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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 15  |  Issue : 2  |  Page : 227-231

A study of corneal topography in myopic patients attending eye outpatient department between 10 and 50 years to examine corneal asphericity and spherical equivalent refraction


Department of Ophthalmology, Jawaharlal Nehru Medical College, Datta Meghe Institute of Medical Sciences (Deemed to be University), Sawangi (Meghe), Wardha, Maharashtra, India

Date of Submission14-Apr-2020
Date of Decision20-Apr-2020
Date of Acceptance30-Apr-2020
Date of Web Publication21-Dec-2020

Correspondence Address:
Dr. Pravin K Tidake
Tidake Eye Clinic, St Colony, Rukmani Nagar, Wardha, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jdmimsu.jdmimsu_115_20

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  Abstract 


Context: Evaluation of corneal curvature by corneal topography in myopic patients. Aims: To evaluate corneal topographical changes in corneal curvature in patients having myopia. Settings and Design: This is a prospective observational study conducted in a period of 6 months. A hundred eyes of fifty patients coming to the eye outpatient department (OPD) with complaint of diminution of distant vision having myopia were examined after they gave their informed consent and taking into consideration the inclusion and exclusion criteria. Subjects and Methods: A hundred eyes of fifty patients coming to the eye OPD with complaint of diminution of distant vision having myopia were examined. Patients were divided into low myopes, moderate myopes and high myopes, and corneal topography was performed in those patients and refractive error was observed. Corneal asphericity, astigmatism, and ratio of axial length (AL) and corneal radius of curvature (CRC) were observed. A correlation between refractive error and astigmatism, correlation between corneal asphericity and astigmatism, and correlation between corneal asphericity and ratio of AL with CRC were studied. Statistical Analysis Used: Statistical analysis was done using descriptive and inferential statistics using Chi-square test, one-way analysis of variance, and Pearson's correlation coefficient, and software used in the analysis were SPSS 24.0 version and GraphPad Prism 7.0 version. P < 0.05 is considered as level of significance. Results: A negative significant correlation was seen between corneal asphericity and astigmatism, corneal asphericity, and ratio of AL and CRC. A significant correlation was observed between refractive error of patients and astigmatism associated with it. Conclusions: Patients having high refractive error (high myopes) found to have higher astigmatism and corneal asphericity in high myopes. With increasing myopia, the tendency of the cornea to flatten less rapidly in the periphery was observed. In high myopes, corneal asphericity was observed to be more positive than low myopes.

Keywords: Astigmatism, corneal asphericity, ratio of axial length and corneal radius of curvature, refractive error


How to cite this article:
Tidake PK, Bajpayee N. A study of corneal topography in myopic patients attending eye outpatient department between 10 and 50 years to examine corneal asphericity and spherical equivalent refraction. J Datta Meghe Inst Med Sci Univ 2020;15:227-31

How to cite this URL:
Tidake PK, Bajpayee N. A study of corneal topography in myopic patients attending eye outpatient department between 10 and 50 years to examine corneal asphericity and spherical equivalent refraction. J Datta Meghe Inst Med Sci Univ [serial online] 2020 [cited 2021 Jan 19];15:227-31. Available from: http://www.journaldmims.com/text.asp?2020/15/2/227/304235




  Introduction Top


In Asian countries and countries undergoing rapid development, myopia is a common and most unavoidable pathological change in the eye. Changes in the eye in myopia include elongated axial length (AL), thinner retina with lattice change and high prevalence of retinal detachment, decreased choroid circulation as well as decreased sclera thickness and elasticity.[1]

Different clinical types of myopia are as follows: congenital myopia, simple or developmental myopia, pathological or degenerative myopia, and acquired myopia.

In myopic patients, there are flatter corneal curvature, decreased corneal thickness as well as endothelial density.[2] There is a high prevalence of retinal detachment, decreased choroid circulation as well as decreased scleral thickness and elasticity as the retina becomes thinner with lattice change.

Corneal topography

Corneal topography is also called as photokeratoscopy and videokeratoscopy and it examines corneal surface and outer structures of eye. It is a non invasive modality.[3] Corneal topography is of clinical importance in determining the quality of vision since the cornea is responsible for 70% of eyes' refractive power. Thus, the purpose of computerized corneal topography is there nowadays.

With refractive error, central corneal curvature tends to vary, but the relation between corneal topography and ametropia is less clear.[3] This study is conducted to determine whether a relation exists between corneal asphericity and myopia. Associations between corneal asphericity and each of the components of refraction are examined.[4],[5] These findings have implications for refractive surgery outcomes and schematic eye modeling.


  Subjects and Methods Top


Study design

This is a hospital-based prospective observational study.

