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Salvador-Roger R, Albarrán-Diego C, Garzón N, García-Montero M, Muñoz G, Micó V, Esteve-Taboada JJ. Revisiting Javal's rule: a fresh and improved power vector approach according to age. Graefes Arch Clin Exp Ophthalmol 2024; 262:249-260. [PMID: 37552315 PMCID: PMC10805827 DOI: 10.1007/s00417-023-06195-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2023] [Revised: 07/19/2023] [Accepted: 07/30/2023] [Indexed: 08/09/2023] Open
Abstract
PURPOSE The scientific community has established Javal's rule as a model linking refractive (RA) and keratometric (KA) astigmatism since its appearance more than 100 years ago. The aim was to improve the accuracy of this relationship according to subject's age by applying the power vector analysis. Posterior corneal curvature has also been studied. METHODS The IOLMaster 700 optical biometer was used to measure the corneal thickness and the radius of curvature of the anterior and posterior corneal surfaces. Refractive error was determined by a non-cycloplegic subjective refraction process with trial lenses. Linear regression analyses were applied using J0 and J45 power vector components. An evaluation was carried out according to the subject's age resulting into eight regression relationships for each astigmatic vector component for each relationship. RESULTS A total of 2254 right eyes from 2254 healthy subjects were evaluated. A trend towards against-the-rule astigmatism (ATR) was found with aging, both for refractive astigmatism (RA) and keratometric astigmatism (KA), with 95.2% of subjects under 20 years old having with-the-rule (WTR) KA, and only 22.8% above 79 years old. The following regression equations were found between RA and KA: [Formula: see text] = 0.73 × [Formula: see text] - 0.18 (R = 0.78) and [Formula: see text] = 0.70 × [Formula: see text] + 0.04 (R = 0.69) and between RA and total corneal astigmatism (TCA): [Formula: see text] = 0.73 × [Formula: see text] + 0.13 (R=0.78) and [Formula: see text] = 0.70 × [Formula: see text] - 0.06 (R = 0.68) for the whole sample, but with sensible differences among age groups, both in the slope and in the intercept. CONCLUSION Ignoring the age of the subject when using Javal's rule could lead to an error in the final cylinder calculation that would increase in high astigmatisms. Applying this new power vector approach based on subject's age could improve the accuracy of the astigmatism prediction.
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Affiliation(s)
- Raquel Salvador-Roger
- Department of Optics and Optometry and Vision Sciences, University of Valencia, 46100, Burjassot, Valencia, Spain.
| | - César Albarrán-Diego
- Department of Optics and Optometry and Vision Sciences, University of Valencia, 46100, Burjassot, Valencia, Spain
| | - Nuria Garzón
- Department of Optometry and Vision, Universidad Complutense de Madrid, 28037, Madrid, Spain
| | - María García-Montero
- Department of Optometry and Vision, Universidad Complutense de Madrid, 28037, Madrid, Spain
| | - Gonzalo Muñoz
- Marqués de Sotelo Ophthalmological Clinic, 46002, Valencia,, Spain
- Baviera Castellón Ophthalmological Clinic, 12003, Castelló de la Plana, Spain
| | - Vicente Micó
- Department of Optics and Optometry and Vision Sciences, University of Valencia, 46100, Burjassot, Valencia, Spain
| | - José J Esteve-Taboada
- Department of Optics and Optometry and Vision Sciences, University of Valencia, 46100, Burjassot, Valencia, Spain
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Bhowmick AK, Jamali A, Bryant D, Pintz S, Bos PJ. Dynamic correction of astigmatism. APPLIED OPTICS 2023; 62:1791-1799. [PMID: 37132927 DOI: 10.1364/ao.477296] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
For the correction of defocus and astigmatism, mechanical approaches are well known, but there is a need for a non-mechanical, electrically tunable optical system that could provide both focus and astigmatism power correction with an adjustable axis. The optical system presented here is composed of three liquid-crystal-based tunable cylindrical lenses that are simple, low cost, and having a compact structure. Potential applications of the concept device include smart eyeglasses, virtual reality (VR)/ augmented reality (AR) head-mounted displays (HMDs), and optical systems subject to thermal or mechanical distortion. Details of the concept, design method, numerical computer simulations of the proposed device, as well as characterization of a prototype, are provided in this work.
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Elshahat A, Hamed AM, El Habbak AH, Tabl MA. Evaluation of Ocular Residual Astigmatism in Eyes with Myopia and Myopic Astigmatism and Its Interaction with Other Forms of Astigmatism. Clin Ophthalmol 2022; 16:4179-4190. [PMID: 36544897 PMCID: PMC9762676 DOI: 10.2147/opth.s393477] [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: 10/19/2022] [Accepted: 11/29/2022] [Indexed: 12/24/2022] Open
Abstract
Purpose To evaluate the prevalence, magnitude, and direction of ocular residual astigmatism (ORA) in eyes with myopia and myopic astigmatism, and its interaction with refractive, anterior corneal, posterior corneal, and true net power astigmatism. Patients and Methods Refractive surgery candidates with myopia and myopic astigmatism were studied. Refractive astigmatism (RA) was measured using the Nidek® AR-310A autorefractometer. Anterior corneal astigmatism (ACA), posterior corneal astigmatism (PCA), and true net power astigmatism (TNP) were measured using the Wavelight® Oculyzer II. Astigmatism was converted from polar to vector notation. ORA was calculated by vector subtraction of ACA from RA vertexed to corneal plane. Compensation factor (CF) was calculated as the ratio of ORA that compensates ACA for both J0 and J45. Results 154 eyes of 88 patients (mean age 31.7±7.1 years) were included. With-the-rule (WTR) astigmatism was the most common for both RA (55.6%) and ACA (74%), while against-the-rule (ATR) was the most common for PCA (87.7%) and ORA (74.0%). The axes of RA and ACA were within 10° of each other in 46.8% of the eyes, and within 30° of each other in 76.0%. The mean difference in value between the axis of RA and ACA was 25.6°. 71.4% of eyes in the study had an ORA ≥ 0.5D, 44.1% had ORA ≥ 0.75D and 26% had ORA ≥ 1D. There was a statistically significant difference between ACA and each of RA and TNP. Using TNP to calculate ORA instead of ACA reduced its magnitude. RA is positively correlated to ACA and more strongly to TNP. The most common pattern of compensation between ORA and ACA was under-compensation for J0 (49%) and same-axis-augmentation for J45 (35%). Conclusion ORA, PCA, and the interaction between ORA and ACA can affect results during refractive planning.
