|Ahead of print publication
The study of relationship between ocular biometry and exophthalmometry in adult Malay population of Kelantan, Malaysia
Ui Lyn Loh1, Fazilawati A Qamarruddin2, Adil Hussein3
1 Department of Ophthalmology, School of Medical Sciences; Department of Ophthalmology, Hospital Universiti Sains Malaysia, Kubang Kerian, Kelantan; Department of Ophthalmology, Hospital Sultanah Nora Ismail, Batu Pahat, Johor, Malaysia
2 Department of Ophthalmology, Hospital Tengku Ampuan Rahimah, Klang, Selangor, Malaysia
3 Department of Ophthalmology, School of Medical Sciences; Department of Ophthalmology, Hospital Universiti Sains Malaysia, Kubang Kerian, Kelantan, Malaysia
|Date of Submission||03-Sep-2020|
|Date of Acceptance||15-Dec-2020|
|Date of Web Publication||29-Mar-2021|
Department of Ophthalmology, School of Medical Sciences, Universiti Sains Malaysia, 16150 Kubang Kerian, Kelantan
Source of Support: None, Conflict of Interest: None
PURPOSE: Exophthalmometry value has great clinical significance in the presence of many orbital diseases which can cause proptosis, including thyroid-associated orbitopathy, tumors, inflammation, head and orbital trauma, and craniofacial abnormalities. Measurements of exophthalmometry and ocular biometry vary between races and countries. This study aimed to present the normative values of exophthalmometry in adult Malays of Kelantan and the relationship between ocular biometry (axial length, corneal curvature, anterior chamber depth, and white-to-white) with the obtained exophthalmometry values.
MATERIALS AND METHODS: This was a hospital-based, cross-sectional study in the Ophthalmology Clinic of Universiti Sains Malaysia, Kubang Kerian, Kelantan, where 267 individuals above 20 years old participated between August 2018 and May 2020. Participants were examined with Hertel exophthalmometer and intraocular lens Master by the same investigator. Data were analyzed using the Statistical Package of the Social Science software (version 24.0). Multiple linear regression was used to assess any significant correlation between exophthalmometric value and each biometric variable.
RESULTS: In the data collected, the mean exophthalmometric value for the right eye was 13.93 ± 2.221 mm and the left eye was 13.93 ± 2.232 mm. Overall, male had a higher exophthalmometric value than the female with a statistically significant P = 0.001. Axial length was uniquely significant for the amount of variance in the exophthalmometric value with P < 0.001, while corneal curvature, anterior chamber depth, and white-to-white showed no statistical significance.
CONCLUSION: Our study had established the normal exophthalmometric value for Malay adults in Kelantan for future clinical reference. The axial length had shown to have a significant positive correlation with exophthalmometric values.
Keywords: Adult, exophthalmos, Malay, ophthalmology, orbital diseases
|How to cite this URL:|
Loh UL, Qamarruddin FA, Hussein A. The study of relationship between ocular biometry and exophthalmometry in adult Malay population of Kelantan, Malaysia. Taiwan J Ophthalmol [Epub ahead of print] [cited 2021 Nov 29]. Available from: https://www.e-tjo.org/preprintarticle.asp?id=312510
| Introduction|| |
Exophthalmometry is the measurement of the anterior position of the eye globe in relation to the orbital rim. Methods consist of clinical exophthalmometry, digital photography, and radiological exophthalmometry (via computed tomography measurement). The assessment of normal globe protrusion has great clinical significance in the presence of many orbital diseases which can cause proptosis, including thyroid-associated orbitopathy, inflammation, tumors, trauma of the head and orbital, and craniofacial abnormalities.,,, It is vital as a parameter to assist diagnosis, management, and further monitoring of progression. The measurement of exophthalmometry should be readily available, easy to use with reproducible results. Computed tomography measurement has great accuracy and correlates well with Hertel exophthalmometry. However, this method's high cost, exposure to radiation, and not easily available pose its limitations for routine exophthalmometry., Photography measurement, although simple and noninvasive, has been found to have a weak correlation which compromises reproducibility. Thus, the Hertel exophthalmometer is still one of the most widely used methods as clinical exophthalmometry is still the easiest, most convenient, and affordable method.,, It allows measurements of the distance between the two lateral orbital rims (i.e., interorbital distance) and the vertical distance of corneal apex to the frontal plane.,,
Literature reviews have shown that normal exophthalmometric values vary according to ethnicity, locality, gender, and age. According to Beden et al., the Turkish adult population with a sample size of 2477 showed a median exopthalmometric value of 13 mm and an upper limit of 17 mm in both eyes in 95% of the sample population. The obtained mean exophthalmometric value was documented as a significant decrease after the third decade. Nath et al. noted in their sample size of 629 among the Indian race that the mean exophthalmometic value of the right eye for male was 15.2 mm and left eye was 14.8 mm, while the female was 14.4 mm for the right eye and left eye was 14.0 mm. The upper limit in adults for the population group study was 22.0 mm. Kumari et al. also conducted a study on the Indian race in a different locality and noted a slightly lower upper limit. An adult male was 19.0 mm and a female was 21.0 mm.
