Abstract
The cornea is aspheric and normally prolate: the central cornea is approximately spherical in front of the pupil and then flattens peripherally through the paracentral and peripheral zones towards the limbal zone, but asymmetrically in different meridia. The centre of the cornea can be defined geometrically (intersection of horizontal and vertical meridia), at the apex, aligned with the pupil centre, or on the visual axis.
Patients with spherical refractions tend to have round or oval patterns. Corneas with regular astigmatism have symmetric or asymmetric bowtie patterns, where as those with irregular astigmatism tend to have an irregular pattern. The right and left eyes of an individual demonstrate enantiomorphism, with mirror image symmetry.
Astigmatism tends to be minimal at birth and then develops “with the rule” (steep in the vertical meridian) during adolescence, possibly due to pressure from the lids. This tends to reduce during middle life and may even reverse to be “against the rule” (steep in the horizontal meridian) later in life.
Contact lens-induced corneal warpage is more common with rigid lenses than soft and is likely to be due to sustained pressure from the lens. Artefacts of corneal shape may arise from errors of alignment and focusing and from tear film drying which manifests as small areas of focal flattening or irregularity.
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References
*References Particularly Worth Reading
*Dingeldein SA, Klyce SD. The topography of normal corneas. Arch Ophthalmol 1989; 107: 512–518.
Fleming JF. Should refractive surgeons worry about corneal asphericity? Refract Corneal Surg. 1990;6:455–7.
Carney LG, Mainstone JC, Henderson BA. Corneal topography and myopia: a cross-sectional study. Invest Ophthalmol Vis Sci. 1997;38:311–20.
*Waring GO. Making sense of keratospeak II: proposed conventional terminology for corneal topography. Refract Corneal Surg 1989; 5: 362–367.
Eghbali F, Yeung KK, Maloney RK. Topographic determination of corneal asphericity and its lack of effect on the outcome of radial keratotomy. Am J Ophthalmol. 1995;119:275–80.
Edmund C, Sjontoft E. The central-peripheral radius of the normal corneal curvature: a photokeratoscopic study. Acta Ophthalmol. 1985;63:670–7.
Wang J, Rice DA, Klyce SD. A new reconstruction algorithm for improvement of corneal topographical analysis. Refract Corneal Surg. 1989;5:379–87.
Holladay JT. Corneal topography using the Holladay diagnostic summary. J Cat Refract Surg. 1997;23:209–21.
Duke-Elder S. System of ophthalmology. Vol V: ophthalmic optics and refraction. St Louis: CV Mosby; 1970. p. 274–95.
Young T. The mechanisms of the eye. Philos Trans. 1801;91:23.
Donders F. On the anomalies of refraction and accommodation of the eye. London: The New Sydenham Society; 1864.
Fredrick S, Wilson G. The relation between eyelid tension, corneal toricity, and age. Invest Ophthalmol Vis Sci. 1983;24:1367–73.
Mandell RB, St Helen R. Stability of the corneal contour. Am J Optom. 1968;45:797–806.
Clark BA. Mean topography of normal corneas. Aust J Optom. 1974;57:107–14.
Clark BA. Topography of some individual corneas. Aust J Optom. 1974;57:65–9.
Mandell RB, St Helen R. Position and curvature of the corneal apex. Am J Optom. 1969;46:25–7.
*Uozato H, Guyton DL. Centring corneal surgical procedures. Am J Ophthalmol 1987; 103: 264–275.
Fay AM, Trokel SL, Myers JA. Pupil diameter and the principal ray. J Cat Refract Surg. 1992;18:348–51.
*Pande M, Hillman JS. Optical zone centration in keratorefractive surgery. Ophthalmology 1993; 100: 1230–1237.
Doane JF, Cavanaugh TB. Optical zone centration for keratorefractive surgery [letter]. Ophthalmology. 1994;101:215–6.
Pande M. Optical zone centration for keratorefractive surgery [reply]. Ophthalmology. 1994;101:216.
Mandell RB. Optical zone centration for keratorefractive surgery [letter]. Ophthalmology. 1994;101:216–7.
Pande M. Optical zone centration for keratorefractive surgery [reply]. Ophthalmology. 1994;101:217–9.
Guyton DL. More on optical zone centration [letter]. Ophthalmology. 1994;101:793.
Pande M, Hillman JS. More on optical zone centration [reply]. Ophthalmology. 1994;101:793–4.
Tomlinson A, Schwartz C. The position of the corneal apex in the normal eye. Am J Optom Phys Optics. 1979;56:236–40.
