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Al-Sharify NT, Nser HY, Ghaeb NH, Al-Sharify ZT, See OH, Weng LY, Ahmed SM. Influence of different parameters on the corneal asphericity (Q value) assessed with progress in biomedical optics and imaging - A review. Heliyon 2024; 10:e35924. [PMID: 39224364 PMCID: PMC11367468 DOI: 10.1016/j.heliyon.2024.e35924] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 07/20/2024] [Accepted: 08/06/2024] [Indexed: 09/04/2024] Open
Abstract
The corneal eye diseases such as Keratoconus cause weakening of the cornea, with this disease the cornea can change in shape. This condition affects between 1 in 3,000 to 1 in 10,000 people. The main reason for the development of such conditions is unknown and can have significant impacts. Over the last decade, with advancements in computerized corneal topography assessments, researchers have increasingly expressed interest in corneal topography for research as well as clinical activities. Up till now, several aspheric numerical models have been developed as well as proposed to define the complex shape of the cornea. A commonly used term for characterizing the asphericity in an eye is the Q value, a common indicator of the aspherical degree of the cornea. It is one of the critical parameters in the mathematical description model of the cornea as it represents the cornea's shape and the eye's characteristics. Due to the utmost importance of this Q value of the cornea, a couple of studies have attempted to explore this parameter and its distribution, merely in terms of its influence on the human eye's optical properties. The corneal Q value is an important factor that needs to be determined to treat for any refractive errors as corneal degeneration are disease that can lead to potential problems with the structure of the cornea. This study aims to highlight the need to understand Q value of the cornea as this can essentially assist with personalising corneal refractive surgeries and implantation of intraocular lenses. Therefore, the relevance of corneal Q value must be studied in association with different patients, especially ones who have been diagnosed with cataracts, brain tumours, or even COVID-19. To address this issue, this paper first carries out a literature review on the optics of the cornea, the relevance of corneal Q value in ophthalmic practice and studies corneal degenerations and its causes. Thereafter, a detailed review of several noteworthy relevant research studies examining the Q value of the cornea is performed. To do so, an elaborate database is created, which presents a list of different research works examined in this study and provides key evidence derived from these studies. This includes listing details on the age, gender, ethnicity of the eyes assessed, the control variables, the technology used in the study, and even more. The database also delivers important findings and conclusions noted in each study assessed. Next, this paper analyses and discusses the magnitude of corneal Q value in various scenarios and the influence of different parameters on corneal Q value. To design visual optical products as well as to enhance the understanding of the optical properties of an eye, future studies could consider the database and work presented in this study as useful references. In addition, the work can be used to make informed decisions in clinical practice for designing visual optical products as well as to enhance the understanding of the optical properties of an Eye.
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Affiliation(s)
- Noor T. Al-Sharify
- Department of Electrical & Electronic Engineering, College of Engineering, Universiti Tenaga Nasional, Malaysia
- Medical Instrumentation Engineering Department, Al-Esraa University College, Baghdad, Iraq
| | - Husam Yahya Nser
- Department of Electrical & Electronic Engineering, College of Engineering, Universiti Tenaga Nasional, Malaysia
| | - Nebras H. Ghaeb
- Biomedical Engineering Department, Al Khawarezmi, Engineering College, University of Baghdad, Iraq
| | - Zainab T. Al-Sharify
- Department of Pharmacy, Al Hikma University College, Baghdad, Iraq
- School of Chemical Engineering, University of Birmingham, Edgbaston, B15 2TT, Birmingham, United Kingdom
| | - Ong Hang See
- Department of Electrical & Electronic Engineering, College of Engineering, Universiti Tenaga Nasional, Malaysia
| | - Leong Yeng Weng
- Department of Electrical & Electronic Engineering, College of Engineering, Universiti Tenaga Nasional, Malaysia
| | - Sura M. Ahmed
- Department of Electrical & Electronic Engineering, College of Engineering, Universiti Tenaga Nasional, Malaysia
