Surg Radiol Anat (1999) 21:371-375

Original articles

Surgical Radiolog,c Anatomy Journal of Clinical Anatomy

© Springer-Verlag 1999

Topoanatomic relations of the ophthalmic artery viewed in four horizontal layers

A. Jo-Osvatic, N. Basic, V. Basic, T. Jukic, V. Nikolic and D. Stimac

Department of Anatomy, School of Medicine, University of Zagreb, Croatia

Summary: In the present paper we have studied the gross anatomy of the ophthalmic artery in 200 human cada- ver dissections viewed in four horizon- tal layers. The ophthalmic artery can be divided into the origin, intracranial, intracanalicular and intraorbital parts. The most common origin of the artery was from the medial half of the anterior side of the internal carotid artery (ICA) in its upper curve (52%), followed by the medial half of the superior side (44%), and in only 4% from the medial side of the upper curve of the ICA. We have examined the topographic anato- my of the ophthalmic artery in detail, and found a rare anastomosis of the ophthalmic artery with the frontal bran- ch of the middle meningea l artery.

Corr61ations anatomo-topogra- phiques de l'art~re ophtalmique examin6e sur 4 plans horizontaux

R~sum6 :Dans ce travail, nous avons 6tudi6 sur 200 pr6parations cadav6- riques l ' ana tomie macroscopique de l 'art6re ophtalmique sur des prdpara- tions en 4 couches horizontales. L'art6- re ophtalmique peut ~tre divis6e en plu-

Correspondence to : A. Jo-Osvatic

sieurs segments : ~ son origine, puis les segments intracr~nien, intracanaliculai- re et intra-orbitaire. L' origine la plus souvent retrouv6e 6tait la moiti6 m6dia- le de la paroi antdrieure (52 %), suivie par la moiti6 m6diale de la paroi sup6- rieure (44 %), et dans seulement 4 % des cas de la paroi m6diale de la cour- bure sup6rieure de l 'a r t6re carotide interne. Nous avons examin6 l 'anato- mie topographique de l'art~re ophtal- mique en d6tail et trouv6 une anastomo- se rare de l'art~re ophtalmique avec la branche frontale de l 'art~re m6ning6e moyenne.

Key words: Ophthalmic artery - Optic nerve- Anatomy

It is necessary to be familiar with the variations in the course of the ophthal- mic artery and its branches for the eva- luation and treatment of certain orbital pathologies, especially those of vascu- lar origin. Several anatomic studies have described in detail the diameter of the artery, but without detailed descrip- tion of its topoanatomic relations to the adjacent structures within the orbit [10, 11, 12, 14]. Their results demonstrated great variability, not only in the course of the ophthalmic a., but also in the ori- gin and number of collateral branches [10, 11, 12, 13, 20]. The topographic

anatomy of the orbital veins and nerves has been described previously [15, 16, 17, 27]. In the present study we investi- gated the gross anatomy of the ophthal- mic a. and its relation to the optic nerve in four horizontal layers.

Material and methods

The topographic relations of the ophthal- mic a. were examined in 200 anatomic specimens prepared from 100 fresh adult Caucasian cadavers. The average age of the subjects was 65.5 years (range 36 to 89). The arterial system was injected with red-dyed neoprene 601A in 10 pre- parations, but as this destroyed the topo- graphic relations in the area we abando- ned this method. However, injection of dye enabled excellent visualisation of the ophthalmic a. and was used for pho- tographic purposes.

The diameter of the ophthalmic a. was measured with a calliper in all spe- cimens before injection of dye, at the exact site of its origin on the internal carotid a., and at other locations as des- cribed below.

Removal of the skullcap and brain exposed the terminal part of the internal carot id a. (ICA) and the cavernous sinus. The orbital part of the frontal bone was removed by careful dissec- tion, thus enabling the visualisation of orbital structures.

