cataracts are among the most common causes of decreased vision and even blindness ( 1 ) and approximately 17.2% of the population over 40 years old in the us will develop a cataract in at least one of their eyes ( 2 ) . one of the most important indexes to evaluate post cataract surgery emmetropia is intraocular lens ( iol ) power ( 3 , 4 ) . numerous methods and formulas have been suggested for the measurements of iol power , which are mostly based on axial length ( al ) , refractive power of the cornea and an estimation of the postoperative distance between the corneal epithelium and the lens . in these measurements , the preoperative anterior chamber depth ( acd ) is considered as a constant part in the formula , because it was believed that by an increase in al , the acd increases accordingly ( 5 ) . in the study by holladay et al . ( 6 ) a new measurement formula was suggested , in which the preoperative acd was implemented in the measurement of the iol and a new formula was introduced as the holladay 2 formula . the formula is shown to be precise in measuring iol power when dealing with patients who have an al of < 20 ( 7 ) . today new iol calculation formulas recognize preoperative acd in addition to al , as an important factor ( 810 ) . it has been proven that basic anatomical parameters ( such as al and acd ) in ophthalmology are variable in different countries according to ethnic groups , genetics and some environmental factors . in result , this may affect some parameters such as iol power calculations , yet no study has specifically evaluated this matter ( 11 , 12 ) . understanding region specific differences regarding iol power calculations is vital for post cataract surgery evaluations . considering race related differences , we hypothesized that this difference may affect the relationship between al , acd and iol power , so here we investigate the relationship between al , acd and iol power in a referral center from eastern iran , among patients who had cataract surgery and we compared it to studies from other regions of the world . in a cross - sectional study from 2011 to 2013 , the records of 698 cataract patients referring to khatam al anbia general hospital in mashhad , iran were extracted . the study protocol was approved by the ethics committee of mashhad university of medical sciences . all patients who visited the medical care center to have cataract operations of one eye in the two year time period , were included in the study . any patient whose biometry was performed outside of the hospital , cases of traumatic cataract , phacomorphic glaucoma and finally any records that had missing data were excluded from the study . a questionnaire which included data on age , sex , al and acd was filled for each patient , based on their records . al and acd measurements were carried out using an optikon sonography machine by a trained medical worker . the biometry testing was carried out using the contact method . in this method a drop of tetracaine is applied in both eyes , in a supine position . while looking at the red light on the probe of the sonography machine , the probe is put in contact with the patient s cornea without applying any pressure . in this method , the probe is set vertical on the corneal surface , in order to obtain the highest echo spike . this was repeated five times for each patient and the average al was calculated by the machine . we considered al<22 mm as short sighted , 22mm < al < 24.5 mm as normal al and al>24.5 mm as long sighted . for acd we considered acd<2.45 mm as low depth , 2.45mm < acd<3.31 mm as normal acd and acd>3.31 as high acd . patients were classified into age groups of less than 30 , 3150 , 5160 , 6170 , and over 70 years old for better comparison and evaluation . the independent - samples t - test was used , to compare quantitative data between two groups . the kendall and the pearson product - moment correlation tests were used , to assess the relationship between al and acd . the linear regression model was used , to obtain a mathematical model to estimate acd using al , age and sex . in a cross - sectional study from 2011 to 2013 , the records of 698 cataract patients referring to khatam al anbia general hospital in mashhad , iran were extracted . the study protocol was approved by the ethics committee of mashhad university of medical sciences . all patients who visited the medical care center to have cataract operations of one eye in the two year time period , were included in the study . any patient whose biometry was performed outside of the hospital , cases of traumatic cataract , phacomorphic glaucoma and finally any records that had missing data were excluded from the study . a questionnaire which included data on age , sex , al and acd was filled for each patient , based on their records . al and acd measurements were carried out using an optikon sonography machine by a trained medical worker . the biometry testing was carried out using the contact method . in this method a drop of tetracaine is applied in both eyes , in a supine position . while looking at the