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Turner JM, Purslow C, Murphy PJ. Comparison of Javal-Schiøtz keratometer, Orbscan IIz and Pentacam topographers in evaluating anterior corneal topography. Clin Exp Optom 2022:1-8. [PMID: 35614035 DOI: 10.1080/08164622.2022.2067470] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
Abstract
CLINICAL RELEVANCE Inter-instrument variation in anterior corneal shape (ACS) measurement has a consequence for ocular clinical practice. BACKGROUND To consider inter-instrument variability in keratometry measurements across the ACS and to explore instrument protocols for determining ACS keratometric analogues (KAs). METHODS Mean keratometry/KAs of the right eye were recorded using Javal-Schiøtz keratometer (J-S), Orbscan IIz and Pentacam from 124 subjects (78 females; mean ± SD age: 24.71 ± 6.61 years). Mean radii of curvature were obtained for 1-mm wide annular zones extending up to 6 mm (horizontally) and 4 mm (vertically) from the apex for Orbscan and Pentacam. Zonal mean radius of curvature was calculated by averaging keratometry values for all measured points within the zone. RESULTS KA (mean ± SD): Horizontal: Orbscan (7.80 ± 0.31 mm) and J-S (7.82 ± 0.29 mm) were not significantly different (p = 0.072). Pentacam (7.86 ± 0.29 mm) was significantly flatter than J-S (p < 0.001) and Orbscan (p < 0.001). Vertical: Orbscan (7.64 ± 0.31 mm) was significantly steeper than J-S (7.67 ± 0.29 mm, p < 0.005) and Pentacam (7.70 ± 0.29 mm, p < 0.001). Pentacam was significantly flatter than J-S (p < 0.001) and significant flatter than Orbscan across the entire profile (1-4 mm zones horizontal and vertical, p < 0.001). LoAs (CI): J-S/Orbscan: ±0.75 mm (0.05-0.18); J-S/Pentacam: ±0.72 mm (0.01-0.12); Pentacam/Orbscan: ±0.16 mm (0.04-0.08). There was a +0.03 mm positive bias for Orbscan compared to J-S, +0.06 mm positive bias for Orbscan compared to Pentacam and -0.03 mm negative bias for Pentacam compared to J-S. CONCLUSIONS Algorithms used by Orbscan and Pentacam to solve the peripheral paraxial ray problem produce significantly different KAs. Instrument-specific KAs cannot be used inter-changeably between instruments. Differences in KA between instruments are not significant for ocular surgery, but may influence rigid contact lens fitting. Pentacam measures flatter than Orbscan and J-S.
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Affiliation(s)
- Jennifer M Turner
- Division of Optometry, Department of Health and Wellbeing, University of the West of England, Bristol, UK.,School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK
| | - Christine Purslow
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK
| | - Paul J Murphy
- School of Optometry and Vision Science, University of Waterloo, Waterloo, Canada
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Accuracy of the posterior corneal elevation values of Pentacam HR from different reference surfaces in early ectasia diagnosis. Int Ophthalmol 2020; 41:629-638. [PMID: 33095345 DOI: 10.1007/s10792-020-01618-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Accepted: 10/05/2020] [Indexed: 10/23/2022]
Abstract
PURPOSE Detecting the accuracy of various posterior elevation (PE) indices of Pentacam HR, and correlating them with some possibly related factors or parameters, in a cohort with early keratoconus (KC). METHODS A cross sectional study that was conducted at Eye World Hospital, Egypt. One hundred and two corneas were enrolled, including two groups; group 1 (50 corneas) having forme fruste or early KC, and group 2 (52 corneas) for healthy controls. Corneas were scanned using Pentacam HR (Oculus, Wetzlar, Germany). The investigated PE parameters were: PE from best fit sphere (BFS), PE from best fit toric ellipsoid (BFTE), PE from exclusion map of Belin Ambrosio's display (BAD), and PE from difference map of BAD. The four PE values were correlated to age, thinnest corneal thickness "TCT," posterior aberrations, and posterior Q value. RESULTS All the investigated indices were significantly different in group 1 compared to group 2 (p < 0.001). Accuracy of PE parameters revealed the highest AUROC for PE from BFTE (AUROC = 0.989, and best cutoff > 4 um with sensitivity 96.00% and specificity 96.15%). PE from difference map was the least accurate. Correlation coefficients showed a significant correlation between all the studied PE parameters and some of the posterior aberrations (root mean square of higher order aberrations, vertical coma, and spherical aberrations), besides a significant correlation with posterior Q value. CONCLUSION PE indices are sensitive detectors of early ectasia. PE from BFTE had the highest deduced AUROC. Alterations in PE values can significantly alter many posterior corneal aberrations and the posterior Q.
