China
Africa
Explore chapters and articles related to this topic
Vitreoretinal surgical anatomy
Published in A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha, Vitreoretinal Surgical Techniques, 2019
The inferior oblique originates from the anteronasal orbital wall and courses temporally and posteriorly beneath the inferior rectus and inserts in the inferotemporal quadrant 10 mm posterior to the lateral rectus insertion (Fig. 1.1c). The ophthalmic artery gives rise to roughly 20 short posterior ciliary arteries; these, along with 10 short posterior ciliary nerves, enter the sclera in a ring around the optic nerve to supply the uvea. There are also two long posterior ciliary arteries and nerves that enter the sclera on either side of the optic nerve at the horizontal meridians. They run anteriorly, to anastomose with short anterior ciliary arteries to form the arterial circle of the iris and ciliary body. These are often used surgically to mark the 3 and 9 o’clock meridians. There are usually seven vortex veins, with at least one in each quadrant. The ampulla of the vortex vein is located just posterior to the equator, and the veins exit 14–18 mm posterior to the limbus. Care must be taken to avoid damaging a vortex vein by sutures or scleral buckling material.
Eye Microcirculation
Published in John H. Barker, Gary L. Anderson, Michael D. Menger, Clinically Applied Microcirculation Research, 2019
The eye receives its blood supply from the ophthalmic artery, which enters the orbita through the optic canal. Inside the orbita, anterior ciliary arteries branch off and follow the extraocular muscles to their insertion anteriorly in the sclera. Here, the main vessel penetrates the sclera to supply the anterior segment of the eye, including the ciliary body and the iris, while smaller branches leave to supply the perilimbal conjunctiva. The posterior ciliary arteries branch from the ophthalmic artery in a variable number just behind the eyeball, with two long vessels branching to the equatorial choroid, and about ten shorter vessels branching to the posterior choroid. After penetration of the sclera, the choroidal vessels branch and end in lobules with large fenestrated capillaries that are in close proximity to the retinal pigment epithelium.1 Structural evidence suggests that choroidal lobules in the periphery are supplied by a central arteriole and are drained by venoles arranged peripherally at the lobule, whereas the reverse arrangement exists in the posterior pole.2 The choroid has the largest blood perfusion in the body per unit tissue weight, and the resulting small oxygen extraction (5%) ensures a high ambient oxygen concentration in the outer retina supplied by this system.3 The choroidal circulation is regulated autonomously with sympathetic innervation from the superior cervical ganglion and parasympathetic innervation from the ciliary and the pterygopalatine ganglions.4
Glaucoma
Published in Mary E. Shaw, Agnes Lee, Ophthalmic Nursing, 2018
The blood supply to and drainage from the angle of the anterior chamber is via Anterior ciliary arteriesAqueous humour vein
Single Muscle Transposition in the Management of Monocular Elevation Deficiency
Published in Journal of Binocular Vision and Ocular Motility, 2020
Louis J. Stevenson, Sheetal Shirke, Elaine Y. H. Wong, Lionel Kowal
The use of single muscle transposition in the management of MED syndrome was first described by Gandhi and Kekkunnaya in 201811 and is inspired by the utility of SR only transposition (SRT) used for Duane’s and sixth nerve palsies.12 This novel technique overcomes a number of limitations inherent to Knapp’s procedure. Anterior segment ischemia is a rare but potentially sight-threatening complication of strabismus surgery caused by disruption to the anterior ciliary arteries. Operations involving three or more recti muscles are at high risk for anterior segment ischemia, and procedures involving three muscles should be avoided or staged.13 Not only does single muscle transposition reduce the risk of anterior segment ischemia overall, it allows for IR recession to be performed during the same procedure as horizontal muscle transposition. By operating on the LR only, compared to both horizontal recti muscles, a broader range of management options are also available for correcting any associated horizontal deviation.
Risk of Anterior Segment Ischemia Following Simultaneous Three Rectus Muscle Surgery: Results from a Single Tertiary Care Centre
Published in Strabismus, 2018
Shailja Tibrewal, Ramesh Kekunnaya
The pathological basis of development of anterior segment ischemia following tenotomy of rectus muscles can be understood by studying the anterior segment circulation. The anterior segment of the eye derives its blood supply from two types of vessels; the long posterior ciliary arteries (LPCA) and the anterior ciliary arteries (ACA). The medial and lateral LPCA run in an intrascleral course beneath the medial and lateral rectus muscles respectively. The anterior ciliary vessels originate within the rectus muscles belly and are derived from the muscular branches of the ophthalmic artery. Barring a few anatomical variations, mostly there are two anterior ciliary arteries in all rectus muscles excepting the lateral rectus muscle which has one ACA.16,17 Primate studies have shown that the LPCA account for around 30% and ACA account for 70–80% of anterior segment circulation.18 Additionally there are three levels of anastomosis between the two sets of circulation; one between the adjacent ACA at the episcleral circle and two between the LPCA and ACA at the intramuscular circle and the major arterial circle. Experimental primate studies have shown that occlusion of the long posterior ciliary arteries in itself produces no changes in the anterior segment circulation.19 Similarly, when two or three rectus muscles are operated simultaneously it leads to transient mild to moderate ASI. However when all four muscles are tenotomised or when the posterior circulation is occluded along with the horizontal rectus muscle surgery, it leads to severe ASI in monkeys.19
Iris vessel dilation and hyphema due to forceps trauma in a newborn
Published in Journal of Obstetrics and Gynaecology, 2019
Alexandra Tantou, Maria Kotoula, Petros Koltsidopoulos, Evangelia Tsironi, Eleni Papageorgiou
The iris and ciliary body are supplied by the anterior ciliary arteries, the long posterior ciliary arteries and anastomotic connections from the anterior choroid vasculature (Kiel 2010). The two long posterior ciliary arteries arise from the ophthalmic artery, pierce the sclera near the posterior pole, and then travel forward to the ciliary body, where they anastomose to form the major arterial circle of the iris. The anterior ciliary arteries travel with the extraocular muscles and pierce the sclera near the limbus to also join the major arterial circle of the iris (Kiel 2010). The iris and ciliary body are drained primarily through the anterior ciliary veins, which participate in the vortex vein system, finally emptying into the cavernous sinus and the jugular veins. The underlying mechanism for an iris haemorrhage may be due to the compression of the foetal head in the birth canal, which is exacerbated by forceps use (Choi et al. 2011). Specifically, under those circumstances the intracranial and central venous pressures increase, which is accompanied by the venous stasis and the engorgement of the ophthalmic veins due to the venous return obstruction (Choi et al. 2011). The iris veins have very thin walls consisting of endothelium surrounded by a thin layer of collagen, thus being susceptible to rupture and haemorrhage. Additionally, a possible hypoxia during a forceps-assisted delivery might be a cause of an iris haemorrhage. It has been suggested that an autoregulatory hypoxic cerebral vasodilatation produces an increase in the intracranial pressure, which in turn increases the retinal venous pressure (Geddes et al. 2003).