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Affiliation(s)
- Ahmed Elshahat
- Department of Ophthalmology, Benha Faculty of Medicine, Benha University, Benha, Qalyopia, Egypt
| | - Abdelmonem M Hamed
- Department of Ophthalmology, Benha Faculty of Medicine, Benha University, Benha, Qalyopia, Egypt,Correspondence: Abdelmonem M Hamed, Email
| | - Ashraf H El Habbak
- Department of Ophthalmology, Benha Faculty of Medicine, Benha University, Benha, Qalyopia, Egypt
| | - Marwa Abdelshafy Tabl
- Department of Ophthalmology, Benha Faculty of Medicine, Benha University, Benha, Qalyopia, Egypt
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Heydarian S, Sardari S, Heidari Z, Yekta AA, Ostadimoghaddam H, Khabazkhoob M. Corneal and Ocular Residual Astigmatism in School-Age Children. J Curr Ophthalmol 2021; 32:355-360. [PMID: 33553837 PMCID: PMC7861098 DOI: 10.4103/joco.joco_8_20] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2020] [Revised: 04/08/2020] [Accepted: 04/21/2020] [Indexed: 11/04/2022] Open
Abstract
Purpose To determine the distribution of residual and corneal astigmatism (CA) in children aged 6-18 years and their relationship with age, sex, spherical equivalent, and biometric parameters. Methods In this cross-sectional study, multi-stage stratified cluster sampling was done to select students from Dezful, a city in Southwestern Iran. Examinations included the measurement of visual acuity with and without optical correction, refraction with and without cycloplegia, and biometry using the Biograph (Lenstar, Germany). The main outcomes in this report were corneal and residual astigmatism. The CA was measured by Biograph (difference between k1 and k2), and residual astigmatism was calculated using Alpine method. The power vector method was applied to analyze the data of astigmatism. Results Of 864 students that were selected, 683 (79.1%) participated in the study. The mean residual and CA were -0.84 diopter (D) and -0.85 D, respectively. According to the results of J0 and J45 vectors, residual astigmatism was -0.33 D and 0.04 D, and CA was 0.38 D and 0.01 D, respectively. With-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism were seen in 3.4%, 66.8%, and 4.5% of the children with residual astigmatism and 67.94%, 1.3%, and 1.5% of the children with CA. Residual astigmatism decreased with an increase in spherical refractive error, whereas CA increased with an increase in spherical refractive error. Conclusion The results of the present study showed a high prevalence and amount of residual astigmatism with ATR pattern among the 6-18-year-old population and the compensatory effect of this type of astigmatism on CA that mostly followed a WTR pattern.
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Affiliation(s)
- Samira Heydarian
- Department of Rehabilitation Science, School of Allied Medical Sciences, Mazandaran University of Medical Sciences, Sari, Iran
| | - Sara Sardari
- Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Tehran, Iran
| | - Zahra Heidari
- Department of Rehabilitation Science, School of Allied Medical Sciences, Mazandaran University of Medical Sciences, Sari, Iran.,Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran
| | - Abbas Ali Yekta
- Department of Optometry, School of Paramedical Sciences, Mashhad University of Medical Sciences, Mashhad, Iran
| | - Hadi Ostadimoghaddam
- Refractive Errors Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
| | - Mehdi Khabazkhoob
- Department of Medical Surgical Nursing, School of Nursing and Midwifery, Shahid Beheshti University of Medical Sciences, Tehran, Iran
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Erdogan G, Kandemir Besek N, Onal Gunay B, Agca A. Outcomes of three surgical approaches for managing ectopia lentis in Marfan syndrome. Eur J Ophthalmol 2021; 32:242-248. [PMID: 33550842 DOI: 10.1177/1120672121992950] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
OBJECTIVE To investigate the clinical outcomes of three surgical approaches for ectopia lentis in Marfan syndrome (MS) patients who had undergone crystalline lens removal with posterior chamber intraocular lens (IOL) implantation techniques comprising the intrascleral fixation of IOL, sutured scleral fixation of IOL, and IOL implantation with the use of a Cionni capsular tension ring (CTR). METHODS This is a retrospective comparative study, including 35 eyes of 21 patients who underwent the intrascleral fixation of IOL (group 1), scleral IOL fixation with the Z-suture (group 2), and IOL implantation with the use of a Cionni CTR (group 3) following crystalline lens removal. The surgical indications were as follows: no improvement in visual function after eyeglasses or contact lens application due to excessive irregular astigmatism and advanced crystalline lens decentration in which the edge of the crystalline lens came up to the optical axis, or dislocation of the crystalline lens resulting in aphakia and secondary glaucoma due to lens dislocation. The surgical outcomes and complications due to surgery were compared between the groups. RESULTS The mean age of the patients in the study was 12.3 ± 8.7 years (5-32 years). There were 10 eyes in group 1, 13 eyes in group 2, and 12 eyes in group 3. Visual acuity improved significantly in each group after surgery. Ocular residual astigmatism did not differ significantly between the groups (p = 0.51). CONCLUSION There were no significant differences between the three surgical approaches in the current study in terms of the postoperative results and complications.