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Asgari S, Hashemi H. OPD scan III accuracy: Topographic and aberrometric indices after accelerated corneal cross-linking. J Curr Ophthalmol 2018; 30:58-62. [PMID: 29564410 PMCID: PMC5859500 DOI: 10.1016/j.joco.2017.09.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Revised: 09/14/2017] [Accepted: 09/21/2017] [Indexed: 12/26/2022] Open
Abstract
Purpose To determine topographic and aberrometric changes after accelerated cross-linking (ACXL; 18 mW/cm2 for 5 min) as measured with OPD Scan III (Nidek Inc., Tokyo, Japan) and their repeatability in patients with mild and moderate keratoconus (KCN). Methods In this prospective study, 25 eyes with mild KCN [Ksteep = 47.24 ± 3.11 diopter (D)] and 20 moderate cases (Ksteep = 52.86 ± 4.39 D) were examined under mesopic conditions (20 lux) twice, 30-45 min apart, at baseline and 6 and 12 months afterwards. Extracted indices were Ksteep, Kflat, ocular and corneal irregularity, ocular and corneal total higher order aberrations (HOAs), coma, trefoil, and spherical aberration (SA). Repeatability index (RI) and intraclass correlation coefficients (ICCs) were determined. Results In mild cases, Ksteep and corneal irregularity had lower RI, but Kflat and ocular irregularity had higher RI (all P > 0.050) at 1 year. The RI for ocular total HOAs, coma, and SA decreased and showed no significant change for trefoil (all P > 0.050). Moderate cases showed non-significant increases in RI for Ksteep, Kflat, ocular and corneal irregularity (all P > 0.050), and all aberrometry indices, and significant increases in RI for ocular coma (P = 0.046) and corneal trefoil (P = 0.037). At 1 year, ICC was >0.75 for all indices except ocular and corneal trefoil (ICC = 0.613 and 0.390) in moderate cases. Conclusions At one year after ACXL, OPD Scan III showed acceptable repeatability in mild cases. In moderate cases, topographic indices had acceptable repeatability but poorer compared to the mild group. Overall, ocular HOAs showed better repeatability than corneal ones. These changes should be considered in the interpretation of measurements.
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Affiliation(s)
- Soheila Asgari
- Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.,Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran
| | - Hassan Hashemi
- Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran.,Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Tehran, Iran
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Xiong Y, Li J, Wang N, Liu X, Wang Z, Tsai FF, Wan X. The analysis of corneal asphericity (Q value) and its related factors of 1,683 Chinese eyes older than 30 years. PLoS One 2017; 12:e0176913. [PMID: 28545078 PMCID: PMC5436654 DOI: 10.1371/journal.pone.0176913] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 04/19/2017] [Indexed: 11/20/2022] Open
Abstract
Purpose To determine corneal Q value and its related factors in Chinese subjects older than 30 years. Design Cross sectional study. Methods 1,683 participants (1,683 eyes) from the Handan Eye Study were involved, including 955 female and 728 male with average age of 53.64 years old (range from 30 to 107 years). The corneal Q values of anterior and posterior surfaces were measured at 3.0, 5.0 and 7.0mm aperture diameters using Bausch & Lomb Orbscan IIz (software version 3.12). Age, gender and refractive power were recorded. Results The average Q values of the anterior surface at 3.0, 5.0 and 7.0mm aperture diameters were -0.28±0.18, -0.28±0.18, and -0.29±0.18, respectively. The average Q value of the anterior surface at the 5.0mm aperture diameter was negatively correlated with age (B = -0.003, p<0.01) and the refractive power (B = -0.013, p = 0.016). The average Q values of the posterior surface at 3.0, 5.0, and 7.0mm were -0.26±0.216, -0.26±0.214, and -0.26±0.215, respectively. The average Q value of the posterior surface at the 5.0mm aperture diameter was positively correlated with age (B = 0.002, p = 0.036) and the refractive power (B = 0.016, p = 0.043). Conclusion The corneal Q value of the elderly Chinese subjects is different from that of previously reported European and American subjects, and the Q value appears to be correlated with age and refractive power.