Study location

This is a tertiary care teaching hospital-based study done in the Department of Ophthalmology, AVBRH, Sawangi, Wardha, Maharashtra.

Ethical Approval

Ethical approval for this study (DMIMS(DU)/IEC/2018-19/884) was provided by the Ethical Committee of Datta Meghe Institute of Medical Sciences (Deemed to be University) on 15/8/2018.


  Result Top


Study duration

The study was done over a period of 1 year from September 2018 to September 2019.

Sample size

A hundred eyes of fifty patients coming to the eye outpatient department (OPD) with complaint of diminution of distant vision having myopia were examined.

Subjects and selection methods

Patients were divided into low myopes, moderate myopes, and high myopes, and corneal topography was performed in those patients and refractive error was observed [Graph 2]a, [Graph 2]b, [Graph 2]c. Corneal asphericity, astigmatism, and ratio of AL and corneal radius of curvature (CRC) were observed. A correlation between refractive error and astigmatism, correlation between corneal asphericity and astigmatism, and correlation between corneal asphericity and ratio of AL with CRC were studied.



Procedure for test

The study adhered to the tenets of the Declaration of Helsinki, and it was approved by an Institutional Ethical Committee of DMIMSU.

Informed consent was obtained from all patients after nature, and the possible consequences of the study were explained to them.

A comprehensive ophthalmic examination, including best-corrected visual acuity, refractive error, slit-lamp examination, intraocular pressure measurement by noncontact tonometer, and fundus examination, was performed on all participants for posterior segment evaluation.

A Snellen chart was used to assess the visual acuity in all participants.

Corneal astigmatism (AST) in the 3.00 mm central zone was evaluated for each patient using a corneal topographer (CA-800 TOPCON). Corneal asphericity and CRC were measured of each patient. AL was measured by keratometer.

Correlation of all data was done.

Inclusion criteria

  • Patients aged between 10 and 50 years
  • Patients were selected having myopia coming to the eye OPD having diminution of distant vision
  • Patients were selected irrespective of sex and age.


Exclusion criteria

  • Patient <10 years and more than 50 years
  • Patients having cataract
  • Patients having uveitis
  • Patients having subluxated lens
  • Patients having posterior segment pathology
  • Patients who are aphakic
  • Patients having corneal pathology
  • Patients having connective tissue disorders
  • Patients who are pseudophakic.


Statistical analysis used

Statistical analysis was done using descriptive and inferential statistics using Chi-square test, one-way analysis of variance, and Pearson's correlation coefficient, and software used in the analysis were SPSS 24.0 version (Chicago, Illinois, USA) and GraphPad Prism 7.0 version (San Diego, CA). P < 0.05 is considered as level of significance.


  Discussion Top


Its as prevalence of myopia is increasing, myopia is a leading cause of loss of vision throughout the world.

As central corneal curvature varies with refractive error thus inter-correlation between main ocular components and their relation with refractive error is examined as in many studies corneal asphericity was found to vary with refractive error and other components of refraction.[14]

The mean value of corneal asphericity determined in the study was slightly more negative than that found in previous studies of corneal topography.

It was found that in the majority of the cases, the cornea flattens in the periphery.[6],[7],[8],[9],[10],[11],[12] These results are consistent with the results of Kiely et al. and Eghbali et al.[14] In our study, a significant correlation between astigmatism and corneal asphericity was found but was negative (r = −0.267), myopia increases corneal curvature flatten in periphery.

Kiely et al. showed that corneal asphericity assumes a much greater contribution to spherical aberration of the human cornea than central corneal curvature alone using calculations of seidel spherical aberration for objects at infinity.[14]

Spherical aberration of the cornea becomes more positive with increasing myopia, which is consistent with observations of Applegate et al.

In the present study, a similar relation was observed overall, although a negative significant correlation was observed between corneal asphericity and astigmatism and corneal asphericity and ratio of AL and CRC.

Changes in AL and CRC are important biometric factors affecting refractive errors. AL has a larger effect on inducing refractive errors as compared to CRC.[13]

Grosvenor et al, ratio of axial length (AL) and CRC(central radius of curvature) is more reliable index than axial length and central radius of curvature.[13] Other studies have shown that AL/CRC was the most important biometric factor in myopia.

Findings in this present study confirm with Grosvenor's hypothesis, we found a linear increase in AL/CRC toward high myopia.


  Conclusion Top


Out of 50 patients evaluated, 29 patients were males and 21 patients were females indicating a higher male preponderance [Graph 1]. The majority of the patients in the study belonged to the age group between 25 and 66 years. The mean age of patients was 53.42 ± 10.91 [Table 1].
Table 1: Age distribution in male and female patients

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According to refractive error, participants were divided into three groups, i.e., low myopes, moderate myopes, and high myopes [Graph 2]a.