Predictors which have been shown to have a positive correlation to exophthalmometric value in literature review include axial length, age, gender, body mass index, weight, height, interpupillary distance, and refraction.,,,,,,,, Various mean ocular biometry values including axial length, anterior chamber depth, and corneal curvature radius were reported by Chen et al. in population-based studies [Table 1]. Currently, there are no normative exophthalmometric data on the Malay population of Malaysia. Ocular biometric reading varies between races.,,,,,,,, There are no conclusive data on the effects of ocular biometry on exophthalmometry value of the Malay population in Malaysia., This study aims to provide normative exophthalmometric data and determine its relationship with ocular biometry (axial length, corneal curvature, anterior chamber depth, and white-to-white) in the adult Malay population of Kelantan.
|Table 1: Mean axial length, anterior chamber depth, and corneal curvature radius reported in population-based studies|
Click here to view
| Methods|| |
Participation and selection criteria
This was a hospital-based, cross-sectional study conducted in the Ophthalmology Clinic of Universiti Sains Malaysia, Kubang Kerian, Kelantan, from August 2018 to May 2020. This study was approved by the Human Research Ethics Committee USM, Division of Research and Innovation (RandI), USM Health Campus, 16150, Kubang Kerian, Kelantan USM/JEPeM/18060268) and was conducted in accordance to the Good Clinical Practice guidelines and principles outlined by the Helsinki Declaration on human research.
Malay adults in Kelantan, hospital staff of Universiti Sains Malaysia, relatives, and friends who accompanied patients during appointments to the Ophthalmology Clinic of Universiti Sains Malaysia, Kubang Kerian, Kelantan, were recruited via poster announcements both in Malay and English language which were placed within the Ophthalmology Clinic compound of Universiti Sains Malaysia, Kubang Kerian, Kelantan.
Eligible participants must be Malay adult individuals, age above 20 years old, born in Kelantan and include all range of refractive errors. Exclusion criteria included a history of orbital disease: inflammatory causes such as orbital cellulitis, idiopathic orbital inflammatory disease, orbital apex syndrome, cavernous sinus thrombosis, neoplastic such as lymphoma, optic nerve sheath meningioma, optic glioma, rhabdomyosarcoma, vascular such as carotid-cavernous fistula, cavernous hemangioma, trauma such as retrobulbar hemorrhage, orbital emphysema, orbital wall fracture, and others such as dermoid cyst and lymphangioma. History of ocular diseases which contributes to change in axial length such as keratoconus, posterior staphyloma, buphthalmos, phthisis bulbi, and endocrine disease such as thyroid eye disease; a history of ocular surgery including anterior segment surgery, for example, corneal graft surgery, pterygium surgery, corneal collagen cross-linking, cataract surgery and post ocular injury repair, posterior segment surgery, for example, pars plana vitrectomy, and post ocular injury repair and orbital wall fracture repair; and a history of ocular injury such as closed globe injuries such as lamellar laceration, iridodialysis, cyclodialysis, angle recession, traumatic hyphema, open-globe injuries including laceration such as penetrating, perforating and intraocular foreign bodies, globe rupture, and orbital fracture were all excluded.