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Affiliation(s)
- Ying Xiong
- Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, China
| | - Jing Li
- Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, China
| | - Ningli Wang
- Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, China
- Beijing Key Laboratory of Ophthalmology and Visual Science, Capital Medical University, Beijing, China
| | - Xue Liu
- Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, China
- Beijing Key Laboratory of Ophthalmology and Visual Science, Capital Medical University, Beijing, China
| | - Zhao Wang
- Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, China
| | - Frank F. Tsai
- Sharp Rees-Stealy Medical Group, San Diego, CA, United States of America
| | - Xiuhua Wan
- Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, China
- Beijing Key Laboratory of Ophthalmology and Visual Science, Capital Medical University, Beijing, China
- * E-mail:
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Mehravaran S, Hashemi H, KhabazKhoob M, Fotouhi A. Distribution of radii of curvature of anterior and posterior best fit sphere in a normal population: The Tehran Eye Study. Cont Lens Anterior Eye 2013; 36:186-90. [DOI: 10.1016/j.clae.2013.02.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2012] [Revised: 01/22/2013] [Accepted: 02/21/2013] [Indexed: 11/27/2022]
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Ying J, Wang B, Shi M. Anterior corneal asphericity calculated by the tangential radius of curvature. JOURNAL OF BIOMEDICAL OPTICS 2012; 17:075005. [PMID: 22894477 DOI: 10.1117/1.jbo.17.7.075005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We propose a method of calculating the corneal asphericity (Q) and analyze the characteristics of the anterior corneal shape using the tangential radius. Fifty-eight right eyes of 58 subjects were evaluated using the Orbscan II corneal topographer. The Q-values of the flat principal semi-meridians calculated by the sagittal radius were compared to those by the tangential radius. Variation in the Q-value with semi-meridian in the nasal and temporal cornea calculated by the tangential radius was analyzed. There were significant differences in Q-values (P<0.001) between the two methods. The mean Q-values of the flat principal semi-meridians calculated by tangential radius with -0.33 ± 0.10 in the nasal and -0.22 ± 0.12 in the temporal showed more negative than the corresponding Q-values calculated by the sagittal radius. The Q-values calculated by tangential radius became less negative gradually from horizontal semi-meridians to oblique semi-meridians in both nasal and temporal cornea. Variation in Q-value with semi-meridian was more obvious in the nasal cornea. The method of calculating corneal Q using the tangential radius could provide more reasonable and complete Q-value than that by the sagittal radius. The model of a whole anterior corneal surface could be reconstructed on the basis of the above method.
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Affiliation(s)
- Jinglu Ying
- Department of Ophthalmology, The Second Affiliated Hospital of Wenzhou Medical College, XueYuan west Road 109, Wenzhou 325027, China
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Kim E, Ehrmann K. Assessment of accuracy and repeatability of anterior segment optical coherence tomography and reproducibility of measurements using a customised software program. Clin Exp Optom 2012; 95:432-41. [PMID: 22571685 DOI: 10.1111/j.1444-0938.2012.00724.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
PURPOSE The aim was to study the reliability of measurements of the RTVue (Optovue, Fremont, CA, USA) anterior segment optical coherence tomographer (AS-OCT) and assess how results can be improved by analysing raw optical coherence tomography data with customised image analysis software and applying correction factors. METHODS Five RTVue AS-OCT instruments (ver. 4.0) were assessed by imaging gauge blocks of three different lengths, single/stepped glass plate (microscope slides) and flat window glass to check for width, depth and linearity of the measurement scans. Five repeats per calibration tool were imaged and averaged. Raw data were exported and loaded into customised image analysis software written in LabWindows/CVI for further analysis. Using two calibration balls with different radii, measurement scans were validated. Repeatability of the optical coherence tomographs and the edge detection procedure were checked and statistical analyses performed. RESULTS Variations ranging from 0.01 to 1.93 mm in scan width and 0.1 to 0.17 mm in scan depth were found between the five instruments. Slight curvature distortion of 0.06 ± 0.01 mm (mean and standard deviation) was found in the raw images. By isolating the three sources of image distortion and applying individual correction factors, accuracy for corneal curvature measurements could be improved to better than 0.1 mm. Manual edge detection limited the coefficient of repeatability value to 0.06 and 0.08 mm for anterior and posterior radii of curvature, respectively. The coefficient of repeatability of corneal thickness measurements was less than 8 µm. CONCLUSIONS Accuracy of the RTVue AS-OCT varied between instruments. By applying calibration scale factors calculated by customised software, accuracy of thickness and curvature values of the anterior eye was improved. The achievable precision is sufficient to detect clinically relevant corneal curvature variations.
