Conference Lectures
Pre-operative orbit-Globe evaluation by anaesthesiologist for regional block
Dr Jaichandran V V, Sankara Nethralaya, Chennai
Ophthalmic Forum,
Elements of ophthalmic evaluation by anaesthesiologist include history of previous ophthalmic surgery, glaucoma, know about the axial length, presence of any staphyloma, and the relationship between globe and orbit. Buckling surgery alters globe dimensions, contour and results in significant scarring within the orbit and so increases the potential of perforation. The axial length and the presence and location of staphyloma can be known from B-scan echography, which is usually done, before cataract surgery, for diopter power calculation. If the axial length is not available, the spherical equivalent in the patient’s eye glass prescription should be reviewed. High myopes tend to have exceptionally long eyes and patients who have axial lengths greater than or equal to 27mm are at risk for posterior staphylomas. After the patient’s eye length has been determined the relationship of the eye within the orbit should be examined. Knowledge of this relationship is used to determine the angle of the block needle as it enters the desired orbital space in order to avoid penetrating the sclera.
Orbital : globe spatial relationship
The orbital axis(OX) is the bisection of line between medial and lateral orbital walls, while visual axis(VX) is the position of the eye in primary gaze. Both the axis diverge at an angle of 230. Normally, the equator of the globe is at or slightly anterior to the lateral orbital rim and the spatial relationship between them is assessed by measuring the distance the globe (top of the cornea) extends over the infraorbital rim and this distance is generally about 8mm.
Forward set globe:
The globe extends quite forwardly over the infraorbital rim (>8 mm) and associated eye lids will be lax with wide palpebral fissure and high brows. Here, the structures in the apex of the orbit are vulnerable to get injured with needle blocks.
Deep set globe:
In this condition there is high chance for the needle to come in contact with the globe. Associated eyelids will be short and tight. From the point of insertion, at the inferolateral quadrant, the needle must not be angulated more than 100 elevation from the transverse plane.
References
- Duker JS, Belmont JB, Benson WE, Brooks HL Jr, Brown GC, Federman JL et al: Inadvertent globe perforation during retrobulbar and peribulbar anesthesia. Ophthalmology 1991;98:519-26.
- Wolff E. Anatomy of the Eye and Orbit. Philadelphia and London: WB Saunders 1966:31.
- Leaming DV. Practice styles and preferences of ASRC members-2003 survey. J Cataract Refract Surg 2004;80:892-900.