Objective: To determine the average central corneal thickness (CCT) of healthy adults in the ophthalmology clinic of a tertiary care hospital of Pakistan.Methods: This was a cross-sectional study conducted in the ophthalmology clinics of Aga Khan University Hospital, Karachi Pakistan. One hundred normal subjects (200 eyes) were studied. An ultrasound pachymeter was used to measure CCT.Results: The mean (+/- SD) age of the study population was 44.29 +/- 15.18 years with a median of 47 years (range: 16-73). Twenty three percent of the subjects had diabetes mellitus, 29% hypertension and 6% had history of ischaemic heart disease. The mean (SD) CCT measurements were 531.08 +/- 33.37) and 531.29 +/- 33.33 micrometers in the right and left eyes respectively and were not significantly different from each other. There was no statistically significant correlation between CCT and IOP (r = 0.158, p = 0.12). We did not find a significant association between CCT and other independent variables like age, sex, presence of co-morbidity i.e. Diabetes Mellitus (DM), Hypertension (HTN), Ischaemic Heart Disease (IHD), myopia, hypermetropia, systemic and eye medication use.Conclusion: The average CCT values obtained in the hospital-based study closely match those of the African Americans. A population-based study would be needed to provide unbiased CCT estimate in Pakistani population

Ahmad, Khabir

Ali, Azam

Channa, Roomasa

Mir, Fazia

Shah, Mahnaz Naveed

eCommons@AKU

eCommons@AKUSection of Ophthalmology Department of SurgeryApril 2009Central corneal thickness of Pakistani adultsRoomasa ChannaAga Khan UniversityFazia MirAga Khan UniversityMahnaz Naveed ShahAga Khan UniversityAzam AliAga Khan UniversityKhabir AhmadAga Khan UniversityFollow this and additional works at: http://ecommons.aku.edu/pakistan_fhs_mc_surg_ophthalmolPart of the Ophthalmology CommonsRecommended CitationChanna, R., Mir, F., Shah, M., Ali, A., Ahmad, K. (2009). Central corneal thickness of Pakistani adults. Journal of the Pakistan MedicalAssociation, 59(4), 225-8.Available at: http://ecommons.aku.edu/pakistan_fhs_mc_surg_ophthalmol/8IntroductionGlobally, glaucoma is the second most common causeof blindness and the leading cause of irreversible blindness.1 In,Pakistan it accounts for 7.1 % of the total causes of blindness.2Early diagnosis and initiation of treatment are important factorsin minimizing the progression of disease and reducing itsburden. Several studies have shown that intraocular pressure(IOP) alone is not an accurate test for detecting glaucoma.Central corneal thickness (CCT) has been identified as animportant factor to consider when measuring IOP.3-5 CCT hasbeen shown to be associated with an over or underestimationof the IOP if the cornea is thick or thin, respectively.6 It hasbeen shown that Goldmann applanation tonometryover/underestimates IOP by as much as 5mmHg for every 70225 J Pak Med AssocOriginal ArticleCentral corneal thickness of Pakistani adultsRoomasa Channa, Fazia Mir, Mahnaz Naveed Shah, Azam Ali, Khabir AhmadSection of Ophthalmology, Department of Surgery, Aga Khan University, Stadium Road, Karachi, Pakistan.AbstractObjective: To determine the average central corneal thickness (CCT) of healthy adults in the ophthalmologyclinic of a tertiary care hospital of Pakistan.Methods: This was a cross-sectional study conducted in the ophthalmology clinics of Aga Khan UniversityHospital, Karachi Pakistan. One hundred normal subjects (200 eyes) were studied. An ultrasound pachymeterwas used to measure CCT.Results: The mean (±SD) age of the study population was 44.29 ± 15.18 years with a median of 47 years (range:16-73). Twenty three percent of the subjects had diabetes mellitus, 29% hypertension and 6% had history ofischaemic heart disease. The mean (SD) CCT measurements were 531.08 ± 33.37) and 531.29 ± 33.33micrometers in the right and left eyes respectively and were not significantly different from each other. There wasno statistically significant correlation between CCT and IOP (r = 0.158, p = 0.12). We did not find a significantassociation between CCT and other independent variables like age, sex, presence of co-morbidity i.e. DiabetesMellitus (DM), Hypertension (HTN), Ischaemic Heart Disease (IHD), myopia, hypermetropia, systemic and eyemedication use.Conclusions: The average CCT values obtained in the hospital-based study closely match those of the AfricanAmericans. A population-based study would be needed to provide unbiased CCT estimate in Pakistanipopulation (JPMA 59:225; 2009).