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Affiliation(s)
- Gurkan Erdogan
- Department of Ophthalmology, University of Health Sciences, Istanbul Beyoglu Eye Training and Research Hospital, Istanbul, Turkey
| | - Nilay Kandemir Besek
- Department of Ophthalmology, University of Health Sciences, Istanbul Beyoglu Eye Training and Research Hospital, Istanbul, Turkey
| | - Betul Onal Gunay
- Department of Ophthalmology, University of Health Sciences, Trabzon Kanuni Training and Research Hospital, Trabzon, Turkey
| | - Alper Agca
- Department of Ophthalmology, University of Health Sciences, Istanbul Beyoglu Eye Training and Research Hospital, Istanbul, Turkey
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6
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Leung TW, Chan CT, Lam CH, Tong YK, Kee CS. Changes in corneal astigmatism and near heterophoria after smartphone use while walking and sitting. PLoS One 2020; 15:e0243072. [PMID: 33270709 PMCID: PMC7714198 DOI: 10.1371/journal.pone.0243072] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Accepted: 11/14/2020] [Indexed: 11/23/2022] Open
Abstract
Background/Aims Smartphone use has become an indispensable part of our daily life. The handy design and powerful processor allow smartphone users to perform diversified tasks even when walking. This study aimed to investigate and compare the optical aftereffect and vergence adaptation of using a smartphone while walking and sitting. Methods Twenty-nine young healthy adults (aged 19 to 24 years old) with normal binocular and accommodative functions were recruited. Participants were asked to watch a movie for 30 minutes using a smartphone while either walking on a treadmill or sitting on a chair. Corneal aberrations and near heterophoria were measured before and after smartphone use by a corneal topographer and modified Thorington heterophoria test, respectively. Results Using the smartphone while walking induced a change in corneal H/V astigmatism, becoming 0.11±0.03 μm less negative (two-way ANOVA repeated measures, Bonferroni post-hoc test, p = 0.001). This optical aftereffect was significantly higher than after smartphone use while sitting by 0.10±0.03 μm (paired t-test, p = 0.003). Although smartphone use did not result in a significant change in near heterophoria (Bonferroni post-hoc test, p > 0.15), the vergence adaptation showed relatively more eso- or less exo-deviation by 0.79±0.36Δ in the walking than the sitting condition (paired t-test, p = 0.037). Conclusions Eyecare practitioners should be cautious of the potential optical after effect and vergence adaptation after prolonged smartphone usage.
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Affiliation(s)
- Tsz Wing Leung
- School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China
- The Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China
- * E-mail:
| | - Chui-Ting Chan
- School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China
| | - Chi-Hin Lam
- School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China
| | - Yuk-Kwan Tong
- School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China
| | - Chea-Su Kee
- School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China
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Nagra M, Dashrathi R, Senthan E, Jahan T, Campbell P. Characterisation of internal, refractive, and corneal astigmatism in a UK university student population. Cont Lens Anterior Eye 2020; 43:333-337. [DOI: 10.1016/j.clae.2020.02.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 12/04/2019] [Accepted: 02/12/2020] [Indexed: 11/25/2022]
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8
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Mohammadi SF, Khorrami-Nejad M, Hamidirad M. Posterior corneal astigmatism: a review article. CLINICAL OPTOMETRY 2019; 11:85-96. [PMID: 31496856 PMCID: PMC6697663 DOI: 10.2147/opto.s210721] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 07/29/2019] [Indexed: 05/15/2023]
Abstract
Most human eyes show at least a small degree of corneal astigmatism and it can arise from both surfaces of the cornea. The shape of the anterior corneal surface provides no definitive basis for knowing the toricity of the posterior surface. In the previous studies, average astigmatism of the posterior corneal surface was -0.26 to -0.78 diopter. The radius of the posterior corneal surface is less than the radius of the anterior corneal surface. Most studies have found a clear correlation between the anterior and posterior corneal asphericities and the asphericity of the posterior surface is independent of the vertex radius of curvature, refractive error and gender. In contrast to the anterior corneal surface, the asphericity of the posterior corneal surface varies significantly between meridians. The anterior and posterior corneal surface would have approximately parallel principal meridians and both of these surfaces are often flatter in the horizontal meridian than the vertical one. This is especially true in the higher degrees of corneal astigmatism, and then about 10% of any anterior corneal astigmatism is neutralized by an astigmatism arising from the posterior corneal surface. Although the second corneal surface only contributes to about 10% of the total refractive power of the eye, a precise knowledge of its morphology is needed for the correct diagnosis and monitoring the corneal diseases or the surgical interventions and in many eyes neglecting the posterior corneal surface measurement may lead to significant deviations from the corneal astigmatism estimation. In this article, we have reviewed the shape and the toricity of the posterior corneal surface and also the effect of age on it. We investigated the contribution of posterior corneal astigmatism to the total corneal astigmatism and evaluated the accuracy of corneal astigmatism estimation by neglecting the posterior corneal surface measurement.