372 A. Jo-Osvatic, et al.: Topographic anatomy of ophthalmic artery

The topographic anatomy of the ophthalmic a. was examined in four layers:

1. After removal of the orbital roof the f i rs t l ayer was exposed . The supraorbital a., posterior ethmoidal a., and the anterior curve of the ophthalmic a. hidden within the fatty tissue bet- ween the superior oblique and levator palpebrae superioris rnm. were visible.

2. For visualisation of the second layer, it was necessary to cut and pull forward the frontal n. and supraorbital a. A medial cut through the muscle body followed by distraction forward and backward was made in the levator palpebrae superioris and superior rectus ram. In this layer, the ophthalmic v. with its tributaries, the anterior part of the ophthalmic a., and the anterior and posterior ethmoidal aa. and lacrimal a. were exposed.

3. The ophthalmic v. was cut at its entrance into the cavernous sinus and bent frontally enabling visualisation of the third layer and its contents (i.e. the ophthalmic a. with its branches).

4. After that, the common tendinous ring was d i ssec ted and cut. It was necessary to cut and remove the optic n., nasociliary n., and ophthalmic a. at their entrance into the orbit to expose the fourth layer of the orbit with the ciliary ganglion, motor nerves, ophthal- mic a. and optic n.

Results

The origin of the ophthalmic a.

Our results demonstrated that in all spe- cimens the ophthalmic a. originated from the upper curve of the ICA (Fig. 1B). In 52% of cases the origin was located on the medial half of the ante- rior side, in 44% on the medial half of the superior side and in only 4% on the medial side of the upper curve of the ICA.

Intracranial and intracanaIicular segments of the ophthalmic a.

At the beginning of the ophthalmic a., two different segments can be distingui- shed: the intracranial (Fig. 1A, ta) and intracanalicular segments (Fig. 1A, lb)

Fig. 1A, B. A Normal pathway of the ophthalmic a. (left orbit). The ophthalmic a. arises from the circum- ference of the ICA, passes through the optic n. canal and enters the orbit, la, intracranial part; lb, intracanNicutar part; 2al, intraorbital part (suboptic division); 2a2, intraorbital part (divi- sion lateral to the optic n.); 2b, intraorbital part (supraoptic division); 2e, intraorbital part (divi- sion located on the medial orbital wall); B Origin of the ophthalmic a. from the ICA. In 52% of cases it originates from the medial half of the anterior side, in 44% from the medial half of the superior side and in 4% from the medial side of the ICA

[5]. The intracranial part of the artery is visible after removing the optic n. (Fig. 1A). In 94% of dissections this part was located below the lateral half and in 5% under the medial half of the optic n. In 2 specimens (1%) it was medial and in 1 specimen lateral to the optic n. The intracanalicular segment of the ophthal- mic a. was located in the double dural membrane of the optic n., visible only after the membrane was removed. In some instances, it was necessary to remove the bony substance between the artery and the optic n. In such cases the optic canal was divided into two canals, the upper for the nerve and the lower for the artery. The length of the intra- cranial segment was 4.66_+3.35 mm, and that of the intracanalicular segment 8.68_+2.16 mm.

In this area, exactly at its origin from the ICA, the diameter of the oph- thalmic a. was 1.94+_1.50 mm (range

0.8 to 2.4 mm). The distance between the point where the ophthalmic a. cros- sed the optic n., and the posterior pole of the eyebal l was 15.28_+1.27 mm (range 12.5 to 18.2 ram). The distance from the entrance of the central retinal a. into the optic n. to the posterior pole of the eyebal l was 11.04_+1.29 m m (range 9.4 to 13.1 ram).

In 9 specimens the axes of the oph- thalmic a. and the optic n. diverged at an acute angle. In these specimens the ophthalmic a. passed under the medial half of the optic n., and the intracranial region was not long enough for the oph- tha lmic a. be fore enter ing into the double dural membrane spreading to its lateral side.

