1 Department of Ophthalmology, Xiangtan Central Hospital, Xiangtan 411100, China 2 Eye Hospital, Wenzhou Medical University, Hangzhou 310000, China 3 Changsha Aier Eye Hospital, Changsha 410000, China
Abstract:Objective: To calculate the total corneal power and the keratometric index based on actual measurements of the anterior and posterior corneal surfaces and the central corneal thickness by Pentacam and evaluate the accuracy of this keratometric index in estimating total and posterior corneal powers. Methods: This was a series case study. Four hundred and nineteen patients (a total of 419 eyes) who had undergone preoperative examination and laser in situ keratomileusis (LASIK) surgery or cataract surgery from February to October 2017 at the Xiangtan Central Hospital and Eye Hospital, Wenzhou Medical University were chosen for the study. The radius of the best-fit sphere for the anterior corneal surface (Ra) and posterior corneal surface (Rp), and central corneal thickness (CCT) were obtained. The ratio of Ra to Rp (AP ratio), anterior corneal power, posterior corneal power and keratometric index were calculated, and the total corneal power in each eye was calculated using the Gaussian optics formula. A paired-samples t-test was used to compare the difference in K values. Results: The means for Ra, Rp, Rsimk, CCT and SimK were 7.73±0.27 mm, 6.34±0.24 mm, 7.73±0.27 mm, 537±33 μm, and 43.65±1.52 D, respectively. The mean calculated AP ratio was 1.220±0.026. The mean calculated keratometric index (Ncal) was 1.328±0.001. Conclusions: The Pentacam-derived keratometric index improves the predictive accuracies of total and posterior corneal powers.
曹建雄1 常平骏2 李瑾2 肖天林3. 基于Pentacam对角膜屈光指数的评价[J]. 中华眼视光学与视觉科学杂志, 2020, 22(8): 596-601.
Jianxiong Cao1,Pingjun Chang2,Jin Li2,Tianlin Xiao3. Evaluation of the Keratometric Index by the Pentacam. Chinese Journal of Optometry Ophthalmology and Visual science, 2020, 22(8): 596-601. DOI: 10.3760/cma.j.cn115909-20191205-00326
Lackner B, Schmidinger G, Pieh S, et al. Repeatability and reproducibility of central corneal thickness measurement with Pentacam, Orbscan, and ultrasound. Optom Vis Sci, 2005, 82(10): 892-899. DOI: 10.1097/01.opx.0000180817.46312.0a.
[5]
Fam HB, Lim KL. Validity of the keratometric index: Large pop ulation study. J Cataract Refract Surg, 2007, 33(4): 686-691. DOI: 10.1016/j.jcrs.2006.11.023.
[6]
Chen D, Lam AK. Intrasession and intersession repeatability of the Pentacam system on posterior corneal assessment in the normal human eye. J Cataract Refract Surg, 2007, 33(3): 448- 454. DOI: 10.1016/j.jcrs.2006.11.008.
[7]
Shankar H, Taranath D, Santhirathelagan CT, et al. Anterior segment biometry with the Pentacam: Comprehensive assessment of repeatability of automated measurements. J Cataract Refract Surg, 2008, 34(1): 103-113. DOI: 10.1016/j.jcrs.2007.09.013.
[8]
Amano S, Honda N, Amano Y, et al. Comparison of central corneal thickness measurements by rotating Scheimpflug camera, ultrasonic pachymetry, and scanning-slit corneal topography. Ophthalmology, 2006, 113(6): 937-941. DOI: 10.1016/j.ophtha.2006.01.063.
[9]
Dubbelman M, Van der Heijde GL. The shape of the anterior and posterior corneal surface of the ageing human cornea. Vision Res, 2006, 46(6-7): 993-1001. DOI: 10.1016/ j.visres.2005.09.021.
[10]
Ho JD, Tsai CY, Tsai RJ, et al. Validity of the keratometric index: Evaluation by the Pentacam rotating Scheimpflug camera. J Cataract Refract Surg, 2008, 34(1): 137-145. DOI: 10.1016/ j.jcrs.2007.09.033.
[11]
Read SA, Collins MJ. Diurnal variation of corneal shape and thickness. Optom Vis Sci, 2009, 86(3): 170-180. DOI: 10.1097/ OPX.0b013e3181981b7e.
[12]
Atchison DA, Thibos LN. Optical models of the human eye. Clin Exp Optom, 2016, 99 (2): 99-106. DOI: 10.1111/cxo.12352.
[13]
Tang M, Li Y, Avila M, et al. Measuring total corneal power before and after laser in situ keratomileusis with high speed optical coherence tomography. J Cataract Refract Surg, 2006, 32(11): 1843-1850. DOI: 10.1016/j.jcrs.2006.04.046.
[14]
Garner LF, Owens H, Yap MK, et al. Radius of curvature of the posterior surface of the cornea. Optom Vis Sci, 1997, 74(7): 496-498. DOI: 10.1097/00006324-199707000-00016.
[15]
Savini G, Barboni P, Carbonelli M, et al. Agreement between Pentacam and videokeratography in corneal power assessment. J Refract Surg, 2009, 25(6): 534-538. DOI: 10.3928/1081597X- 20090512-07.
[16]
Dunne MC, Royston JM, Barnes DA. Normal variations of the posterior corneal surface. Acta Ophthalmol (Copenh), 1992, 70(2): 255-261. DOI: 10.1111/j.1755-3768.1992.tb04133.x.
[17]
Eryildirim A, Ozkan T, Eryildirim S, et al. Improving estimation of corneal refractive power by measuring the posterior curvature of the cornea. J Cataract Refract Surg, 1994, 20(2): 129-131. DOI: 10.1016/s0886-3350(13)80151-4.
[18]
Husain SE, Kohnen T, Maturi R, et a1. Computerized videokeratography and keratometry in determining intraocular lens calculations. J Cataract Refract Surg, 1996, 22(3): 362-366. DOI: 10.1016/s0886-3350(96)80251-3.
[19]
Seitz B, Langenbucher A, Nguyen NX, et al. Underestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy. Ophthalmology, 1999, 106(4): 693-702. DOI: 10.1016/S0161-6420(99)90153-7.
[20]
Olsen T. On the calculation of power from curvature of the cornea. Br J Ophthalmol,1986, 70(2): 152-154. DOI: 10.1136/ bjo.70.2.152.
[21]
Holladay JT. Standardizing constants for ultrasonic biometry, keratometry, and intraocular lens power calculations. J Cataract Refract Surg, 1997, 23(9): 1356-1370. DOI: 10.1016/s0886- 3350(97)80115-0.
[22]
Retzlaff JA, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refract Surg, 1990, 16(3): 333-340. DOI: 10.1016/s0886- 3350(13)80705-5.
[23]
Hoffer KJ. The Hoffer Q formula: A comparison of theoretic and regression formulas. J Cataract Refract Surg, 1993, 19(6): 700- 712. DOI: 10.1016/s0886-3350(13)80338-0.