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ORIGINAL ARTICLE
Year : 2018  |  Volume : 21  |  Issue : 4  |  Page : 456-461

Analysis of corneal astigmatism with NIDEK axial length scan in caucasian cataract surgery candidates


1 Department of Ophthalmology, School of Medicine, Afyon Kocatepe University, Afyonkarahisar, Turkey
2 Department of Clinical Biostatistics, School of Medicine, Afyon Kocatepe University, Afyonkarahisar, Turkey

Date of Acceptance08-Aug-2017
Date of Web Publication02-Apr-2018

Correspondence Address:
Dr. R Duman
Department of Ophthalmology, School of Medicine, Afyon Kocatepe University, Afyonkarahisar
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_117_17

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   Abstract 


Aims and Objectives: The aim of the study was to analyze and quantify the pattern of corneal astigmatism in Caucasian cataract surgery patients using a new optical biometer (axial length [AL] Scan, NIDEK Co., Gamagori, Japan). Patients and Methods: The datasets of cataract surgery patients acquired between March 1, 2014, and April 15, 2016, were collected and analyzed. The corneal power (flat keratometry, steep keratometry, and mean keratometry), negative cylinder power, and axis of astigmatism were recorded. Keratometry values were optically measured by optical low coherence interferometry (AL-Scan, NIDEK Co., Ltd.,) before cataract extraction. Results: The study comprised 1233 eyes of 838 consecutive cataract candidates with a mean age of 66.8 ± 10.7 years (range 40–97 years). The mean keratometry value and corneal astigmatism were 43.69 ± 1.61 D and 0.84 ± 0.70 D, respectively. Corneal astigmatism of 1.00 D or greater was found in 344 eyes (27.9%), and 548 eyes (44.4%) had against-the-rule astigmatism. A trend toward decreasing J0 and J45 with age was found by linear regression models. The per-year increase in age was associated with a J0 and J45 decrease of 0.002 D and 0.001D, respectively. Conclusion: This study provides the distribution of astigmatism axis and power for cataract patients in age subsets from Turkey.

Keywords: Astigmatism, Cornea, NIDEK axial length-scan, optical biometer


How to cite this article:
Duman R, Duman R, Cetinkaya E, Sabaner M C, Inan S, Doğan M, Doğan &. Analysis of corneal astigmatism with NIDEK axial length scan in caucasian cataract surgery candidates. Niger J Clin Pract 2018;21:456-61

How to cite this URL:
Duman R, Duman R, Cetinkaya E, Sabaner M C, Inan S, Doğan M, Doğan &. Analysis of corneal astigmatism with NIDEK axial length scan in caucasian cataract surgery candidates. Niger J Clin Pract [serial online] 2018 [cited 2019 Nov 11];21:456-61. Available from: http://www.njcponline.com/text.asp?2018/21/4/456/229078




   Introduction Top


Obtaining accurate measurements of anterior segment parameters is essential for intraocular lens (IOL) power calculation in cataract surgery to achieve the best refractive outcomes. Modern optical biometry devices measure anterior segment parameters such as keratometry (K), axial length (AL), anterior chamber depth (ACD), and horizontal white-to-white (WTW). The AL-Scan (NIDEK Co., Ltd.) is a modern optical biometry device that uses the principle of optical low coherence interferometry (OLCI). Optical biometry devices that use the principle of low coherence interferometry were found to be more reproducible and repeatable than ultrasound biometry devices.[1],[2],[3],[4],[5],[6]

The prevalence of regular corneal astigmatism in the different cataract population has been reported by teams from the United States,[1] Europe,[2],[3] and Asia.[4],[5],[6] However, to our knowledge, there is no large series of corneal astigmatism measurements with OLCI in the literature in a Caucasian cataract population. The purpose of this study was to evaluate and quantify the pattern of corneal astigmatism as measured using the AL-scan optical biometric device in healthy cataract patients.


   Patients and Methods Top


In this retrospective study, patient datasets were acquired between March 1, 2014 and April 15, 2016, at the Department of Ophthalmology, Afyon Kocatepe University. The Bursa Yüksek Ihtisas Hospital's Ethics Committee approved the study. The criteria for inclusion were cataract and age 40 years or older. The exclusion criteria were ocular surface disorders, corneal disease, previous corneal surgery, contact lens wear, history of ocular trauma, and inflammation. The patients were divided into five groups on the basis of age as follows: 40–49 years, 50–59 years, 60–69 years, 70–79 years, and 80 years and older.