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Affiliation(s)
- Seyed-Farzad Mohammadi
- Translational Ophthalmology Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences
, Tehran, Iran
| | - Masoud Khorrami-Nejad
- Translational Ophthalmology Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences
, Tehran, Iran
- School of Rehabilitation, Shahid Beheshti University of Medical Sciences
, Tehran, Iran
| | - Moein Hamidirad
- School of Rehabilitation, Shahid Beheshti University of Medical Sciences
, Tehran, Iran
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9
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Chen Z, Liu L, Pan C, Li X, Pan L, Lan W, Yang Z. Ocular residual and corneal astigmatism in a clinical population of high school students. PLoS One 2018; 13:e0194513. [PMID: 29630629 PMCID: PMC5890987 DOI: 10.1371/journal.pone.0194513] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2017] [Accepted: 03/05/2018] [Indexed: 11/18/2022] Open
Abstract
Purpose Total refractive astigmatism is usually the first consideration that guides the selection of contact lens type (e.g., spherical or toric), while the ocular source of the astigmatism is a second, but more important consideration, for the final clinical decision. This study was conducted to provide detailed data on this topic by evaluating astigmatic components in Chinese adolescents. Methods Participants were recruited from healthy high school students undergoing an annual ocular examination at a local hospital. Total astigmatism (TA), corneal astigmatism (CA), and ocular residual astigmatism (ORA) were determined by a Hartmann-Shack wavefront analyzer system (KR-1W, Topcon) with the natural pupil. The axis relationship between CA and ORA was placed into three categories: on-axis, defined as an axis with a difference of 0 ± 10°; opposite-axis, a difference of 90 ± 10°; and the rest defined as oblique-axis. Results The study consisted of 1,466 students (57.84% girls, age: 16.49 ± 1.05 years). ORA was present in 83.97%, 66.64%, and 45.23% of participants, according to the various criteria for astigmatism (≥ 0.50 D, ≥ 0.75 D, and ≥ 1.00 D, respectively). While with-the-rule was the most common axis orientation for both TA (76.28%) and CA (89.94%), against-the-rule predominated in ORA (93.82%; χ2 = 1688.544, p < 0.001). Opposite-axis was the major type of axis difference (90.96%) of clinical significance (i.e., ≥ 1.00 D) between CA and ORA, which also prevailed in all levels of TA (range: 56.25–82.26%). Conclusions ORA is common in high school students and usually demonstrates a compensation relationship with CA, which should be taken into consideration when determining the design of contact lenses to correct refractive error.
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Affiliation(s)
- Zhao Chen
- Aier Institute of Optometry and Vision Science, Aier School of Ophthalmology, Central South University, Changsha, Hunan Province, China
| | - Luoru Liu
- Anyang Eye Hospital, Anyang, Henan Province, China
| | - Chenglin Pan
- Aier Institute of Optometry and Vision Science, Aier School of Ophthalmology, Central South University, Changsha, Hunan Province, China
| | - Xiaoning Li
- Aier Institute of Optometry and Vision Science, Aier School of Ophthalmology, Central South University, Changsha, Hunan Province, China
| | - Lun Pan
- Aier Institute of Optometry and Vision Science, Aier School of Ophthalmology, Central South University, Changsha, Hunan Province, China
| | - Weizhong Lan
- Aier Institute of Optometry and Vision Science, Aier School of Ophthalmology, Central South University, Changsha, Hunan Province, China
- * E-mail: (WL); (ZY)
| | - Zhikuan Yang
- Aier Institute of Optometry and Vision Science, Aier School of Ophthalmology, Central South University, Changsha, Hunan Province, China
- * E-mail: (WL); (ZY)
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10
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Schuster AKG, Pfeiffer N, Schulz A, Hoehn R, Ponto KA, Wild PS, Blettner M, Beutel ME, Lackner KJ, Münzel T, Mirshahi A. Refractive, corneal, and ocular residual astigmatism: distribution in a German population and age dependency-the Gutenberg Health Study. Graefes Arch Clin Exp Ophthalmol 2017; 256:445-446. [PMID: 29082449 DOI: 10.1007/s00417-017-3822-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Accepted: 10/05/2017] [Indexed: 11/29/2022] Open
Affiliation(s)
| | - Norbert Pfeiffer
- Department of Ophthalmology, University Medical Center Mainz, Langenbeckstr. 1, 55131, Mainz, Germany
| | - Andreas Schulz
- Preventive Cardiology and Preventive Medicine / Department of Medicine 2, University Medical Center Mainz, Mainz, Germany
| | - René Hoehn
- Department of Ophthalmology, University Medical Center Mainz, Langenbeckstr. 1, 55131, Mainz, Germany.,Department of Ophthalmology, Inselspital, University Hospital of Bern, University of Bern, Bern, Switzerland
| | - Katharina A Ponto
- Department of Ophthalmology, University Medical Center Mainz, Langenbeckstr. 1, 55131, Mainz, Germany.,Center for Thrombosis and Hemostasis (CTH), University Medical Center Mainz, Mainz, Germany
| | - Philipp S Wild
- Preventive Cardiology and Preventive Medicine / Department of Medicine 2, University Medical Center Mainz, Mainz, Germany.,Center for Thrombosis and Hemostasis (CTH), University Medical Center Mainz, Mainz, Germany.,German Center for Cardiovascular Research (DZHK), partner site Rhine-Main, Mainz, Germany
| | - Maria Blettner
- Institute of Medical Biostatistics, Epidemiology and Informatics, University Medical Center of the Johannes Gutenberg-University Mainz, Mainz, Germany
| | - Manfred E Beutel
- Department of Psychosomatic Medicine and Psychotherapy, University Medical Center Mainz, Mainz, Germany
| | - Karl J Lackner
- Institute of Clinical Chemistry and Laboratory Medicine, University Medical Center Mainz, Mainz, Germany
| | - Thomas Münzel
- Center for Cardiology, University Medical Center Mainz, Mainz, Germany
| | - Alireza Mirshahi
- Department of Ophthalmology, University Medical Center Mainz, Langenbeckstr. 1, 55131, Mainz, Germany.,Dardenne Eye Hospital, Bonn-Bad Godesberg, Germany
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11
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Remón L, Monsoriu JA, Furlan WD. Influence of different types of astigmatism on visual acuity. JOURNAL OF OPTOMETRY 2017; 10:141-148. [PMID: 27639497 PMCID: PMC5484781 DOI: 10.1016/j.optom.2016.07.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Revised: 07/18/2016] [Accepted: 07/25/2016] [Indexed: 05/20/2023]
Abstract
PURPOSE To investigate the change in visual acuity (VA) produced by different types of astigmatism (on the basis of the refractive power and position of the principal meridians) on normal accommodating eyes. METHODS The lens induced method was employed to simulate a set of 28 astigmatic blur conditions on different healthy emmetropic eyes. Additionally, 24 values of spherical defocus were also simulated on the same eyes for comparison. VA was measured in each case and the results, expressed in logMAR units, were represented against of the modulus of the dioptric power vector (blur strength). RESULTS LogMAR VA varies in a linear fashion with increasing astigmatic blur, being the slope of the line dependent on the accommodative demand in each type of astigmatism. However, in each case, we found no statistically significant differences between the three axes investigated (0°, 45°, 90°). Non-statistically significant differences were found either for the VA achieved with spherical myopic defocus (MD) and mixed astigmatism (MA). VA with simple hyperopic astigmatism (SHA) was higher than with simple myopic astigmatism (SMA), however, in this case non conclusive results were obtained in terms of statistical significance. The VA achieved with imposed compound hyperopic astigmatism (CHA) was highly influenced by the eye's accommodative response. CONCLUSIONS VA is correlated with the blur strength in a different way for each type of astigmatism, depending on the accommodative demand. VA is better when one of the focal lines lie on the retina irrespective of the axis orientation; accommodation favors this situation.
