keratometer


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Related to keratometer: Pachymeter, Lensometer

keratometer

 [ker″ah-tom´ĕ-ter]
an instrument for measuring the curves of the cornea.

ker·a·tom·e·ter

(ker'ă-tom'ĕ-tĕr),
An instrument for measuring the curvature of the anterior corneal surface.
Synonym(s): ophthalmometer
[kerato- + G. metron, measure]

ker·a·tom·e·ter

(ker'ă-tom'ĕ-tĕr)
An instrument for measuring the curvature of the anterior corneal surface.
Synonym(s): ophthalmometer.
[kerato- + G. metron, measure]

keratometer

An optical instrument used to measure the radius of curvature of the cornea. See also KERATOMETRY.

keratometer

Optical instrument for measuring the radius of curvature of the cornea in any meridian. By measuring along the two principal meridians, corneal astigmatism can be deduced. The principle is based on the reflection by the anterior surface of a luminous pattern of mires in the centre of the cornea in an area of about 3.6 mm in diameter. Knowing the size of the pattern h and measuring that of the reflected image h′ and the distance d between the two, the radius of curvature r of the cornea can be determined using the approximate formula.
r = 2d (h′/h)
In addition, a doubling system (e.g. a bi-prism) is also integrated into the instrument in order to mitigate the effect of eye movements, as well as a microscope in order to magnify the small image reflected by the cornea. This instrument is used in the fitting of contact lenses and the monitoring of corneal changes occurring as a result of contact lens wear (Fig. K2). The range of the instrument can be extended approximately 9 D by placing a +1.25 D lens in front of the objective to measure steeper corneas. The range in the other direction can be extended by approximately 6 D using a −1.00 D lens to measure flatter corneas. Syn. ophthalmometer. See fitted on K; keratoscope; liquid lens; photokeratoscopy; Wollaston prism; Javal's rule; Topogometer; videokeratoscope.
Fig. K2 Schematic diagram of the Reichert keratometerenlarge picture
Fig. K2 Schematic diagram of the Reichert keratometer

Table K2 Extended keratometer range
with 21.00 Dwith 11.25 D
actual drum reading (D)extended value (D)actual drum reading (D)extended value (D)
36.0030.8745.0052.46
36.5031.3045.5053.05
37.0031.7346.0053.63
37.5032.1646.5054.21
38.0032.5947.0054.80
38.5033.0247.5055.38
39.0033.4548.0055.96
39.5033.8848.5056.55
40.0034.3049.0057.13
40.5034.7349.5057.71
41.0035.1650.0058.30
41.5035.5950.5058.88
51.0059.46
51.5060.04
52.0060.63
References in periodicals archive ?
Additionally, manual keratometers and topographers (when analyzing the simulated keratometry value SimK of the latter), measure the radius of curvature based on the reflection of some mires in the cornea in an area of 3.00 mm of diameter on average, but do not directly take into account the pupil's smaller central area, were visual axis is located (which is less than approximately, 2.00 mm of diameter).
Greatest and least powers, called principal powers (initially assumed to be distinct) and the directions of their meridians from, say, a keratometer, are analogous to eigenvalues and eigenvectors of data arrays [1], respectively, (see numerical Example 2 and the optical cross in Figure 1).
In 1991, Bennett and Rabbetts [5] derived the anterior surface of the cornea cross section with the calculation formula, [r.sub.s.sup.2] = [r.sub.0.sup.2] + (1 -p)[y.sup.2], to calculate the asphericity by the sagittal radius of curvature ([r.sub.s]) using a keratometer. Although Bennett's equation is widely used in the studies of corneal shape, it still has its limitations.
In the present study, manual keratometer was used to study corneal astigmatism at central 3 mm before and after pterygium excision with CLAG.
Anterior segment clinic is equipped with Photo slit lamp for anterior segment photography and an auto refractor Keratometer.
Tenders are invited for Imported/indigenous autorefractometer with keratometer
An automatic refractor was used to determine refraction status of the patients (Humphrey Zeiss 5015 Auto Refractor Keratometer, Carl Zeiss Meditec, California).
Keratometry was done to measure corneal curvature using Bausch and Lomb keratometer. Ultrasound biometry was using contact probe biomedix with digital display to assess anterior chamber depth, lens thickness, axial length and vitreous chamber depth in all subjects in both eyes.
Keywords: Auto refractor, Keratometer, WTR, ATR, Oblique astigmatism, Prevalence.