Written by Prof. Khalil Al-Salem M.D
Anterior segment ischemia (ASI) is a rare but potentially serious condition that affects the front portion of the eye. It occurs when there is insufficient blood flow to the structures in the anterior segment, leading to tissue damage and visual impairment. In this article, we will explore the causes of anterior ischemic syndrome, symptoms, and treatment of anterior segment ischemia.
Causes of anterior segment ischemia
I have devided causes of Anterior segment ischemia into three categories:
Strabismus surgery: The most common cause of anterior segment ischemia is a complication of strabismus surgery. particularly when extensive muscle surgery is performed. The excessive manipulation or trauma to the eye muscles during surgery can disrupt the blood supply to the anterior segment.
The anterior ciliary vessels contribute to several vascular plexuses, including the episcleral limbal plexus, the intramuscular circulation within the ciliary body, and the major arterial circle in the iris root. When the rectus muscles are disinserted from the sclera, the overlying anterior ciliary vessels are also interrupted. Interruption of the ciliary vessels leads to a decrease in the blood supply to the various anterior segment vascular plexuses that they support.
The anatomical advantage of having more blood vessels supplying the vertical muscles incomparison to the horizontal muscles. Makes tenotomizing horizontal rectus muscles more resilient to cause ischemia in comparison to tenotomizing vertical rectus muscles.
Orbital trauma or surgery: Severe trauma to the eye or orbital region, as well as certain types of eye surgery. Such as orbital decompression surgery for thyroid eye disease, can lead to anterior segment ischemia. The blood vessels supplying the anterior segment may be damaged or compressed, reducing blood flow.
ophthalmic artery obstruction, carotid-cavernous fistula, leukemia, sickle cell disease, Might all cause ASI
Ocular inflammation: Inflammatory conditions affecting the eye, such as uveitis or scleritis, can cause anterior segment ischemia. The inflammation and associated vascular changes can compromise blood flow to the anterior segment structures.
Other risk factors for ASI include advanced age, vascular disease, diabetes mellitus, hyperviscosity, hemoglobinopathies. And 360 degree scleral buckling surgery for retinal detachment.
Symptoms of anterior ischemic syndrome
The symptoms of anterior segment ischemia can vary depending on the extent and duration of the condition. Some common signs and symptoms include:
Decreased vision: Blurred or reduced vision in the affected eye is a common symptom of anterior segment ischemia. The severity of visual impairment can range from mild to severe, depending on the extent of tissue damage.
Eye pain: Some individuals may experience eye pain or discomfort, especially if there is associated inflammation or increased intraocular pressure.
Redness and swelling: The affected eye may appear red and swollen due to the underlying inflammation and vascular changes. The patient might have anterior chamber flare and cells.
ASI sevirity can alter the signs and symptoms. For Example, In its mildest form, ASI presents with decreased iris perfusion and pupillary abnormalities. As severity increases, patients may demonstrate uveitis, keratopathy, hypotony and rarely cataract, corneal scar, and macular changes. Left untreated, the most severe cases can result in phthisis bulbi.
Investigations in anterior segment syndrome
Iris angiography in ASI typically reveals diffuse iris leakage or iris vascular filling defects. These are noticed near the quadrants adjacent to tenotomized muscles. It is worth noticing that iris fluorescein angiography is difficult in heavily pigmented irises. Inaddition, indocyanine green angiography has been used with better success in these patients.
Treatment of anterior segment ischemia
Various recommendations have been made to minimize the risk of ASI in patients undergoing strabismus surgery. Firstly; Avoid surgery on three or four rectus muscles simultaneously. secondly, additional techniques such as plication, vessel-sparing technique, and partial tenotomies have been reported to lower the incidence of ASI. Additionally, some surgeons prefer to use fornix-based incisions and minimally invasive techniques to preserve the perilimbal episcleral vessels.
The management of anterior segment ischemia aims to calm down inflamation to give the body time to restore blood flow to the affected structures and prevent further complications. The treatment options may include:
Medical intervention treatment of anterior segment ischemia:
A) 0.1/5 mL topical dexamethasone drops (16 times/day),
B) Cyclopentolate hydrochloride drops (3 times/day)
C) 1-2mg/KG oral fluocortolone (3 times/day)
Tips and tricks to avoid ASI in Strabismus with multiple Muscle surgery
A) Avoid working on vertical muscles
B) Avoid doing more than 2 muscles during operations with a lag time of 6 months at least to give the body time for adequate revasularization.
C) During muscle plication try to put the stiches at the far end of the muscles spare the middle and put the muscle 1-2 mm away from insetion.
D) In case of resection vessel sparing procedure might be handy. Though might be difficult in some cases
E) During operation on Thyroid eye disease, it will be very useful to lower down inflammation as minimal. This can be achieved by adding topical and systeminc steroid prior to surgery. Finally, In thyroid cases, it is prefered to operate on a single muscle using adjustable sutures.
F) Try to Identify high risk patients ; for Example elderly, previous trauma and surgeries, you might be amazed that a minor intervention in such cases might end up with anterior segment ischemia.