Sampling size calculation
The sample size was calculated using formula estimated mean via sample size calculator for estimations (ver.1.0.03; Naing L, Winn T and Rusli BN) and obtained 267 participants compared to 85 participants using linear regression formula usingG*Power software (ver. 220.127.116.11; Heinrich-Heine-Universität Düsseldorf). Thus, in view that sample size calculation was larger by using formula estimated mean compared to linear regression formula, the sample size was according to the former calculation of 267 individuals.
The simple random sampling method was used to recruit individuals who fit into the inclusion criteria with written consent. Patient's age and gender are confounding factors as they have different normal exophthalmometry values in a normal healthy adult population., Thus, individuals in this study were grouped according to gender and age: young adulthood (21–44 years old), middle adulthood (45–64 years old), and elderly (above 65 years old).
Inami Hertel exophthalmometer
Inami Hertel exophthalmometer was used for precise measurement of corneal projection through simple alignment of twin prism, linear vertical targets. The device allowed measurement of the forward distance of the corneal apex from the lateral orbital rim. The method for exophthalmometry examination was done as described by Kumari Sodhi et al. At the primary position of gaze, the participants sat down with their faces at the same level as the examiner. The footplates of the instrument were positioned gently at the lateral bony margin of the orbits without exerting excessive pressure. The left footplate was fixed and was placed on the right lateral orbital rim, while the other footplate was adjusted until both footplates rested on lateral orbital rims symmetrically. The rest of the instrument was held parallel to the frontal plane of the patient in line with the pupils. To avoid error, Hertel exophthalmometer was held horizontally with the parallax correcting device (red line) aligned with the vertical target to ensure prism alignment. When these targets overlapped, the degree of projection can be read directly off the superimposed millimeter scale (mm). The right eye of the investigator was used to read the participant's left exophthalmometry values, while the left eye was used for the participant's right eye. Measurement was taken to the nearest 1 mm of the measuring scale of Hertel's exophthalmometer coinciding with the apex of the cornea.
Intraocular lens master
Intraocular lens (IOL) Master from ZEISS was used to measure axial length, cornea curvature, anterior chamber depth, and determination of white-to-white in the calculation for required IOL. The corneal curvature was determined by measuring the distance between reflected light images projected onto the cornea. The results were obtained in millimeters radius and were converted to diopters using the keratometric refractive index 1.3375. This index accounted for the negative power introduced by the posterior corneal surface. The corneal power in diopters was given by Φ = 337.5/R, for R in mm. The white-to-white was determined from the image of the iris, measuring the horizontal width from white sclera to opposite white sclera. Measurement of anterior chamber depth was the distance between the corneal endothelium and anterior surface of the natural crystalline lens.
The IOL Master measured the axial length using light via the distance from the anterior surface of the cornea to the retinal pigmented epithelium. Thus, the axial length obtained was slightly longer than that of A-scan ultrasound which reflects off the surface of the internal limiting membrane at the macula.
The measurement procedures were automated after the operator had adjusted the device to the patient's eye and initiated measurement. The signal-to-noise ratio (SNR) is a measure of accuracy and decreased with increasing cataract density. SNR >2.0 was valid and good if repeatable, SNR between 1.6 and 2.0 was borderline but usable if repeatable, and SNR <1.6 was not usable.
All eligible participants who fulfilled the inclusion and exclusion criteria were given a thorough explanation about the study. Written consent was then obtained if agreeable. The study did not offer treatment or payment to participants. Each participant was given full information regarding their eye examination results.
All participants underwent a comprehensive ocular examination that included visual acuity, anterior and posterior segment examination under a slit lamp, intraocular pressure via air-puff tonometer, and autorefraction to exclude further individuals who did fit into the selection criteria. The eligible individual's ocular biometry measurement (axial length, corneal curvature, anterior chamber depth, and white-to-white) and exophthalmometry measurements were conducted. All ocular parameters of data collection required about half an hour per participant. Participants received information about their eye status from any eye examination done in the study. Data collected were categorized according to gender and age group.