Corneal astigmatism of the patients was divided into three groups on the basis of the axis of correcting minus cylinder. Corneal astigmatism was designated as with-the-rule (WTR) when the axis of correcting minus cylinder was within 180° ± 30°, against-the-rule (ATR) when the correcting minus cylinder axis was within 90° ± 30°s, and oblique if it was neither WTR nor ATR [Figure 1].[1]
Figure 1: Diagram of the definitions for with-the-rule, against-the-rule, and oblique astigmatism. (ATR = Against-the-rule; WTR = With-the-rule; OBL = Oblique)

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Measurement device and technique

Measurements were taken with the NIDEK AL-Scan (NIDEK Co., Gamagori, Japan). The AL-Scan relies on a OLCI technique and uses low coherence superposition of light waves emitted from an 830 nm super luminescent diode to measure the AL of the eye within the range 14–40 mm. Corneal power was measured by analyzing the images of double-mire rings projected onto the cornea at the 2.4 mm zone and 3.3 mm zone (360°C).[7],[8] In this study, the flattest K, steepest K, and mean K measurements of 2.4 mm zone recorded. Measurements were performed according to their respective manufacturer's guidelines. The patients were instructed to fixate on an internal fixation target within the device. Only high-quality measurements were included in the subsequent analysis.

The measurements were routinely performed by two trained doctors between 10 am and 5 pm. Three measurements were performed in each eye, and the values were averaged. Five major parameters (flat K, steep K, mean keratometry, negative cylinder power, and axis of astigmatism) were recorded.

Statistical analysis

Statistical analyses were performed using SPSS software (version 16; SPSS Inc., Chicago, IL, USA). P < 0.05 was considered statistically significant. Distributions of normality of the ocular biometric parameters were checked with Kolmogorov–Smirnov test (P > 0.05).

Differences between groups were compared using an unpaired t-test or analysis of variance for normally distributed variables and a Mann–Whitney U-test or Kruskal–Wallis test for nonnormally distributed variables. Bivariate correlations were evaluated using Pearson or Spearman rank correlation coefficient for nonnormally distributed variables.

The power vector method, J0 and J45 values, and linear regression models were used to assess the association between age and astigmatism. The power vector method was used to assess the quantitative relationship between astigmatism and age. This method was described by Thibos et al.[9] and the following formulas were applied: J0 = (−C = 2) cos2α, J45 = (−C/2) sin2α, where C is the negative cylinder power, α is the cylinder axis, and J is the Jackson astigmatic vectors. The J0 value is the cylinder power set at the 90°C and 180°C meridians. A positive J0 value indicates WTR astigmatism and a negative J0 value, ATR astigmatism. The J45 value refers to a cross-cylinder set at 45°C and 135°C, representing oblique astigmatism.[10]


   Results Top


The study evaluated 1233 eyes of 838 consecutive cataract patient datasets. Three hundred and ninety-five patients' bilateral eyes are concluded in this study. The mean age of the 490 men (58.5%) and 348 women (41.5%) was 66.8 ± 10.7 (range 40–97). [Table 1] summarizes the measured parameters: corneal power (flat K, steep K, and mean K), negative cylinder power, and axis of astigmatism. The distributions of corneal power (K1, K2, and mean K) were normal (P > 0.05).
Table 1: Distribution of ocular biometric parameters

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[Figure 2] summarizes the percentage of eyes by level of corneal astigmatism. Results revealed that 72.1% of eyes had corneal astigmatism equal to or lower than 1.00 D, 24.9% of eyes have corneal astigmatism between 1 and 2.5 D, and 24.9% of eyes had astigmatism of 2.50 D or higher.
Figure 2: Corneal astigmatism distribution in 0.50 D steps in the entire sample (1233 eyes)

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[Figure 3] summarizes the percentage of the distribution of corneal astigmatism in 0.50 D in each group. The number of eyes in the five age groups was as follows: 40–49 years - 79 eyes, 50–59 years - 214 eyes, 60–69 years - 405 eyes, 70–79 years - 379 eyes, and 80 years - older 156 eyes.
Figure 3: Frequency distribution of corneal astigmatism in 0.50 D steps for the 5 age groups

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[Figure 4] summarizes the frequency of the astigmatism axis in the five age groups. Regarding the distribution of the astigmatism axis, 457 eyes (37.1%) had WTR astigmatism, 548 eyes (44.4%) had ATR astigmatism, and 228 eyes (18.5%) had oblique astigmatism.
Figure 4: Frequency distribution of the astigmatism axis in five age groups

