Pak J Ophthalmol. 2022, Vol. 38 (3): 199-204 199 Original Article Correlation and Comparison of Anterior and Posterior Corneal Surface Parameters in Healthy Eyes Muhammad Suhail Sarwar 1 , Muhammad Arslan Ashraf 2 , Faisal Mehmood 3 , Muhammad Arbab Azeem 4 , Sobia Yousaf 5 Department of Ophthalmology, 1,2,4,5 Mayo Hospital, Lahore, 3 Rashid Latif Medical College, Lahore ABSTRACT Purpose: To correlate and compare anterior and posterior corneal surface parameters like Kflat, Ksteep, Kavg, R1, R2, Ravg and astigmatism in healthy eyes. Study Design: Descriptive correlational study. Place and Duration of Study: This study was conducted At Mayo Hospital, Lahore from June 2020 to Dec. 2020. Methods: This study included 176 subjects (86 males and 90 females) with mean age of 28.06 ± 9.68 and 28.13 ± 8.24 respectively. The data was collected through non-random convenient sampling technique by self-made proforma after taking patients’ consent. Anterior and posterior corneal parameters (Kflat, Ksteep, Kavg, R1, R2, Ravg and astigmatism) were measured with GALILEI G4. Pearson correlation test was used for correlation and independent sample t-test/Mann-Whitney U test was used for comparing means of anterior and posterior corneal parameters. Data was entered and analyzed in SPSS-21. Results: Mean of anterior and posterior corneal curvatures was 44.21 ± 1.01 D and -6.22 ± 0.19 D [p < 0.001], Kflat was 43.76 ± 0.99 D and -6.08 ± 0.19 D [p < 0.001] and Ksteep was 44.66 ± 1.08 D, -6.34 ± 0.21 D, respectively [p < 0.001]. The anterior and posterior corneal curvature Ravg was 7.63 ± 0.17 mm, 6.44 ± 0.200 mm [p < 0.001], mean R1 was 7.71 ± 0.17 mm, 6.58 ± 0.21 mm, [p < 0.001] and mean R2 was 7.56 ± 0.18 mm, 6.31 ± 0.21 mm, respectively [p < 0.001]. Anterior posterior corneal astigmatism was 0.90 ± 0.55 D and -0.25 ± 0.11 D, respectively [p < 0.001]. Anterior corneal parameters also show strong correlation with posterior corneal parameters. Conclusion: There is significant difference between corneal parameters of anterior and posterior surface. Strong correlation was also found in anterior and posterior corneal parameters except corneal astigmatism. Key Words: Cornea, Corneal curvature, Corneal astigmatism, Corneal topography. How to Cite this Article: Sarwar MS, Ashraf MA, Mehmood F, Azeem MA, Yousaf S. Correlation and Comparison of Anterior and Posterior Corneal Surface Parameters in Healthy Eyes. Pak J Ophthalmol. 2022, 38 (3): 199-204. Doi: 10.36351/pjo.v38i3.1380 Correspondence: Muhammad Arslan Ashraf Department of Ophthalmology, Mayo Hospital, Lahore Email: rajkumararslan@yahoo.com Received: March 10, 2022 Accepted: June 9, 2022 INTRODUCTION Cornea which is an avascular tissue acts as a structural barrier and protects the eye from outer insults. 1 Anterior refractive surface of the eye is also provided by pre-corneal tear film. The contribution of cornea in refractive power is about two third. 2 It is the most sensitive and highly innervated tissue in the body. 3,4 It measures 9 to 11 mm vertically and 11 to 12 mm horizontally. In males and females, the corneal average Muhammad Arslan Ashraf, et al 200 Pak J Ophthalmol. 2022, Vol. 38 (3): 199-204 diameter is 11.77 ± 0.37mm and 11.64 ± 0.47mm, respectively. 5,6 Cornea has different power in various meridians which results in astigmatism. Importance of corneal refractive power is that it is used in calculation of power of intraocular lens and in refractive surgeries. 7 Non-contact devices like Pentacam and Galilei G4 make three dimension images of corneal anterior section, mark corneal topography and pachymetry. Pentacam utilizes a rotating Scheimpflug camera to make topographical images of anterior segment, a twofold Scheimpflug camera and a Placido topographical framework. Likewise, there are different instruments used for corneal curvature measurements; Orbscan, Javal-Schiotz keratometer, Verion Optical Imaging System etc. 8-10 These parameters and their correlation are important in accurate measurement of different intraocular lens implants. 11,12 Finding out concordance among different topographic and tomographic instruments is important in clinical practice. 