Anterior Segment Optical Biometric Parameters and Refractive Errors in a Sample of Iraqi Population View PDF

^*Hussein A Al Hammami
Department Of Ophthalmology, Medical College, University Of Kufa, Najaf, Iraq

^*Corresponding Author:

Hussein A Al Hammami
Department Of Ophthalmology, Medical College, University Of Kufa, Najaf, Iraq
Email:hussein.alhammami@uokufa.edu.iq

Published on: 2020-06-06

Abstract

Background: There are few population-based age norms for refraction and ocular biometry in Iraqi population, and the anterior segment parameters are of paramount importance in the prediction of liability of person to primary angle closure glaucoma, and this study tries to explore any relation of anterior segment parameters and refractive errors in a sample of Iraqi population.
Objective: define the of anterior segment biometric parameters in a sample of Iraqi population with refractive errors and to find the correlation between those parameters and refractive errors.
Patients and Methods: In a cross sectional study 371 patients in whom the refractive errors were measured with subjective and objective measures the mean for myopia in male was -4.66±4.86 D and 5.31±4.86 D in female the mean for hyperopia +1.94±2.07 D and 1.74±1.84 D for male and female respectively.
The anterior chamber angle, depth and K-readings were measured by Pentacam® (Oculus, HG, Germany), Examination of the anterior segment using slit lamp and fundoscopy using Volk 90 D were done to exclude any underlying pathology manifest and cycloplegic refraction done by both auto refractometer (Topcon ker. 800) and retinoscopy.
Results: 371 patients (742 eyes), mean age 29.48 ±7.33, myopia presented in 311 and hypermetropia in 60.

There is an increase in anterior chamber angle width in myopia and decreased width in hyperopia.
There is an increase in AC angle width when increased corneal curvature and vice versa.
Positive correlation between ACA width and AC depth.
The anterior chamber depth increased in myopia and decreased in hypermetropia.

Keywords

Anterior Chamber Angle; Anterior Chamber Depth; Optical Coherence Tomography; Myopia; Hypermetropia

Introduction

Anterior chamber angle and depth have been identified as an important risk factor for angle-closure glaucoma and progression of open-angle glaucoma. For almost a century, gonioscopy has been used to semi quantitatively analyze anterior chamber angle width [1-5]. More recently, quantitative imaging modalities including ultrasound bio microscopy, optical coherence tomography, and Scheimpflug imaging have been developed. In contrast to ultrasound bio microscopy, optical coherence tomography and Scheimpflug imaging offer noncontact imaging of the anterior segment and make these methods attractive for patients and doctors alike [6-15]. To interpret measurements from Scheimpflug imaging and to integrate the results into a clinical context, it is important to know the distribution of anterior chamber angle width and to understand associations with clinical factors. The underlying idea is that a narrower anterior chamber angle width is associated with clinically suspicious risk factors for acute angle closure, namely female sex, older age, hyperopic refraction, shorter axial length, and thicker crystalline lens. Preliminary methodology of thinking regarding the relation of refractive errors with state of anterior segment parameters including anterior chamber depth is not fully investigated in clinical studies, the idea of wider angle in myopic eye and vice versa in hypermetropic eye is based mainly on theoretical assumption of longer and shorter axial length of the globe in myope and hypermetrope respectively [16-18].

Aim of Study

To find the relation between the ACA width and other anterior segment parameters with refractive error.

Patients and Methods

The study was carried out at Ibsar Eye center in AL-Najaf city from January 2017 to September 2018.

In a cross sectional study 371 (742 eyes) patients in whom the refractive errors were measured with a subjective and objective measures. The mean for myopia in male was -4.66±4.86 D and -5.31±4.86 D in females the mean for hyperopia + 1.94±2.07 D and 1.74±1.84 D for male and female respectively. The mean of myopic astigmatism 1.59±1.24 while hyperopic astigmatism 1.10±0.76.

The anterior chamber angle, depth and K-readings were measured by Oculus Pentacam and anterior segment Scheimpflug imaging.

Examination of the anterior segment using slit lamp and fundoscopy using volk 90 D were done to exclude any underlying pathology. Data was collected and included in a data based system and analyzed by statistical package of social sciences ((SPSS, Inc., Chicago, IL, USA)) version 20.

Parametric data were expressed as mean ± standard deviation (SD). It was analyzed statistically using student t-test and ANOVA test.

