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ORIGINAL ARTICLE
Year : 2017  |  Volume : 9  |  Issue : 1  |  Page : 10-15

To study the effects of central corneal thickness, axial length, and anterior chamber depth on intraocular pressure


1 Department of Optometry, College of Applied Medical Sciences, Qassim University, Qassim, Kingdom of Saudi Arabia; Department of Ophthalmology, Allied Hospital, Punjab Medical College, Faisalabad, Pakistan
2 Department of Optometry, College of Applied Medical Sciences, Qassim University, Qassim, Kingdom of Saudi Arabia; Department of ophthalmology, Liaqat University of Medical and Health Sciences, Jamshoro, Pakistan
3 Department of Optometry, College of Applied Medical Sciences, Qassim University, Qassim, Kingdom of Saudi Arabia

Date of Web Publication19-Sep-2017

Correspondence Address:
Muhammad Ijaz Ahmad
Department of Optometry, College of Applied Medical Sciences, Qassim University, Qassim, Kingdom of Saudi Arabia

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DOI: 10.4103/sjopthal.sjopthal_17_17

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  Abstract 

Purpose: The aim of the research project is to study the effects of central corneal thickness (CCT), axial length (AL), and anterior chamber (ACD) depth on intraocular pressure (IOP). Study Period: It was a cross-sectional study and was conducted from February 2015 to June 2015. Methodology: A total of 100 participants of varying age groups were selected from Qassim University clinics who had clinically normal corneas and then were divided into different groups based on their ages. All the participants had no evidence of any ocular disease and both eyes were examined in each participant. Anterior chamber depth (ACD) and CCT were measured with Pentacam (OCULUS). IOP was measured with air puff tonometer. AL was measured by A-scan ultrasonography. Results: Two hundred eyes of one hundred participants were examined. The ages of the participants ranged between 18 and 30 years. Mean age was 23.94 years with ± 2.994 standard deviations The number of emmetropes, myopes, and hypermetropes was 50, 19, and 31, respectively. The mean corneal thickness in the right eye was 541.64 μm (±34.80) and in the left eye, it was 543.46 μm (±33.65). IOP was found to increase with increased CCT and it was statistically significant (P < 0.001). There was a positive correlation between refractive errors, CCT, and IOP. On the other hand, very weak correlation was observed between IOP and AL and ACD. Conclusion: It can be concluded that people with increased CCT and steep cornea need to be monitored closely for their IOP because of strong positive correlation between increased corneal thickness and IOP and high IOP should not be considered as the only factor for diagnosis and it should be related with optic disc evaluation and visual field examination to avoid the over treatment.

Keywords: Anterior chamber depth, axial length, central corneal thickness, intraocular pressure, refractive state


How to cite this article:
Ahmad MI, Qureshi MA, Aldebasi YH. To study the effects of central corneal thickness, axial length, and anterior chamber depth on intraocular pressure. Sudanese J Ophthalmol 2017;9:10-5

How to cite this URL:
Ahmad MI, Qureshi MA, Aldebasi YH. To study the effects of central corneal thickness, axial length, and anterior chamber depth on intraocular pressure. Sudanese J Ophthalmol [serial online] 2017 [cited 2017 Oct 21];9:10-5. Available from: http://www.sjopthal.net/text.asp?2017/9/1/10/215107


  Introduction Top


Glaucoma affects about 60 million people in the world and is one of the major causes of irreversible blindness and in about 8.4 million people it causes bilateral blindness.[1] Primary open-angle glaucoma is the most common type of glaucoma that causes the ganglion cell death.[2],[3] Different community-based surveys show that glaucoma is ranked as the second leading cause of blindness responsible for 8% of blindness among the 39 million people who are blind worldwide and is considered responsible for 15% of blindness in different African countries, and in this region, the highest prevalence of blindness is detected as compared to other parts of the world.[4],[5] It was estimated that in 2013, there were 64.3 million people with glaucoma aged 40–80 years and supposed to increase to 76.0 million by the year 2020 and 111.8 million in 2040.[6]

Studies show significant association between increased central corneal thickness (CCT) and younger age, male sex, and higher intraocular pressure (IOP) but not for the glaucoma or any disturbance to cup to disc ratio.[7] Although the corneal thickness is very important factor for IOP measurements, racial and ethnic differences should also be considered along with other ocular findings such as optic disc evaluation with perimetry. Chinese have the thickest CCT but lowest IOP among the different ethnic groups. On the other hand, other Asians such as Malays have more positive relationship between IOP and CCT.[8]

