Jagdish Dukre

INTRODUCTION

Angioid streaks were first described by Doynein 1889.

They are also called Knapp’s striae as he first coined the term in 1892 because of their marked resemblance to blood vessels.

However it was in 1917 that Kofler correctly determined that they represented changes at the level of Bruch’s membrane.

EPIDEMIOLOGY

Angioid streaks have been documented in early childhood but are not thought to be present at birth.

No known sex or race predilection exists.

PATHOGENESIS

Angioid streaks represent breaks or dehiscences in a thickened, calcified, and abnormally brittle Bruch’s membrane.

Whether the breaks occur spontaneously or are caused only by trauma, even if minor, is not known.

The initiating stimulation for the calcification and degeneration of Bruch’s membrane in patients who have angioid streaks is not yet known.

The elastic lamina that occupies the midsegment of Bruch’s membrane is primarily affected, which results in disintegration and fraying of the elastic fibers.

Diffuse and extensive basophilic stains caused by the deposition of calcium are commonly seen with routine hematoxylin and eosin.

The choriocapillaris and RPE are minimally affected initially; however, with progression these structures become secondarily degenerated..

Eventually, neovascular vessels from the choroid may penetrate through the breaks in Bruch’s membrane.

It results in subretinal hemorrhage, exudation, and edema followed by the fibrovasculardeposition that is typical of a disciform scar.

All cases of angioid streaks studied histopathologically have shown identical changes despite different underlying systemic diseases

Clinical appearance Angioid streaks appear as narrow, jagged lines

deep to the retina, almost always bilaterally.

They can closely resemble blood vessels because of their size, shape, color, and course.

Angioid streaks typically radiate out in a cruciate pattern from an area of peripapillary pigment alterations, although they may circumferentially ring the peripapillary area as well.

Generally, they taper and fade a few millimeters away from the optic disc; however, they have been reported to extend farther anteriorly.

Very rarely they occur in a random distribution throughout the posterior pole.

The number of streaks can be variable. Progression of the streaks with time has been observed.

The color of angioid streaks depends on the background coloration of the fundus and the degree of atrophy of the overlying retinal pigment epithelium (RPE).

In lightly colored fundi, angioid streaks are red, reflecting the pigmentation of the underlying choroid.

In patients who have darker background pigmentation, angioid streaks are usually a medium to dark brown.

The factors responsible for the characteristic radiating configuration of angioid streaks are not clear.

It has been suggested that the pull of the extraocular muscles creates stress forces against the fixed point of the optic nerve, which results in the characteristic pattern.

Other associated fundus

findingsPeau d’orange change

Appear as diffuse mottling of

RPE, represent focal defects in

Bruch’s membrane and

choriocapillaries

produce hypofluorescent areas on

fluorescein angiography (FA) and

speckled pattern in mid periphery

on ICG.

They are usually seen in the

temporal midperiphery and may

be observed even before the

appearance of angioid streaks.

Fresh haemorrhages.

Paired red spots along streaks.

Cracked egg shell appearance of fundus- diffuse type of angioidstreaks.

Salmon spots Peripheral punched out focal yellowish atrophic RPE lesions.Optic disc drusen - They are seen in around 10% of patients.They are produced due to attachment of calcium containing macromolecules to elastic fibres of cribriformplate which disrupt the axonal flow.

Clinical course and

complications

Patients with angioid streaks are generally asymptomatic unless the lesions extend towards the foveola or develop complications .

The increase in length and width of streaks is considered an expected feature of disease.

The various complications seen in such patients

are:

Choroidal neovascularisation (CNV)

Macular degeneration

Traumatic membrane ruptures

RPE tears

Choroidal neovascularisation

(CNV)

It is the most common and serious complication seen in 72-86% of patients.

Commonly involves both the eyes but not simultaneously, there is roughly an interval of 18 months.

The risk of development of CNV increases with age and it is seen that the wider and longer are the streaks the higher the risk of CNV

There is higher the risk of CNV specially if the lesions are located in the distance less than one optic disc diameter from the foveola.

The standard outcome is poor if CNV in macular region remains untreated as it will lead to more extensive subfoveal scarring causing severe vision deterioration.

Macular degeneration

It is seen in 72% of these patients and is of two types:

Exudative

It is more common and its occurrence is associated with:

length of streak,

the distance of streak from fovea or

‘cracked shell type of streak’

however it does not occur in all the patients with streak passing through fovea.

Atrophic

Traumatic membrane ruptures

Patients with angioid streaks develop breaks in Bruch’s membrane even after relatively mild injuries since their Bruch’s membrane is brittle.

