
In this study, the measurements were obtained using a hand-held reflex keratometer (HandyRef-K). Previous reports have used retinoscopy to measure the refractive values during general anesthesia,5–7,30 and although the results showed good reproducibility,7 the results of the retinoscopy measurements are known to depend on the skill level and subjective judgment of the measurer,31 and small pupils would make judgment challenging. On the other hand, the portable autorefractive keratometer is easy to use and has reliability for objective examinations. It has good accuracy with no difference in the values measured in the supine position25 and allows for reproducible measurements even during general anesthesia.8,32 Another advantage of the portable autorefractive keratometer used in this study is that it can automatically measure the refractive value, corneal refractive value, and pupil diameter under the same conditions.