Attempted eyelid closure affects intraocular pressure measurement

PURPOSE: To evaluate the effect of attempted eyelid closure on intraocular pressure measurement. METHODS: Normal subjects underwent intraocular pressure measurement in both eyes using Goldmann applanation tonometry and Tono-pen XL (Mentor, Inc, Norwell, Massachusetts) by the same examiner holding the eyelids open, both with and without the subject simultaneously attempting forced eyelid closure. Subjects were seated during all measurements and waited 5 minutes between measurements with each instrument; the order of measurement was randomized. RESULTS: Thirty eyes of 15 subjects (six men, nine women) were enrolled. Mean age was 30.5 +/- 5.2 years (range, 24 to 40 years). With Goldmann applanation tonometry, intraocular pressure increased in both eyes with attempted eyelid closure by a mean of 1.5 +/- 2.0 mm Hg (P =.0002, paired t test; range, -2 to 8 mm Hg). With the Tono-pen XL, intraocular pressure also increased in both eyes with attempted eyelid closure by a mean of 1.9 +/- 2.7 mm Hg (P =.0002, paired t test; range, -2 to 9 mm Hg). Tono-pen XL mean intraocular pressure values in both eyes (14.4 +/- 2.3 mm Hg) consistently overestimated those of Goldmann applanation tonometry (13.0 +/- 2.2 mm Hg) by a mean of 1.4 +/- 2.3 mm Hg. CONCLUSIONS: Attempted forced eyelid closure is a common and statistically significant source of error in routine outpatient measurement of intraocular pressure and could influence clinical management of glaucoma.     

Clinical comparison of the ProTon and Tono-Pen tonometers with the Goldmann applanation tonometer.

A clinical evaluation of a new electron ProTon tonometer was performed comparing the values of intraocular pressure (IOP) measured using this instrument with those determined by a similar instrument, Tono-Pen XL, and by Goldmann applanation tonometry. The mean IOP measured in 106 eyes with the ProTon tonometer was not significantly different from that determined with Goldmann applanation, while the IOP values measured with Tono-Pen XL were significantly lower. The 95% limits of agreement between applanation tonometry and ProTon tonometry were between -4 mm Hg and 5 mm Hg and between applanation tonometry and Tono-Pen XL tonometry between -3 mm Hg and 8 mm Hg. The ProTon tonometer appears to have a higher level of accuracy than the Tono-Pen XL tonometer in clinical practice.     

Tonometry after laser in situ keratomileusis treatment

PURPOSE: To assess the reliability of intraocular pressure measurements by Goldmann applanation tonometry versus pneumotonometry after laser in situ keratomileusis for myopia. PATIENTS AND METHODS: In this prospective study, corneal Goldmann applanation tonometry and pneumotonometry measurements were made in 118 eyes of 60 patients before and 1 and 3 months after undergoing laser in situ keratomileusis for myopia. Manifest refraction, ultrasonic corneal thickness measurements, and keratometry readings were also obtained. RESULTS: Preoperative intraocular pressure showed a good correlation between Goldmann applanation tonometry and pneumotonometry values (Pearson r = 0.71; P < 0.001). although Goldmann applanation tonometry readings were slightly higher at low intraocular pressure values and slightly lower at high intraocular pressure values. After a mean stromal ablation depth of 77.1 microm, mean intraocular pressure by Goldmann applanation tonometry decreased significantly (P < 0.001) from a preoperative value of 14.8 +/- 11.9 mm Hg to 11.9 +/- 2.1 mm Hg and 11.7 +/- 1.7 mm Hg after 1 and 3 months, respectively. Mean pre- and post-laser in situ keratomileusis measurements by pneumotonometry were similar (P = 0.8). Differences of postoperative intraocular pressure measurements by Goldmann applanation tonometry and pneumotonometry were statistically significant. After 3 months, there was a poor correlation between Goldmann applanation tonometry and pneumotonometry intraocular pressure values (Pearson r = 0.58). Postoperative intraocular pressure decrease in applanation tonometry correlated with changes in keratometry, spherical equivalent, and central corneal thickness. Regression analysis showed a decrease of 2.9 mm Hg per 70 microm reduction in central corneal thickness. CONCLUSIONS: Contact pneumotonometry measures the IOP reliably after laser in situ keratomileusis for myopia, whereas Goldmann applanation tonometry underestimates the intraocular pressure. This may be important in the treatment of any future glaucoma.     

