Published Manuscripts

Abstracts of Published Refereed Manuscripts

Accuracy and reliability of the Keeler Pulsair EasyEye Non-contact Tonometer.

Purpose. To evaluate the accuracy and reliability of the Keeler Pulsair EasyEye noncontact tonometer in a normotensive population. Methods. This masked prospective clinical study included 72 right eyes of 72 subjects. Two sets of intraocular pressure measurements were made 1 week apart. Intraocular pressure assessment with the Goldmann tonometer was always subsequent to that with the noncontact tonometer. Each method was assessed for within-session and test-retest repeatability and both methods were assessed for limits of agreement, twice. The level of significance for this study was 0.05. Results. Both methods were repeatable within-sessions to within +/-2 mm Hg, and between sessions to within +/-3 mmHg. Neither the within-session differences nor the between session differences differed significantly between the Goldmann tonometer and the Pulsair EasyEye noncontact tonometer. The mean differences (+/- SD) between both methods (0.1 +/- 1.6 mm Hg and 0.05 +/- 1.7 mm Hg, for the first and second sessions, respectively) were not statistically significant, but the intraocular pressure measured with the Pulsair EasyEye tonometer was consistently higher than that measured with the Goldmann tonometer. Conclusions. The Pulsair EasyEye noncontact tonometer is considered an accurate reliable method in the normotensive population studied but because of a systematic bias in a small number of subjects, it cannot be used interchangeably with the Goldmann tonometer.

Optom Vis Sci. 2008 Jan;85(1): In press.

Al-Mubrad TM, Ogbuehi KC.

Clinical investigation of the effect of topical anaesthesia on intraocular Pressure.

BACKGROUND/AIMS. Contact tonometry is generally considered more accurate than non-contact tonometry in the assessment of intraocular pressure (IOP). This study was designed to investigate the effect of ocular anaesthesia, a pre-requisite for contact tonometry, on the IOP in a sample of visually normal subjects. METHODS. In a random sample of 120 young visually normal subjects (divided equally among three groups), the Topcon CT80 non-contact tonometer was used to measure IOP before, at the second minute and at the fifth minute following instillation of one drop of one of three eyedrops – Carboxymethylcellulose sodium 0.5% (control), Oxybuprocaine hydrochloride 0.4% and Proparacaine hydrochloride 0.5%. RESULTS. The IOP measured before instilling the ophthalmic drops did not vary significantly among the three groups of subjects (p > 0.05). In the control group, the average IOP of 15.1 ± 2.6 mmHg did not vary significantly (p > 0.05) 2 minutes and 5 minutes following instillation of one drop of Carboxymethylcellulose sodium. There were statistically significant reductions of IOP 2 minutes (p < 0.01) and 5 minutes (p < 0.001) after the instillation of one drop of Oxybuprocaine hydrochloride. One drop of Proparacaine hydrochloride caused significant reductions in the average IOP after 2 minutes (p < 0.001) and after 5 minutes (p < 0.001). CONCLUSIONS. One drop of topical Proparacaine or Oxybuprocaine may cause a small but a statistically significant reduction in IOP which
could lead to lower IOP readings.

Clin Ophthalmol. 2007; 1(3):305-9.

Al-Mubrad TM, Ogbuehi KC.

Smith-method assessment of anterior chamber depth for screening for narrow anterior chamber angles.

PURPOSE. To compare the axial anterior chamber depth (ACD) using the Smith method, in patients under treatment for primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG), with an age-matched control group. MATERIALS AND METHODS. Triplicate just-touching-slit-length (JTSL) measurements of the axial anterior chamber depth were determined in 198 eyes of 99 patients (39 control; 36 POAG; and 24 PACG) recruited from King Saud University clinics, Riyadh, Saudi Arabia. Goldmann tonometry and gonioscopy were carried out as a part of the patient's routine examination. Subjects with a history of intraocular surgery for glaucoma or any other anterior segment disease were excluded form the study. The average ACD estimate by the JTSL method were compared among the various groups. RESULTS. The average JTSL estimates were: Control group 2.33+/-0.68 mm (axial ACD estimate = JTSL estimate x 1.4); POAG group 1.98+/-0.97 mm; PACG group 0.65+/-0.41 mm. There was no significant reduction (P = 0.068) of the JTSL estimate in the POAG group, compared to the control group. There was a statistically significant (P < 0.001) reduction of the JTSL estimate in the PACG group, compared to both the control and POAG groups. CONCLUSION. The Smith-method JTSL technique may be used for non-invasive rapid screening, to help identify patients at risk of developing angle-closure, during routine examination of patients in the ophthalmology clinic.

Indian J Ophthalmol. 2006 Sep;54(3):165-8.

Ogbuehi KC.

Assessment of the accuracy and reliability of the Topcon CT80 non-contact tonometer.

BACKGROUND. The reliability of non-contact tonometers has been reported extensively in the literature. This study was designed to assess reliability of the new Topcon CT80 non-contact tonometer in normotensive subjects, using the Goldmann tonometer as the standard. METHODS. The accuracy of the Topcon CT 80 non-contact tonometer was assessed by comparing its IOP assessments with those of the Goldmann applanation tonometer, on 60 right eyes of young healthy subjects with normal intraocular pressures. Each subject's intraocular pressure was assessed with each technique on two separate occasions, one week apart. The reliability of each technique was determined by the assessment of its inter-session repeatability using the Bland-Altman method. The 95 per cent limits of agreement for the two methods were also determined. RESULTS. No statistically significant difference was found between the average intraocular pressures measured with the two techniques (p > 0.05). The inter-session repeatability indices for the two techniques did not differ significantly (p > 0.05). The mean difference in intraocular measurements between the two techniques was 0.2 +/- 1.5 mmHg (mean +/- SD) and the 95 per cent limits of agreement were -3.14 and +2.74 mmHg, with the non-contact tonometer returning higher readings than the Goldmann tonometer. CONCLUSION. In this sample of normotensive subjects, the Topcon CT80 non-contact tonometer proved to be accurate and as reliable as the Goldmann tonometer in the assessment of intraocular pressure. Thus, it can be used as an objective clinical method for the assessment of normal intraocular pressure.

