INTRODUCTION

Macular telangiectasia sometimes referred to as idiopathic juxtafoveal macular telangiectasia (abbreviated MacTel), is a disease that affects the macula, causing degradation of central vision. Essentially, macular telangiectasia causes disease within the tiny blood vessels that affect the fovea causing loss of fine detail, especially reading the fine print.

EPIDEMIOLOGY OF MACULAR TELANGIECTASIA

Patients with idiopathic macular telangiectasia type 1 are typically 40 years of age or older. They may have a coincident history of ischemic vascular diseases such as hypertension, diabetes or, coronary disease but these do not appear to be causative factors.

Macular telangiectasia type 2 usually presents first between the ages of 50 and 60 years, with a mean age of 55–59 years.

SIGNS AND SYMPTOMS OF MACULAR TELANGIECTASIA

They may present with a wide range of visual impact, from totally asymptomatic to substantially impaired; in most cases, however, patients retain functional acuity of 6/60 or better. Metamorphopsia may be a subjective complaint. Due to the development of paracentral scotomata, reading ability is impaired early in the disease course. It might be even the first symptom of the disease.

MacTel may remain stable for extended periods, sometimes interspersed with sudden decreases in vision. Patients’ loss of visual function is disproportionately worse than the impairment of their visual acuity. MacTel does not cause total blindness, yet it commonly causes a gradual loss of the central vision required for reading and driving.

PATHOPHYSIOLOGY OF MACULAR TELANGIECTASIA

There are three types of macular telangiectasia, Type 1 (aneurysmal type) Type 2 (perifoveal type) and Type 3(occlusive type).

Type 1 macular telangiectasia, the less common form, usually affects only one eye. The blood vessels in the macula become dilated and form microaneurysms. Microaneurysms are small outpouchings that occur in the blood vessels. Fluid can build up in the macular area causing swelling and loss of vision. In addition, there is atrophy of the neurosensory retina. Typically, the first clinical finding is decreased retinal transparency of parafoveal macula, often referred to as ‘retinal graying.’ There are also crystalline deposits, depletion of the macular pigment and dilated macular venules and arterioles at right angles.

Atypical intraretinal and subretinal anastomoses may occur. Hyperplastic plaques of retinal pigment epithelium (RPE) may be found at the end of dilated vessels and are sometimes surrounded by atrophy of the RPE.

These plaques follow photoreceptor loss and are typically associated with an absolute scotoma. These changes occur just temporal to the fovea, initially, but may later expand to include the fovea.

Neovascularisation of the retina can occur, as can small retinal haemorrhages with or without neovascularisation. The neovascularisation complexes originate from the deep capillary plexus but may invade the subretinal space and rarely can form shunts with the choroid.

Type 2 macular telangiectasia is much more common. The blood vessels in the macula become dilated and leak fluid causing swelling and scarring which can lead to vision loss. Sometimes new blood vessels grow beneath the macula, affecting the macular photoreceptors and causing loss of vision. Type 2 tends to affect both eyes and both genders, as opposed to Type 1, which most often affects only one eye. Visual acuity may be mildly reduced in the early stages of MacTel type 2, typically better than 6/15 until foveal atrophy begins to occur. Visual acuity often declines slowly or remains stable for many years, and rarely becomes lower than 6/60. Metamorphopsia and paracentral scotoma can occur.

MacTel type 2 includes enlargement of the foveal avascular zone in proportion to disease severity; decreased retinal capillary density; and ectasia, dilation, truncation and telangiectasis of the vessels of the retinal capillary plexi, beginning temporally early in the disease and eventually encircling the fovea.

Milder or early MacTel type 2 may show dilated vessels in the deep retinal capillary plexus mostly temporal to the fovea, but the superficial capillary plexus will appear normal. With progression, OCT may reveal telangiectatic vessels emanating from the central retina and extending to the inner and outer retinal layers that may appear aneurysmal, associated with disruptions of the ellipsoid zone.

