Biomedical Engineering Reference
In-Depth Information
threatening complications may be observed with the use of sharp
needles [
13
]. Therefore, to avoid complications during drug
administration to subtenon's space, cannulated needles have been
introduced. Following small incision across conjunctiva into sub-
tenon space, the individual is directed to look downwards. Subse-
quently, a blunt-tipped, 2.5 cm long cannulated needle is passed
into tenon's capsule at temporal edge of superior rectus muscle.
The injection is directed posteromedially to deliver ~4 mL of drug
solution around the ocular muscles behind the equator [
14
]. Sub-
conjunctival hemorrhage may be observed during this procedure
due to tearing of conjunctival blood vessels in tenon's space. Com-
monly observed complications with this procedure include ocular
pain and swelling of conjunctiva (chemosis). As the advantages
overweigh side effects for this procedure, this technique is widely
employed for ocular anesthesia during ocular surgeries.
Peribulbar is also referred to as extraconal injection. This mode of
drug administration is safer but less effective relative to other
techniques such as retrobulbar. In this technique the injection is
made at the location external to the four rectus muscles and intra-
muscular septa (Fig.
2
)[
15
]. Peribulbar injection can be divided
into two categories depending on the location of drug delivery,
i.e., injection site—anterior and posterior peribulbar injection.
A 25 gauge, 1.25 in. needle is recommended and is directed beyond
the equator of the eye. It is performed by one of the two procedures
such as (a) injection at the inferotemporal position and (b) injection
at the superonasal position. Inferior peribulbar injections are given
at the junction of outer third and inner two-thirds of lower orbital
rim by directing the needle away from the eye and towards orbital
floor [
14
]. On the other hand, superior injections are given nasally
or temporally towards orbital roof. Following these techniques a
volume of 8-10 mL of anesthetic may be administered.
2.3.3
Peribulbar Injection
Retrobulbar injections are also referred as intraconal injections. In
this technique drug solutions are placed inside the conical compart-
ment within the confines of four rectus muscles and their inter-
muscular septa [
15
]. Retrobulbar route of drug administration is
more effective than peribulbar in anesthetizing the eye. To perform
the injection, a 25-27 gauge blunt needle is employed. The needle
is inserted at the inferotemporal orbital margin aimed at lower edge
of superior orbital fissure with the globe in primary gaze position
[
16
]. The needle is directed from the sagittal plane and superiorly at
45
and 10
, respectively. Therefore, care must be taken when the
needle is penetrated until this depth has been reached from the
point of injection, i.e., from corneal surface. This technique may
cause optic nerve trauma. In order to avoid such complications
needles may be placed in the temporal half of the orbit with pene-
tration no deeper than 1.5 cm behind the eye [
17
].
2.3.4 Retrobulbar
Injection