Another study conducted in Korea showed a significant positive correlation between CCT and IOP although they showed no correlation between axial length (AL) and IOP.[9]

Different studies conducted showed that deepening of anterior chamber depth (ACD) is associated with lowering of IOP.[10],[11],[12]

IOP presents a fundamental factor of ocular health and disease and it is important not only in the diagnosis and management of glaucoma but also in the assessment of the postoperative course of all intraocular surgical interventions. IOP measurements are affected by CCT, ACD, and AL.[13],[14],[15]

The IOP is maintained by equilibrium between the aqueous production from the ciliary body and it is drainage through the trabecular complex. The mean IOP varies between 10 and 21 mm Hg (mean 16 ± 2.5).[16]

An elevated IOP is one of the major risk factors for developing glaucoma and its progression. Glaucoma is a common ophthalmic disease worldwide and a significant cause of visual impairment and blindness. It is the second leading cause of blindness which is responsible for 23% of all the blindness cases.[17],[18] Blindness leads not only to a reduced economic and social status but it may also result in early death.[19]

Air puff tonometry is based on the principle of applanation; the central part of cornea is flattened by a jet of air to measure the level of IOP. The main advantages of noncontact tonometer are that they are noninvasive and thus comfortable for the patient with a minimal risk of infection.[20],[21]

The Pentacam measurement process takes less than two seconds and minute eye movements are captured and corrected simultaneously. By measuring 25,000 true elevation points, precise representation, repeatability, and analysis are guaranteed. It can measure like AL and CCT, etc.[22]

A-scan is an amplitude modulation scan. It gives the information in the form of one dimensional. it is used to detect the presence of flaws in the materials. The A-scan provides data on the length of the eye, which is a major determinant in common sight disorders. The most common use of the A-scan is to determine AL for intraocular lens calculation.[23]

Kiuchi et al. (2012) showed that the IOP was low in old age people and males had significantly greater displacement of the central cornea.[24]

Wen Wei et al. (2014) showed that every 10 μm increase in CCT leads to 0.15–1.0 mmHg increase in IOP. The CCT as well as IOP is important for assessing the glaucoma considering the low CCT will lead to the underestimation of IOP and interfere the prognosis of glaucoma.[25]

Aims

The aim of the present research is to study the effects of CCT, AL, and ACD on IOP.

Objectives

The objective was to study the effects of these variables in different refractive states.


  Methodology Top


This cross-sectional study was conducted after getting the approval of Research Committee of College of Applied Medical Sciences, Qassim University. One hundred individuals were randomly selected who visited our clinics for routine ocular examination. Age range of the participants was found to range between 18 and 30 years. We divided the patients into three groups based on the age, first group ranged between 18 and 22 years, second group 23–26 years, and last group 27–30 years. Emmetropic and ametropic (myopia and hypermetropia) patients who were not having any eye ocular disorder and without usage of any ocular drugs were recruited for the study.

The written informed consent of the participants was obtained. After taking a brief ocular and systemic history, the IOP was measured by air puff tonometer. This device will push air toward the central corneal to measure the IOP. The CCT, ACD, and K readings were measured by scheimpflug imaging by Pentacam.

AL was measured with A-scan ultrasonography (E-Z Scan AB5500+). Before measuring AL, cornea was anaesthetized with 2–3 drops of 4% topical proparacaine. After five minutes, AL was measured with A-scan ultrasound and in the end broad spectrum, antibiotic eye drops were instilled to avoid any infection.

The results were presented as means and standard deviations (SD). The t-test was used for comparing means of the two groups. Correlation analyses were performed to assess the relationship between the different variables. A P < 0.05 was considered as statistically significant.

Data were entered and maintained in Microsoft Excel 2007. Statistical analysis was done using SPSS 17.0. (SPSS Inc, Chicago, IL, USA)

Inclusion criteria

  • Males among age 18–30 years
  • Healthy volunteers
  • Ametropia (myopia, hypermetropia).


Exclusion criteria

  • Male, age >18 or more the 30 years
  • Females
  • Any patients with a history of ocular pathology
  • History of contact lens user.



  Results Top


The ages of the participants ranged between 18 and 30 years. The distributions of the participants in the different age groups are shown in [Table 1].
Table 1: Describes the frequency of various age groups

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Mean age was 23.94 years with ± 2.994 SD

Participants were also divided into three groups based on their refractive status, emmetropic, myopic, and hypermetropic.