While non-parametric data were expressed as percentages and were analyzed using chi square. The Pearson correlation coefficients (r) were used to study the correlation between age and anterior chamber depth of eyes. Significance was set at the P ≤ 0.05 level in all analyses.

Results

A cross sectional study enrolled 371patients, Mean age 29.48±7.33 years, myopia presented in 311 (83.8%) and hyperopia in 60 (16.2%). The mean of anterior chamber depth of right eye 3.2± 0.39 and left eye 3.1±0.42. K reading for right eye, mean of anterior surface of cornea 43.6±3.02 and posterior surface -6.2±0.8, while in left eye K reading mean for anterior surface of cornea 43.6±1.9 and posterior surface -6.3±7.9. Male to female ratio 1:1.6, male constitute 46.1% and female 53.9% as in table 1.

Table 1: Gender distribution.

		No.	Percent
Sex	Male	171	46.1
	Female	200	53.9
	Total	371	100

Out 371 of patients, 36.1% in age group 18-25 years, 41.5% in age group 26-35 years and 22.4% of patient age ≥36 years as in figure 1.

There were no association between gender and age group distribution in sample, 35% of male in age group 18-25 years while female 37% in same age group, 43.8% of male in age groups 26-35 years, in female sample 39.5% in these age group, as shown in table 2.

Table 2: Age comparison with gender.

		Age groups			Total
		18-25 y	26-35 y	≥36 y	Total	p-value
Ex	Male	60 (35%)	75 (43.8%)	36 (21.2%)	171	0.63
Ex	Female	74 (37%)	79 (39.5%)	47 (23.5%)	200	0.63
Total		134	154	83	371

In table 3 show the difference in measurement of anterior chamber width of two eyes in different age groups, there were significant difference between measurement of anterior chamber angle of right and left eye with age groups of patients, there were decrease in mean of angle width of left and right eye with increase age.

Table 3: Show the comparison between age group by mean and standard deviation of angle width.

Age group	No.	Angle width RT eye	Angle width LT eye
18-25 y	134	41.31±5.72	41.4±5.9
26-35y	154	39.8±6.15	39.76±7.2
≥36y	83	38.47±6.76	38.5±6.74
p-value		0.003	0.01

In table 4 show the difference in measurement of anterior chamber depth of two eyes and K reading of both anterior and posterior surface in different age groups, there were significant difference between measurement of anterior chamber depth of right and left eye with age with p-value < 0.001. On other hand the difference not significant in mean of K reading of anterior and posterior surface of cornea with age.

Table 4: show the comparison between age group by mean and standard deviation of refraction measurement.

Age group	No.	RT eye ACD	LT eye ACD	K reading RT eye anterior	K reading LT eye anterior	K reading RT eye posterior	K reading LT eye posterior
18-25 y	134	3.29±0.8	3.2±0.8	43.4±3.9	43.6±1.9	-6.1±1.1	-6.1±1.2
26-35y	154	3.20±0.3	3.1±0.2	43.7±2.4	43.5±2.3	-6.3±0.7	-6.2±3.2
≥36y	83	3±0.8	3±0.7	44±2.1	43.8±1.7	-6±0.2	-6.2±6.7
p-value		0.001	0.001	0.91	0.75	0.31	0.72

The following result reveal the measurement of anterior chamber angle width of two eyes in relation to gender, there were no significant difference in these measurement in both eye with sex of patients, as shown in table 5.

Table 5: The difference between gender and ACA measurement.

	Sex	No.	Mean± Std. Deviation	p-value
RT angle width	Male	171	39.96±6.104	0.21
RT angle width	Female	199	40.18±6.09	0.21
LT angle width	Male	171	40.16±7.26	0.47
LT angle width	Female	199	42.23±29.63	0.47

The anterior chamber angle width of both eyes were statistically different between myopia and hyperopia, as shown below myopia had wider anterior chamber angle than hyperopia patients, in myopia had mean of anterior chamber angle for left eye 41.1±6.7, and for right eye 40.9±5.53 in hyperopia for left eye 35.5±7.06 and right eye 35.6±7.19, as shown in table 6.

Table 6: Comparison of refraction error with anterior chamber angle width.

	No.	Angle width RT	Angle width LT
Myopia	311	40.93±5.53	41.1±6.7
Hyperopia	60	35.66±7.19	35.57±7.06
p-value		0.001	0.001

There were positive correlation between anterior chamber angle width and depth of anterior chamber that is when increase in width of angle lead to increase in depth of anterior chamber of both eye, in left eye Pearson

Correlation coefficient r = 0.298, p<0.04 and in right eye Pearson correlation coefficient r = 0.457, p<0.01 as shown in table 7.