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Affiliation(s)
- Eon Kim
- Vision Cooperative Research Centre, Sydney, New South Wales, Australia.
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Srivannaboon S, Chotikavanich S, Chirapapaisan C, Kasemson S, Po-ngam W. Precision analysis of posterior corneal topography measured by Visante Omni: repeatability, reproducibility, and agreement with Orbscan II. J Refract Surg 2011; 28:133-8. [PMID: 22149665 DOI: 10.3928/1081597x-20111122-03] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Accepted: 08/24/2011] [Indexed: 11/20/2022]
Abstract
PURPOSE To evaluate the repeatability and reproducibility of posterior corneal curvature and posterior corneal elevation best-fit sphere (BFS) obtained with the Visante Omni (Carl Zeiss Meditec) and to compare the results with the Orbscan II (Bausch & Lomb). METHODS Thirty eyes from 30 healthy volunteers were included in this study. All patients were examined 5 times with the Visante Omni and Orbscan II by 2 independent operators. The posterior corneal curvature (3- and 6-mm zone) and posterior corneal elevation BFS (5- and 8-mm zone) were generated for each system. Intraoperator repeatability and interoperator reproducibility and agreement between the systems were evaluated using the intraclass correlation coefficient (ICC) and the Bland-Altman method. RESULTS The repeatability of posterior corneal curvature and posterior corneal elevation BFS measured by the Visante Omni was high for all analysis zones (ICC, 0.99 to 1.00). The reproducibility also showed similar results (ICC, 0.99 to 1.00). Agreement between the Visante Omni and Orbscan II was high for posterior corneal curvature (ICC, 0.94 to 0.97) and posterior corneal elevation BFS (ICC, 0.96 to 0.98) with 95% limits of agreement at -0.26 to 0.22 diopters for posterior corneal curvature and 0.11 to 0.69 mm for posterior corneal elevation BFS. CONCLUSIONS The Visante Omni provides good repeatability and reproducibility of posterior corneal topography. Overall agreement with the Orbscan II system was high.
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Affiliation(s)
- Sabong Srivannaboon
- Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand
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Faramarzi A, Soheilian M, Jabbarpoor Bonyadi MH, Yaseri M. Corneal astigmatism in unilateral Fuchs heterochromic iridocyclitis. Ocul Immunol Inflamm 2011; 19:151-5. [PMID: 21595529 DOI: 10.3109/09273948.2011.555054] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE To analyze the results of scanning slit topography in both eyes of patients with unilateral Fuchs heterochromic iridocyclitis (FHI). METHODS A noninterventional, case-controlled study was conducted with 30 patients with unilateral FHI. Corneal topographic parameters, obtained with the Orbscan II (Bausch & Lomb), were compared between the two eyes and analyzed statistically. The same number of age-matched normals was enrolled as a control group. RESULTS Thirty patients were enrolled in this study. The mean age was 33.3 years ± 10.6 (SD). The mean Sim K astigmatism was 1.65 ± 1.27 diopter in the FHI eyes and 0.88 ± 0.52 diopter in the normal eyes (p = .001). CONCLUSION Corneal astigmatism is a common finding in patients with FHI and disparity of corneal astigmatism between the two eyes can be considered a sign of the unilateral form of this disease.
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Affiliation(s)
- Amir Faramarzi
- Ophthalmic Research Center and Department of Ophthalmology, Labbafinejad Medical Center, Shaheed Beheshti Medical University, Tehran, Iran.
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KhabazKhoob M, Hashemi H, Yazdani K, Mehravaran S, Yekta A, Fotouhi A. Keratometry measurements, corneal astigmatism and irregularity in a normal population: the Tehran Eye Study. Ophthalmic Physiol Opt 2010; 30:800-5. [DOI: 10.1111/j.1475-1313.2010.00732.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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