Measures to minimize study error
Steps were taken to minimize the study error. The same instruments and equipment were used. Instruments were calibrated. Interobserver agreement between investigator and qualified senior ophthalmologist ensured correct measurement via Hertel exophthalmometer (this was done by achieving 100% agreement during the examination of the first five participants). The examination procedure was performed by the same investigator.
Data were analyzed using the Statistical Package of the Social Science (SPSS) software (IBM Corp. Released 2016. IBM SPSS Statistics for Windows, Version 24.0. Armonk, NY: IBM Corp.). Mean and standard deviation of exophthalmometric values were calculated for both eyes separately, different age groups, and gender. Multiple linear regression was used to assess any significant correlation between exophthalmometric value and each biometric variable with data of the whole sample population. The level of significance was set at P < 0.05.
| Results|| |
Mean exophthalmometric value
In the total sample size of 267, the mean measurement of exophthalmometric value of the adult Malay population in Kelantan obtained in this study for the right eye was 13.93 ± 2.221 mm and left eye was 13.93 ± 2.232 mm. The difference between both eyes was analyzed using independent samples t-test and obtained P = 0.984 which was statistically insignificant [Table 2].
|Table 2: Mean of exophthalmometric values of adult Malay in the Kelantan population|
Click here to view
The sample population was divided into three groups: 78 in young adulthood with a mean age of 31.00 ± 7.396 years old, 94 in middle adulthood with a mean age of 55.72 ± 5.575 years old, and 95 in elderly with a mean age of 71.91 ± 4.578 years old. The mean exophthalmometric value of males in all three different age groups was generally higher than females [Table 3]. The mean exophthalmometric values were obtained for overall male and female of all ages for each eye and were analyzed using independent samples t-test. P = 0.001 was obtained and showed a statistically significant difference between exophthalmometric values of male and female. Among the different age groups, the mean exophthalmometric values of the young adults were highest, followed by middle adults and the lowest in the elderly group. The data were analyzed using multiple comparisons and obtained P < 0.001 which was statistically significant [Table 4]. In the multiple linear regression analysis for the correlation between exophthalmometric values and age, we observed a significant negative correlation with P = 0.002 [Table 5] and [Table 6].
|Table 3: Mean of exophthalmometric values of adult Malay in the Kelantan population according to different age groups|
Click here to view
|Table 4: Mean exophthalmometric values of adult Malay in Kelantan by different age groups|
Click here to view
|Table 5: Multiple linear regression of right eye exophthalmometric values with age|
Click here to view
|Table 6: Multiple linear regression of left eye exophthalmometric values with age|
Click here to view
Correlation between exophthalmometric value and ocular biometry
The mean ocular biometry analysis had shown that there were no significant differences between the measurements of both eyes [Table 7]. P values obtained via independent samples t-test for difference between both eyes' axial length, corneal curvature, anterior chamber depth, and white-to-white were 0.703, 0.840, 0.462, and 0.930, respectively.
In the multiple linear regression analysis for the right eye, the R2 value was 0.130; taken as a set, the right eye axial length, corneal curvature, anterior chamber depth, and white-to-white account for 13% of the variance of right eye exophthalmometric value. In ANOVA analysis (test using alpha = 0.05), the overall regression model was significant; F (4, 262) =9.799, P < 0.001, R2 = 0.13. However, when individual variants were analysed (test each predictor at alpha = 0.05), we observed that only the right eye axial length was statistically significant with P < 0.001. Based on the unstandardized coefficient, each 1 mm increase of axial length, there is an increase in 0.535 mm of exophthalmometric value [Table 8]. Thus, right eye axial length was uniquely significant for the amount of variance in right eye exophthalmometric value.