Intraocular pressure measurement over amniotic membrane patch in human subjects

PURPOSE: To investigate the accuracy of intraocular pressure (IOP) measurement over amniotic membrane patching on human ocular surface using Tono-Pen tonometry. METHODS: The IOP of 28 normal eyes in 14 volunteers (mean age, 27.6 years; range, 25-34) was measured by a handy applanation tonometer and the Tono-Pen XL. Then, a single layer of amniotic membrane (approximately 50 microm) was placed onto the corneal surface of the volunteers and the IOP was again measured using the Tono-Pen XL. RESULTS: The average IOP using handy applanation tonometry and the Tono-Pen was 14.3 +/- 2.1 and 14.3 +/- 2.4 mm Hg, respectively. In the presence of amniotic membrane, the average IOP was not significantly overestimated (14.7 +/- 2.6 mm Hg). The bias between handy applanation tonometry or the Tono-Pen XL without amniotic membrane and the Tono-Pen XL with amniotic membrane was only -0.40 and -0.18 mm Hg, respectively. CONCLUSIONS: The Tono-Pen XL is accurate and useful for IOP monitoring even in eyes with amniotic membrane patching.     

Pressure phosphene tonometry versus Goldmann applanation tonometry for measuring intraocular pressure before and after LASIK

PURPOSE: To compare pressure phosphene tonometry with Goldmann applanation tonometry for measuring intraocular pressure (IOP) before and after LASIK. METHODS: Forty-three (18 men and 25 women) consecutive healthy patients underwent complete pre- and postoperative LASIK ophthalmologic assessments including manifest and cycloplegic refraction, keratometry, and central corneal thickness. Three repetitive sets of pressure phosphene tonometry and Goldmann applanation tonometry measurements were performed the day before and 3 months following uneventful LASIK. RESULTS: Mean preoperative spherical equivalent refraction was -4.70 +/- 2.50 diopters (D) (range: -1.50 to -12.90 D) and mean preoperative keratometry was 43.95 +/- 1.08 D. After LASIK, spherical equivalent refraction was +0.23 +/- 0.11 D and mean keratometry was 39.46 +/- 2.28 D. Preoperative pressure phosphene tonometry (12.16 +/- 1.58 mmHg) and Goldmann applanation tonometry (12.01 +/- 1.55 mmHg) IOP measurements were similar. Postoperative IOP was 10.30 +/- 1.16 mmHg with Goldmann applanation tonometry and 12.20 +/- 1.62 mmHg with pressure phosphene tonometry. The postoperative IOP difference between Goldmann applanation tonometry and pressure phosphene tonometry was 0.15 +/- 1.12 mmHg (P = .41). The mean change in pachymetry after LASIK was 68.73 +/- 73 microm. The change in Goldmann applanation between preoperative and postoperative LASIK values was 1.71 +/- 1.43 mmHg (P < .0001), a change that was strongly correlated with changes in corneal thickness (R = 0.75, P < .0001) and keratometry (R = 0.72, P < .0001). No such correlations were found with pressure phosphene tonometry. CONCLUSIONS: Goldmann applanation tonometry-measured IOP decrease after LASIK is strongly correlated with a decrease in central corneal thickness and changes in keratometry, whereas pressure phosphene tonometry-measured IOP is independent of corneal thickness. Pressure phosphene tonometry appears to be a more reliable method for recording tonometry in these patients.     

The effect of contact lens induced corneal edema on Goldmann applanation tonometry measurements

