Anterior Chamber Angle, Intraocular Pressure, and Globe Biometric Parameters in the Children with β-Thalassemia Major

INTRODUCTION

One of the most common inherited blood disorders is thalassemia major. It is caused by mutation in the gene responsible for the synthesis of the beta chain of adult hemoglobin. Red blood cell maturation leads to ineffective erythropoiesis.¹ Chronic anemia, iron accumulation in the tissues resulting from the red blood cell destruction, repeated blood transfusion, and the use of iron chelators (all these factors) affect organs negatively.²

β-Thalassemia affects more than 42,000 newborns every year all over the world. Populations with the highest prevalence are the Mediterranean, Central Asia, Middle East, India, and the Far East.³

β-Thalassemia major has both systemic and ocular affections. β-Thalassemia affects both anterior and posterior segments of the eye. Ocular surface disorder with goblet cell loss and squamous metaplasia of the conjunctiva,⁴ abnormal conjunctival vessels, against-the-rule pattern astigmatism, steeper corneal curvature, cataract, and thicker lens are some of the anterior segment manifestations of β-thalassemia major. However, retinal pigment epithelium (RPE) degeneration, RPE hypertrophy, angioid streaks, venous tortuosity, and optic nerve head drusen are some posterior segment manifestations. Other manifestations include shorter axial length (AL),² color blindness, and decrease in the visual acuity.

The aim of this study was to find the effect of β-thalassemia on the angle of anterior chamber (ACA), intraocular pressure (IOP), and the other globe parameters.

MATERIALS AND METHODS

The study included 84 eyes. Forty-two eyes of children with thalassemia major (18 male and 24 female) and 42 eyes of control healthy children of the same age-group (12 male and 30 female). The thalassemia major children are on blood transfusion iron-chelating agents. Informed consent was obtained from the parents after detailed information was given. The study protocol was approved by the declaration of Helsinki protocol.

Exclusion criteria included amblyopia, aphakia, strabismus, cataract surgery, history of corneal disease, and systemic disease effect on refractive errors.

Head circumference, height, and weight were recorded for all patients. Complete ophthalmologic examinations were performed for all participants, including the best corrected visual acuity (BCVA), slit lamp biomicroscopic examination, external eye examination, IOP by Goldmann applanation tonometery and fundoscopy.

RESULTS

In this study, the mean age of thalassemia patients was 16.43 ± 3.99, and for the control group was16.29 ± 3.83. The height of thalassemia patients was significantly shorter than the control group with p value of 0.000. However, the head circumference in thalassemia group was more than the control group with p value of 0.000 (Table 1). An insignificant change was observed in best corrected visual acuity (BCVA) with p value of 0.306 (Table 2).

As regards the ACA, the temporal angle (T-ACA) in thalassemia patients was significantly narrower than the control group with p value of 0.008. While the nasal angle showed a nonsignificant narrowing with p value of 0.153 (Table 2), the angle of anterior chamber was positively correlated with height and negatively correlated with the head circumference and IOP. The IOP was statistically higher in thalassemia patients with p value of 0.000 (Table 2). The increased IOP was positively correlated with the head circumference and the LT. However, it was negatively correlated with T-ACA, AL, VCD, and ACD (Figs 1 to 5).

AL, ACD and VCD were significantly shorter in in thalassemia group than the control group with p value = 0.000 for all (Table 3); AL, ACD, and VCD were positively correlated with the height and negatively correlated with the head circumference and IOP (Figs 6 to 17).

The lens was thicker in the thalassemia group than the control group with p value of 0.000 (Table 3). This increase in LT was positively correlated with the head circumference and IOP but negatively correlated with the height (Table 4). As regards relative lens position, no difference was found between both groups with p value of 0.090 (Table 3).

Also, there was steeper corneal curvature in thalassemia group with p value of 0.023 and 0.015 (for K₁ and K₂, respectively). No significant change was observed in corneal thickness in both groups with p value of 0.810 (Table 3).

DISCUSSION

Thalassemia major is a hereditary disease that affects those living in the Mediterranean area, including Egypt, especially with a high incidence of the consanguineous marriages. The disease needs long-lasting follow-up and treatment. It creates an economic and social problem. Many factors affect the life span and the systemic symptoms such as the patient’s socioeconomic and environmental situation. The progression of the disease in patients with thalassemia major, frequent blood transfusions, and the usage of chelating agents could affect the systemic symptoms.⁵ So, it is important to study the effect of thalassemia in different countries.

In this study, ACA was reported to be narrower in thalassemia patients, T-ACA was statistically significant, but N-ACA was statistically nonsignificant. There were no references to other studies to compare these results with others. This narrowing in T-ACA may be due to the increased length thickness that bush iris anteriorly, leading to T-ACA narrowing in the same mechanism of narrowing the angle with age. The affection of temporal angle with sparing of nasal angle is not well understood. But this finding has been found by Chen et al.⁶ who reported that the temporal angle is the angle that narrows with age.

The corneal thickness in both groups was not statistically different. So the increased IOP in thalassemia patients reported in this study and in other studies was not due to the difference in pachymetery. But it may be due to steeper corneal curvature as explained by Nowroozzadeh et al.⁷ However, the increased IOP in thalassemia patients may be due to the short AL, ACD, and VCD and due to the thick lens as supported by the negative correlation between the IOP and AL, ACD, and VCD found in this study (Figs 1 and 2). Also, the positive correlation between the LT and IOP reinforces this hypothesis. The narrower T-ACA may play a role in the increased IOP because a negative correlation between IOP and T-ACA was found in this study (Fig. 5).

Thalassemia major affects the biometric parameters of the globe. In this study, the AL, ACD, and VCD decreased in thalassemia patients. This matches with Khalaj et al.,⁸ Nowroozzadeh et al.,⁷ Heydarian et al.,⁹ and Elkitkat et al.¹⁰ All reported shorter AL and ACD of thalassemia patients. This can be due to the skeletal abnormality affecting the bony orbit as a result of the bone marrow expansion. Pereira and Allemann¹¹ found a correlation between AL, ACD, VCD and the height in normal population. As thalassemia patients have shorter height, they have shorter AL, ACD, and VCD as a part of generalized growth retardation. This hypothesis was supported by the positive correlation between the AL, ACD, VCD, and the height found in my study (Figs 6 to 9).

This study demonstrated an increase in LT in thalassemia patients as reported in some studies.^7–10 The cause of this is not well understood. It might be due to precipitation of iron in lens matter. Despite the lens was thicker in thalassemia patients compared to the control, the relative lens position did not show statistical difference in both groups. This is because the increased LT is compensated by the short AL and ACD.

The thalassemia patients had steeper corneal curvature than the control group, which has been reported by Nowroozzadeh et al.,⁷ Heydarian et al.,⁹ and Elkitkat et al.¹⁰ The cause of this steep cornea has not been understood yet, but the change in a bony orbit may be the cause or it may be a compensatory mechanism for short AL.

The steeper corneal curvature and the increased LT compensate shorter AL. So no statistical difference in BCVA.

CONCLUSION

Thalassemia affects ACA, IOP, and the biometric globe parameters. Narrower T-ACA and increased IOP were found in thalassemia patients. Shorter AL, VCD, and ACD were reported. Also, steeper corneal curvature and thicker lens were found. The CCT and the relative lens position were the same in both thalassemia patients and control groups.

REFERENCES

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