Intraocular pressure and ocular pulse amplitude using dynamic contour tonometry and contact lens tonometry

Background

The new Ocular Dynamic Contour Tonometer (DCT), investigational device supplied by SMT (Swiss Microtechnology AG, Switzerland) allows simultaneous recording of intraocular pressure (IOP) and ocular pulse amplitude (OPA). It was the aim of this study to compare the IOP results of this new device with Goldmann tonometry. Furthermore, IOP and OPA measured with the new slitlamp-mounted DCT were compared to the IOP and OPA measured with the hand-held SmartLens^®, a gonioscopic contact lens tonometer (ODC Ophthalmic Development Company AG, Switzerland).

Methods

Nineteen healthy subjects were included in this study. IOP was determined by three consecutive measurements with each of the DCT, SmartLens^®, and Goldmann tonometer. Furthermore, OPA was measured three times consecutively by DCT and SmartLens^®.

Results

No difference (P = 0.09) was found between the IOP values by means of DCT (mean: 16.6 mm Hg, median: 15.33 mm Hg, SD: +/- 4.04 mm Hg) and Goldmann tonometry (mean: 16.17 mm Hg, median: 15.33 mm Hg, SD: +/- 4.03 mm Hg). The IOP values of SmartLens^® (mean: 20.25 mm Hg, median: 19.00 mm Hg, SD: +/- 4.96 mm Hg) were significantly higher (P = 0.0008) both from Goldmann tonometry and DCT. The OPA values of the DCT (mean: 3.08 mm Hg, SD: +/- 0.92 mm Hg) were significantly lower (P = 0.0003) than those obtained by SmartLens^® (mean: 3.92 mm Hg, SD: +/- 0.83 mm Hg).

Conclusions

DCT was equivalent to Goldmann applanation tonometry in measurement of IOP in a small group of normal subjects. In contrast, SmartLens^® (contact lens tonometry) gave IOP readings that were significantly higher compared with Goldmann applanation tonometer readings. Both devices, DCT and SmartLens^® provide the measurement of OPA which could be helpful e.g. for the management of glaucoma.

     

Normalisation of ocular pulse amplitude after embolisation of dural cavernous sinus arteriovenous fistula

BACKGROUND: The difference in the ocular pulse amplitude between an individual's eyes may reflect abnormalities of the cerebrovascular circulation and has been shown to be helpful in assessing patients with cavernous sinus arteriovenous fistulas. HISTORY AND SIGNS: A 71-year-old woman presented with episcleral injection, proptosis, bruit and retro-orbital pain on the left side. Ocular pulse amplitude as measured by dynamic contour tonometry was 4.38 +/- 1.23 mm Hg in the right and 9.57 +/- 2.71 mm Hg in the left eye. Angiography revealed the haemodynamics of a dural left cavernous sinus arteriovenous fistula. THERAPY AND OUTCOME: Successful occlusion of the fistula was performed by transvenous embolisation. After embolisation, ocular pulse amplitude was 2.84 +/- 0.60 mm Hg in the right and 1.88 +/- 0.29 mm Hg in the left eye. Conclusion: In this case of a dural arteriovenous fistula the ocular pulse amplitude as measured by dynamic contour tonometry parallels closely both clinical findings and neuroimaging.     

Measurement of intraocular pressure using the Tono-Pen in comparison with Goldmann applanation tonometry - a clinical study in 100 eyes

BACKGROUND: In clinical practice ophthalmologists often need a tonometer which is independent of a slit lamp. Such a hand-held device is the Tono-Pen. We compared the precision of two equal Tono-Pens with Goldmann applanation tonometry. MATERIAL AND METHODS: Measurement of intraocular pressure (IOP) was done in 100 eyes of 51 patients (mean age 63 +/- 15 years) suffering from ocular hypertension or glaucoma. According to a random table either the right or left eye was measured using Goldmann tonometer first and the Tono-Pen second. For the other eye the measurement was reversed. One of the two equal Tono-Pens (Solan/USA) was used according to a second random table. Three measurements were obtained with each instrument on both eyes within 15 minutes subsequently. Patients were placed in an upright position for all measurements. RESULTS: Even for well-trained ophthalmologists a learning curve of approximately 10 measurements was observed using the Tono-Pen. The Tono-Pen measured an average IOP of 16.9 mm Hg in all 100 eyes. The Goldmann tonometer measured an average IOP of 17.7 mm Hg. The difference was not statistically significant. The standard deviation for all measurements was better for the Tono-Pen (4.7 mm Hg vs 5.8 mm Hg for Goldmann tonometer). No reduction of the IOP after Tono-Pen measurement was observed (in contrast to the Goldmann tonometer). The reproducibility of the Tono-Pen on the same eye was inferior to the Goldmann tonometer by a factor of 2. There was an almost significant difference in reproducibility between two equal Tono-Pens. CONCLUSIONS: Measurement of IOP with the Tono-Pen is comparable to Goldmann applanation tonometry if an average of 3 measurements is used. The difference between two equal Tono-Pens indicates the need for improvement of the quality check during production.     