AIM: To determine the effect of small increases in corneal hydration on the accuracy of Goldmann applanation tonometry estimates of intraocular pressure (IOP). MATERIALS AND METHODS: Twenty-five young healthy subjects presented on 3 separate days approximately 1 week apart. On 2 visits, subjects were required to wear a hydrogel contact lens with either a center thickness of 0.3 and 0.7 mm (HEMA 38% water content, parallel surface curve) in 1 eye only under closed-eye conditions for 2 hours to induce corneal swelling. The third visit acted as a control. IOP, corneal thickness, and corneal curvature were measured in both eyes before and after contact lens wear on all visits. RESULTS: There was a statistically significant increase in corneal thickness of 40.2+/-14.4 microm (P<0.001) and 41.9+/-16.4 microm (P<0.001) after wearing the 0.3 and 0.7 mm thick contact lenses, respectively (2-tailed paired t test). There was an increase in IOP of 2.8+/-2.2 mm Hg (P<0.001) after wearing the 0.3 mm thick contact lens, and a statistically insignificant difference of 1.3+/-3.0 mm Hg (P=0.058) after wearing the 0.7 mm thick contact lens (2-tailed paired t test). There was a statistically significant Pearson correlation between the change in corneal thickness and the change in IOP after lens wear (r=0.500, P<0.001, 0.3 mm lens and r=0.399, P<0.001, 0.7 mm lens). The corneal hydration-induced measurement error was 0.46 mm Hg per 10 microm change in corneal thickness (0.3 mm lens) and 0.35 mm Hg per 10 microm change in corneal thickness (0.7 mm lens). CONCLUSION: A small increase in corneal hydration and thickness may cause a clinically significant overestimation of IOP when measured using Goldmann applanation tonometry.     

Intraocular pressure measurement after hyperopic LASIK.

PURPOSE: Previous studies have shown that Goldmann applanation tonometry (GAT) underestimates intraocular pressure (IOP) following photorefractive keratometry (PRK) and myopic laser in situ keratomileusis (LASIK). The purpose of this study was to evaluate the reliability of intraocular pressure (IOP) measurements by Goldmann applanation tonometry and pneumotonometry (PT) after hyperopic LASIK. METHODS: The IOPs of 20 eyes of 15 patients who underwent hyperopia LASIK were prospectively evaluated. Central and peripheral IOP were measured with GAT and PT, and central and peripheral corneal thicknesses were measured with ultrasonographic pachymetry. Patients were evaluated preoperatively and at 12 months postoperatively. RESULTS: Postoperative GAT measurements of IOP made from the central (13.1+/-2.7 mm Hg) and peripheral (13.9+/-3.3 mm Hg) corneal areas were significantly lower (P <0.001) than central IOP measured preoperatively (17.0+/-2.5 mm Hg). Postoperative PT measurements from the central (17.4+/-3.2 mm Hg) and peripheral (17.6+/-2.9 mm Hg) corneal areas were slightly lower than preoperative central IOP (18.4+/-2.4 mm Hg), but not statistically significant. There were no significant differences between central and peripheral IOP measurements using either method. CONCLUSION: The data demonstrate that GAT may underestimate IOP measurement, following hyperopic LASIK.     

Measurement of intraocular pressure in LASIK and LASEK patients using the Reichert Ocular Response Analyzer and Goldmann applanation tonometry

PURPOSE: To determine the efficacy of the Reichert Ocular Response Analyzer (ORA) to measure intraocular pressure (IOP) following corneal laser refractive surgery. METHODS: Intraocular pressure was measured using Goldmann applanation tonometry preoperatively and 3 months following LASIK and LASEK for all levels of myopia and low levels of hyperopia. In LASIK eyes, 120-microm flaps were cut using the Hansatome XP. The ORA was used to measure Goldmann correlated IOP and corneal compensated IOP 3 months postoperatively. Postoperative central corneal thickness, hysteresis, and corneal curvature were assessed to determine their relationship with postoperative change in Goldmann applanation tonometry IOP. Efficacy of ORA IOP measurement was analyzed by comparing Goldmann applanation tonometry IOP with Goldmann correlated IOP. RESULTS: LASEK was performed on 35 eyes, and LASIK was performed on 90 eyes. In the LASIK group, mean Goldmann applanation tonometry IOP decreased 3.7+/-2.3 mmHg postoperatively (P=.00). Postoperative Goldmann applanation tonometry did not differ significantly (P=.06) from postoperative ORA Goldmann correlated IOP (10.2+/-2.1 mmHg). In the LASEK group, mean Goldmann applanation tonometry IOP decreased 3.9+/-2.3 mmHg (P=.00). Postoperative Goldmann applanation tonometry did not differ significantly (P=.6) from postoperative ORA Goldmann correlated IOP (10.7+/-2.5 mmHg). Postoperative decrease in Goldmann applanation tonometry IOP did not correlate with age, ablation depth, pre- and postoperative central corneal thickness or corneal hysteresis, or postoperative decrease in corneal curvature. CONCLUSIONS: Intraocular pressure measurements were similar using both the ORA Goldmann correlated IOP and Goldmann applanation tonometry following keratorefractive surgery.     