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Affiliation(s)
- Laura Remón
- Centro de Tecnologías Físicas, Universitat Politècnica de València, 46022 Valencia, Spain
| | - Juan A Monsoriu
- Centro de Tecnologías Físicas, Universitat Politècnica de València, 46022 Valencia, Spain
| | - Walter D Furlan
- Departamento de Óptica y Optometría y Ciencias de la Visión, Universitat de València, 46100 Burjassot, Spain.
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12
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Signes-Soler I, Hernández-Verdejo JL, Estrella Lumeras MA, Tomás Verduras E, Piñero DP. Refractive error study in young subjects: results from a rural area in Paraguay. Int J Ophthalmol 2017; 10:467-472. [PMID: 28393041 DOI: 10.18240/ijo.2017.03.22] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2016] [Accepted: 04/28/2016] [Indexed: 11/23/2022] Open
Abstract
AIM To evaluate the distribution of refractive error in young subjects in a rural area of Paraguay in the context of an international cooperation campaign for the prevention of blindness. METHODS A sample of 1466 young subjects (ranging from 3 to 22 years old), with a mean age of 11.21±3.63 years old, were examined to assess their distance visual acuity (VA) and refractive error. The first screening examination performed by trained volunteers, included visual acuity testing, autokeratometry and non-cycloplegic autorefraction. Inclusion criteria for a second complete cycloplegic eye examination by an optometrist were VA <20/25 (0.10 logMAR or 0.8 decimal) and/or corneal astigmatism ≥1.50 D. RESULTS An uncorrected distance VA of 0 logMAR (1.0 decimal) was found in 89.2% of children. VA <20/25 and/or corneal astigmatism ≥1.50 D was found in 3.9% of children (n=57), with a prevalence of hyperopia of 5.2% (0.2% of the total) in this specific group. Furthermore, myopia (spherical equivalent ≤-0.5 D) was found in 37.7% of the refracted children (0.5% of the total). The prevalence of refractive astigmatism (cylinder ≤-1.50 D) was 15.8% (0.6% of the total). Visual impairment (VI) (0.05≤VA≤0.3) was found in 12/114 (0.4%) of the refracted eyes. Main causes for VI were refractive error (58%), retinal problems (17%, 2/12), albinism (17%, 2/12) and unknown (8%, 1/12). CONCLUSION A low prevalence of refractive error has been found in this rural area of Paraguay, with higher prevalence of myopia than of hyperopia.
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Affiliation(s)
- Isabel Signes-Soler
- Non-governmental Organization Vision Without Borders (Visio Sense Fronteres), Alicante 03710, Spain; School of Advanced Education, Research and Accreditation (SAERA), Castellón de la Plana 12001, Spain
| | - José Luis Hernández-Verdejo
- Non-governmental Organization Vision Without Borders (Visio Sense Fronteres), Alicante 03710, Spain; Faculty of Optics and Optometry, University Complutense of Madrid, Madrid 28037, Spain
| | - Miguel Angel Estrella Lumeras
- Non-governmental Organization Vision Without Borders (Visio Sense Fronteres), Alicante 03710, Spain; European University of Madrid, Madrid 28108, Spain
| | - Elena Tomás Verduras
- Non-governmental Organization Vision Without Borders (Visio Sense Fronteres), Alicante 03710, Spain; School of Advanced Education, Research and Accreditation (SAERA), Castellón de la Plana 12001, Spain
| | - David P Piñero
- Foundation for the Visual Quality (FUNCAVIS), Alicante 03016, Spain; Department of Optics, Pharmacology, and Anatomy, University of Alicante, Alicante 03690, Spain
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13
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Abstract
PURPOSE To examine internal astigmatism (IA) in myopes and non-myopes using a new method to assess compensation of corneal astigmatism (CA) by IA, to look for predictors of high IA in young adult myopes, and to determine if as CA changes IA changes to reduce refractive astigmatism (RA) in an active compensatory process in myopes. METHODS Right eye keratometry and cycloplegic autorefraction were measured annually over 14 years in 367 myopes and once in 204 non-myopes age- (mean 21.91 ± 1.47 years), gender-, and ethnicity-matched to myopes at year 12. CA and RA at the corneal plane were expressed as J0, J45. IA = RA - CA. Inverse power transformation provided cylinder power and axis of IA for the compensation factor (IA/CA). Analyses included (1) paired and unpaired t-tests (refractive data), (2) chi-square tests (distributions of compensation factor), (3) logistic regression analysis (predictors of high IA), and (4) linear mixed models (time effect on RA, CA, and IA). RESULTS The magnitude of IAJ0 varied by refractive error (myopes -0.25 ± 0.24 vs. non-myopes -0.32 ± 0.21, p < 0.001). Compensation of CA by IA was poorer in myopes than non-myopes (χ p < 0.001). When matched by CA, compensation remained poorer in myopes than non-myopes (χ all p ≤ 0.04). Within each refractive group, compensation was better when CA was low than high (χ p < 0.001). When CA was low in myopes, high IA (≥1.00D) was less likely (p = 0.01). Longitudinal follow-up of myopes found no evidence for an active compensatory role for IA as CA increased over time. There were differences in IAJ0 by ethnicity over time (p < 0.0001). CONCLUSIONS In myopic and non-myopic eyes with low amounts of CA, IA may reduce CA's contribution to RA, but IA is not a constant. However, there is no evidence for an active compensatory role for IA reducing CA in myopes.