Clinical comparison of the Icare tonometer and Goldmann applanation tonometry

PURPOSE: To compare a new method of intraocular pressure (IOP) measurement, using the Icare tonometer, with Goldmann applanation tonometry (GAT). PATIENTS AND METHODS: Two observers obtained IOP readings in 292 eyes (143 right and 149 left) of 153 subjects, using the Icare without topical anesthetic. A GAT reading was subsequently obtained by a consultant ophthalmologist, without the knowledge of the Icare readings. Central corneal thickness (CCT) was obtained on all eyes with ultrasound pachymetry. Patient comfort after IOP measurement was assessed in a consecutive subset of patients. RESULTS: The intraclass correlation coefficient between the 2 modalities of IOP measurement was r=0.95 for the right and r=0.93 for the left eye. The mean difference (Icare-GAT) between the IOP measured by the 2 methods was 0.4 mm Hg in the right eye (SD 3.0, 95% confidence interval -5.5 to 6.3), and 0.8 mm Hg in the left eye (SD 3.0, confidence interval -4.7 to 6.2). GAT measurements did not vary with CCT [correlation coefficient=0.09 (P=0.25) right and 0.14 (P=0.09) left eyes]. However, IOP measured with Icare tonometry increased with increasing CCT [correlation coefficient=0.16 (P=0.05) right and 0.21 (P=0.01) left eyes]. For every 100-microm increase in CCT, the difference (Icare-GAT) increased by 1 mm Hg. Of the 38 consecutive patients surveyed, 28 (73.7%) rated the Icare more comfortable than GAT, with only 2 (5.3%) rating it less comfortable (P<0.001). CONCLUSIONS: There is good correlation between the 2 methods of IOP measurement, even at extremes of IOP. The Icare instrument was easy to use and recorded rapid and consistent readings with minimal training. It seems to be more comfortable than GAT and obviates the need for topical anesthesia.     

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.     

兔眼中央角膜厚度与Perkins压平眼压关系的研究

目的探讨中央角膜厚度(CCT)与Perkins压平眼压的关系,建立CCT、真实眼压与Perkins压平眼压三者关系的数学模型和CCT对Perkins压平眼压的校正公式。方法健康新西兰大耳白兔32只,双眼中1只眼行准分子激光屈光性角膜切削术(PRK),另1只眼测得的数据对行PRK眼得出的数据进行验证。采用随机数字表法随机取1只眼,采用PRK,人为改变兔眼的CCT,建立不同CCT的活体眼模型,分别采用Perkins压平眼压计、A型超声角膜测厚仪、角膜曲率计测量术前、术后Perkins压平眼压、CCT、角膜曲率以及应用电子直接眼压计测量真实眼压,分别对术前和术后测量值做相关分析和多元线性回归分析,并对另1组未行PRK眼测得的真实眼压、Perkins压平眼压、CCT对实验组得出的公式进行验证。结果兔眼双眼Perkins压平眼压、CCT、角膜曲率无统计学差别,无论是术前还是术后Perkins压平眼压与CCT均显著相关(r=0.761P<0.01;r=0.829,P<0.01),与角膜曲率无关(r=0.098,P>0.05;r=0.260P>0.05)。对术前、术后Perkins压平眼压与CCT建立回归公式,曲线的斜率分别为0.066、0.053,Perkins压平眼压的改变与CCT的改变有关。对真实眼压Y与Perkins压平眼压、CCT三者的关系建立回归公式为Y=12.107+1.254X1-0.033X2(X1=Perkins压平眼压,X2=CCT)。结论CCT的改变影响Perkins压平眼压的测量值,临床上应根据CCT来校正Perkins压平眼压的测量值。     

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.     