Relation between corneal thickness and intraocular pressure measurement by noncontact and applanation tonometry.

PURPOSE: To assess whether there is a significant difference in intraocular pressure (IOP) measurements between noncontact and applanation methods and if so, whether the difference is correlated with corneal thickness. SETTING: I?ik Eye Clinic, Ankara, Turkey. METHODS: This prospective study comprised 120 eyes of 60 randomly selected patients. Noncontact tonometry, applanation tonometry, and pachymetry were performed in each eye. The results were compared and an analysis was performed to determine whether there was a correlation between the differences in IOP measurements and corneal thickness in the entire group and in subgroups composed of the halves and quarters of the group. RESULTS: The mean IOP in the entire group was 20.38 mm Hg +/- 4.97 (SD) with the noncontact tonometer and 18.84 +/- 4.47 mm Hg with the Goldmann applanation tonometer. The difference between the measurements with the noncontact method and those with the applanation method was statistically significant (P <.01) except in cases having a corneal thickness between 513 microm and 539 microm (P >.01). There was a positive correlation between corneal thickness and the difference in measurements by noncontact and applanation tonometry, and the magnitude of correlation was greater in cases with thicker corneas. CONCLUSION: The reliability of tonometers decreased with increasing corneal thickness, in which case higher readings were found, especially with the noncontact tonometer.     

相干光断层扫描仪检测正常人及青光眼患者中央角膜厚度

目的探讨相干光断层扫描仪(OCT)测量正常人、原发性开角型青光眼(POAG)、正常眼压性青光眼(NTG)、高眼压症(OHT)患者的中央角膜厚度(CCT)。方法采用OCT3测量正常人143例(143只眼)、POAG患者36例(36只眼)、NTG患者39例(39只眼)及OHT患者40例(40只眼)的CCT,并进行单因素4水平设计定量资料的方差分析;用线性回归方法分析正常人CCT与Goldmann压平眼压测量值的相关关系;对OCT测量CCT观察者间和观察者内的一致性进行类内相关系数(ICC)分析。结果正常组、POAG组、NTG组及OHT组的平均CCT值分别为(523.66±32.13)μm、(530.92±27.32)μm、(506.92±21.49)μm及(573.13±27.39)μm。POAG组与正常人组的平均CCT值差异无统计学意义(P=0.099);OHT组的平均CCT值大于其他各组,均P<0.01;NTG组的平均CCT值小于其他各组,均P<0.01。正常组CCT与眼压值呈正相关(r=0.318,R2=0.101,P<0.01)。OCT测量CCT的测量者间和测量者内的ICC值分别为0.995和0.996。结论OCT可以准确地测量CCT;NTG患者平均CCT比正常人薄,而OHT患者比正常人厚;CCT可以影响Goldmann压平眼压计的测量值,但贡献率较小。(中华眼科杂志,2006,42:199-203)     

Should Orbscan pachometry be performed before or after Goldmann applanation tonometry?

PURPOSE: To compare the Orbscan central corneal thickness (CCT) values before and after intraocular pressure (IOP) measurement with Goldmann applanation tonometry in young normal adults. MATERIALS AND METHODS: Fifty-three eyes of 53 subjects who were free from any ocular problems were studied. The measurements included optical pachometry by the Orbscan II system, followed by Goldmann applanation tonometry, and finally Orbscan optical pachometry again. Standard Goldmann technique was adopted with the application of one drop of 0.4% benoxinate and fluorescein sodium prior to the measurement. The same operator was involved in the Orbscan pachometry before and after Goldmann tonometry. Another investigator was responsible for Goldmann tonometry. Three readings were obtained in each case, and the means were used for analysis. RESULTS: The mean IOP of the sample was 14.6 +/- 2.6 mmHg. There was no significant difference (paired t-test: p = 0.50) in the mean CCT values before and after the Goldmann tonometry (551 +/- 32 and 552 +/- 35 microm respectively). CONCLUSION: Standard Goldmann applanation tonometry does not affect the Orbscan CCT values. Measurement of CCT for the adjustment of true IOP can be carried out either before or after Goldmann tonometry.     