Type 3 macular telangiectasia exists but is extremely rare. Patients with Type 3 tend to have more vessels diseased, causing the blood vessels to become occluded.

MANAGEMENT OF MACULAR TELANGIECTASIA

Diagnosis of macular telangiectasia is made by first having a comprehensive eye examination. The eye care practitioner will perform an Amsler Grid test to determine if there are any distorted areas in central vision. MacTel diagnosis may be aided by the use of advanced imaging techniques such as fluorescein angiography (FA), fundus autofluorescence (FAF), and optical coherence tomography (OCT). These can help to identify the abnormal vessels, pigment plaques, retinal crystals, foveal atrophy and intraretinal cavities associated with this disorder. The advent of OCT has allowed better characterisation of the nature of the inner and outer lamellar cavities. Loss of central masking seen on autofluorescence studies, apparently due to loss of luteal pigment, is now recognised as probably the earliest and most sensitive and specific MacTel abnormality.

Optometrists are encouraged to refer MacTel patients to retinal specialists for further management. Since macular telangiectasia is considered a relatively rare condition, there is still much we do not fully understand. The MacTel research Project guides practitioners in management. We do know that some patients may only need careful monitoring and may not need treatment at all. If the blood vessels begin to leak fluid and cause swelling and scarring, ophthalmologists may use laser treatments to help relieve the swelling and reduce complication. Photocoagulation should be used sparingly to reduce the chance of producing a symptomatic paracentral scotoma and metamorphopsia. Small burns (100–200 μm) of moderate intensity in a grid-pattern and on multiple occasions, if necessary, are recommended. It is unnecessary to destroy every dilated capillary, and, particularly during the initial session of photocoagulation, those on the edge of the capillary-free zone should be avoided. Intra-vitreal injection of steroids is sometimes used to quell inflammation, and newer drugs, such as anti-vascular endothelial growth factor (anti-VEGF) drugs, are being used to stop abnormal blood vessel growth.

CLINICAL PEARLS

• Mactel type 1 is best defined as an acquired capillary ectasia (i.e., a focal expansion or outpouching) and dilation in the parafoveal region, leading to vascular incompetence. The telangiectatic vessels develop micro-aneurysms, which subsequently leak fluid, blood, and occasionally, lipid. Patients with this condition may have it for years with little or no symptoms. As the disease progresses, they experience the following: blurred vision, distorted vision, loss of central vision and skipping letters or words.
• MacTel type II is characterised by telangiectatic vessels in the juxtafoveolar region, most commonly temporal to the fovea, of both eyes. Additional findings include graying of the parafoveal retina, superficial crystalline deposits, subfoveal cavities, and right-angle vessels. Symptoms include blurred vision, metamorphopsia, and paracentral scotomas.  Fluorescein angiography will highlight the parafoveal telangiectatic vessels that show early hyperfluorescence with late leakage. OCT will show subfoveal cystoid spaces without cystoid macular oedema. Fundus autofluorescence is very diagnostic in that the normal hypoautofluorescence at the fovea is lost and will show abnormally increased foveal autofluorescence.
• FA imaging is recommended to confirm the diagnosis by the presence of temporal juxtafoveal leakage, distinctly different than diabetic macular oedema or choroidal neovascularisation, and to rule out other pathologies such diabetic retinopathy or wet age-related macular degeneration.
• Familiarity with the distinctive rectangular-shaped cavity appearance on OCT is key for correct diagnosis. It is important to remember that all cystic spaces on OCT are not fluid or cystoid oedema.

CONCLUSION

Since Macular Telangiectasia is subject to lost photoreceptors that cannot be recovered, early diagnosis and treatment appear to be essential to prevent loss of visual function.

REFERENCES

1. The MacTel Project. http://www.lmri.net. Accessed 11 January 2019.
2. Gass JD, Oyakawa RT. Arch Ophthalmol. 1982;100:769-80.
3. Gass JD, Blodi BA. Ophthalmology. 1993;100:1536-1546. & Francis.
4. Hua J, et al. Invest Ophthalmol Vis Sci. 2011;52:2809-16.