13,14 Current study deals with measuring corneal parameters of both anterior and posterior corneal surface. This study finds the correlation and comparison of corneal parameters of both sides of cornea, which will be helpful in understanding the effect of change of anterior or posterior corneal parameters on each other. METHODS This cross-sectional study was conducted at outdoor of eye department of Mayo Hospital and College of Ophthalmology and Allied Vision Sciences. Non probability convenient sampling method was used. The study period was from June 2020 to December 2020 during which 176 eyes of 88 normal individuals were studied. There were 44 males and 44 females. Data was collected through self-made proforma after taking patients’ consent. Following parameters were studied; Kflat, Ksteep, Kavg, R1, R2, Ravg and astigmatism. Galilei G4 was used for all these readings. Healthy individuals between 11 to 60 years of age, myopic, hyperopic or emmetrope males and females were recruited for study. For coorelation between anterior and posterior corneal parameters Pearson’s correlation test was applied. Pearson value greater than 0.7 was considered as excellent correlation. Quantitative variables like Age, Kflat, Ksteep, Kavg, R1, R2, Ravg and astigmatism were presented with mean and standard deviation. Independent sample t-test / Mann-Whitney U test were applied for comparing means of corneal parameters. P- value less than 0.05 was considered significant. Data was entered and analyzed by using SPSS-21. Graphs were also made by using SPSS-21 software. For tabulation, Microsoft Excel-16 was used. The research protocol was approved by the Ethical Review Board of College of Ophthalmology and Allied Vision Sciences. RESULTS Anterior mean K showed strong negative correlation with posterior mean K and posterior mean R (-0.78). Anterior flat K showed strong negative correlation with posterior flat K (-0.75). Anterior steep K showed strong negative correlation with posterior steep K (-0.75). Anterior mean R showed strong positive correlation with posterior mean R (0.78). Anterior R1 showed strong positive correlation with posterior R1 (0.76). Anterior R2 showed strong and positive correlation with posterior R2 (0.76). Anterior astigmatism showed poor but negative correlation with posterior astigmatism (-0.33) (Table 2). Anterior and posterior corneal curvature mean K was 44.21 ± 1.01 D and -6.22 ± 0.19 D, respectively with p < 0.001. Anterior and posterior corneal curvature Kflat was 43.76 ± 0.99 D and -6.08±0.18 D, respectively with a difference of 49.84 D was noted (p < 0.001). Anterior and posterior corneal curvature mean Ravg was 7.64 ± 0.17 mm and 6.44 ± 0.200 mm, respectively with a difference of 1.19 mm was noted (p < 0.001). The mean R1 of anterior and posterior corneal curvature was 7.72 ± 0.17 mm and 6.58 ± 0.202 mm, respectively with a difference of 1.13 mm was noted (p < 0.001). Likewise, anterior and posterior corneal curvature mean R2 was 7.56 ± 0.18 mm and 6.31 ± 0.211 mm, respectively. The difference of 1.24 mm was noted (p < 0.001). The steep k of anterior and posterior corneal curvature was 44.67 ± 1.09 D and -6.34 ± 0.21 D, respectively and a difference of 51.01 D was noted (p < 0.001). The astigmatism of anterior and posterior corneal curvature was 0.91 ± 0.55 D and -0.26 ± 0.11 D, respectively and a difference of 1.17 D was noted (p < 0.001) (Table 3). Correlation and Comparison of Anterior and Posterior Corneal Surface Parameters in Healthy Eyes Pak J Ophthalmol. 2022, Vol. 38 (3): 199-204 201 Table1: Age Gender Distribution. Descriptive Statistics Gender N Minimum Maximum Mean Std. Deviation Age Male 172 11 54 28.06 9.653 Female 180 11 50 28.13 8.215 Table 2: Table of Correlation. Correlations Post_K Post_Flt Pst_Stp Post_R Post_R1 Post_R2 Post_Ast Sim_K -.778 ** -.773 ** -.757 ** -.784 ** -.775 ** -.755 ** -0.126 Ant_Flat -.741 ** -.754 ** -.702 ** -.747 ** -.757 ** -.700 ** -0.036 Ant_Stp -.756 ** -.736 ** -.754 ** -.761 ** -.737 ** -.753 ** -.199 ** Ant_R .778 ** .774 ** .757 ** .784 ** .776 ** .756 ** 0.123 Ant_R1 .743 ** .756 ** .702 ** .749 ** .758 ** .701 ** 0.034 Ant_R2 .758 ** .738 ** .756 ** .764 ** .739 ** .756 ** .198 ** Ant_Ast -.148 * -0.085 -.218 ** -0.148 -0.082 -.219 ** -.328 ** **. Correlation is significant at the 0.01 level (2-tailed). *. Correlation is significant at the 0.05 level (2-tailed). Table 3: Table of Comparison. Category Mean Std. Deviation Std. Error Mean Mean Diff. P value Mean K (D) Anterior 44.21 1.01 0.08 50.43 < 0.001 Posterior -6.22 0.19 0.01 Flat K (D) Anterior 43.76 0.99 0.08 49.84 < 0.001 Posterior -6.08 0.18 0.01 Mean R (mm) Anterior 7.64 0.17 0.01 1.19 < 0.001 Posterior 6.45 0.21 0.02 R1 (mm) Anterior 7.72 0.17 0.01 1.13 < 0.001 Posterior 6.58 0.20 0.02 R2 (mm) Anterior 7.56 0.18 0.01 1.24 < 0.001 Posterior 6.31 0.21 0.02 Steep K (D) Anterior 44.67 1.09 0.08 51.01 < 0.001 Posterior -6.34 0.21 0.02 Astigmatism (D) Anterior 0.91 0.55 0.04 1.17 < 0.001 Posterior -0.26 0.11 0.01 Figure 1: Scatter chart of anterior and posterior mean R (R 2 : 0.615). Figure 2: Scatter chart of anterior and posterior mean Ksteep (R 2 : 0.569) Muhammad Arslan Ashraf, et al 202 Pak J Ophthalmol. 