|Table 7: Mean ocular biometry of adult Malay in Kelantan by different age groups|
Click here to view
|Table 8: Multiple linear regression of right eye exophthalmometric values with ocular biometry of adult Kelantanese Malay|
Click here to view
From an analysis of the left eye via multiple linear regressions, R2 was 0.123; taken as a set, the left eye axial length, corneal curvature, anterior chamber depth, and white-to-white account for 12% of the variance of left eye exophthalmometric value. The ANOVA analysis (test using alpha = 0.05) showed that the overall regression model was significant; F (4, 262) =9.156, P < 0.001, R2 = 0.12. However, when individual variants were analyzed (test each predictor at alpha = 0.05), only left eye axial length was statistically significant with P < 0.001. Based on the unstandardized coefficient, each 1 mm increase of axial length, there is an increase in 0.485 mm of exophthalmometric value [Table 9]. Thus, left eye axial length was also uniquely significant for the amount of variance in left eye exophthalmometric value.
|Table 9: Multiple linear regression of left eye exophthalmometric values with ocular biometry of adult Kelantanese Malay|
Click here to view
| Discussion|| |
The steady increase of ocular protrusion from age 3 to 20 was noted by Lang et al. Kashkouli et al. also described a positive correlation between age and ocular protrusion at 6–19 years' old. Thus, to avoid the confounding factor of increasing exophthalmometric value attributed to the emmetropic growth of the globe, the minimum age of adults recruited into this study was 21 years' old. The sample population was then further divided into different age groups according to the provisional guidelines on standard international age classifications by the United Nations: young adulthood (21–44 years' old), middle adulthood (45–64 years' old), and elderly (above 65 years' old).
In this study with a sample size of 267, the difference between mean exophthalmometric values obtained for both eyes had no statistical significance. This similarity between both eyes was also noted by Wu et al. which documented 19.0 mm for the right eye and 18.8 mm for the left eye.
Among the different age groups in this study, we observed a statistically significant decrease in mean exophthalmometric values with age. This was also observed by Wu et al. where adults were with a mean age of 39.1 ± 14 which showed a slightly higher mean exophthalmometric value of 15.7 ± 1.8 mm compared to the elderly with a mean age of 76.6 ± 4.1 which showed a slightly lower value of 15.3 ± 2.2 mm. However, this pattern of a gradual decrease in exophthalmometric value in the elderly was not observed by Bilen et al. who reported no statistical significance difference between age groups. In our study, for each year increase of age, there is a decrease in exophthalmometric value by 0.024 mm for both right and left eyes.
Migliori and Gladstone conducted a study on the African-American and Caucasian race of the United States of America and documented a higher male mean exophthalmometric values in both African-American with 18.5 mm and Caucasian race with 16.5 mm compared to female with 17.8 mm for the former and 15.4 mm for the latter. We also observed significantly higher mean exophthalmometric value in male compared to female in all three age groups.
The mean exophthamometric value obtained in this study showed variation from other races and countries as seen in other literature.,,,,,,,,,, [Table 10]. The mean results were close to that seen among Chinese in Taiwan by Tsai et al. with a male of 13.97 ± 2.26 mm and female 13.86 ± 2.39 mm. However, they were lower than that compared to Chinese in Hong Kong by Quant and Woo who reported right eye 16.7 ± 1.9 mm and left eye 16.6 ± 1.8 mm and Chinese Han in northern China by Wu et al., The upper limit for both eyes in all age groups in this study ranged from 18 mm to 19 mm.
|Table 10: Comparison of Exophthalmometric Values of Adult Population According to Race with Other Literature|
Click here to view
The ocular biometry measurements were compared to the Singapore Malay Eye Study results which also used IOL Master in Malay race. The mean axial length in this study according to different age groups was noted to be highest among the young adults with right eye 24.00 ± 1.173 mm and left eye 23.95 ± 1.146 mm and lowest in middle adults with right eye 23.48 ± 0.986 mm and left eye 23.46 ± 0.972 mm. The values obtained reflected that the average mean axial length among Malay adults in Kelantan (right eye 23.72 ± 1.188 mm and left eye 23.68 ± 1.176 mm) was higher than the mean in Singapore Malay Eye Study of 23.55 mm. The anterior chamber depth and corneal curvature mean data in this study were noted to be higher too. The respective measurements were anterior chamber depth (right eye 3.24 ± 0.431 mm and left eye 3.27 ± 0.425 mm) noted to be higher than 3.10 mm and corneal curvature (right eye 44.40 ± 1.577 D and left eye 44.42 ± 1.506 D) was steeper than 7.65 mm (44.12D).
