Cataract is the leading cause of avoidable blindness in the world¹, and accounts for over half of the causes of blindness in Pakistan².Cataract surgery can be carried out under general or local anesthesia. Due to unwanted effects of general anesthesia³ local anesthesia is preferred by most surgeons and patients for cataract surgery; the latter having good analgesia and quick recovery⁴.

Local anesthesia includes topical anesthesia and regional anesthesia. Topical anesthesia affects only the nerve endings of the trigeminal nerve in the cornea and conjunctiva so akinesia of the globe will not be achieved. Therefore, surgical training and good patient cooperation is required for safe use of topical anesthesia⁵. One type of regional anesthesia is peribulbar which is performed by injecting the anesthetic solution in the orbit around the equator of the eye ball (outside the muscle cone) using sharp needle⁶ and the other is subtenon anesthesia which involves the use of blunt canula⁷. Serious complications such as sight threatening globe perforation and life threatening brainstem depression have a 2.5 fold greater risk in sharp needle techniques (peribulbar, retrobulbar) as compared with subtenon block⁸. Subtenon block has 2.3 times more risks of minor complications like subconjuctival haemorrhages and conjunctival chemosis⁸.

The goal of ideal local anesthesia is to obtain complete anesthesia and akinesia of the eye ball and low intraocular pressure in order to provide optimal surgical conditions⁹. This study was aimed at comparing the changes in intraocular pressure after subtenon and peribular local anaesthesia in patients undergoing cataract surgery.

MATERIAL AND METHODS

This prospective interventional study was conducted in the Department of Ophthalmology Khyber Teaching Hospital Peshawar. The duration of study was one year i.e. from October 2009 to October 2010. Before starting the study, approval was taken from the ethical review board of the hospital.

Patients admitted to Eye unit for cataract surgery in the age group between 50 – 70 years were included in the study.Patients with uncontrolled diabetes mellitus, glaucoma or ocular hypertension, systemic hypertension, carotid stenosis, anterior chamber abnormalities, hypersensitivity to lignocaine, uncooperative patients like mentally retarded, history of convulsions or epilepsy and on topical systemic antihypertensive medicine were excluded from the study. Written informed consent was taken from all the patients.

The cases were randomly divided into two groups as group “A” and group “B”. Patients in group “A” received subtenon anesthesia and in group “B” received peribulbar anesthesia. Digital compression was started after anesthesia administration and continued for 10 minutes with interval for 10 seconds after every 2 minutes. All procedures were performed by a single and experienced surgeon. Intraocular pressure (IOP) was measured with Perkins tonometer (Clement Clarke London) just before, one minute after and 10 minutes after the anesthesia administration in lying position. All the data were recorded on a pre-designed proforma.

SPSS 20.0 was used for data analysis. Descriptive statistics like mean and standard deviation were calculated for age and IOP while frequencies and percentages were calculated for gender. P-value was generated using student t-test for comparison of IOP after both types of anesthesia procedures. p-value of <0.05 was considered significant.

RESULTS

There were 152 patients in each group. Mean age for group “A” was 59.74 ± 5.58 years and for group “B” it was 59.88 ± 5.91 years (P value = 0.83). In group “A” there were 79 (52%) females and 73 (48 %) males and in group “B” there were 77 (50.7%) female and 75 (49.3%) male (P value = 0.73).

There was no significant difference in mean IOP in the two groups just before the administration of anesthesia (P value = 0.72). One minute after anesthesia the IOP increased to 14.99 ± 1.25 mmHg in group “A” and 17.37 ± 1.28 mmHg in group “B” (P value < 0.0001). So the difference between the mean IOP of both groups 1 minute after injection was statistically significant. However after 10 minutes of injection the mean IOP returned to its base level in both groups and there was no significant difference in mean IOP in both groups after 10 minutes (P value = 0.52), as shown in Table 1.

Table 1: Comparison of intraocular pressure between two groups.

	Group “A” Mean ± SD	Group “B” Mean ± SD	P value
IOP just before anesthesia	12.16 ± 1.23 mmHg	12.11 ± 1.22 mmHg	0.72
IOP 1 minute after anesthesia	14.99 ± 1.25 mmHg	17.37 ± 1.28 mmHg	<0.0001
IOP 10 minute after anesthesia	11.97 ± 1.22 mmHg	11.88 ± 1.25 mmHg	0.52

IOP: Intraocular pressure. Group “A” subtenon anesthesia. Group “B” peribulbar anesthesia.

DISCUSSION

Ophthalmic surgery is one of the most frequent surgical procedures requiring anesthesia in developed countries¹⁰. In the past most of the cataract surgeries used to be performed under general anesthesia.¹¹ With the passage of time, new advances and developments in the cataract surgeries were made. The time of surgery was reduced and incision became smaller and now most of the surgeries are performed under safe and effective means of local anesthesia¹²and hence the unwanted effects of general anesthesia are obviated with the use of local anesthesia³.

