A noncontact applanation tonometer. Description and clinical evaluation

Reproducibility with the Keeler Pulsair 2000 non-contact tonometer

AIMS

The IOP variation on repeated testing with the recently introduced Keeler Pulsair 2000 instrument was investigated.

METHODS

One hundred normal individuals (50 male and 50 female) new to the instrument had three sets of IOP recordings within a 15 minute time period.

RESULTS

The mean of the first set of IOPs from both right and left eyes was significantly higher than those from subsequent sets (p < 0.0001 for right eyes and p = 0.01 and < 0.0002 for left eyes). This tendency increased significantly with increasing IOP. Second and third IOP sets were, however, similar indicating stabilisation of IOP measurements. The coefficient of repeatability of the instrument between second and third sets was 4.2 mm Hg for right eyes and 3.6 mm Hg for left eyes.

CONCLUSION

The Pulsair 2000 passes the British standard for reproducibility of a standard test method.

Effect of bicycle ergometer test on intraocular pressure in elderly athletes and controls

To evaluate the effect of intensive physical exercise on intraocular pressure (IOP) in 66- to 85-year-old subjects IOP was measured before and after a maximal bicycle ergometer test. The non-glaucomatous subjects comprised 85 males and 36 female athletes and 16 male and 22 female controls of corresponding age drawn from a population register. IOP was measured using a non-contact tonometer. The results indicated a decrease (> or = 2 mmHg) in 34% of the subjects, no change in 57% and an increase in 9%. The decrease was more pronounced in subjects with higher pre-test values. In all four subjects with a pre-test value above 22 mmHg a reduction from 4 to 11 mmHg was observed. The change in IOP during physical loading was not significantly associated with the intensity and duration of exercise test. Three of the 5 male subjects with diagnosed glaucoma and undergoing hypotensive medication, who were analyzed separately, also showed a reduction in IOP during loading. In the pre- or post-test values there were no differences between the athletes and controls, while women tended to have higher IOP values than men. It is concluded that physical loading has predominantly a moderating effect, if any, on IOP in elderly men and women.

Intra-eye pressure range and pulse profiles in normals with the Pulsair non-contact tonometer

The difference in intraocular pressure (IOP) between the highest and lowest measurements on an eye with noncontact tonometry (the range) has been reported to be less than 4 mmHg in most normals. The range of IOP to be expected with the Keeler Pulsair in normals over the age of 50 years was determined by analysing the results of IOP recordings on 741 normal individuals. Between 56% and 62% of eyes recorded a range > 4 mmHg and between 4% and 8% a range > 10 mmHg when four pulses per eye were used. Population pulse profile analysis indicated that this was not due to an erroneously high first pulse in a set of four, and that IOP asymmetry previously reported when screening females is due to a generalised tendency for IOPs in right eyes to measure higher than those recorded in the left. The occurrence of a range of IOP recordings up to 10 mmHg in an eye is relatively common with the Pulsair and individuals undergoing glaucoma screening with this instrument should not be referred purely on the basis of a large IOP range.

The Pulsair-Keeler non-contact tonometer in self-tonometry: preliminary results

The authors considered the possibility of using the Pulsair-Keeler non-contact tonometer in self-tonometry. For this reason, 45 patients have been trained to use the instrument and, after a reasonable trial period, were able to self-measure their IOP. The results have been compared to the tonometric values measured with Goldmann tonometer to evaluate statistically the limits and the dependability of this method of measurement. The results shows that self-tonometry with the Pulsair-Keeler tonometer can be used in monitoring glaucomatous patients at home.

Intraocular pressure asymmetry in a population tested with the Pulsair non-contact tonometer

Intraocular pressure asymmetry as measured by noncontact tonometry (NCT) was analysed in a population of 874 individuals aged over 50 years. In both males and females the intraocular pressure (IOP) measured in the right eye exceeded that of the left. Pressure asymmetry followed a normal distribution in a population subgroup known to have normal fields, discs and pressures. The 95% confidence intervals for the equation R IOP--L IOP in normals were 0.63+ or -5.46 mmHg when the mean of four pulses per eye were used to calculate the IOP, increasing to 0.80+ or -6.56 mmHg for two pulses per eye (thus expanding the limits by 20%). The range of asymmetry for NCT in normals therefore exceeds that reported for Goldmann applanation tonometry. Asymmetry was greater in females than males. Knowledge of the normal range of IOP asymmetry in each sex will help glaucoma screeners using NCT in their decision as to when to refer. A minimum of four pulses per eye should be used to assess the IOP when screening.