ProTon tonometer determination of intraocular pressure in patients with scarred corneas

PURPOSE: To evaluate the measure of intraocular pressure (IOP) in patients with scarred corneas obtained from the affected and non-affected areas. MATERIALS AND METHODS: Eighteen patients with small maculo-leucomatous corneal opacity following microbial keratitis were prospectively included in the study. Goldmann applanation tonometry was done first on the non-affected corneal surface. ProTon tonometry (PT) was then carried out on the same eye, to obtain IOP measurements from the non-affected (PT1) and the affected area (PT2) of the cornea. The IOP measurements were compared using a two-tail paired t test. RESULTS: The mean of IOP measurements of PT 2 and PT1 was 22 mm of Hg (SD +/- 5.2) and 14.8 mm of Hg (SD +/- 5.4), respectively. The higher reading of PT2 was statistically significant ( P < 0.001). The mean Goldmann applanation tonometry was 14.6 mm of Hg (SD 5.4) and it did not differ significantly ( P = 0.86) from the PT1 readings of 14.8 mm of Hg (SD 5.4). CONCLUSION: In patients with maculo-leucomatous corneal opacity, determination of IOP by ProTon tonometer varies from the affected to the non-affected area. The ProTon tonometer overestimates the level of IOP when it is applied to a leucomatous corneal opacity.     

The effect of corneal thickness on intraocular pressure measurement in patients with corneal pathology

BACKGROUND/AIM: To compare intraocular pressure (IOP) measurements taken by the Goldmann applanation tonometer, the Tono-Pen and the ocular blood flow pneumotonometer in eyes with varying central corneal thickness (CCT) due to penetrating keratoplasty (PK), keratoconus (KC), and Fuchs' endothelial dystrophy (FED). METHODS: IOP was measured with the Goldmann applanation tonometer, Tono-Pen XL, and OBF pneumotonometer in 127 eyes with the following corneal abnormalities. There were 56 eyes that had undergone PK, 37 eyes with KC, and 34 eyes with FED. CCT was measured using an ultrasound pachymeter after IOP determinations had been made. RESULTS: Mean IOP measurements in all three patient groups were significantly higher when measured by OBF pneumotonometer. Linear regression analysis showed that patients with FED had a significant increase in IOP with increasing CCT of 0.18 mm Hg/10 microm using the Goldmann tonometer, 0.15 mm Hg/10 microm with the Tono-Pen, and 0.26 mm Hg/10 microm with the OBF pneumotonometer. In patients with KC and after PK, linear regression analysis did not show a significant effect of CCT on IOP. A multivariate linear regression model controlling for age, sex, graft size, and patient group, showed that the effect of CCT on IOP for Tono-Pen (0.13 mm Hg/10 microm CCT) and Goldmann (0.14 mm Hg/10 microm CCT) were significantly lower than for the OBF pneumotonometer (0.26 mm Hg/10 microm CCT). CONCLUSIONS: This study found that mean IOP measurements using the OBF pneumotonometer were significantly higher than those made using the Goldmann applanation tonometer or Tono-Pen in eyes with a variety of cornel pathologies. The OBF pneumotonometer was found to be most affected by variation in CCT. For all three instruments, the relation between IOP and CCT depended on the corneal pathology and was greatest for FED.     

Intraocular pressure measurements using dynamic contour tonometry after laser in situ keratomileusis

PURPOSE: Thinning of the corneal stroma by laser in situ keratomileusis (LASIK) results in inaccurate low intraocular pressure (IOP) readings by Goldmann applanation tonometry (GAT). Dynamic contour tonometry (DCT) is a novel measuring technique, designed to measure IOP largely independent of corneal thickness and curvature. The purpose of this study was to compare IOP measurements using GAT and DCT in eyes undergoing LASIK for correction of myopia. METHODS: In a prospective, single-center study, central corneal thickness (CCT) and IOP were measured in patients undergoing first-time LASIK for myopia. IOP was measured before and after surgery using GAT and DCT. The untreated contralateral eyes served as paired controls. RESULTS: There was good concordance between the two tonometers in 62 normal eyes before LASIK. Corneal ablation of 90.0 +/- 49.18 micro m (median +/- SD) reduced IOP readings as measured by GAT by 3.0 +/- 1.9 mm Hg (P < 0.001). In contrast, no significant change in IOP readings was recorded by DCT (-0.2 mm Hg +/- 1.5 mm Hg, P = 0.30). There was no change in IOP in the untreated control eyes as measured by GAT and DCT. CONCLUSIONS: Significant decreases in IOP were recorded by GAT after LASIK for myopia. Measurements by DCT, however, did not reveal any significant changes in IOP.     