Intraorbital segment

The intraorbital part of the ophthalmic a. was longer than the initial segment and had a more compl ica ted course (Fig. 1A, 2a-c). From this segment, all the branches arose from the ophthalmic a., except the small arteries for the vas- cularisation of the dural membrane of the optic n.

a. The first part of the intraorbital course of the ophthalmic a. was straight in the majority of our specimens. It was located in the apical part of the orbit, most often lying along the lower part of the optic n., initially located under the optic n., than under the lateral edge of the nerve where the artery changed its course again (Fig. 1A, 2al). After that, its path was parallel to the lateral side of the optic n. where it gently sloped diagonally upwards and forwards (Fig 1A, 2a). Eighteen mm behind the poste- rior edge of the eyeball, the artery chan- ged d i rec t ion and entered into the second part of the intraorbital course, crossing over the optic n. f rom the superior side (Fig. 1A, 2b). From the beginning of the first part of its intraor- bital course of the ophthalmic a., arte- ries that supply the optic n. and the cen- tral retinal a. branched from the main arterial trunk. These arteries travelled parallel with and close to the optic n., up to the point where they entered the nerve. The lateral posterior ciliary a. and lacrimal a. left the ophthalmic a. at the point where the ophthalmic a. for-

A. Jo-Osvatic, et al.: Topographic anatomy of ophthalmic artery 373

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Fig. 2 Cadaveric specimen (left) and diagram (right) of the most usual pathway of the ophthalmic a. 1, ophthal- mic a.; 2, lacrimal a.; 3, posterior ciliary a.; 4, muscular branches; 5, anterior ethmoidal a.

med a sharp angle travelling into its second intraorbital segments. The dia- meter of the ophthalmic a. where it crossed the optic n. ranged from 1.0 to 2.9 (mean value 1.95+0.8 mm).

b. The second part of the intraorbital course of the ophthalmic a. began where the artery approached the lateral side of the optic n. and started to cross over it at a right, acute, or obtuse angle from the

superior or inferior side. In this part of its course, the artery was oriented ante- riorly between the medial rectus and superior oblique ram. and it became sinuous (Figs. 1A, 2b). The point where the artery changed direction and shape presented the end-point of the second part of the intraorbital segment. In spe- cimens in which the artery crossed over the optic n. from the superior side, the

Fig. 3 Cadaveric specimen (left) and diagram (right) of the ophthalmic a. crossing the optic n. from the inferior side; 1, ophthalmic a.; 2, lacrimal a.; 3, posterior ciliary a.; 4, muscular branches; 5, anterior ethmoidal a.

nasociliary n. was located medial to the artery, and above the ophthalmic v. and superior rectus m.

c. The third part of the intraorbital course of the ophthalmic a. was located in the angle between the upper edge of the superior rectus and superior oblique mm., with the nasociliary n. running parallel with it (Figs. 1A, 2c). In the frontal part of the orbit, the ophthalmic a. was located between the eyeball and the medial orbital wall, and below the superior oblique m. It divided into two terminal branches, the supratrochlear and dorsal nasal aa. From the third part of the intraorbital course of the ophthal- mic a. that arose the anterior and poste- rior ethmoidal aa., supraorbital a., mus- cular aa. for the media l rectus and superior oblique mm., anterior ciliary aa. and medial palpebral aa. In 21.5% of cases the ophthalmic a. did not cross over the optic n. from the superior side. In 12 cases (6%), the ophthalmic a. had a similar path as when it crossed over the optic n. from the superior side. The first part of the intraorbital course of the ophthalmic a. ended under the lateral half of the optic n. The ophthalmic a. then changed direction at a right or obtuse angle, travelled medially and forwards, and crossed the optic n. from the inferior side (Fig. 3). Nineteen spe- cimens (9.5%) showed a simple course of the ophthalmic a. In these specimens, the ophthalmic a. travelled anteriorly and medially directly after entering the orbit. In these cases the axes of the oph- thalmic a. and optic n. formed an acute angle. On the medial side of the optic n., the ophthalmic a. ran upwards and travelled 15 to 20 mm behind the eye- ball in the third part of its intraorbital course.

