Ocular Histoplasmosis Syndrome - Causes and Treatment

Introduction

Certain eye diseases develop as an extension of underlying disease conditions affecting some other parts of the body. Ocular Histoplasmosis Syndrome is a peculiar condition that is closely connected with a fungal infection.

What Is Ocular Histoplasmosis Syndrome?

Ocular histoplasmosis syndrome (OHS) emerges and progresses as a consequence of a systemic infection - histoplasmosis. The infectious agent in histoplasmosis is a fungus that typically invades the lungs and causes infection. Ocular invasion of Histoplasma is not highly distinguishable until remarkable changes in vision are inflicted in the eyes by the fungus. In the eyes, the fungus specifically impacts the retinal choroid.

What Is Histoplasmosis?

Histoplasmosis is a specific form of fungal infection affecting the lungs. A yeast-like fungus known as Histoplasma capsulatum is the culprit behind histoplasmosis. Histoplasma capsulatum is generally a less virulent fungus in healthy individuals and they cause infections only when the immunity is compromised and weakened. The infection is precipitated by inhalation of air contaminated with fungal spores. It is often elicited in the form of fever, chills, and cough. There will be pain around the chest region as well as in and around the joints.

General weakness is often manifested in certain patients. In most cases, it does not necessitate treatment and resolves independently, even without any therapy. Rarely, it may persist for longer, demanding treatment and attention, especially in individuals with extremely weakened immune responses.

What Causes Ocular Histoplasmosis Syndrome?

• Histoplasma capsulatum fungus is responsible for this ocular version of histoplasmosis infection. The exact mechanism by which the Histoplasma invades the eye is still unclear and various studies are ongoing on the topic to figure it out.

• Some of the reliable hypotheses suggest that ocular histoplasmosis syndrome develops from a previous histoplasmosis infection in the lungs.

• For the condition to develop in the eyes, the fungal spore has to move from the lung tissues to the retinal tissues. The journey of fungal spores to the eyes is still open to discussion.

• Certain theories propose that the fungal spores migrate to the eyes through the circulatory medium (blood), however, there are no scientific pieces of evidence supporting the same.

• It is not necessary that both lung and eye infections develop at the same time. At times the fungal spores linger in the lung tissue in an inert form without causing any infection in the lungs but, later extend into the retinal tissue to cause scarring. In addition, it can also induce the growth of unusual blood vessels in the retinal tissues, which eventually leads to fading of the eyesight.

What Are the Signs and Symptoms Associated With Ocular Histoplasmosis Syndrome?

Ocular histoplasmosis syndrome does not elicit diverse manifestations. It is often associated with limited symptoms, hence, it mostly remains undetected, especially in the initial stages of the condition. Some of the signs and symptoms manifested in the later stages include the following:

• Visual Disturbances: Vision becomes blurry and vague. Blurriness becomes more and more prominent over a longer period. Later, it progresses into vision loss.

• Painless: There is a progressive diminishing of vision however, it is not associated with any kind of pain in the eye.

• Metamorphopsia: It manifests in the form of visual deformations and disfigurement, in which the person perceives straight lines as twisted and wavy. As a result, the person experiences trouble recognizing the object’s actual shape.

• Compromised Central Vision: Fading of the vision is more pronounced in the central vision largely sparing the side vision (peripheral vision).

• Scotomas: These are dark-colored, foggy, and hazy spots encountered in the line of view. These atypical dark spots are more frequently seen in the central and paracentral positions. These spots sometimes appear to blink and flash.

• Compromised Color Vision: The person experiences trouble with color vision, colors appear somewhat dull and somber.

• Defective Object Size Perception: The size of the object is perceived differently by two eyes. The visual defects are not consistent in both eyes, there will be a disparity between the images seen in each eye.

How Is Ocular Histoplasmosis Syndrome Diagnosed?

Ocular histoplasmosis syndrome is largely asymptomatic in the early phase, creating challenges in the diagnosis process. Apart from clinical findings and medical history additional diagnostic tests are required to arrive at a confirmatory diagnosis. Some of the routinely advised diagnostic tests include the following:

• Dilated Eye Examination: Rather than a simple eye examination dilated pupil examination is preferred. A specific agent is applied in the form of an eye drop which facilitates the enlargement or widening of the pupil so that, defects or irregularities can be easily detected. This test aids in the detection of white spots (histo spots), bleeding, and scarring in the retina.

• Fluorescein Angiography: It helps in identifying abnormal and unusual blood vessels in the retina.

• Fundoscopy: It reveals minute scarring which appears as white spots on the retina.

• Optical Coherence Tomography: It provides a more clear picture of the scar, which helps in identifying the exact site and intensity of the scarring. In addition, it also identifies the newly growing blood vessels (neovascularization), thus facilitating the diagnosis.

• Histoplasmin Antigen Skin Test: Specific antigen skin test is done to confirm the presence of Histoplasma capsulatum.

How Is Ocular Histoplasmosis Syndrome Treated?

Ocular histoplasmosis syndrome does not necessitate treatment unless there are severe visual disturbances. Though it sounds like a fungal infection, it is not, hence antifungal therapy is not fruitful. The severity of the symptoms greatly influences the treatment strategies. Different treatment modalities include the following:

• Medical Therapy: Medicines that potentially check neovascularization is advised for OHS, in the form of shots. Some of the widely prescribed medicines include antivascular endothelial growth factors (anti-VEGF) like Ranibizumab and Bevacizumab. It also enhances vision and compensates for vision loss.

• Laser Therapy: A beam of laser is employed for arresting the growth of anomalous blood vessels. Small bleeding points in the retina imparted by neovascularization can be efficiently tackled with the help of laser therapy. It seals off the bleeding points and enhances vision, thereby facilitating visual recovery.

• Surgical Therapy: With the advancement in effective and successful non-surgical treatment methodologies, surgical correction lost its significance and is no longer in practice.

Conclusion

Ocular histoplasmosis syndrome is quite an unusual ophthalmic syndrome that is considered to have deep-rooted relation with systemic histoplasmosis infection. Treatment therapy is indicated only in the presence of visual disparities. Frequently it can be dealt with simple intraocular injections.