Evaluation of Keeler Pulsair non-contact tonometry: reliability and reproducibility

Intraocular pressure was evaluated in 414 eyes using Keeler Pulsair tonometry in comparison with values obtained by Goldmann tonometry. No statistically significant differences were found between the two techniques. Landis K statistical analysis was used to evaluate the measurements obtained by two operators in 125 eyes, with the results indicating good reproducibility. In 20 eyes, a statistically significant difference was found between values obtained with patients in the seated vs supine positions, whereas measurements made with subjects' heads in a supported or unsupported position yielded no statistically different values.

Evaluation of the Keeler Pulsair non-contact tonometer

The recently-introduced Pulsair non-contact tonometer (Keeler Instruments, Inc, Broomall, PA) was evaluated against the Goldmann applanation tonometer in cannulated post mortem human eyes, and in living subjects at three clinical centers. Statistical analysis of the findings revealed strong linear relationships between Goldmann or manometric and Pulsair intraocular pressure readings, with correlation coefficients ranging from 0.79 to 0.97. However, with the Pulsair reading as the dependent variable, the slope of the relationship in each case was significantly less than 1.0 (range 0.65 to 0.83), while the intercept was positive (range 1.31 to 2.33 mmHg). Thus, the Pulsair tended to read low at intraocular pressure above the normal range. Conversion factors and a calibration table allowing intraocular pressure estimates more comparable to Goldmann tonometry using the current (J-series) Pulsair are provided herein. A calibration algorithm could be integrated into the circuitry of future production models of the Pulsair instrument.

Prevention of IOP-rise following Nd-YAG laser capsulotomy with topical timolol and indomethacin

Short term observation following Nd-YAG laser capsulotomy indicates that serious elevation of intra-ocular pressure may occur, unrelated to the amount of incident energy used. In this study we evaluated the effect of pre-treatment with anti-prostaglandin eyedrops on the rise in IOP. The IOP in forty pseudophakic patients, undergoing Nd-YAG laser posterior capsulotomy, was measured before capsulotomy and 2 and 4 hours afterwards. The fellow-eye was used as a control. Thirty minutes pre-operatively the patients were given one of the four following combinations of eyedrops: 1 drop timolol 0.5% and 1 drop placebo, 1 drop indomethacin 1% and 1 drop placebo, 1 drop timolol 0.5% and 1 drop indomethacin 1%, 1 drop placebo and 1 drop placebo. Statistical analysis of the results showed that indomethacin alone has little influence on the IOP-rise, whereas timolol has. When indomethacin is added to timolol there is no significant enhancement.

A new handheld air impulse tonometer

A new type of non-contact tonometer is described. The instrument is handheld and incorporates a system which automatically generates the measuring pulse of air when the alignment is correct. A brief description of the design and the results of clinical trials are presented. These establish a good correlation with paired Goldmann readings (correlation coefficient, r = 0.88 to 0.95, standard deviation, S.D. 1.56 to 2.66 mm Hg).

Prevention of IOP-rise following Nd-YAG laser capsulotomy with pre-operative timolol eye-drops and 1 tablet acetazolamide 250 mg systematically

Short-term observation following Nd-YAG laser capsulotomy indicates that serious elevation of intra-ocular pressure may occur, unrelated to the amount of energy used. In this study the IOP in 3 groups of 10 pseudophakic patients undergoing Nd-YAG laser posterior capsulotomy was measured before capsulotomy and 2 and 4 hours afterwards, using the fellow-eye as control. The first group received no medication, the second received timolol 1/2% eyedrops preoperatively, the third group a combination of timolol 1/2% and 1 tablet of acetazolamide 250 mg systemically. Pretreatment with timolol 0.5% minimizes IOP-rise but does not give complete protection. The combination of timolol 0.5% with 1 tablet of acetazolamide 250 mg proves to be a safe procedure for the prevention of IOP-rise after YAG laser capsulotomy. To prevent other complications it is advisable to make a small capsulotomy of 2-3 mm diameter using as little energy as possible. Also a defocussing system in the laser is a great advantage. Indomethacin drops during a period of 6 weeks after Nd-YAG laser capsulotomy should prevent cystoid macular edema.