µm corneal thickness above or below the mean.3 A meta-analysis showed that the IOP-CCT interrelationship wasdifferent for glaucomatous and non-glaucomatous eyes. Theyconcluded that for normal eyes, a 53 µm difference in CCTwould be expected to produce a 1.1mmHg shift in themeasured IOP. For, patients with long standing glaucoma a 53µm difference in CCT would be expected to produce a 2.5mmHg shift in the measured IOP value.6Copt and colleagues had to reclassify 56% of patientspreviously followed up for ocular hypertension as beingnormotensive on the basis of higher than average CCTs. TheIOP of an additional 31% of the individuals was found to beelevated after correcting for CCT.7Several studies have recently reported that CCT variesfrom one population or race to another. In the United States,African Americans who are at a higher risk for developingglaucoma were found to have a significantly lower mean CCTcompared with their Caucasian counterparts (531.0 ± 36.3 µmversus 558.0 ± 34.5 µm).8A study from South Korea gave theaverage CCT as 553um,9while one from Israel gave a value of555 ± 32.10 Despite its importance, CCT evaluation hasreceived little attention in most South East Asian countries,including Pakistan, the sixth most populous country in theworld (population of 160 million). In this report, we describethe mean CCT values and factors associated with them in aselected Pakistani adult population.Subjects and MethodsBetween February 1 2007 and March 31 2007, asample of individuals undergoing executive check-up at theAga Khan University Hospital (AKUH), Karachi was selectedthrough convenience sampling for this study. AKUH is a well-equipped privately owned tertiary care university hospital. Itsexecutive check-up programme includes a series of laboratorytests, a chest X-ray, dental check-up and an electrocardiogram(ECG), followed by physical examination, and counselingregarding risk factors and abnormal test results if any. Informedwritten consent was taken from all participants and they wereexamined at the ophthalmology clinics of the AKUH. Ourexclusion criteria were: any history of ocular surgery, includinglaser surgery; any history of contact lens use reported bypatient; history of intraocular trauma and presence of cornealpathology. The questionnaire was pre-tested on 5 adults beforeusing it for the study. All participants underwent a standard eyeexamination which included measurement of visual acuity, slitlamp examination, measurement of IOP and CCT, indirect anddirect ophthalmoscopy. CCT was measured using an ultrasonic Pachymeter(Topcon) in an upright position. All readings were taken in themorning to eliminate the effect of diurnal variation.11Pachymetry readings were taken by two of the authors (RC andFM), who were trained by an ophthalmologist. Before thestudy, 20 normal eyes were examined by both doctors. Both ofthem took pachymetry readings on the same eyes and werefound to have consistent results. IOP readings were measuredtwice in each eye by an ophthalmologist and the mean wasrecorded. IOP was measured using Goldmann Applanationtonometry. Refractive error was recorded by an ophthalmictechnician using the auto refractor machine.Information about the patient's age, sex, co-morbids i.e.diabetes, hypertension, eye diseases, and any eye medicationsand systemic medications being used currently was recorded.Interviewers first collected this information by asking thepatients and later verified it from their medical record; in caseof discrepancy, the hospital's most recent records regarding thepatient were seen.Five readings of CCT were obtained from each eye. Allvalues were recorded, but the minimum value of cornealthickness for each eye was used for analysis. This value isbelieved to represent the most accurate measurement as it ismost likely to be perpendicular to the central corneal surface.8The data was entered and analyzed using SPSS version15.0 (SPSS Inc., Chicago, IL). Means, standard deviations,median and ranges were calculated for CCT and othercontinuous variables such as IOP and age. The total number of the study population was hundredwith no missing data, and we calculated only frequencies. Ahistogram was plotted to show the distribution of CCTmeasurements. Means were compared using t-test andproportions were compared using chi square test.Linear regression was performed to see if there was arelation between CCT measurements and independentvariables. A correlation plot was computed, which shows therelationship between CCT and IOP.ResultsA total of 120 adults were requested to participate inthe study of whom 