McAlinden C. Corneal refractive surgery: past to present. Clin Exp Optom. 2012;95(4):386–98.
Mosquera SA, Verma S, McAlinden C. Centration axis in refractive surgery. Eye Vis (Lond). 2015;2:4.
Knoll HA. Corneal contours in the general population as revealed by the photokeratoscope. Am J Optom. 1961;38:389–97.
*Bogan SJ, Waring GO, Ibrahim O, Drews C, Curtis L. Classification of normal corneal topography based on computer-assisted videokeratography. Arch Ophthalmol 1990; 108: 945–949.
Rabinowitz YS, Yang H, Brickman Y, Akkina J, Riley C, Rotter JI, Elashoff J. Videokeratography database of normal human corneas. Br J Ophthalmol. 1996;80:610–6.
Alvi NP, McMahon TT, Devulappally J, Chen TC, Vianna MAG. Characteristics of normal corneal topography using the EyeSys corneal analysis system. J Cataract Refract Surg. 1997;23:849–55.
*Naufal SC, Hess JS, Friedlander MH, Granet NS. Rasterstereography-based classification of normal corneas. J Cataract Refract Surg 1997; 23: 222–230.
Marin-Amat M. The physiological variations of the corneal curvature during life, their significance in ocular refraction. Bull Soc Belg Ophthalmol. 1957;136:263.
Sawada A. Refractive errors in an elderly Japanese population: the Tajimi study. Ophthalmology. 2008;115(2):363–70.
Kiely PM, Carney LG, Smith G. Diurnal variations of corneal topography and thickness. Am J Optom Physiol Optic. 1982;59:976–82.
Read SA, Collins MJ, Carney LG. The diurnal variation of corneal topography and aberrations. Cornea. 2005;24(6):678–87.
Clark BAJ. Variations in corneal topography. Aust J Optom. 1973;56:399–413.
El Hage SD, Beaulne C. Changes in central and peripheral corneal thickness with menstrual cycle. Am J Optom Physiol Optic. 1973;50:863–71.
Kiely PM, Carney LG, Smith G. Menstrual cycle variations of corneal topography and thickness. Am J Optom Physiol Optic. 1983;60:822–9.
Giuffrè G, Di Rosa L, Fiorino F, Bubella DM, Lodato G. Variations in central corneal thickness during the menstrual cycle in women. Cornea. 2007;26(2):144–6.
Ghahfarokhi NA, Vaseghi A, Ghoreishi M, et al. Evaluation of corneal thickness alterations during menstrual cycle in productive age women. Indian J Ophthalmol. 2015;63(1):30–2.
Schornack M. Hydrogel contact lens-induced corneal warpage. Cont Lens Anterior Eye. 2003;26(3):153–9.
Ruiz-Montenegro J, Mafra CH, Wilson SE, Jumper JM, Klyce SD, Mendelson EN. Corneal topographic alterations in normal contact lens wearers. Ophthalmology. 1993;100:128–34.
Wilson SE, Lin DTC, Klyce SD, Reidy JJ, Insler MS. Topographic changes in contact lens-induced warpage. Ophthalmology. 1990;97:734–44.
Wang J, Rice DA, Klyce SD. Analysis of the effects of astigmatism and misalignment on corneal surface reconstruction from photokeratoscopic data. Refract Corneal Surg. 1991;7:129–40.
*Hubbe RE, Foulks GN. The effect of poor fixation on computer-assisted topographic corneal analysis. Ophthalmology 1994; 101: 1745–1748.
Singh D. Effect of cataract on corneal topography results. J Cataract Refract Surg. 1996;22:1506–8.
Karabatsas CH, Hoh HB. Is it cataract or misalignment that affects corneal topography measurements? [letter]. J Cataract Refract Surg. 1997;23:694–5.
Mishima S. Some physiological aspects of the precorneal tearfilm. Arch Ophthalmol. 1965;73:233.
*Pavlopoulos GP, Horn J, Feldman ST. The effect of artificial tears on computer-assisted corneal topography in normal eyes and after penetrating keratoplasty. Am J Ophthalmol 1995; 119: 712–722.
Novak KD, Kohnen T, Chang-Godinich A, Soper BA, Kennedy P, Wang Q, Padrick T, Koch DD. Changes in computerised videokeratography induced by artificial tears. J Cat Refract Surg. 1997;23:1023–8.
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Corbett, M., Maycock, N., Rosen, E., O’Brart, D. (2019). Normal Topography. In: Corneal Topography. Springer, Cham. https://doi.org/10.1007/978-3-030-10696-6_6
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DOI: https://doi.org/10.1007/978-3-030-10696-6_6
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