In two specimens, a rare variation of the ophthalmic a. was observed. In the left and right orbits of the same skull a relatively narrow ophthalmic a. (0.8 mm) entered under the middle part of the optic n. From this point the ophthal- mic a. ran a parallel course with the optic n. anteriorly, and after 5 mm it divided into two branches of equal dia- meter. The medial branch was located medially and in front of the usual cour- se of the ophthalmic a. At a distance of 14 mm behind the posterior pole of the

374 A. Jo-Osvatic, et al.: Topographic anatomy of ophthalmic artery

Fig. 4

5--- !

8-"

Cadaveric specimen (left) and diagram (right) of the anastomosis between the ophthalmic and middle meningeal aa. 1, ophthalmic a.; 2, lacrimal a.; 3, posterior ciliary a.; 4, muscular branches; 5, anterior eth- moidat a.; 6, anastomosis with the middle meningeal a.; 7. branch of the maxillary a.; 8, central retinal a.

e y e b a l l this b r anch run in a c u r v e d (third) part of the in t raorbi ta l course. The lateral branch of the ophthalmic a. was l oca t ed pa ra l l e l wi th the la te ra l edge of the optic n. in front and formed a length of 15 mm behind the eyeball, where it branched out into the supraor- b i ta l a., p o s t e r i o r l a te ra l c i l i a ry aa., l a c r i m a l a. and m u s c u l a r aa. for the super ior rectus and levator pa lpebrae superioris ram. The ophthalmic a. exi- ted besides these arteries from the late- ral branch and the arteries that t ravel t h rough the s u p e r i o r o rb i t a l f i s su re under the lacrimal a., and anastomosed with the frontal branch of the middle meningeal a. (Fig. 4). The diameter of the anastomosis was 0.6 ram.

Discussion Microsurgical procedures in the treat- ment of orbital disorders demand detai- led descriptions of all orbital structures. A number of studies have emphasised the significance of the topoanatomy of the ophthalmic a. [5, 7, 8, 9, 14, 18, 19, 25, 27].

The most usual origin of the oph- thalmic a. is from the ICA [1, 2, 3, 10, 11, 22]. Some authors have descr ibed an or igin f rom the midd le meningea l and pos ter ior communica t ing aa. [18,

24], whi le others repor t or igin of the middle meningeal a, from the ophthal- mic a. [4].

The extreme diameters of the oph- thalmic a. ranged from 0.7 to 1.56 m m as measured 2 rnm from its origin [13, 20], while our results demonstrated that the diameter measured precisely at its origin from the internal carotid a. ranged from 0.8 to 2.4 mm. The diameter of the oph- thalmic a. is of great clinical importance in Doppler studies. Preoperative evalua- t ion of ophtha lmic and carot id aa. in patients using transcranial Doppler sono- graphy enables determination of the cere- brovascular vasospasm and the extent of vascular occlusion. For this reason it is important to have data about the normal

size of the ophthalmic a. This paper confirms the well-known

va r i ab i l i ty o f the oph tha lmic ar ter ia l branches and their relation to the optic n. These variations have been discussed and d e s c r i b e d w i t h r e s p e c t to t he embryonic development [6, 10, 11, 12, 22, 26]. Their distribution is cl inically important. Endonasal operations on the ethmoid and neurosurgical approach to the h y p o p h y s e a l a r e a can s e v e r e l y damage some of the branches as well as the main trunk of the ophthalmic a. It is impor tan t to d i f ferent ia te in t raorbi ta l from intracranial lesions of the ophthal-

m i c a . A typical example is an aneu- rysm of the first part of the ophthalmic a., which is and behaves as a cerebral aneurysm [21]. An unusual case of an ophthalmic a. arising from the middle men ingea l a. was a s soc ia t ed with an occlusion of the central retinal a. [24].

The advance of new methods pro- v ides i nc reased poss ib i l i t i e s for stu- dying the blood circulation in the orbit, thus e m p h a s i s i n g the i m p o r t a n c e o f detailed knowledge about the anatomic variations in this area. However, for the c o m p a r i s o n of d i f f e r e n t p a r a m e t e r s regarding the ophthalmic a. it is neces- sary to adopt a single and well-defined system of investigation.

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Received July 6, 1998 / Accepted in final Jbrm June 21, 1999