The mean values obtained in this study for white-to-white were right eye 11.99 ± 0.464 mm and left eye 11.99 ± 0.415 mm which were both higher than 11.80 mm in adults of Northern Iran as documented by Hashemi et al.
Chan et al. had documented a statistically significant positive correlation between axial length and ocular protrusion; every 4 mm increase in axial length was associated with a 1 mm increase in exophthalmometric measurement. Karti et al. also demonstrated that every 4.7 mm increase in axial length was associated with a 1 mm increase in exophthalmometric value. In our study, we found that only the axial length has significant positive correlation with exophthalmometric value [Table 8] and [Table 9]. When analyzed with the unstandardized coefficients of axial length in the tables, every increase of 1.87 mm in the right eye and 2.06 mm in the left eye was associated with a 1 mm increase in exophthalmometric value. There was no significant correlation between exophthalmometric value with corneal curvature, anterior chamber depth, and white-to-white in this study.
A positive correlation between axial length and anterior chamber depth had been documented.,,,,, This was also observed in our study when analyzed with linear regression, anterior chamber depth had P < 0.001 correlation with axial length. However, despite the statistically significant correlation, anterior chamber depth was not correlated with exophthalmometric value. We postulate this could be contributed by the higher number of older patients in our sample population: 78 in young adulthood with a mean age of 31.00 ± 7.396, 94 in middle adulthood with mean age 5of 5.72 ± 5.575, and 95 in elderly with a mean age of 71.91 ± 4.578. Studies have shown that anterior chamber depth decreased with age and may be due to the thickening of the lens in the progression of senile cataract.,,,
A strong correlation between white-to-white corneal diameter with axial length and corneal curvature was documented by Hashemi et al. Using the multiple linear regression correlation with axial length, we documented a nonsignificant white-to-white P = 0.505 and a significant corneal curvature P < 0.001. Lee et al. reported corneal curvature increased while axial length, anterior chamber depth, and white-to-white decreased with age. Hashemi et al. noted that white-to-white significantly decreased linearly from 11.91 mm in the 40–44-year-old age group to 11.67 mm in the 60– 64-year-old age group. However, when study was conducted by Hashemi et al. in Tehran, this relationship was not observed. They noted corneal diameter had no significant correlation with age but showed an increase of 0.18 mm for each millimeter increase in the anterior chamber depth. In our study, we found that the young adults had the highest values in axial length, corneal curvature, anterior chamber depth, and white-to-white.
There were a few limitations in this study. First, the sample population recruited participants with clear lens and various stages of cataract which might have been a confounding factor to anterior chamber depth measurements. Second, this was a cross-sectional study. Thus, the evaluation of changes in correlation between exophthalmometric value and ocular biometry cannot be followed up with age. Third, refraction, interpupillary distance, weight, height, and body mass index which have a strong correlation with exophthalmometry were not analyzed in this study.,, To address the limitations of this study, larger population-based prospective studies with the analysis of the severity of cataract, refraction, interpupillary distance, weight, height, and body mass index should be conducted to reflect more accurate results on the correlation between exophthalmometric values and ocular biometry.
| Conclusion|| |
Our study had established the normal exophthalmometric value for Malay adults in Kelantan for future clinical reference. The axial length had shown to have a significant positive correlation with exophthalmometric values. There was no significant correlation between exophthalmometric value with corneal curvature, anterior chamber depth, and white-to-white in this study.
Financial support and sponsorship
Conflicts of interest
The authors declare that there are no conflicts of interests of this paper.
| References|| |
Wu D, Liu X, Wu D, Di X, Guan H, Shan Z, et al
. Normal values of Hertel exophthalmometry in a Chinese Han population from Shenyang, Northeast China. Sci Rep 2015;5:8526.