Paradoxical hypotony after laser in situ keratomileusis

We present a case of paradoxically low (0 to 2 mm Hg) intraocular pressure (IOP) measured by Goldmann applanation and Tono-Pen tonometry in an eye with corticosteroid-induced high IOP after laser in situ keratomileusis. The patient complained of blurred vision and ocular pain in both eyes. The eyes were firm by palpation, and the IOP measured by Schiotz indentation tonometry was 38 mm Hg. An interface fluid pocket was identified by slitlamp examination, and the corneal surface became steeper. These findings resolved after flap relifting, interface irrigation, and addition of antiglaucoma medications. We postulate that the paradoxically low reading by applanation tonometry was due to fluid accumulation within the flap-bed interface. The applanation tonometry reflected the interface fluid pocket pressure rather than the real high IOP. An exceedingly low IOP should be verified by palpation or by Shiotz indentation tonometry, and interface fluid should be identified.     

Impact factors on intraocular pressure measurements in healthy subjects

AIM: To evaluate whether intraocular pressure (IOP) calculation by applanation tonometry is determined more essentially by the subject's neck position or by neck constriction. METHODS: 23 right eyes of 23 healthy subjects (12 male, 11 female) were included. IOP was measured by applanation tonometry with the TonoPen on sitting participants under four different conditions: with open collar upright (A) or with the head in the headrest of a slit lamp (B), with a tight necktie upright (C) or in slit lamp position (D). All measurements with neck constriction were performed 3 minutes after placing the necktie. RESULTS: Mean IOP was 16.9 (SD 2.3) mm Hg (range 11-21 mm Hg) (A), 18.1 (SD 2.2) mm Hg (range 14-22 mm Hg) (B), 17.9 (SD 2.9) mm Hg (range 12-25 mm Hg) (C) and 18.7 (SD 2.7) mm Hg (range 13-24 mm Hg) (D). Mean IOP increased by 1.3 (SD 2.6) mm Hg (p = 0.028, paired t test, range +0.2 to +2.4 mm Hg) if subjects changed position from A to B. There was no statistically significant difference between measurements with or without neck constriction. CONCLUSION: Applanation tonometry may be inaccurate if performed in slit lamp position. In contrast, tight neckties do not significantly affect IOP evaluation in healthy subjects.     

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.     

正常人中央角膜厚度与Goldmann压平眼压的关系

目的:了解正常人中央角膜厚度(central corneal thickness,CCT)的分布特点并探讨其与压平眼压测量值的关系。方法:采用光学角膜测厚仪及Goldmann压平眼压计检测169名正常人CCT和压平眼压。结果:169名受检者右眼平均CCT为0.547mm(95%可信区间0.443~0.651mm),左眼0.551mm(95%可信区间0.453~0·649)。压平眼压右眼平均15.8mmHg,左眼15.5mmHg。CCT与年龄无相关关系,但与压平眼压测量值显著相关。线性回归分析表明,CCT每增加0.018mm,压平眼压增加1mmHg。结论:CCT变异是眼压测量误差的主要来源。CCT较厚的正常个体可表现"眼压增高"被误诊为高眼压症,而CCT偏薄的原发性开角型青光眼患者则可能因眼压测量"正常"被误诊为正常眼压性青光眼。在诊断青光眼或高眼压症时,特别是在眼压值与其他临床表现不符时,应考虑CCT有无变异。     

Does smoking affect intraocular pressure? Findings from the Blue Mountains Eye Study

PURPOSE: To assess the relationship between smoking and intraocular pressure. MATERIALS AND METHODS: The Blue Mountains Eye Study examined 3654 residents aged 49 years and older in an area west of Sydney, Australia from 1992 to 1994. A trained interviewer collected a detailed history of smoking. Intraocular pressure was measured using Goldmann applanation tonometry; as the correlation between right and left eyes was very high, only right-eye data are presented. Participants using glaucoma medications or who had evidence of previous cataract surgery were excluded. RESULTS: Current smokers (15.8% of participants) had slightly higher mean intraocular pressures (16.34 mm Hg) than nonsmokers (16.04 mm Hg). Intraocular pressure (in the right eye) was significantly associated with current smoking, after adjusting for age and sex (P = 0.03). This association remained unchanged after simultaneous adjustment for other variables associated with intraocular pressure, including blood pressure, diabetes, myopia, glaucoma, family history, and pseudoexfoliation (P = 0.02). CONCLUSIONS: This study identified a modest cross-sectional positive association between current smoking and intraocular pressure.     