Timolol and intra-ocular pressure elevation following neodymium: YAG laser surgery

The intra-ocular pressure in 76 patients, undergoing Neodymium: YAG laser surgery was measured just before treatment, and one and two hours afterwards. The fellow eye served as a control. Serious elevation of the intra-ocular pressure was demonstrated, especially in capsulotomy in the aphakic eye, to a lesser extent in pseudophakic eyes. Intra-ocular pressure elevation of more than 20 mm was seen in iridectomies. Timolol 1/2% eyedrops given before Neodymium: YAG laser treatment minimized the elevation of the intra-ocular pressure. Prolonged follow-up of the intra-ocular pressure is recommended.

The influence of oxybuprocaine (Novesine) on the intraocular pressure

Patients with raised intraocular pressure often have lower tension during hospital admissions than on out-patient measurement, even though the therapy is the same. A prospective study on 18 volunteers and 10 glaucoma patients was set up to find out whether oxybuprocaine eyedrops or repeated applanation tonometry could have anything to do with this. The tension was measured at least 3 times a day with the non-contact tonometer (NCT). In the case of the volunteers oxybuprocaine was instilled into the eye 3 times a day for one week. In the case of the patients the tension in one eye was measured with the Goldmann tonometer on several days after the application of oxybuprocaine drops. No reduction in intraocular pressure was found during the observation period, nor was there an obvious difference between the test eyes and the control eyes. In hospital, patients had at 11 o'clock in the morning intraocular pressure which was on the average 2.2 +/- 1.5 mmHg lower than that measured at out-patient checks, in spite of receiving the same therapy.

Association between ocular pressure and certain health parameters

Intraocular pressure (IOP) was measured in a mixed population of 12,803 apparently healthy employed people. Mean IOP was 13.5 +/- 3.3 mmHg, without sex difference. Frequency distribution demonstrated skewness towards high values. IOP weakly correlated with age (R = 0.06), and older subgroups showed more marked skewness, but further analysis showed this effect to be spurious. The correlations of IOP with heart rate and with systolic blood pressure were small, but stronger than with age (R = .16 and .15, respectively). Moreover, when corrected for heart rate, the effect of age was nullified. Other factors found to be correlated with IOP included blood glucose and hemoglobin concentration, smoking, and height. None of these factors significantly increased the correlation between IOP and heart rate or blood pressure, and the skewness was not fully explained by any of these factors or their combinations. The value of the epidemiologic approach to detection of factors responsible for ocular hypertension is stressed.

The non-contact tonometer. Its value and limitations

A review of the literature and a comparative study against Goldmann applanation tonometers suggest that the non-contact tonometer is reliable for measuring intraocular pressures within the normal range. In addition, the non-contact tonometer eliminates the need for corneal contact and topical anesthesia, thereby avoiding the potential problems of corneal abrasion, spread of infection, and drug reactions. The instrument can be used reliably by paramedical personnel and has particular value in mass screening and possibly in studies of topical antiglaucoma drugs. The non-contact tonometer is less reliable in patients with elevated intraocular pressure, since comparative studies against the Goldmann applanation tonometers have shown poorer correlations in the higher pressure ranges. The instrument is also limited by an abnormal cornea or poor fixation, which may interfere with accurate pressure measurements. Furthermore, the non-contact tonometer is less portable than many tonometers and more expensive than most.

The noncontact tonometer. Clinical evaluation on normal and diseased eyes

The measurement of intraocular pressure with a noncontact tonometer was correlated to a Goldmann tonometer in 20 normal persons, 20 glaucomatous patients, and 8 patients suffering from corneal diseases. In normal persons the error in measurement for the noncontact tonometer was related to their skill in fixation, and in eye patients to height of pressure and corneal state. Acceptable correlation was found between noncontact tonometry and Goldmann applanation tonometry when the cornea was normal and the pressure below 35 mmHg (Goldmann), otherwise noncontact tonometry was only a guide, and in the presence of corneal disease, unreliable. Good fixation reduced the method error. The standard deviation was 1.09 mmHg at poor fixation and 0.60 mmHg at good fixation. Repeated measurements on the same eye with noncontact tonometry did not alter the intraocular tension.