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14
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Abstract
PURPOSE Subjects with Down syndrome have structural differences in the cornea and lens, as compared with the general population. This study investigates objectively measured refractive and corneal astigmatism, as well as calculated internal astigmatism in subjects with and without Down syndrome. METHODS Refractive (Grand Seiko autorefraction) and anterior corneal astigmatism (difference between steep and flat keratometry obtained with Zeiss Atlas corneal topography) were measured in 128 subjects with Down syndrome (mean [±SD] age, 24.8 [±8.7] years) and 137 control subjects without Down syndrome (mean [±SD] age, 24.9 [±9.9] years), with one eye randomly selected for analysis per subject. Refractive astigmatism and corneal astigmatism were converted to vector notation (J0, J45) to calculate internal astigmatism (Refractive - Corneal) and then converted back to minus cylinder form. RESULTS Mean [±SD] refractive astigmatism was significantly greater in subjects with Down syndrome than in control subjects (-1.94 [±1.30] DC vs. -0.66 [±0.60] DC, t = -10.16, p < 0.001), as were mean corneal astigmatism (1.70 [±1.04] DC vs. 1.02 [±0.63] DC, t = 6.38, p < 0.001) and mean internal astigmatism (-1.07 [±0.68] DC vs. -0.77 [±0.41] DC, t = -4.21, p < 0.001). A positive linear correlation between corneal and refractive astigmatism was observed for both study populations for both the J0 and J45 vectors (p < 0.001 for all comparisons; R(2) range, 0.31 to 0.74). The distributions of astigmatism orientation differed significantly between the two study populations for comparisons of corneal and calculated internal astigmatism (χ(2), p < 0.007), but not refractive astigmatism (p = 0.46). CONCLUSIONS This study demonstrates that corneal astigmatism is predictive of overall refractive astigmatism in subjects with Down syndrome, as it is in the general population. The greater magnitudes of astigmatism and wider variation of astigmatism orientation in subjects with Down syndrome for refractive, corneal, and calculated internal astigmatism are likely attributable to previously reported differences in the structure of the cornea and internal optical components of the eye from that of the general population.
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15
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Abulafia A, Hill WE, Franchina M, Barrett GD. Comparison of Methods to Predict Residual Astigmatism After Intraocular Lens Implantation. J Refract Surg 2015; 31:699-707. [DOI: 10.3928/1081597x-20150928-03] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Accepted: 08/10/2015] [Indexed: 11/20/2022]
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16
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Bregnhøj JF, Mataji P, Naeser K. Refractive, anterior corneal and internal astigmatism in the pseudophakic eye. Acta Ophthalmol 2015; 93:33-40. [PMID: 25043890 DOI: 10.1111/aos.12418] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2013] [Accepted: 03/16/2014] [Indexed: 11/30/2022]
Abstract
PURPOSE To evaluate the correlation between refractive astigmatism (RA) and anterior corneal astigmatism (ACA), and determine the internal astigmatism (IA) in 184 pseudophakic eyes. METHODS The study was a prospective non-masked single-centre study. Patients were examined 8 weeks after phacoemulsification with implantation of aspheric one-piece monofocal IOLs. Examination included autokeratometry and subjective refraction. All refractive data were converted to the corneal plane. The corneal refractive index, taken to be 1.376, was used to estimate the ACA. All astigmatisms were converted to net curvital and net torsional powers with the steeper corneal plane as the reference meridian. Curvital power is the force acting along a given meridian, and torsion is the power twisting the astigmatic direction out of that plane. The internal astigmatism (IA) was calculated as the difference between RA and ACA. RESULTS For curvital powers, the refractive astigmatism (KP(Φ)RA ) could be described as a function of anterior corneal astigmatic magnitude (KP(Φ)ACA ) and direction α by the multiple linear regression equation: KP(Φ)RA = -0.09 + 0.61*KP(Φ)ACA + 0.33*cos2α, (r(2) = 0.59, p < 0.0001). The average internal astigmatism amounted to 0.47 D inclined 92° relative to the steeper anterior corneal meridian. The magnitude of internal astigmatism depended on the angle α of the steeper anterior corneal meridian, averaging 0.86 D at 91° for with-the-rule, 0.37 D at 95° for oblique and 0.17 D at 97° for against-the-rule corneal astigmatisms. CONCLUSIONS The internal astigmatism varies as a function of the direction of the anterior steeper corneal meridian. In patient candidates to surgical correction of astigmatism, measuring only the curvature of the anterior corneal surface and neglecting that of the posterior corneal surface can lead to inaccurate evaluation of total corneal astigmatism.