20 (16.6%) declined. Of 100 individualswho were included in the study, 64 were men and 36 werewomen. The mean age of the study population was 44.29 ±15.18 years  with a median of 47 years (range: 16-73).Twenty three percent of them had diabetes mellitus, 29%had hypertension and 6% had history of ischaemic heartdisease. Table 1 shows the demographic and clinicalcharacteristics of the sample.CCT and IOP measurements were analyzed for theright eye (n=100) and the left eye (97) separately. The mean(SD) CCT measurements were 531.08 ± 33.37 and 531.29 ±33.33 micrometers in the right and left eye respectively(Table 1). The two means were not significantly different(Table 1, Figure 1).Vol. 59, No. 4, April 2009 226The mean IOP in the right eye was 13.86 (± 2.79) andleft eye 13.67 ± 2.68 mmHg.The median IOP in the right eye was 14.00 mmHg(range 8-22) and in the left eye 14.00 mmHg (range 7-20).For linear regression/correlation analysis, CCTmeasurements for the right (not left) eye were chosen. Figure 2is a scatter plot which shows that there is no statisticallysignificant correlation(r = 0.158, p = 0.12) between CCT andIOP in the study population. There was also no statisticallysignificant linear association between CCT and otherindependent variables like age, sex, presence of a co-morbidityi.e. DM, HTN, IHD, existing eye disease, myopia,hypermetropia, systemic and eye medication in use.DiscussionTo the best of our knowledge, this is the first report onthe average CCT value in a selected Pakistani adultpopulation. A study from another city in Pakistan,12 looked atthe association between IOP and CCT. It did not, however,give the mean CCT value of healthy population. Theknowledge of the average CCT in a particular population isrequired in order to predict the risk of glaucoma in thatpopulation. The Ocular Hypertension Treatment Studyrecognized CCT as a strong predictor for the development ofpredict the onset of primary angle glaucoma (POAG).13 In thisstudy it was seen that individuals with CCTs of 555 µm or lesshad a 3 times greater risk of developing glaucoma comparedwith patients with CCTs of greater than 588 µm.13 Theaverage CCT in our population was 531 ± 33 µm.Extrapolating from that study, would lead us to believe thatour population is also at a high risk for the development ofPOAG. Racial variation influences CCT.8 This implies thatevery population will have a unique CCT reading. Thevaried population bases used by different studies makecomparison difficult. However, average CCT of ourpopulation (531+ 33 µm) closely matches that of theAfrican Americans (531.0 ± 36.3 µm),8 the Japanese (531.7µm),14 the Indians (537 ± 34 µm)15 but is significantlydifferent from that of the Caucasian population (558 + 34.5µm). Population surveys done on Caucasians have been thebasis for the definition of the "normal" range of IOP.16 The227 J Pak Med AssocTable 1: Demographic and clinical characteristicsof the study population.Variable Frequency (n=100)Age (mean ± SD) 44.29 ± 15.18Sex (Male : Female) 64:36Presence of at least one co-morbidity 39Hypertension 29Diabetes mellitus 23Ischemic heart disease (IHD) 6Existing eye disease* 3Myopia 35Hypermetropia 22Eye medication (current) 2Systemic medication use (current) 24Central corneal thickness measurements (µm)right eye(n=100)mean ± SD 531.08±33.37Median 524.50Minimum, Maximum 470, 624Central corneal thickness measurements (µm)left eye(n=100)mean ± SD 531.29± 33.33Median 527Minimum, maximum 467, 620*Other than refractive error, details in textFigure 1: Distribution of ultrasound pachymetry central corneal thickness (righteye) in the study population (n=100).Figure 2: Scatterplot demonstrating the correlation between central cornealthickness (micrometers) and intraocular pressure in the study population. Thecorrelation is not statistically significant (r = 0.158, p = 0.12).implications of this difference in average CCT aresignificant in terms of the correct determination of elevatedIOP in our population. Glaucoma patients in our populationwill need to maintain a lower level of IOP. Several factors including age, gender , diurnalchanges, refractive error, genetic influence and diseases likediabetes have been shown to affect CCT.11,17-19 In our study,we did not find any significant association between diabetes,hypertension, pre-existing ischaemic heart disease, age, sexand average CCT - although our study was not adequatelypowered to assess this question.Patients with ocular hypertension and glaucomahave thicker central cornea than their controls. Our studydid not have