Comparison of dynamic contour tonometry with goldman applanation tonometry over a wide range of central corneal thickness

PURPOSE: To compare dynamic contour tonometry with Goldmann applanation tonometry in structurally normal corneas over a wide range of central corneal thickness (CCT). PATIENTS AND METHODS: Twenty-five patients each with normal CCT (group A), thin corneas (group B), and thick corneas (group C) had IOP measured with the Goldmann (GAT) and dynamic contour tonometer (DCT). RESULTS: In group A (mean CCT = 552 +/- 16 microm) the mean GAT was 15.9 +/- 3.1 mm Hg and mean DCT was 16 +/- 3.3 mm Hg (P = 0.91). In group B (mean CCT = 491 +/- 19 microm) the mean GAT was 13.2 +/- 3.5 mm Hg and the mean DCT was 15.9 +/- 3.5 mm Hg (P = 0.009). For group C (mean CCT = 615 +/- 22 microm), the mean GAT was 17.4 +/- 3.8 mm Hg and the mean DCT was 17.4 +/- 3.5 mm Hg (P = 0.95). The 95% agreement limits for DCT were -3.1 mm Hg to 2.9 mm Hg. The mean GAT-DCT difference was -2.6 mm Hg in thin corneas and -0.06 mm Hg in thick corneas. Below 520 microm reduction of 10 microm in CCT appears to result in a significant underestimation of the GAT IOP by 0.7 mm Hg (P < .001) and above 580 microm a non-significant overestimation of 0.2 mm Hg per 10 microm increase in CCT (P = 0.27). CONCLUSION: Dynamic contour tonometer agrees well on average with GAT but the agreement limits are wide. In structurally normal thin corneas DCT may give a more accurate assessment of the true IOP but it does not appear to have any benefit over GAT in thick corneas.     

Tono-Pen tonometry in normal and in post-keratoplasty eyes.

Oculab Tono-Pen tonometry was compared with Goldmann applanation tonometry in 82 eyes of 82 patients with normal corneas and in 54 eyes of 54 patients who had undergone penetrating keratoplasty and whose corneas did not preclude the use of Goldmann tonometer. We found that the intraocular pressure (IOP) in 48% of the eyes with normal corneas and in 57% after keratoplasty has different measurements with Goldmann and Tono-Pen pressures of 3 mm Hg or more. Despite the correlation between the Goldmann tonometer and the Tono-Pen in the group of eyes with normal corneas (r = 0.83) as well as in the group of eyes after keratoplasty (r = 0.79) the Tono-Pen tended to significantly overestimate the Goldmann tonometer reading (p < 0.0001). The mean difference between the two instruments was highest across the lower IOP range (< 9 mm Hg) in the group of eyes after keratoplasty. Because the mean absolute values of the paired differences between Goldmann and Tono-Pen measurements varied significantly across all IOP intervals it was not possible to establish a correction factor which could be used when comparing the two measurements. Based on this study the Tono-Pen consistently overestimated the actual IOP in an unpredictable manner. Where possible Goldmann measurements of the IOP are still to be preferred.     

Young's modulus in normal corneas and the effect on applanation tonometry.

OBJECTIVES: To determine the statistically normal range of corneal Young's modulus in young healthy eyes in vivo, and to establish if this variation has a clinically significant influence on intraocular pressure (IOP) measurement using applanation tonometry. METHODS: Central corneal curvature, central corneal thickness (CCT), and applanation IOP (Goldmann tonometer) were measured using standard clinical techniques in one eye of 100 normal human subjects (22.0 +/- 2.9 years) in vivo. The Orssengo-Pye algorithm was used to calculate the corneal Young's modulus of these experimental subjects, and to produce a theoretical model of potential errors in Goldmann applanation tonometry estimates of IOP due to variations of Young's modulus and CCT. RESULTS: Corneal Young's modulus was 0.29 +/- 0.06 MPa [95% confidence interval (CI) 0.17 to 0.40 MPa]. According to the Orssengo-Pye model, the relationship between Young's modulus and the error in applanation IOP is linear; the slope was 23 mm Hg per MPa. An increase from the minimum to the maximum value of the calculated limits of agreement (95% CI) of Young's modulus caused a variation in applanation IOP of 5.35 mm Hg. The anticipated error at the extremes of the limits of agreement (95% CI) of CCT was similar at 4.67 mm Hg. CONCLUSION: Physiological variations in corneal Young's modulus may cause clinically significant errors in Goldmann applanation tonometry estimates of IOP.     