2022, Vol. 38 (3): 199-204 Figure 3: Scatter chart of anterior and posterior mean Kflat (R2: 0.569). Figure 4: Scatter chart of anterior and posterior mean K (R 2 : 0.605). Figure 5: Scatter chart of anterior and posterior mean R2 (R 2 : 0.572). Figure 6: Scatter chart of anterior and posterior mean R1 (R 2 : 0.575). Figure 7: Scatter chart of anterior and posterior mean Astigmatism (R 2 : 0.108). DISCUSSION With the advancement in medical sciences, proper preoperative evaluation of refractive surgeries has improved the surgical outcomes. Imaging techniques in the field of ophthalmology played a key role for such purposes. Corneal imaging techniques provide more precise information. Raul Montalban et al. conducted a study to correlate anterior and posterior corneal radius of curvature which showed correlation coefficient value of 0.86. 15 Raúl Montalbán et al. also found significant difference between anterior and posterior corneal surface in healthy subjects whereas, non-significant difference was found in patients with Correlation and Comparison of Anterior and Posterior Corneal Surface Parameters in Healthy Eyes Pak J Ophthalmol. 2022, Vol. 38 (3): 199-204 203 Keratoconus. 16 Faik Orucoglu et al. also found similar results. 17 In another study, comparison of anterior and posterior corneal parameters were analyzed in five hundred and fifteen healthy subjects. The study found an average flat K of anterior and posterior corneal surface as 43.03 ± 1.57 D and -6.13 ± 0.26 D respectively, whereas Ksteep was 44.17 ± 1.58 D and -6.41 ± 0.28 D respectively. 18 Gender and age related changes of cornea were studied by another group of authors, which showed similar results. 19 The Gullstrand eye model measured anterior radius of corneas as 7.8mm while 6.5 mm of posterior surface. By using the method of Purkinje image, the Ravg was 6.42 mm. Eom Eom Y et al measured the astigmatism of anterior surface as 2.21 D and posterior corneal surface as 0.43 D. 20 Yuta Ueno et al. found a shift of against the rule astigmatism from with the rule with age. 21 This study also showed similar results. Limitations of this study are that we did not compare the results of different age groups. Similarly comparison among different refractive errors was not made. We included normal eyes in our study. Further research can be done by comparing with the eyes with corneal ectasia. CONCLUSION Significant difference was found in anterior and posterior corneal parameters like Kflat, Ksteep, Kavg, R1, R2, Ravg and astigmatism in healthy cornea. A strong negative correlation was found between Kflat, Ksteep, and Kavg of anterior and posterior corneal surface. Whereas, a strong positive correlation was found in R1, R2, Ravg of anterior and posterior corneal surface. Astigmatism showed poor but negative correlation. Conflict of Interest: Authors declared no conflict of interest. Ethical Approval The study was approved by the Institutional review board/Ethical review board (COAVS/1061/22). REFERENCES 1. Del Monte DW, Kim T. Anatomy and physiology of the cornea. J Cataract Refract Surg. 2011; 37 (3): 588- 598.Doi:10.1016/j.jcrs.2010.12.037. 2. Shaheen BS, Bakir M, Jain S. Corneal nerves in health and disease. Surv Ophthalmol. 2014; 59 (3): 263-285. 10.1016/j.survophthal.2013.09.002. 3. 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Muhammad Arslan Ashraf; Diagnostic Oculist: Literature search, Data acquisition, Data analysis, Statistical analysis, Manuscript preparation, Manuscript editing, Manuscript review. Faisal Mehmood; Consultant Ophthalmologist: Literature search, Manuscript preparation, Manuscript editing, Manuscript review. Muhammad Arbab Azeem; Diagnostic Oculist: Literature search, Data acquisition, Manuscript preparation. Sobia Yousaf; House Officer: Manuscript editing, Manuscript review. .…  …. https://doi.org/10.1016/j.ajo.2009.04.028 https://doi.org/10.1007/s00417-013-2261-3 https://doi.org/10.1155/2015/925414 https://doi.org/10.1016/j.clae.2015.03.009 https://doi.org/10.1097/ico.0000000000000238 https://doi.org/10.1016/j.ajo.2015.07.011 https://doi.org/10.3928/1081597x-20140218-01