The eye in sickle cell disorder

Introduction

Sickle Cell Disorder (SCD) is inherited from both parents and in West Africans, the predominant types are sickle cell anaemia (Hb SS) and less commonly, sickle cell haemoglobin C disorder (Hb SC). Apart from a longer average life-span, people with Hb SC generally enjoy a better quality of life with far less frequent or severe crises of pain and/or anaemia. However, eye complications seem to affect persons with Hb SC more than those with Hb SS.

 

Structure of the eye

For simplicity, the eye can be divided into three parts:

1. The outer lining of the eye (the conjunctiva membrane) and the coats
2. The anterior segment
3. The posterior segment respectively separated by the crystalline lens.

In SCD, ocular manifestations also occur and will be discussed as they affect the 3 parts of the eye.

 

The conjuctiva membrane

This membrane is very rich in blood vessel which divide and thin outwards. The loops and tortuosity of the vessels are more obvious in people with SCD and they tend to bleed into the membrane because they are fragile. Such bleeding presents as blood-shot eyes but does not affect vision. The bleeding is reabsorbed over one or two weeks but can recur. No treatment is necessary except reassurance by the eye doctor if they become frequent.

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The anterior segment

Within the anterior segment of the eye lies the brown band with a central hole – the IRIS. The vessels within the iris can also bleed and when they do, the blood is seen as fresh blood within the eye with a level. This type of bleeding depending on its severity can interfere with vision. When this occurs, the eye doctor (Ophthalmologist) should be consulted immediately for treatment. Admission to the hospital or even a minor operation to wash out the blood from the eye may be necessary. If delayed, a complication such as cataract may develop. This type of bleeding is commoner in persons with Hb SC than in those with Hb SS and may even be the first indication of SCD in patient.

Posterior segment

In this part is the vitreous (jelly-like) fluid. Most of the sight-threatening manifestations of SCD occur in this posterior segment. They include:

(i)    Bleeding into the vitreous: this is quite common especially in Hb SC but does also occur in Hb SS and rarely in Hb AS. The patient will complain of sudden reduction or loss of vision in one eye – rarely in both eyes. The degree of reduction or loss of vision depends on the severity of the bleeding. The bleeding is gradually reabsorbed over time, with residual fibrous tissue formation in the vitreous, it tends to recur and with each episode and re-absorption, the fibrous tissue formation increases.

(ii)   Bleeding into the macula (the part of the eye used for focusing): this may also occur and present as a sudden reduction or loss of vision depending on the severity of the haemorrhage

(iii)  Bleeding into the retina (the inner membrane of the coat of the eye): this is common but may not be accompanied by loss of vision except the macula is involved. Often, this is found on routine eye examination or the eye examination following a resolving or resolved vitreous bleeding.

(iv)   Development of abnormal, fragile blood vessels: with retinal bleeding and absorption, abnormal, fragile blood vessels develop in areas of previous retinal bleeding. These new vessels are formed haphazardly and so tend to bleed more often.

 

Visual complications in scd

The scar in the vitreous areas forms a string-like pattern which becomes attached to the retina. With recurrent bleeding and scaring, the string-like (fibrous) membrane pulls on the retina and may have abnormal fragile vessels developing within the membrane. This may lead to the detachment of the retina from the outer coat of the eye and further bleeding into the vitreous

 

Detached retina

This is the most dreaded eye complication in SCD. It causes sudden loss of vision associated with seeing flashes of light. Surgery is mandatory in this condition to restore vision.

All persons with SCD, particularly those with Hb SC should have a regular eye check-up at least once every year. However, where there are complaints (symptoms) the patient should consult an Ophthalmologist immediately for proper diagnosis and treatment. Post consultation follow-up visits to the eye doctor should be made until the eye doctor discharges the patient from further appointments concerning that episode. Notwithstanding this, annual eye check-ups should still be made.

 

Conclusion

A stitch in time saves nine. Early diagnosis and treatment of eye disease and complications in SCD prevents Blindness.

Culled from the Sickle Cell Bulletin Vol. 10. No. 1