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Affiliation(s)
- Jesper F. Bregnhøj
- Department of Ophthalmology; Aarhus University Hospital; Aarhus Denmark
- Department of Ophthalmology; Randers Regional Hospital; Randers Denmark
| | - Pourang Mataji
- Department of Ophthalmology; Aarhus University Hospital; Aarhus Denmark
- Department of Ophthalmology; Randers Regional Hospital; Randers Denmark
| | - Kristian Naeser
- Department of Ophthalmology; Aarhus University Hospital; Aarhus Denmark
- Department of Ophthalmology; Randers Regional Hospital; Randers Denmark
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17
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Influence of the difference between corneal and refractive astigmatism on LASIK outcomes using solid-state technology. Cornea 2014; 33:1287-94. [PMID: 25321937 DOI: 10.1097/ico.0000000000000272] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE To evaluate the influence of the difference between preoperative corneal and refractive astigmatism [ocular residual astigmatism (ORA)] on outcomes obtained after laser in situ keratomileusis (LASIK) surgery for correction of myopic astigmatism using the solid-state laser technology. METHODS One hundred one consecutive eyes with myopia or myopic astigmatism of 55 patients undergoing LASIK surgery using the Pulzar Z1 solid-state laser (CustomVis Laser Pty Ltd, currently CV Laser) were included. Visual and refractive changes at 6 months postoperatively and changes in ORA and anterior corneal astigmatism and posterior corneal astigmatism (PCA) were analyzed. RESULTS Postoperatively, uncorrected distance visual acuity improved significantly (P < 0.01). Likewise, refractive cylinder magnitude and spherical equivalent were reduced significantly (P < 0.01). In contrast, no significant changes were observed in ORA magnitude (P = 0.81) and anterior corneal astigmatism (P = 0.12). The mean overall efficacy and safety indices were 0.96 and 1.01, respectively. These indices were not correlated with preoperative ORA (r = -0.15, P = 0.15). Furthermore, a significant correlation was found between ORA (r = 0.81, P < 0.01) and PCA postoperatively, but not preoperatively (r = 0.12, P = 0.25). Likewise, a significant correlation of ORA with manifest refraction was only found postoperatively (r = -0.38, P < 0.01). CONCLUSIONS The magnitude of ORA does not seem to be a predictive factor of efficacy and safety of myopic LASIK using a solid-state laser platform. The higher relevance of PCA after surgery in some cases may explain the presence of unexpected astigmatic residual refractive errors.
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Delrivo M, Ruiseñor Vázquez PR, Galletti JD, Garibotto M, Fuentes Bonthoux F, Pförtner T, Galletti JG. Agreement between placido topography and Scheimpflug tomography for corneal astigmatism assessment. J Refract Surg 2014; 30:49-53. [PMID: 24864328 DOI: 10.3928/1081597x-20131217-06] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To evaluate inter-device agreement between Placido topography (iTrace; Tracey Technologies, Houston, TX) and Scheimpflug tomography (Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany) for measuring corneal power and cylinder and axis of astigmatism. METHODS Observational case series of 54 eyes from 54 subjects with no ocular disease. Main outcome measures were corneal power, cylinder power, and axis of astigmatism and their agreement was assessed by Bland–Altman analysis. RESULTS For corneal power and corneal cylinder, 95% limits of agreement (LoA) were considered good (−0.38 to 0.45 diopters [D] and −0.49 to 0.27 D, respectively). In contrast, the 95% LoA for corneal astigmatism axis exceeded the clinically relevant margins (−14.8 to 13.5): 28 eyes (52%) had a greater than 5° difference, 10 eyes (19%) had a greater than 10° difference, and 4 eyes (7%) had a greater than 20° difference between instruments. This absolute difference was significantly correlated with average corneal cylinder (Spearman’s r = −0.379, P = .005) but not with average corneal power. In eyes with corneal astigmatism 2 D or greater, the 95% LoA for axis were −8.7° to 6.7°, whereas in those with corneal astigmatism less than 1 D, the 95% LoA for axis were −19.1° to 16.6°. CONCLUSIONS Placido topography and Scheimpflug tomography show good agreement for corneal power and cylinder, but not for corneal astigmatism axis. These instruments could be used interchangeably only in eyes with corneal astigmatism of 2 D or greater.
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Abstract
PURPOSE Myopia and astigmatism are highly prevalent in the Hong Kong Chinese. This study aimed to determine the effects of age and myopic astigmatism (MA) on the corneal shape factors in the Hong Kong Chinese. METHODS One hundred subjects with compound MA or emmetropia (EM) were recruited from three age groups: 10 to 15 years (n = 32), 20 to 25 years (n = 37), and 40 to 45 years (n = 31). Refractive errors were measured by noncycloplegic subjective refraction. Corneal astigmatism and corneal shape factors were measured by the Scheimpflug-based Pentacam. The effects of age and refractive errors on the whole corneal shape (mean-P) and the semimeridian corneal shapes (semi-Ps) at the nasal, temporal, superior, and inferior corneal quadrants (from corneal apex to 3 mm peripheral cornea) were analyzed. RESULTS Age had significant effects on the mean-P and semi-Ps (both p < 0.001), with both EM and MA showing less prolate corneal shapes in older age groups. Partial correlation analyses adjusted for age showed that mean-P and semi-Ps were correlated with multiple refractive-error components (Pearson r = -0.30 to -0.78, all p < 0.05), with higher correlations found along the horizontal semi-Ps in MA (Pearson r = +0.37 to -0.78, all p < 0.01). Compared with EM, MA had more prolate temporal semi-Ps in all the three age groups (p < 0.05). Strikingly, age and refractive errors also had significant impacts on the asymmetry of the corneal shape along the horizontal meridian. CONCLUSIONS Corneal shapes were influenced by age and MA in the Hong Kong Chinese. These results highlight the importance of controlling these factors when designing a study on corneal shape.