Bahn RS. Graves' ophthalmopathy. N Engl J Med 2010;362:726-38.
Lim NC, Sundar G, Amrith S, Lee KO. Thyroid eye disease: A Southeast Asian experience. Br J Ophthalmol 2015;99:512-8.
Lim SL, Lim AK, Mumtaz M, Hussein E, Wan Bebakar WM, Khir AS. Prevalence, risk factors, and clinical features of thyroid-associated ophthalmopathy in multiethnic Malaysian patients with Graves' disease. Thyroid 2008;18:1297-301.
Kim IT, Choi JB. Normal range of exophthalmos values on orbit computerized tomography in Koreans. Ophthalmologica 2001;215:156-62.
Bingham CM, Sivak-Callcott JA, Gurka MJ, Nguyen J, Hogg JP, Feldon SE et al
. Axial globe position measurement: A prospective multi-center study by the international thyroid eye disease society. Ophthalmic Plast Reconstr Surg 2016;32:106.
Pereira TDS, Kuniyoshi CH, Leite CDA, Gebrim EM, Monteiro ML, Pieroni Gonçalves AC. A Comparative Study of Clinical vs. Digital Exophthalmometry Measurement Methods. Journal of Ophthalmology.2020;vol. 2020:Article ID 1397410. Available from: https://www.hindawi.com/journals/joph/2020/1397410
. [Last accessed on 2020 Nov 29].
Beden U, Ozarslan Y, Oztürk HE, Sönmez B, Erkan D, Oge I. Exophthalmometry values of Turkish adult population and the effect of age, sex, refractive status, and Hertel base values on Hertel readings. Eur J Ophthalmol 2008;18:165-71.
Nath K, Gogi R, Rao GS, Krishna G, Zaidi N. Normal exophthalmometry. Indian J Ophthalmol 1977;25:47-52.
] [Full text]
Kumari Sodhi P, Gupta VP, Pandey RM. Exophthalmometric values in a normal Indian population. Orbit 2001;20:1-9.
Chan W, Madge SN, Senaratne T, Senanayake S, Edussuriya K, Selva D, et al
. Exophthalmometric values and their biometric correlates: The Kandy Eye Study. Clin Exp Ophthalmol 2009;37:496-502.
Karti O, Selver OB, Karahan E, Zengin MO, Uyar M. The effect of age, gender, refractive status and axial length on the measurements of hertel exophthalmometry. Open Ophthalmol J 2015;9:113-5.
Chen H, Lin H, Lin Z, Chen J, Chen W. Distribution of axial length, anterior chamber depth, and corneal curvature in an aged population in South China. BMC Ophthalmol 2016;16:47.
Lang J, Schäfer WD, Grafen W, Wallner B. Side differences in the position of the corneal apex in relation to the lateral orbital margin (measurements with the Hertel exophthalmometer). Klin Monatsblätterfür Augenheilkd 1985;187:521-4.
Kashkouli MB, Nojomi M, Parvaresh MM, Sanjari MS, Modarres M, Noorani MM. Normal values of hertel exophthalmometry in children, teenagers, and adults from Tehran, Iran. Optom Vis Sci 2008;85:1012-7.
Cheung JJC, Chang DL, Chan JC, Choy BN, Shih KC, Wong JK, et al
. Exophthalmometry values in the Hong Kong Chinese adult population from a population-based study. Medicine (Baltimore) 2019;98:e17993.
Smolders MH, Graniewski-Wijnands HS, Meinders AE, Fogteloo AJ, Pijl H, de Keizer RJ. Exophthalmos in obesity. Ophthalmic Res 2004;36:78-81.
de Juan E Jr., Hurley DP, Sapira JD. Racial differences in normal values of proptosis. Arch Intern Med 1980;140:1230-1.
Migliori ME, Gladstone GJ. Determination of the normal range of exophthalmometric values for black and white adults. Am J Ophthalmol 1984;98:438-42.