In this study, low myopes were found to be 11%, moderate myopes 16%, and high myopes 73% [Table 2].
Table 2: Age and sex distribution for the three refractive error groups

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The correlation between refractive error and astigmatism was studied in all the three refractive error groups [Graph 3], [Graph 4], [Graph 5]. It was observed that a group of high myopes have higher astigmatism as compared to other refractive error groups.



It was found to be significant with P < 0.05.

A correlation between corneal asphericity and astigmatism was observed in all three refractive error groups.

Values are found to be significant according to Pearson's correlation coefficient with P < 0.05 [Table 3].
Table 3: Correlation between astigmatism for the three refractive error groups

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It was observed that there was a negative correlation between astigmatism and corneal asphericity [Table 4].
Table 4: Correlation between astigmatism and corneal asphericity Pearson's correlation coefficient

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A correlation between corneal asphericity and ratio of AL with CRC was also observed.

Values are found to be significant according to Pearson's correlation coefficient with P < 0.05.

It was observed that there was a negative correlation between ratio of AL and CRC (AL/CRC) and corneal asphericity [Table 5].
Table 5: Correlation between corneal asphericity and AL/CRC Pearson's correlation coefficient

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Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Kiely PM, Smith G, Carney LG. The mean shape of the human cornea. Optica Ada 1982;29:1027-40.  Back to cited text no. 1
    
2.
Mandell RB. Everett Kinsey lecture. The enigma of the corneal contour. CLAO J 1992;18:267-73.  Back to cited text no. 2
    
3.
Bonnet R, Cochet P. New method of topographical ophthalmometry—its theoretical and clinical applications (Translation by E. Eagle). Am J Optom Arch Am Acad Optom 1962;39:227-51.  Back to cited text no. 3
    
4.
Le Grand Y. Studies on the human cornea: Application to the aphakic eye. In: Transactions of the International Ophthalmic and Optometric Congress, 1961. British Optical Association. London: Crosby Lockwood; 1961. p. 67-86.  Back to cited text no. 4
    
5.
Lotmar W. Theoretical eye model with aspherics. J Opt Soc Am 1971;61:1522-29.  Back to cited text no. 5
    
6.
Eghbali F, Yeung KK, Maloney RK. Topographic determination of corneal asphericity and its lack of effect on the relative outcome of radial keratotomy. Am J Ophthalmol 1995;119:275-80.  Back to cited text no. 6
    
7.
Sheridan M, Douthwaite WA. Corneal asphericity and refractive error. Ophthalmic Physiol Opt 1989;9:235-8.  Back to cited text no. 7
    
8.
Zadnik K, Mutti DO, Bullimore MA. Use of statistics for comparing two measurement methods. Optom Vis Sci 1994;71:539-41.  Back to cited text no. 8
    
9.
Millodot M, Sivak J. Contribution of the cornea and lens to the spherical aberration of the eye. Vision Res 1979;19:685-7.  Back to cited text no. 9
    
10.
Applegate RA, Howland HC, Buettner J, Cottinghan AJ, Sharp RP, Yee RW. Corneal aberrations before and after radial keratotomy (RK) calculated from videokeratometric measurements. In: Vision Science and its Applications, 1994 Technical Digest Series. Vol. 2. Washington, DC: Optical Society of America; 1994. p. 58-61.  Back to cited text no. 10
    
11.
Howland HC, Buettner J, Applegate RA. Computation of the shapes of normal corneas and their monochromatic aberrations from videokeratome trie measurements. In: Vision Science and its Applications, 1994 TechnicalDigest Series. Vol. 2. Washington, DC: Optical Society of America; 1994. p. 54-7.  Back to cited text no. 11
    
12.
Lam CS, Goh WS. The incidence of refractive errors among school children in Hong Kong and its relationship with the optical components. Clin Exp Optom 1991;74:97-103. 26. Fledelius HC. Corneal curvature radius. Oculometric considerations with reference to ag.  Back to cited text no. 12
    
13.
Hashemi H, Khabazkhoob M, Miraftab M, Emamian MH, Shariati M, Abdolahi-Nia T, et al. Axial length to corneal radius of curvature ratio and refractive errors. J Ophthalmic Vis Res 2013;8:220-6.  Back to cited text no. 13
  [Full text]  
14.
Carney LG, Mainstone JC, Henderson BA. Corneal topography and myopia. A cross-sectional study. Invest Ophthalmol Vis Sci 1997;38:311-20.  Back to cited text no. 14
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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