Table 7: Show the correlation between anterior chamber angle width and anterior chamber depth.

Variable	Pearson coefficient	p-value
RT anterior chamber angle width and RT anterior chamber depth	0.457	0.01
LT anterior chamber angle width and LT anterior chamber depth	0.298	0.04

In Consequently the correlation also present between mean of K reading of anterior and posterior surface of corneal curvature and width of angle of left and right eye, in left eye Pearson correlation coefficient r = 0.182, p<0.02 and in right eye Pearson correlation coefficient r = 0.154, p<0.003 as shown in table 8.

Table 8: Show the correlation between anterior chamber angle width and k reading.

Variable	Pearson coefficient	p-value
RT anterior chamber angle width and RT k reading	0.154	0.003
LT anterior chamber angle width and LT K reading	0.182	0.02

Discussion

To our knowledge this is the first study to describe the anterior segment biometric parameters in population set of Iraqi community and analyze the distribution of the ACA width in evaluation of the relation with the refractive state of the eye [19-25].

We found a mean ACA width as measured with Scheimpflug imaging with a mean ACA 40.6°±12.27° with a range from 20.2° to 55.2° [26-35]. Previous studies reported similar values for the ACA width using Scheimpflug imaging in a smaller cohort and optical coherence tomography.

Myopic refraction was associated with a wider ACA and this explain the high percentage of wider angle eyes in the sample size. Hyperopic refraction has been described as a risk factor for angle-closure glaucoma.

Associated with the narrower angle. However, several other studies incorporating ocular parameters (e.g., axial length) in their statistical models were not able to confirm this association [36-45].

The ACA was independently associated with a shallower anterior chamber, as previously reported by other groups. This was similar to observations in patients with angle-closure glaucoma, who tend to have a shallower anterior chamber and a thicker crystalline lens [46-50].

Primary glaucoma affects 67 million people worldwide, the Asians accounting for almost half of this number. Primary angle-closure glaucoma (PACG) is a major cause of visual morbidity in East Asia. Recent studies in southern India found that the prevalence of PACG in Indians is also higher than that seen in European people, with rates approaching those seen in Mongolia [51-55]. The high prevalence of angle closure in China and India means that PACG may be at least as common as primary open-angle glaucoma and therefore a major form of glaucoma worldwide. Eyes with primary angle closure tend to share certain biometric characteristics. These include shallow central anterior chamber depth (ACD), thick lens, anterior lens position, small corneal diameter and radius of curvature, and short axial length. Among these, shallow ACD is regarded as the cardinal risk factor in most ethnic groups, although comparative studies suggest that this may not be true for East Asian people, where the role of non–pupil-block angle closure in relatively deep anterior chambers has been debated.

The prevalence of myopia has been increased over the past few decades, especially in East Asians. Among Singaporean adults aged over 40 years, the overall prevalence of myopia was reported to be 38.7%. Such a trend was even prominent in the younger generations. In the sequential nationwide surveys conducted in Taiwan, the prevalence of myopia among the teenagers between 16 and 18 years has increased from 74% in 1983 to 84% in 2000. In addition, the prevalence of myopia in freshmen at National Taiwan University reached 91.3% in 2005.

Corneal shape was also linked to ACA width. A flatter cornea was associated with narrower ACA. This is in concordance with a report in Chinese showing an independent negative association with the ACA and central corneal thickness [56-60].

The main factor was anterior chamber depth. Presumably, genetic variations between Caucasians and Asians contribute to different ocular geometry and its relation to angle-closure glaucoma. In Asians, almost one-quarter of angle-closure patients are myopic, while in a multiethnic population, patients with angle-closure were far more hyperopic [61-64].

Other German study sample was recruited from 5 years follow up Gutenburg Health (GHS) cohort study including subject with an age 40 to 79 years, the statistical analysis reveal an independently association between a smaller ACA.

And female sex, higher age, and more hyperopic refraction. When including biometric parameter, shallow anterior chamber depth, shorter axial length, higher central corneal thickness( CCT) and lower corneal power were independently associated with a narrower mean of +ACA width.

Conclusion

Presence of certain type of refractive errors (hypermetropia may predict for higher risk of angle closure or narrow angle glaucoma but not for all most of the myopic eyes (without other ocular abnormalities) is of very low risk of narrow angle glaucoma due to wider angle configuration.