Tsai CC, Kau HC, Kao SC, Hsu WM. Exophthalmos of patients with Graves' disease in Chinese of Taiwan. Eye (Lond) 2006;20:569-73.
Bilen H, Gullulu G, Akcay G. Exophthalmometric values in a normal Turkish population living in the Northeastern part of Turkey. Thyroid 2007;17:525-8.
Erb MH, Tran NH, McCulley TJ, Bose S. Exophthalmometry measurements in Asians. Investig Ophthalmol Vis Sci 2003;44:662.
Kook KH, Kim YK, Lee SY. Exophthalmometric values of Korean using Hertel and Naugle exophthalmometers. J Korean Ophthalmol Soc 2003;44:10-5.
Dohvoma VA, Epée E, Ebana Mvogo SR, Lietcheu NS, Ebana Mvogo C. Correlation between Hertel exophthalmometric value and refraction in young Cameroonian adults aged 20 to 40 years. Clin Ophthalmol 2016;10:1447-51.
Ibraheem WA, Ibraheem AB, Bekibele CO. Exophthalmometric value and palpebral fissure dimension in an African population. Afr J Med Health Sci 2014;13:90. [Full text]
Fledelius HC, Christensen AS, Fledelius C. Juvenile eye growth, when completed? An evaluation based on IOL-Master axial length data, cross-sectional and longitudinal. Acta Ophthalmol 2014;92:259-64.
Quant JR, Woo GC. Normal values of eye position in the Chinese population of Hong Kong. Optom Vis Sci 1992;69:152-8.
Lim LS, Saw SM, Jeganathan VS, Tay WT, Aung T, Tong L, et al
. Distribution and determinants of ocular biometric parameters in an Asian population: The Singapore Malay eye study. Invest Ophthalmol Vis Sci 2010;51:103-9.
Hashemi H, Khabazkhoob M, Emamian MH, Shariati M, Yekta A, Fotouhi A. White-to-white corneal diameter distribution in an adult population. J Curr Ophthalmol 2015;27:21-4.
Francois J, Goes F. Ultrasonographic study of 100 emmetropic eyes. Ophthalmologica 1977;175:321-7.
Jivrajka R, Shammas MC, Boenzi T, Swearingen M, Shammas HJ. Variability of axial length, anterior chamber depth, and lens thickness in the cataractous eye. J Cataract Refract Surg 2008;34:289-94.
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.
Leung CK, Palmiero PM, Weinreb RN, Li H, Sbeity Z, Dorairaj S, et al
. Comparisons of anterior segment biometry between Chinese and Caucasians using anterior segment optical coherence tomography. Br J Ophthalmol 2010;94:1184-9.
Park SH, Park KH, Kim JM, Choi CY. Relation between axial length and ocular parameters. Ophthalmologica 2010;224:188-93.
O'Donnell C, Hartwig A, Radhakrishnan H. Correlations between refractive error and biometric parameters in human eyes using the LenStar 900. Cont Lens Anterior Eye 2011;34:26-31.
Wong TY, Foster PJ, Ng TP, Tielsch JM, Johnson GJ, Seah SK. Variations in ocular biometry in an adult Chinese population in Singapore: The Tanjong Pagar Survey. Invest Ophthalmol Vis Sci 2001;42:73-80.
Ooi CS, Grosvenor T. Mechanisms of emmetropization in the aging eye. Optom Vis Sci 1995;72:60-6.
Lee DW, Kim JM, Choi CY, Shin D, Park KH, Cho JG. Age-related changes of ocular parameters in Korean subjects. Clin Ophthalmol 2010;4:725.
Lee KE, Klein BE, Klein R, Quandt Z, Wong TY. Age, stature, and education correlations with ocular dimensions in an older white population. Arch Ophthalmol 2009;127:88.
Hashemi H, KhabazKhoob M, Yazdani K, Mehravaran S, Mohammad K, Fotouhi A. White-to-white corneal diameter in the Tehran Eye Study. Cornea 2010;29:9-12.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10]