Abstract
Objectives
The present study was undertaken to determine the possible effects of the placement two different types of eyelid speculum on intraocular pressure (IOP) measurement in clinically normal cats.
Methods
Thirty healthy cats were divided randomly into two groups of 15, group B (Barraquer wire speculum) and group W (Williams eye speculum). All cats were sedated with intramuscular medetomidine (Dorbene vet; 100 μg/kg) then placed in right lateral recumbency, and IOP was recorded in the left eye using a Tono-Pen Vet tonometer without and with an eyelid speculum in place in both groups.
Results
The without-speculum IOPs for cats in group B and group W were 13.8 ± 3.0 mmHg and 13.2 ± 3.6 mmHg, respectively, and did not differ significantly. A significant increase in IOP (19.8 ± 3.7 mmHg) was observed in group W in with-speculum measurements in comparison to the without-speculum values (P <0.001).There was no significant difference between with- and without-speculum IOP values (13.8 ± 2.7 mmHg) in group B (P = 1.0).
Conclusions and relevance
The Barraquer wire speculum has no effect on IOP compared with the Williams eye speculum in normal cats, and may be an appropriate choice in cats for intraocular surgeries that cannot tolerate acute increases in IOP.
Introduction
The need to maintain intraocular pressure (IOP) within or below the reference interval during ocular surgeries has been the subject of extensive research in the veterinary literature in the past decade. Several studies have evaluated the effects of different sedatives, anaesthetic agents and body position on IOP in dogs and cats.1–5 Preventing IOP elevation is very important in patients with near-perforating corneal lesions or glaucoma. The abrupt increases in IOP during anaesthesia and ocular surgery can cause damage to the optic nerve, globe rupture or prolapse of the ocular contents, thus increasing morbidity and worsening prognosis. Furthermore, in animals undergoing intraocular surgery for their ocular disease, the importance of a sudden increase in IOP and maintaining globe shape could have a clinically significant impact on their surgical outcomes, which should be considered.2,6
It has been documented in humans that eyelid speculums increase IOP.7,8 There is no published information regarding the possible effects of eyelid speculums on IOP measurements in cats. Therefore, the objective of this study was to investigate the effect of placement of two different eye speculums on IOP in clinically normal cats.
Materials and methods
The study was approved by the Iran Society for Prevention of Cruelty to Animals in accordance with Iranian ethical codes for studies on laboratory animals. Prior to entering the study, all cats were determined to be free of disease by means of physical and ocular examination using bio-microscopy (Reichert, Dan Scott & Associates), tonometry (Reichert Tono-Pen Vet Applanation Tonometer) and indirect ophthalmoscopy (Topcon).
The same examiner (MSG) performed all ocular tests, examinations and measurements. No obvious abnormalities were noted during the ophthalmic examinations.
Thirty sexually intact crossbred domestic shorthair cats (15 males, 15 females) were used. The age of the cats ranged between 11 and 18 months. Thirty cats were divided randomly into two groups of 15: group B (Barraquer wire speculum; Tavana Abzar Parto) and group W (Williams eye speculum; Tavana Abzar Parto) (Figure 1). At the start of the trial, all cats were sedated with intramuscular medetomidine (Dorbene vet; 100 μg/kg). The time interval between the injection and tonometry varied between 10 and 15 mins. In both groups two measurements were made with and without an eyelid speculum in place. All cats were placed in right lateral recumbency and IOP was recorded in the left eye using a Tono-Pen Vet tonometer (Reichert Tono-Pen Vet) without and with an eyelid speculum in place. The order in which the measurements were made with and without placing the eyelid speculum was alternated. All measurements were taken between 1 and 3 PM to minimise the possible variations associated with diurnal changes in IOP. Prior to each IOP measurement, one drop of proparacaine hydrochloride 0.5% ophthalmic solution (Paracain; Sunways) was applied topically to each eye. In the present investigation, we only considered IOP measurements that were within 5% variance (5% displays on a Tono-Pen).Statistical analysis was performed using SPSS version 16.0 for Windows. Data are expressed as mean ± SD. Normality was tested by a one-sample Kolmogorov–Smirnov test. A paired-samples t-test was used to compare IOP values in both groups. The level of significance was considered to be P <0.05.
Barraquer wire speculum (left); Williams eye speculum (right)
Results
The mean IOP values in both treatment groups are shown in Figure 2. All data are expressed as mmHg. The without-speculum IOPs for cats in group B and group W were 13.8 ± 3.0 mmHg and 13.2 ± 3.6 mmHg, respectively, and these were not statistically significantly different (P = 0.36). A significant increase in IOPs (19.8 ± 3.7 mmHg) was observed in group W in with-speculum measurements in comparison to without-speculum values (P <0.001). There was no significant difference between without- and with-speculum IOP values (13.8 ± 2.7 mmHg) in group B (P = 1.0).
With- and without-speculum intraocular pressure (IOP) values in group B (Barraquer wire speculum) and group W (Williams eye speculum)
Discussion
The IOP values observed without and with an eyelid speculum in the cats in this study were similar to those reported in normal cats. The reported range for IOP values obtained by applanation tonometry in normal cats is 9–31 mmHg. 9
In the present investigation, a significant increase in IOP values was observed only in group W in with-speculum measurements. We found that the Williams eye speculum produced an increase in IOP of 6.6 mmHg, or about 33%, compared with without-speculum values.
Our results regarding with-speculum measurements in group W are in agreement with those of similar studies in human medicine. In humans, the Barraquer wire speculum causes less of an increase in IOP than the the Universal eye speculum.7,8
The exact mode of action of the eye speculum in increasing IOP in cats is unclear. However, the suggested mechanisms include the following: during the placement of the eyelid speculum a pressure applied by the speculum to the orbit could result in compressing soft tissues surrounding the orbit and increasing ocular venous pressure. The other possible mechanism is that the eyelid speculum itself could directly elevate IOP by compressing the orbit.7,10,11
Klein et al discussed the effect of eyelid manipulation on IOP in dogs. 12 In their study, the degree of elevated IOP was proportional to the degree of compression of the jugular vein and eyeball traction. They also discussed the fact that lateral eyelid extension produced a greater IOP elevation than dorsoventral eyelid extension. 12
The reason why the Williams eye speculum significantly increased IOP over without-speculum values compared with the Barraquer speculum may be attributed to the degree of pressure applied by the Williams speculum to the orbit. It appears that the Williams speculum applies a much greater pressure to the orbit than the Barraquer speculum.
The use of intramuscular medetomidine for immobilising cats in this study might have some bearing on the IOP values obtained. However, a recent investigation reported that administration of intramuscular medetomidine had no significant effect on IOP in normal cats. 13
Conclusions
The Barraquer wire speculum has no effect on IOP, compared with the Williams eye speculum in normal cats. The Barraquer wire speculum may be an appropriate choice in cats for intraocular surgeries that cannot tolerate acute increases in IOP.
Footnotes
Acknowledgements
We wish to thank Dr Mahdavi (DVM) for his assistance during the study.
Conflict of interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Ethical approval
This work involved the use of experimental animals only, and followed established internationally recognised high standards (‘best practice’) of individual veterinary clinical patient care. The study had ethical approval from an established committee as stated in the manuscript.
Informed consent
Informed consent (either verbal or written) was obtained from the owner or legal custodian of all animal(s) described in this work for the procedure(s) undertaken. No animals or humans are identifiable within this publication, and therefore additional informed consent for publication was not required.