There are different techniques of local anesthesia available for cataract surgeries. Topical anesthesia^10,13is free of serious and life threatening complications and can be used in selected cases¹⁴, however it lacks akinesia and a possible association between topical anesthesia and endophthalmitis has also been noted.¹⁵Patients undergoing cataract surgery under topical anesthesia experience more postoperative pain and discomfort as compared to those receiving subtenon anaesthesia¹⁶. Subconjunctival block is pain free¹⁷ provides anesthesia to the anterior segment and is not very popular¹⁸. Needle blocks like peribulbar and retrobulbar anesthesia provides excellent analgesia and akinesia however serious and life threatening complications can occur with these procedures. Therefore, these techniques require intravenous lines and presence of anesthetist and can be performed under the supervision of senior and experienced ophthalmic surgeon as suggested by joint report of Royal College of Anesthesia and Royal College of Ophthalmologists.¹⁹Subtenon technique is safe, effective and painless and is perfect block^20,21. There is a statistically significant increased risk of serious complications with sharp needle anesthesia compared with subtenon technique⁸.

An ideal anesthetic technique must be safe from serious complications, effective in terms of providing good akinesia and analgesia and must not elevate intraocular pressure in order to provide optimal surgical conditions.

In this study we compared the changes in IOP after subtenon and peribulbar local anesthesia in patients undergoing cataract surgery. IOP was measured with Perkins tonometer just before, one minute after and 10 minutes after the anesthesia administration in lying position.

IOP measured just before and then 1 minute after administration of anesthesia revealed that there was a greater increase in mean IOP just after anesthesia administration in group “B” as compared to group “A”. Mean IOP just before anesthesia in group “A” was 12.16 ± 1.23 mm Hg which increased to 14.99 ± 1.25 mm Hg 1 minute after injection. Mean IOP just before anesthesia in group “B” was 12.11 ± 1.22 mmHg which increased to 17.37 ± 1.28 mmHg 1 minute after injection. So comparing the difference between the mean IOP before and 1 minute after administration of anesthesia there was a significant rise of mean IOP in group “B” as compared to group “A” (P value < 0.0001). This is comparable with the results of other study in which there was a significant rise in IOP following the peribulbar injections (median rise 0.5 mmHg sub-Tenon’s method, 3.5 mmHg peribulbar method, p = 0.02) but for both methods, IOP fell to a similar level at 5 min after use of the pressure lowering device²².

Another study showed that one minute after the injection, IOP increased significantly in the peribulbar group (mean 7.97 mm Hg ± 8.80 [SD]) (P< .05). There was no significant increase in the sub-Tenon’s injection group (mean 0.12 ± 3.09 mm Hg). In both groups, IOP returned to pre-injection levels by 10 minutes postoperatively. The mechanism of this increase in IOP may be attributed to the restricted orbital space in which a larger volume of anesthetic solution is injected.²³

In both groups mean IOP declined to the base level 10 minute after anesthesia administration i.e. in group “A” IOP decreased to 11.97 ± 1.22 mmHg and in group “B” it decreased to 11.88 ± 1.25 mmHg. Thus, 10 minute of anesthesia administration, there was no significant difference in the intraocular pressure in both groups (P value = 0.52), which is comparable with other studies.^22,23Therefore both groups have equally optimal surgical conditions.

With peribulbar anesthesia the IOP may be elevated to the level, although for a short time, sufficient to cause reduction in pulsatile ocular blood flow which may cause potential problems for the patient with ocular vascular compromise²⁴.

CONCLUSION

Peribulbar anesthesia leads to significant rise in intraocular pressure as compared to peribulbar anesthesia immediately after the injection. However, 10 minutes after injection the intraocular pressure declines to its base level in both groups.

Author’s Affiliation

Dr. Sher Akbar khan

Principal Author FCPS

District Ophthalmologist Saidu Teaching Hospital, Swat.

Dr. Mir Ali Shah (Corresponding Author)

FCPS, ICO (Retina)

Associate professor of Ophthalmology, Lady Reading Hospital Peshawar.

Prof Ibrar Hussain

FCPS, FRCS

Chairman Department of Ophthalmology, Khyber Teaching Hospital Peshawar

Dr. Faisal Nawaz

FCPS, VR Fellow LRH

Lady Reading Hospital Peshawar.

Dr. Mumtaz Alam

FCPS, Consultant ophthalmologist KSA.

Role of Authors

Dr. Sher Akbar khan

Concept and design, Data collection/Assembly.

Dr. Mir Ali Shah (Corresponding Author)

Concept and design, Drafting, Statistical expertise, Critical revision.

Prof Ibrar Hussain

Concept and design, Critical revision.

Dr. Faisal Nawaz

Drafting, Statistical expertise

Dr. Mumtaz Alam

Data collection/Assembly.

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