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[Figure 5] summarizes the amount of astigmatism for each meridian (rounded to 5°C). [Figure 6] is the scatterplots of J0 and J45, respectively, against age in eyes. Linear regression analyses showed that the J0 and J45 value significantly decreased with age. JO and J45 decrease with age; a per-year decrease in age was associated with a decrease of 0.002 D of J0 (95% confidence interval [CI],−0.004-0.00; P = 0.029) and a decrease of 0.001 D of J45 (95% CI,−0.003-0.01; P = 0.303).
Figure 5: Frequency of corneal astigmatism in all eyes

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Figure 6: The J0 against age in all eyes (ß = 0.002, P = 0.029) and J45 against age in all eyes (β = 0.001, P = 0.303)

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   Discussion Top


The management of astigmatism is an important topic for cataract surgeons. This problem has led to an increasing number of toric IOL options. For accurate toric IOL implantation, the prevalence of regular corneal astigmatism in the different cataract population is important to manufacturers. Since 2009, biometry measurements have been frequently performed with the IOL Master (Carl Zeiss Meditec) based on partial-coherence interferometry (PCI) and other devices based on OLCI such as the Lenstar (Haag-Streit AG), the AL-Scan (NIDEK Co. Ltd.), the Galilei G6 (Ziemer), and the Aladdin (Topcon EU, Visia Imaging). Previous studies have shown that the PCI and OLCI provide similar measurements.[11],[12],[13],[14]

The AL-Scan is a new optical biometry that combines optical interference and the Scheimpflug principle to perform ocular measurements including central corneal thickness, ACD, AL, K values, flat K, steep K, and WTW distance. There are many reports in the literature of the epidemiology of corneal astigmatism and biometry data in different ethnicities; however, no Caucasian study has yet been done. Here, we assessed the prevalence and distribution of different axis and types of corneal astigmatism in our population. [Table 2] summarizes a comparison of our study and several other studies from different countries.
Table 2: Summary of clinical studies of prevelance of astigmatism in cataract patients

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Our mean astigmatism value is 0.84 D and is lower than the value reported by Khan and Muhtaseb,[2] Ferrer-Blasco et al.,[3] Mohammadi et al.,[4] Prasherand Sandhu,[5] Yuan's et al.,[6] and Ünlü et al.[15] Although the mean keratometry values are different from each other in different ethnic studies, our mean flat and steepest keratometry values are lower than the values from Khan and Muhtaseb,[2] Mohammadi et al.,[4] Prasher and Sandhu,[5] Yuan's et al.,[6] Ünlü et al.,[15] and Chen et al.[16]

In our population, the astigmatism axis was predominantly ATR (44.4%), and the frequency of ATR astigmatism increased with age. These results agree with those in previous studies.[1],[2],[3],[4],[17],[18] Read et al.[19] determined that with increasing age, there is a shift in the axis of astigmatism from a predominance of WTR astigmatism (in adults younger than 40 years) to a predominance of ATR astigmatism (in adults older than 40 years). This shift may be related to the changes in the corneal tissue structure, reduction in pressure of the eyelids, extraocular muscle tension, visual feedback, and the effects of intraocular pressure on the curvature of the cornea.[19]

We found that 27.9% of cataract patients had corneal astigmatism of 1.00 D or more, which is lower than the results reported by Ferrer-Blasco et al.[3] (35%) and Khan and Muhtaseb [2] (40.41%), as well as Hoffmann and Hütz,[1] (36%). In Turkey, 12.2% of all eyes are potential candidates for toric IOL (1.5 D and more than astigmatism).

Ferrer-Blasco et al.[3] and Liu et al.[10] found that corneal J0 value decreased significantly for every 10 years with a mean decrease of approximately 0.15 D (P = 0.001) and 0.017. In our study, a significant reduction in both J0 and J45 values (J0 and J45 decrease of 0.002 D and 0.001D) was detected less than seen in these other studies.

This study had only one limitation. Multicenter studies with different localizations from our country may be more valuable in this aspect.