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Read SA, Vincent SJ, Collins MJ. The visual and functional impacts of astigmatism and its clinical management. Ophthalmic Physiol Opt 2014; 34:267-94. [PMID: 24635572 DOI: 10.1111/opo.12128] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2014] [Accepted: 02/25/2014] [Indexed: 01/14/2023]
Abstract
PURPOSE To provide a comprehensive overview of research examining the impact of astigmatism on clinical and functional measures of vision, the short and longer term adaptations to astigmatism that occur in the visual system, and the currently available clinical options for the management of patients with astigmatism. RECENT FINDINGS The presence of astigmatism can lead to substantial reductions in visual performance in a variety of clinical vision measures and functional visual tasks. Recent evidence demonstrates that astigmatic blur results in short-term adaptations in the visual system that appear to reduce the perceived impact of astigmatism on vision. In the longer term, uncorrected astigmatism in childhood can also significantly impact on visual development, resulting in amblyopia. Astigmatism is also associated with the development of spherical refractive errors. Although the clinical correction of small magnitudes of astigmatism is relatively straightforward, the precise, reliable correction of astigmatism (particularly high astigmatism) can be challenging. A wide variety of refractive corrections are now available for the patient with astigmatism, including spectacle, contact lens and surgical options. CONCLUSION Astigmatism is one of the most common refractive errors managed in clinical ophthalmic practice. The significant visual and functional impacts of astigmatism emphasise the importance of its reliable clinical management. With continued improvements in ocular measurement techniques and developments in a range of different refractive correction technologies, the future promises the potential for more precise and comprehensive correction options for astigmatic patients.
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Affiliation(s)
- Scott A Read
- Contact Lens and Visual Optics Laboratory, School of Optometry and Vision Science, Queensland University of Technology, Brisbane, Australia
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21
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Abstract
PURPOSE To examine the agreement and relationship between refractive and corneal astigmatism in a population of pseudophakic eyes. METHODS Patients of age at least 40 years, visual acuity 20/40 or better, and no ocular disease were included (n = 111). Refractive astigmatism was obtained by subjective refraction. Corneal astigmatism was measured by automated keratometry and Scheimpflug scanning analysis. All refractive values were converted to power vector components J0 and J45 for comparison and regression analysis of refractive versus corneal astigmatism. Main outcome measures were refractive and corneal astigmatism components. RESULTS Median single Jackson cylinder (J) was similar in refractive [0.37 diopter (D)], keratometric (0.46 D), and Pentacam astigmatism (0.49 D) (P = 0.157). Median J0 astigmatic component was slightly negative, indicating against-the-rule (ATR) astigmatism, in refractive and Scheimpflug, but not in keratometric astigmatism (refractive J0: -0.10 D; keratometric J0: 0.05 D; Pentacam J0: -0.08 D) (P = 0.049). J45 astigmatic component was nearly zero and similar with the 3 methods (P = 0.416). Refractive and keratometric J0 were significantly correlated (r = 0.7, P < 0.01), as well as the corresponding J45 values (r = 0.65, P < 0.01). Refractive and Pentacam astigmatic components were worse correlated (J0: r = 0.36, P = 0.01; J45: r = 0.45, P < 0.01). Keratometric and Pentacam astigmatic components were also significantly correlated (J0: r = 0.58, P < 0.01; J45: r = 0.51, P < 0.01). CONCLUSIONS Mean internal ATR astigmatism, which comes mainly from the posterior corneal surface, adds to anterior corneal astigmatism, resulting in ATR refractive astigmatism. Correlation between refractive and corneal astigmatism components is better when keratometric data are used.
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Affiliation(s)
- Jaime Tejedor
- Department of Ophthalmology, Hospital Ramón y Cajal, Madrid, Spain.
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Correlation of the corneal toricity between anterior and posterior corneal surfaces in the normal human eye. Cornea 2013; 32:791-8. [PMID: 23328698 DOI: 10.1097/ico.0b013e31827bf898] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
PURPOSE To evaluate the correlation of the magnitude of corneal toricity and power vector components of both corneal surfaces measured with a Scheimpflug photography-based system. METHODS A total of 117 healthy normal eyes of 117 subjects selected randomly with ages ranging from 7 to 80 years were included. All eyes received an anterior segment and corneal analysis with the Sirius system (CSO) evaluating the anterior and posterior mean toricity for 3 and 7 mm (aAST and pAST). The vector components J0 and J45 as well as the overall strength blur (B) were calculated for each keratometric measurement using the procedure defined by Thibos and Horner. RESULTS The coefficient of correlation between aAST and pAST was 0.52 and 0.62 and the mean anteroposterior ratio for toricity was 0.46 ± 0.39 and 0.57 ± 0.75 for 3 and 7 mm, respectively. These ratios correlated significantly with aAST, anterior corneal J0, and manifest refraction J0 (r ≥ 0.39, P < 0.01). The coefficient of correlation was 0.69 and 0.81 between anterior and posterior J0 for 3 and 7 mm, respectively. For J45, the coefficients were 0.62 and 0.71, respectively. The linear regression analysis revealed that the pAST and power vectors could be predicted from the anterior corneal data (R2 ≥ 0.40, P < 0.01). CONCLUSIONS The toricity and astigmatic power vector components of the posterior corneal surface in the human healthy eye are related to those of the anterior and therefore can be predicted consistently from the anterior toricity and astigmatic power vectors.
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Réfraction moyenne et variation de réfraction calculées dans un espace dioptrique. J Fr Ophtalmol 2010; 33:659-69. [DOI: 10.1016/j.jfo.2010.09.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2010] [Accepted: 08/29/2010] [Indexed: 11/19/2022]
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