red light on the probe of the sonography machine , the probe is put in contact with the patient s cornea without applying any pressure . in this method , the probe is set vertical on the corneal surface , in order to obtain the highest echo spike . this was repeated five times for each patient and the average al was calculated by the machine . we considered al<22 mm as short sighted , 22mm < al < 24.5 mm as normal al and al>24.5 mm as long sighted . for acd we considered acd<2.45 mm as low depth , 2.45mm < acd<3.31 mm as normal acd and acd>3.31 as high acd . data were analyzed by the spss version 18 ( spss inc . , chicago , il , usa ) . patients were classified into age groups of less than 30 , 3150 , 5160 , 6170 , and over 70 years old for better comparison and evaluation . the independent - samples t - test was used , to compare quantitative data between two groups . the kendall and the pearson product - moment correlation tests were used , to assess the relationship between al and acd . the linear regression model was used , to obtain a mathematical model to estimate acd using al , age and sex . overall 698 cases ( eyes ) were studied and among whom , 361 cases were men ( 51.7 % ) . the mean ( sd ) age of the men and women was 61.116.3 and 61.914.8 years old , respectively . the two sexes did not display a statistically meaningful difference in their age ( p = 0.53 ) ( table 1 ) . four hundred and sixty - seven patients had normal al ( 66.9 % ) , 87 patients were long sighted ( 12.5% ) and 144 patients were short sighted ( 20.6% ) . four hundred and seventy seven patients had normal acd ( 68.3% ) , 117 patients had high acd ( 16.8% ) and 104 patients had low acd ( 14.9% ) ( table 2 ) . men had significantly longer al in comparison to women ( 23.7  2.4 mm vs. 22.9  2.1 mm ; p < 0.001 ) . the mean ( sd ) the overall acd was statistically higher in men in comparison to women ( 2.93  0.45 mm vs. 2.82  0.42 mm , p = 0.002 ) . data analysis showed that there is an overall meaningful difference in the distribution of patients , based on the classification of al and acd ( p < 0.001 ) . the kendal correlation and the pearson correlation tests showed that there is a direct ( linear ) and positive relationship between al and acd ( r = 0.308 ; p = 0.001 ) . this was only seen in cases with normal al ( r = 0.175 ; p = 0.001 ) , and was not significant in short and long sighted patients . overall , there was a significant and inverse relationship between al and age ( r = 0.287 ; p = 0.001 ) . we found a positive and direct correlation between age and al in short sighted patients ( r = 0.537 ; p = 0.001 ) and an inverse correlation in long sighted patients ( r = 0.615 ; p = 0.001 ) , no significant correlation was seen between age and al in the group of patients with normal al ( p = 0.14 ) . overall acd and age displayed an inverse correlation ( r = 0.173 ; p = 0.001 ) . this correlation was seen in patients with normal acd ( r = 0.134 ; p = 0.001 ) . there was no significant correlation between acd and age in patients with high and low acd ( p = 0.83 and p = 0.87 , respectively ) . the linear regression model was used , to assess the relationship between acd , age , sex and al and the following result was obtained : acd = 1.822 + 0.051 ( al )  0.003 ( age ) + 0.0644 ( sex ) . in this model , 1 for males and 0 for females in this study , we evaluated the relationship between al and acd with iol in a sample of iranian patients undergoing cataract surgery and we found that similar to recent studies in other populations ( 10 , 13 , 14 ) and contrary to previous belief , the majority of our patients with short and long sightedness had normal acd values ( 63.9% and 59.8% , respectively ) , indicating the use of third and fourth generation iol power calculation formulas in the iranian population . in a study published in 2010 , hoffmann and hutz ( 15 ) analyzed al , acd and the corneal radius of 15,448 patients during a six year period in germany . they found that the mean ( sd ) al and acd were 23.43  1.51 mm and 3.11  0.43 mm , respectively . hoffer ( 16 ) evaluated 7,500 patients with cataracts , and found that the mean al and acd among these patients were 23.65  1.35 mm and 3.24  0.44 mm which was comparable to our study ( al : 23.3  2.35 mm and acd : 2.8  0.44 mm ) . in the study by holladay ( 13 ) among 1000 patients , 82% had normal al and only 0.9% of patients had short sightedness . the number of short sighted patients , documented in the latter study , was less than that documented in our study ( 20.6% ) . the average al was significantly higher in men compared to women and this was seen only in the group with normal al . ( 14 ) , where they studied 750 patients and documented that among patients referring for refractive surgery , male patients had longer al ( 23.76 + / 1.00 mm versus 23.27 + / 1.01 mm ) and a younger age for disease presentation . ( 13 ) found that among long sighted patients , 90% have normal acd , 10% have high acd and none of them have short acd ( 59.8% , 37.9% and 2.3% in our study , respectively ) . in the group of patients