Corneal hysteresis and intraocular pressure measurement in children using the reichert ocular response analyzer

PURPOSE: To examine corneal hysteresis in children with normal eyes and congenital glaucoma and assess intraocular pressure (IOP) measurement with the Reichert Ocular Response Analyzer (RORA). DESIGN: Observational, cross-sectional study. METHODS: setting: Clinical practice. patients: Corneal hysteresis and intraocular pressure (Goldmann correlated [IOPg] and corneal compensated [IOPcc]) were recorded with RORA. IOP was also measured by Goldmann applanation tonometry. RESULTS: Mean corneal hysteresis of 12.5 mm Hg was recorded in 81 [corrected] normal eyes of 42 children. It was markedly lower (mean 6.3 mm Hg) in 11 eyes of eight children with congenital glaucoma. No correlation was found between age and corneal hysteresis (r = -0.08). IOPg did not differ significantly from Goldmann applanation tonometry (P = .27). IOPcc was statistically significantly greater than IOPg (P = .014). RORA measurement was not possible in the presence of nystagmus but was possible with applanation tonometry. Cooperation with IOP measurement was much higher with RORA (89.8%) compared with applanation tonometry (78.7%). CONCLUSIONS: Corneal hysteresis in children is similar to that reported in adults. No correlation was found with age. In the presence of nystagmus, IOP measurement was possible with Goldmann applanation tonometry but not RORA. Cooperation with IOP measurement was better with RORA than with Goldmann applanation tonometry.     

Dynamic contour tonometry for intraocular pressure measurement

PURPOSE: To compare dynamic contour tonometry as a new method for intraocular pressure measurement with Goldmann applanation tonometry. DESIGN: Clinical observational study. METHODS: The study included 176 eyes of 126 subjects (39 eyes with open-angle glaucoma, 137 normal eyes) and consisted of 528 dynamic contour measurements and 352 Goldmann tonometry measurements. Corneal pachymetry measurements were additionally performed. RESULTS: Mean dynamic contour tonometric measurements (18.71 +/- 5.90 mm Hg) were significantly (P < .001) higher than mean applanation tonometric values (16.98 +/- 5.86 mm Hg), correlating significantly with each other (r(2) = .905, P < .001). The slope of the regression line was 0.95. Correlation with central corneal thickness was significant for applanation tonometry (P = .036), while dynamic contour tonometry was statistically independent of corneal thickness (P = .32). CONCLUSIONS: For measurement of intraocular pressure, dynamic contour tonometry may offer a new technology, which, compared with applanation tonometry, may show a lower dependence on central corneal thickness.     

Effect of a tight necktie on intraocular pressure

AIM: To evaluate the effect of a tight necktie on intraocular pressure (IOP) measurement using Goldmann applanation tonometry. METHODS: 40 eyes of 20 normal subjects and 20 open angle glaucoma patients (all male) were enrolled. IOP was measured with an open shirt collar, 3 minutes after placing a tight necktie, and 3 minutes after loosening it. All measurements were made by the same examiner. RESULTS: Mean IOP in normal subjects increased by 2.6 (SD 3.9) mm Hg (p=0.008, paired t test; range -3 to +14 mm Hg) and in glaucoma patients by 1.0 (1.8) mm Hg (p=0.02, paired t test; range -2 to +4.5 mm Hg). In normal subjects, IOP in 12 eyes was increased by >/=2 mm Hg and in seven eyes by >/=4 mm Hg. In glaucoma patients, IOP in six eyes was increased by >/=2 mm Hg and in two eyes by >/=4 mm Hg. CONCLUSION: A tight necktie increases IOP in both normal subjects and glaucoma patients and could affect the diagnosis and management of glaucoma.