   Conclusion Top


We report astigmatism data in a large sample of the patients before cataract surgery. Our reports into the prevalence of the axis and power of corneal astigmatism are an important normative reference for Caucasian ophthalmologists and help with planning in the toric lens manufacturing industry.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Hoffmann PC, Hütz WW. Analysis of biometry and prevalence data for corneal astigmatism in 23,239 eyes. J Cataract Refract Surg 2010;36:1479-85.  Back to cited text no. 1
    
2.
Khan MI, Muhtaseb M. Prevalence of corneal astigmatism in patients having routine cataract surgery at a teaching hospital in the United Kingdom. J Cataract Refract Surg 2011;37:1751-5.  Back to cited text no. 2
    
3.
Ferrer-Blasco T, Montés-Micó R, Peixoto-de-Matos SC, González-Méijome JM, Cerviño A. Prevalence of corneal astigmatism before cataract surgery. J Cataract Refract Surg 2009;35:70-5.  Back to cited text no. 3
    
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Mohammadi M, Naderan M, Pahlevani R, Jahanrad A. Prevalence of corneal astigmatism before cataract surgery. Int Ophthalmol 2016;36:807-17.  Back to cited text no. 4
    
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Prasher P, Sandhu JS. Prevalence of corneal astigmatism before cataract surgery in İndian population. Int Ophthalmol 2017;37:683-89.  Back to cited text no. 5
    
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Yuan X, Song H, Peng G, Hua X, Tang X. Prevalence of corneal astigmatism in patients before cataract surgery in Northern China. J Ophthalmol 2014;2014:536412.  Back to cited text no. 6
    
7.
Youn SM, Lim, SH, Lee HY. Measurement comparison of anterior segment parameters between Al-Scan® and Pentacam®. J Korean Ophthalmol Soc 2014;55:801-8.  Back to cited text no. 7
    
8.
Dervişoğulları MS, Totan Y, Gürağaç B. Comparison of anterior chamber depth measurements of Nidek AL-Scan and Galilei Dual Scheimpflug Analyzer. Cont Lens Anterior Eye 2015;38:85-8.  Back to cited text no. 8
    
9.
Thibos LN, Wheeler W, Horner D. Power vectors: An application of Fourier analysis to the description and statistical analysis of refractive error. Optom Vis Sci 1997;74:367-75.  Back to cited text no. 9
    
10.
Liu YC, Chou P, Wojciechowski R, Lin PY, Liu CJ, Chen SJ, et al. Power vector analysis of refractive, corneal, and internal astigmatism in an elderly Chinese population: The Shihpai Eye Study. Invest Ophthalmol Vis Sci 2011;52:9651-7.  Back to cited text no. 10
    
11.
Salouti R, Nowroozzadeh MH, Zamani M, Ghoreyshi M, Salouti R. Comparison of the ultrasonographic method with 2 partial coherence interferometry methods for intraocular lens power calculation. Optometry 2011;82:140-7.  Back to cited text no. 11
    
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Holzer MP, Mamusa M, Auffarth GU. Accuracy of a new partial coherence interferometry analyser for biometric measurements. Br J Ophthalmol 2009;93:807-10.  Back to cited text no. 12
    
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Buckhurst PJ, Wolffsohn JS, Shah S, Naroo SA, Davies LN, Berrow EJ, et al. A new optical low coherence reflectometry device for ocular biometry in cataract patients. Br J Ophthalmol 2009;93:949-53.  Back to cited text no. 13
    
14.
Huang J, Savini G, Li J, Lu W, Wu F, Wang J, et al. Evaluation of a new optical biometry device for measurements of ocular components and its comparison with IOLMaster. Br J Ophthalmol 2014;98:1277-81.  Back to cited text no. 14
    
15.
Ünlü C, Vural ET, Erdoğan G, Akçay BİS, Bayramlar H. Evaluation of the Astigmatic Profile in Our Cataract Surgery Patients. Glokom Katarakt 2010;5:199-202.  Back to cited text no. 15
    
16.
Chen W, Zuo C, Chen C, Su J, Luo L, Congdon N, et al. Prevalence of corneal astigmatism before cataract surgery in Chinese patients. J Cataract Refract Surg 2013;39:188-92.  Back to cited text no. 16
    
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Hayashi K, Hayashi H, Hayashi F. Topographic analysis of the changes in corneal shape due to aging. Cornea 1995;14:527-32.  Back to cited text no. 17
    
18.
Gudmundsdottir E, Jonasson F, Jonsson V, Stefánsson E, Sasaki H, Sasaki K, et al. “With the rule” astigmatism is not the rule in the elderly. Reykjavik Eye Study: A population based study of refraction and visual acuity in citizens of Reykjavik 50 years and older. Iceland-Japan Co-Working Study Groups. Acta Ophthalmol Scand 2000;78:642-6.  Back to cited text no. 18
    
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Read SA, Collins MJ, Carney LG. A review of astigmatism and its possible genesis. Clin Exp Optom 2007;90:5-19.  Back to cited text no. 19
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

  [Table 1], [Table 2]



 

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