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.     

Dynamic contour tonometry for post-LASIK intraocular pressure measurements

BACKGROUND: Standard applanation tonometers are subject to systematic errors when applied to corneas with non-standard properties. Dynamic contour tonometry has been proposed as an alternative method for obtaining correct IOP data from such corneas. We have examined its applicability for patients who have undergone LASIK surgery. PATIENTS AND METHODS: 20 healthy individuals scheduled for bilateral myopic LASIK were selected. Pre- and postoperative examination (3 months) included applanation tonometry (Goldmann), contour tonometry, pachymetry, keratometry, and refraction. LASIK was performed with an MEL-70 Excimer Laser and a Hansatome Microkeratome. A tobramycin/dexamethasone preparation (Tobradex eye drops) was prescribed during one week after surgery. RESULTS: Applanation tonometry and contour tonometry furnished comparable IOP results prior to surgery (GAT: 15.1 +/- 2.2 mm Hg [mean +/- SD] DCT: 17.0 +/- 2.2 mm Hg), with corneal thickness ranging from 473 - 601 micro m (mean: 555 micro m). 3 months postoperatively, mean corneal thickness was reduced by - 85 micro m. Contour tonometer readings were not significantly different from preoperative results (16.0 +/- 2.4 mm Hg); whereas the Goldmann tonometer furnished significantly lower values at 11.8 +/- 1.3 mm Hg. CONCLUSIONS: Preoperative IOP measurements with the two types of tonometer were in good agreement. Post-operative results with the contour tonometer agree well with preoperative figures. However, the Goldmann tonometer furnishes values 3.3 mm Hg lower on average. This result is indicative of a significant measurement error of this device on post-LASIK eyes, which persists even 3 months postoperatively. The Dynamic contour tonometer appears to be suitable, reliable, and easy to use for IOP measurements after LASIK 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.     

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.     

Agreement between two Goldmann type applanation tonometers

The aim of the study was to assess agreement between two commercially available applanation tonometers for the measurement of intraocular pressure (IOP). Forty subjects underwent IOP measurement on two accurately calibrated Goldmann type applanation tonometers (Zeiss AT 030 (GATZ) and Inami L-5110(GATI)). The order of examination was randomized and observers were masked to the IOP recorded. The mean of two consecutive readings, from a randomly selected eye for each subject, was used for analysis. Agreement was assessed using the Altman and Bland plot. The mean (SD) IOP readings on GATZ was 15.32 (+/-6.80) mm Hg and on GATI was 13.52 (+/-5.65) mm Hg (p< 0.001, 95% CI of the difference: -2.48 to -1.11). The 95% limits of agreement on the Altman and Bland plot were:-2.47 to 6.16 mm Hg). There was significant inter-instrument variability between the two accurately calibrated Goldmann type applanation tonometers studied.     

Falsely elevated intraocular pressure due to an abnormally thick cornea in a patient with nevus of Ota

BACKGROUND: Several ocular complications, including glaucoma and ocular hypertension, have been reported in patients with nevus of Ota. CASE: A 12-year-old boy with nevus of Ota on the left side of his face was referred for further examination of elevated intraocular pressure in his left eye. OBSERVATIONS: Intraocular pressure measured with Goldmann tonometry was 19 mm Hg OD and 25 mm Hg OS. No visual field defects were detected by Goldmann or Humphrey perimetry. With ultrasonic pachymetry, the mean +/- SD of central corneal thickness was 560 +/- 4 microm in the right eye and 652 +/- 9 microm in the left. CONCLUSION: Ophthalmologists should be aware that the abnormally thick cornea of patients with nevus of Ota may produce falsely elevated intraocular pressure readings.     

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.