Clin Exp Optom. 2006 Sep;89(5):310-4.

Ogbuehi KC, Almubrad TM.

Repeatability of central corneal thickness measurements measured with the Topcon SP2000P specular microscope.

BACKGROUND. The non-contact specular microscope has become the method of choice for a quick, accurate and non-invasive assessment of central corneal thickness (CCT), which is an important variable to monitor before and after refractive surgery. The consistency of the results produced by such widely used methods/equipment must be assessed to determine their reliability. The purpose of this study was to assess within- and between-observer repeatability of, and to determine if a systematic bias exists in the measurements made by, the Topcon SP2000P specular microscope. METHODS. The CCT of the right eyes of 70 adult subjects, divided equally between men and women, was assessed on two separate occasions (4-7 days apart) by each of two examiners using the low-intensity auto mode of the SP2000P specular microscope. RESULTS. The average CCT values for men and women, measured by one observer, were 0.52+/-0.03 mm (mean +/- SD) and 0.52+/-0.04 mm, respectively. The average for the entire sample was 0.52+/-0.04 mm. Within- and between-observer repeatability were assessed by plotting the mean difference (for each subject) between two readings made by the same observer or one each by both observers against the combined average CCT reading of both sessions; the mean difference between two sets of observations was not significantly different from zero (P<0.05). For the first observer, the 95% limits of repeatability were between -0.015 and 0.017 mm. For the second observer, the 95% limits of repeatability were between -0.018 and 0.018 mm. For the between-observer repeatability, the 95% limits of agreement were between -0.016 and 0.016 mm. For both within- and between-observer repeatability, we found no systematic bias of the mean difference with the average CCT reading. CONCLUSION. The within- and between-observer limits of agreement we found were similar to those previously reported for the Topcon SP2000P specular microscope; the range of the 95% limits of repeatability were within +/-1 SD of the average CCT reading for both sessions. We suggest that a technique be considered reliable if: (1) the mean difference between two measurements does not vary significantly from zero, (2) there is no systematic bias of the mean difference with the magnitude of the measured quantity and (3) the error inherent in a measurement technique is within +/-1 SD of the average measurement of the two sessions.

Graefes Arch Clin Exp Ophthalmol. 2005 Aug;243(8):798-802.

Ogbuehi KC, Almubrad TM.

Limits of agreement between the optical pachymeter and a noncontact specular microscope.

PURPOSE. To determine the limits of agreement between central corneal thickness (CCT) measurements made with the slit lamp-attached optical pachymeter and the SP2000P noncontact specular microscope. METHODS. Triplicate readings for CCT were obtained for each of 130 (right) eyes of 130 patients, using the slit lamp-attached optical pachymeter and then the SP2000P noncontact specular microscope. The average CCT measured by each method was compared. Subsequently, the mean difference between both sets of measurements was assessed, and the 95% confidence interval (limits of agreement) between both techniques was determined. RESULTS. The mean +/- SD CCT measured by the optical pachymeter was 543 +/- 34 microm and 532 +/- 34 microm for the specular microscope. We found a statistically significant (P < 0.001) mean bias of 10 mum between CCT values measured with both types of equipment, with the optical pachymeter returning the higher values. The coefficient of variation was 6.3% for the optical pachymeter and 6.4% for the specular microscope. CONCLUSIONS. The right eye CCT measurements made by the optical pachymeter are, on average, 10 microns thicker than those made with the SP2000P specular microscope, which suggests that both pieces of equipment cannot be used interchangeably to monitor CCT changes in patients. Excluding left eye measurements, the reliability of the optical pachymeter is identical to that of the noncontact specular microscope.

Cornea. 2005 Jul;24(5):545-9.

Osuobeni EP, Oduwaiye KA, Ogbuehi KC.

Intra-observer repeatability and inter-observer agreement of the Smith method of measuring the anterior chamber depth.

The Smith (1979) method provides a means of estimating the anterior chamber depth without additional attachments to the slit lamp [Smith, R. J. H. (1979). A new method of estimating the depth of the anterior chamber. Br. J. Ophthalmol. 63, 215-220]. In this study, the 95% intra-observer limits of repeatability and the 95% inter-observer limits of agreement of this method have been determined. The intra-observer limits of repeatability were determined by plotting the difference vs the mean of the estimated anterior chamber depth obtained in two different sessions by each of two examiners, while the inter-observer limits of agreement are represented by a plot of the difference vs the mean estimated anterior chamber depth between the two examiners. For one examiner, the 95% intra-observer limits of repeatability was -0.36 to 0.58 mm, while for the other examiner the 95% intra-observer limits of repeatability was -0.25 to 0.37 mm. The 95% inter-observer limits of agreement were -0.31 to 0.23 mm and -0.41 to 0.25 mm for the first and second sessions respectively. The intra-observer limits of repeatability are comparable with those reported for A-scan ultrasonographic measures of the anterior chamber depth. These results imply that the Smith method can be used with a high degree of repeatability and agreement to clinically monitor longitudinal changes in anterior chamber depth.

Ophthalmic Physiol Opt. 2000 Mar;20(2):153-9.