The distributions of the participants based on the different refractive status are shown in [Table 2].
Table 2: Describes the frequency of different refractive states

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The different values of CCT are shown in [Table 3] with mean and standard deviations and [Figure 1] describes frequency of distribution of corneal thickness in both eyes. The distribution of IOP, AL and ACD in both eyes are shown in [Table 4], [Table 5], [Table 6] respectively.
Table 3: Describes various statistical values of central corneal thickness for both eyes

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Figure 1: (a) Corneal thickness in right eye, (b) Corneal thickness in left eye

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Table 4: Describes the distribution of intraocular pressure in both eyes

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Table 5: Describes the distribution of axial length between two eyes

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Table 6: Describes the distribution of anterior chamber depth in both eyes

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The frequency and nature of distribution of IOP, AL and ACD in both eyes are shown in [Figure 2], [Figure 3], [Figure 4] respectively. A correlation analysis was performed to assess the relationship between IOP and CCT and it was statistically significant (P < 0.001) as shown in [Figure 5].
Figure 2: (a) Intraocular pressure in right eye, (b) Intraocular pressure in left eye

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Figure 3: (a) Axial length in right eye, (b) Axial length in left eye

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Figure 4: (a) Anterior chamber depth in right eye, (b) Anterior chamber depth in left eyeerque

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Figure 5: Desribes the correlation between the intraocular pressure and central corneal thickness

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Regression analysis for correlation between the IOP and CCT was also performed.

The effect of various variables such as AL, AXL, CCT, and ACD on IOP was also studied.

A correlation analysis was performed to assess the relationship between IOP and CCT and this relationship was statistically significant (P < 0.001). On the other hand, regression analysis was performed to assess the relationship of IOP and AL and ACD. The relationship among these variables was weak and not statistically significant (P > 0.05).

This study showed positive correlation between the CCT and different refractive states and it is shown in [Figure 6].
Figure 6: Describes the relationship between corneal thickness and refractive state

Click here to view



  Discussion Top


Glaucoma is the most common cause of irreversible blindness worldwide and the second most common cause of blindness overall after cataract. It affects approximately 70 million people and among them, 7 million are blind.[26] Role of CCT in glaucoma diagnosis and management is well documented and understood, but the extent of importance is still debatable and it usually does not influence the type of glaucoma.[27],[28]

The IOP is widely regarded as the most important modifiable risk factor which is associated with the development of glaucomatous optic neuropathy.[29],[30]

In the present study, the IOP was found to be positively associated with CCT and the relationship was statistically significant value (P < 0.001). A recently conducted study shows the positive relationship of IOP with CCT although there is a little variation between normal and glaucoma patients.[31] The relationship between IOP and CCT is proven by many studies and it is also affected by the type of instrument used for measurement. It has been shown that pneumotonometry is more affected by the corneal thickness as compared to Goldman applanation tonometry, but it is not significant. The same study also shows the positive relationship of IOP and corneal thickness as shown by our study.[32] A recent study conducted in Korea also shows positive relationship of IOP and CCT in normal population.[6]

In our study, we did not find any significant relationship between the IOP, AL, and ACD and P > 0.05. Different studies conducted to evaluate the effects of AL and ACD have also shown that IOP is not affected by these variables and the findings from these studies match the outcome of our study.[33],[34]

Different refractive states may affect the IOP and we have observed that CCT is more in myopic eyes as compared to emmetropic and hypermetropic eyes. In the present study, we found that IOP was higher in the myopic eyes as compared to hypermetropic eyes. However, these findings may be affected by the age, ethnicity, and other associated factors such as cataract and the amount of refractive errors. One study has shown that IOP is higher in myopic population as compared to myopic groups but also showed that difference in IOP before and after the onset of myopia is not significant although with advancing age, the IOP is shown to be increased. Another study conducted in Korea showed that high IOP is associated with myopia in young- and middle-aged groups but not in older groups. This study also showed that IOP is also associated with the female gender, higher body mass index, diabetes, hypertension, and hypercholesterolemia (P < 0.05).[35],[36]

The findings from this study indicate that the IOP is increased with increased CCT and it was statistically significant. The IOP and CCT were positively and significantly correlated with the IOP.


  Conclusion Top


It is concluded that persons with high CCT needs to be monitored closely for their IOP because there is strong positive corelationship between increased corneal thickness and IOP and high IOP should not be considered as the only factor rather it should be related with optic disc findings and detailed visual field examination. Similarly, the people with low CCT may be at increased risk of having glaucoma because they may show low IOP which actually may be high and mandates complete ocular examination.

Financial support and sponsorship

This research project was funded by the Research Deanship of Qassim University, Kingdom of Saudi Arabia.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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