with normal al , they found that 90% of patients had normal acd , none of them had low acd and 10% had high acd ( 71.3% , 13.5% and 15.2% in our study , respectively ) . in patients with short sightedness they found that 20% have low acd , 80% have normal acd and none of them have high acd ( 27.1% , 63.9% and 9% in our study , respectively ) . in a study by hosny et al . ( 17 ) , they evaluated 211 patients in spain and found that acd has a positive and meaningful relation with al and the diameter of the cornea . ( 14 ) who documented positive correlation between al and acd ( r = 0.423 ; p < 0.001 ) . we also documented a linear and positive correlation between al and acd , although k j hoffer in 1993 ( 18 ) , postulated a curve like relationship between al and acd . in our study the linear relationship was only seen in patients with normal al and not in short and long sighted patients . we documented a positive correlation between al and age , in the group with an al of less than 22 mm ( short sightedness ) , but this was an inverse correlation in the group who had an al of more than 24.5 mm ( long sightedness ) . overall an inverse relationship was observed between age and al , this finding was also seen in the studies by hosny et al . we found an inverse correlation between acd and age , which was seen only in the group with normal acd . hsu et al . ( 19 ) studied 1,480 preoperative cataract patients from 2006 to 2010 and evaluated the correlation between acd and age , sex and body height . they found that acd has an inverse correlation with age , while sex was not an independent associating factor for acd . in order to obtain a mathematical model and to assess the relationship between acd , al , age and sex , we used the regression model , and found that acd is dependent on al , age and sex . first was its retrospective nature which did not allow an assessment of other factors which may have affected al and acd , including lens thickness and corneal diameter . although our study mostly aimed to evaluate region specific differences regarding iol power calculation , al and acd , our results were similar to what was published in previous literature . since our study had a retrospective nature , we were not able to alter the al calculation method which was used in our study ( contact method ) , which is among the least accurate methods of al measurement . our study findings were mostly similar to studies from other regions of the world and although some anatomical variations may exist in ophthalmic anatomy , factors such as race and geographical area have little effect on the relationship between acd , al and iol power calculation . similar to previous literature , our results support the use of third and fourth generation formulas for iol power calculation in the iranian population . prospective multi - centered studies and systematic reviews should be designed to evaluate the changes in iol power calculation and its relationship to al and acd in different regions of the world .
introductionbasic anatomical parameters in ophthalmology are variable in different countries according to ethnic groups , genetics and some environmental factors . 
 the aim of this study was to determine the relationship between axial length ( al ) , anterior chamber depth ( acd ) and intraocular lens power ( iol ) in a referral center from eastern iran among patients who had cataract surgery , in comparison to studies from other regions of the world.methodsin a cross - sectional retrospective study from 2011 to 2013 , the records of 698 cataract patients referring to khatam al anbia general hospital in mashhad , iran were evaluated . 
 we divided patients , based on their al and acd , into three separate groups and compared their results . 
 the spss software was used for data analysis . the chi - square test and 
 the independent - samples t - test were used to compare qualitative and quantitative data between two groups , respectively . 
 the kendall and the pearson product - moment correlation tests were used to assess the relationship between al and acd . the linear regression model was used to obtain a mathematical model to estimate acd , using al , age and sex.resultsamong individuals who had normal al ( between 2224.5 mm ) , there was a positive correlation between al and acd ( p<0.001 , r=0.17 ) , however , among individuals with short ( al<22 mm ) or long sightedness ( al>24.5 mm ) , no significant correlation was detected . 
 we also found that older people have shorter al ( p=0.001 and r=0.287 ) . 
 men have an average longer al ( 23.72.4 mm vs. 22.92.1 mm ; p<0.001 ) and deeper acd compared to women ( 2.930.45 mm vs. 2.820.42 mm , p=0.002).conclusionour findings were mostly similar to previous literature from other regions of the world and although some anatomical variations may exist regarding ophthalmic anatomy , factors like race and geographical area have little effect on the relationship between acd , al and iol power calculation , furthermore our results support the use of third and fourth generation formulas for iol power calculation .