They are frequently followed by subretinalhaemorrhages which can be misinterpreted as CNV.

These haemorrhages appear next to angioidstreaks and sometimes disseminate to macular area.

RPE tears

They have also been reported in angioid streaks.

Systemic associations

Common systemic findings associated with angioid streaks include

pseudoxanthoma elasticum (34%),

Paget’s disease (10%),

hemoglobinopathies (6%).

Upto 50% cases are, however, idiopathic.

Diagnosis

Fluorescein angiography (FA)

First the initial photographs are taken with filters on but before injecting the dye

angioid streaks present the phenomenon of autofluoresence.

Also optic disc drusen associated with them also show this phenomenon.

Typically, angioid streaks show ‘window defect’ in FA due to RPE atrophy adjacent to them, demonstrating early hyperfluorescence of the streaks with late staining.

Others have reported hypofluorescence of streaks with hyperfluorescence of margins with late staining.

Leakage of fluorescein is evident when CNV is present .

On FA the angioid streaks will only become visible when there are concomitant RPE alterations like loss of pigment granules or ruptures in cell layer.

Indocyanine green angiography (ICG)

It has been found to be superior to FA in delineating angioid streaks and peau d’ orange changes.

Besides occult CNVM can be better detected on ICG.

Optical Coherence Tomography (OCT)

Detects the breaks in Bruch’s membrane and helps in detecting and monitoring associated abnormalities such as CNV.

Recently Near Infrared Reflectance imaging studies using diode of 820 nm have shown very high sensitivity in detection of angioid streaks.

Management

Because even minor ocular trauma can cause subretinal hemorrhages, patients should be encouraged to use eye protection and avoid contact sports.

Therapy is possible and indicated only whenever a CNV has developed.

Prophylactic photocoagulation of angioid streaks may stimulate CNV formation and is contraindicated.

Laser photocoagulation

It has been widely used to treat well defined juxtafoveal and extrafoveal CNV

But high recurrence rates have been seen in CNV associated with angioid streaks.

Moreover laser induced scar progression has also been reported resulting in deterioration of visual acuity precluding its use in subfoveallesions.

Photodynamic therapy (PDT)

Subfoveal lesions have been treated with PDT with verteporfin.

The short term benefits of PDT are limiting the visual damage.

But the long term results include:

enlargement of the CNV lesion to a disciform scar

associated visual loss,

ruptures of already brittle Bruch’s membrane and

damage to collateral choriocapillaries.

It has also been seen that though PDT alone can occlude CNV but it tends to cause transient inflammatory response and increase in capillary permeability along with enhanced expression of vascular endothelial growth factor (VEGF) shortly after the treatment.

The VEGF upregulation typically peaks one week post PDT resulting in recurrence of CNV and limiting the efficacy of PDT alone.

Combination therapy like PDT with intravitreal Triamcinolone Acetonide (IVTA) or preferably PDT with intravitreal Bevacizumab has also been found to be efficacious not only in terms of regression of CNVM and visual improvement but also in reducing the number of treatments required.

Anti VEGF agents

Because of their unprecedented visual outcomes in treatment of CNV due to age related macular degeneration, anti-VEGF agents have been tried in CNV associated with angioid streaks.

In contrast to previous therapeutic regimens which result in disciform scarring and irreversible loss of RPE and overlying retina, intravitreal anti-VEGFs have shown an improvement in visual acuity and anatomic outcomes without causing a scar formation especially in eyes that have not received any treatment previously.

Other treatment modalities which have been used in treatment of CNV in angioid streaks are :

transpupillary thermotherapy with unfavourable outcome in terms of spreading of lesions and

macular translocation surgery whose role is yet to be determined fully.

Take home Message Angioid streaks are visible irregular crack-like dehiscences in

Bruch’s membrane that are associated with atrophic degeneration of the overlying RPE.

They may be associated with pseudoxanthoma elasticum, Paget’s disease, sickle-cell anemia, but also appear in patients without any systemic disease.

Patients with angioid streaks are generally asymptomatic, unless the lesions extend towards the foveola or develop complications such as traumatic Bruch’s membrane rupture or macular CNV.

The visual prognosis in patients with CNV secondary to angioidstreaks if untreated is poor and most treatment modalities, until recently, have failed to limit the devastating impact of CNV in central vision.

However, it is likely that treatment with anti-VEGF agents, especially in treatment-naive eyes yields favourable results and this has to be investigated in future studies