glaucoma patients or ocular hypertensives--median IOP in the right and left eyes were 14.00 mmHg(range 8-22) and 14.00 mmHg (range 7-20), respectively.This probably means our CCTs values are slightlyunderestimated. However, changing few data values wouldnot affect the median much because median is not sensitiveto the extreme values (unlike mean).A major limitation of our study was that it was donein a clinic setting. For our study population, we used adultsvisiting the clinic for executive check-up and not having anyknown ocular diseases other than refractive error. However,it is not a population based study and is prone to selectionbias because the subjects we selected represents only thosepeople who can afford to pay for an executive check up atthis hospital, which costs about US$ 200. The next stepcould be to do a population based study to estimate themean CCT values, taking into account the socioeconomicfactors, ethnic distribution and several other characteristicsof the general population.In conclusion, our hospital-based study reports theaverage CCT of our population as 531 ± 33 µm. We did notfind any significant association between CCT and othervariables. The average CCT values of this selected studypopulation closely match those of the African Americans andmay be suggestive of a higher risk of development of primaryopen-angle glaucoma in Pakistani population also. Our studycalls for further research aimed to provide unbiased CCTestimate in Pakistani population. References1. Resnikoff S, Pascolini D, Etya ale D, Kocur I, Parajasegaram R, Pokharel GP, etal. Global data on visual impairment in the year 2002. Bull World Health Organ2004; 82: 844-51.2. Dineen B, Bourne RR, Jadoon Z, Shah SP, Khan MA, Foster A, et al. Causes ofblindness and visual impairment in Pakistan. The Pakistan national blindness andvisual impairment survey. Br J Ophthalmol 2007; 91: 1005-10.3. Ehlers N, Bramsen T, Sperling S. Applanation tonometry and central cornealthickness. Acta Ophthalmol (Copenh) 1975; 53: 34-43.4. Whitacre MM, Stein RA, Hassanein K. The effect of corneal thickness onapplanation tonometry. Am J Ophthalmol 1993; 115: 592-6.5. Hansen FK, Ehlers N. Elevated tonometer readings caused by a thick cornea.Acta Ophthalmol (Copenh) 1971; 49: 775-8.6. Doughty MJ, Zaman ML. Human corneal thickness and its impact on intraocularpressure measures: a review and meta-analysis approach. Surv Ophthalmol 2000;44: 367-408.7. Copt RP, Thomas R, Mermoud A. Corneal thickness in ocular hypertension,primary open-angle glaucoma, and normal tension glaucoma. Arch Ophthalmol1999; 117: 14-6.8. La Rosa FA, Gross RL, Orengo-Nania S. Central corneal thickness of caucasiansand African Americans in glaucomatous and nonglaucomatous populations. ArchOphthalmol 2001; 119: 23-7.9. Lee ES, Kim CY, Ha SJ, Seong GJ, Hong XJ. Central corneal thickness ofKorean patients with glaucoma. Ophthalmology 2007; 114: 927-30.10. Morad Y, Shavon E, Hefetz L, Nemet P. Corneal thickness and curvature innormal-tension glaucoma. Am J Ophthalmol 1998; 125: 164-8.11. Kiely PM, Carney LG, Smith G. Diurnal variations of corneal topography andthickness. Am J Optom Physiol Opt 1982; 59: 976-82.12. Mukhtar S. Central corneal thickness and its relation with measured Intra OcularPressure-A Retrospective study of 668 eyes of normal adults in a private practice.Pak J Ophthalmol 2004; 20: 23-5.13. Gordon MO, Beiser JA, Brandt JD, Hever DK, Higginbotham EJ, et al. Theocular hypertension treatment study: Baseline factors that predict the onset ofprimary open-angle glaucoma 2002; 126: 714-20.14. Aghaian E, Choe JE, Lin S, Stamper RL, et al. Central corneal thickness ofCaucasians, Chinese, Hispanics, Filipinos, African Americans, and Japanese in aglaucoma clinic. Ophthalmology 2004; 111: 2211-9.15. Thomas R, Korah S, Muliyil J. The role of central corneal thickness in thediagnosis of glaucoma. Indian J Ophthalmol 2000; 48: 107-11.16. Colton T, Ederer F. The distribution of intraocular pressures in the generalpopulation. Surv Ophthalmol 1980; 25: 123-9.17. Alsbirk PH. Corneal thickness. II. Environmental and genetic factors. ActaOphthalmol (Copenh) 1978; 56: 105-13.18. Harper CL, Boultan ME, Bennett D, Marcyniuk B, Jarris-Evans JH, Tullo AB,et al. Diurnal variations in human corneal thickness. Br J Ophthalmol 1996;80: 1068-72.19. Pedersen L, Hjortdal J, Ehlers N. Central corneal thickness in high myopia. ActaOphthalmol Scand 2005; 83: 539-42.Vol. 59, No. 4, April 2009 228

Central corneal thickness of Pakistani adults

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