Tono-Pen XL Research Articles

Comparison of three methods of tonometry in normal subjects: Goldmann applanation tonometer, non-contact airpuff tonometer, and Tono-Pen XL.

ObjectiveWe aimed to compare intraocular pressure (IOP) measurements via three different tonometers: the Goldmann applanation tonometer (GAT), the Tono-Pen® XL (TPXL), and a non-contact airpuff tonometer (NCT).MethodsThis was a cross-sectional study of 200 eyes from 200 patients. Right eyes of all patients were included in this study. IOP was measured via GAT, NCT, and TPXL by three physicians. Each physician used one of the tonometers. Measurements via the three devices were compared.ResultsThe mean IOP was 15.5±2.2 mmHg (range 10–22) with the GAT, 16.1±3.0 (range 9–25) with the TPXL, and 16.1±2.8 (range 10–26) with the NCT. Bland–Altman analysis showed that the mean difference between measurements from the NCT and the GAT was 0.6±2.3 mmHg. The mean difference between the TPXL and GAT measurements was 0.7±2.5 mmHg. The mean difference between the NCT and TPXL measurements was −0.02±3.0 mmHg. There was no significant difference between the groups according to a one-way analysis of variance (ANOVA) test. P-values were 0.998 for NCT–TPXL, 0.067 for NCT–GAT, and 0.059 for TPXL–GAT.ConclusionThe NCT and TPXL provide IOP measurements comparable to those of the gold standard GAT in normotensive eyes.

Comparison of three methods of tonometry in normal subjects: Goldmann applanation tonometer, non-contact airpuff tonometer, and Tono-Pen XL

Comparison of three methods of tonometry in normal subjects: Goldmann applanation tonometer, non-contact airpuff tonometer, and Tono-Pen XL

Intraocular Pressure Elevation after Vitrectomy for various Vitreoretinal Disorders

To determine the incidence of and risk factors for intraocular pressure (IOP) elevation in the immediate postoperative period after vitrectomy for various vitreoretinal disorders. A prospective study was performed in 228 consecutive patients with various vitreoretinal disorders. The IOP was measured before surgery, at the end of surgery, and at 5 hours and 1 day after surgery using Tono-Pen XL. The IOP at the end of surgery was adjusted to 15.0 ± 2.0 mm Hg. Intraocular pressure elevation (>25 mm Hg) was found in 55 (24.1%) and 52 (22.8%) patients at 5 hours and 1 day postoperatively, respectively. The IOP at 5 hours was significantly lower in patients with macular hole (MH) than in those with diabetic macular edema, proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy, or rhegmatogenous retinal detachment (RD). The IOP at 1 day was significantly higher in patients with PDR and RD than in those with MH and epiretinal membrane. Multiple regression analysis revealed that IOP at 5 hours postoperatively had a significant correlation with the number of laser photocoagulation, preoperative IOP, combined cataract surgery, and 20-gauge vitrectomy. The IOP at 1 day postoperatively was significantly associated with these 4 parameters as well as the severity of postoperative vitreous hemorrhage and use of expanding gas tamponade. Intraocular pressure elevation was found in approximately one-quarter of cases within 1 day following vitrectomy. The risk factors for IOP elevation included number of laser photocoagulation, combined cataract surgery, severity of postoperative vitreous hemorrhage, and use of expanding gas tamponade.

Tono-pen measurement of intraocular pressure under topical anaesthesia in full term normal newborns.

Tono-pen measurement of intraocular pressure (IOP) under topical anaesthesia in full term normal newborns. The IOP measurements were taken using Tono-pen XL tonometer under topical anaesthesia in 150 newborns (300 eyes) within 24h after birth, over a period of three months, in a university hospital. Gender, gestation period, mode of delivery and birth weight of newborns were noted from medical records. There were 70 males and 80 females. All babies were Malays. The IOP measurements were taken between 12 and 24h after birth. The gestation period of babies ranged between 37 and 41 weeks; 118 babies were delivered by spontaneous vaginal delivery and 32 by caesarian section. The birth weight of babies ranged between 2.1 and 4.3kg. The mean IOP of 300 eyes was 15.99±2.79mmHg (range 8-22). There was no statistically significant difference of mean IOP and gender, laterality of eye, type of delivery, gestation age, or birth weight of newborns. The IOP in full term normal newborns was 16mmHg. Tono-Pen appears to be ideal instrument for taking IOP in newborns because of its small size and easy handling.

Comparison of two handheld applanation tonometers and the association of central corneal thickness, age, and intraocular pressure in normal and diseased canine eyes

To compare the intraocular pressure (IOP) measurements from two applanation tonometers (Tono-Pen XL(®) and AccuPen(®) in normal and diseased canine eyes (including corneal disease, cataract, glaucoma, uveitis, and noninflammatory intraocular disease) and evaluate the associations among the central corneal thickness (CCT), IOP measurements, and age. Sixty-eight normal and 191 diseased eyes. A topical anesthetic agent was applied to each eye. One minute later, IOP was measured with the Tono-Pen XL(®) and then the AccuPen(®), and then CCT was measured with an ultrasonic pachymeter. Measurements for the right eye were always taken first. The Tono-Pen XL(®) successfully measured IOP in all eyes, whereas the AccuPen(®) registered measurements in only 98.4% of diseased eyes. The AccuPen(®) measurements were significantly lower than the Tono-Pen XL(®) measurements in both normal and diseased eyes. The CCT did not affect the Tono-Pen XL(®) or AccuPen(®) measurements in normal or diseased eyes. Spearman's correlation coefficient by rank analysis of CCT and IOP yielded correlation coefficients (r) of 0.144 and 0.101 for the Tono-Pen XL(®), and 0.108 and 0.175 for the AccuPen(®) in normal and diseased eyes, respectively. In normal canine eyes, age correlated inversely with the CCT (r = -0.128) and IOP as measured using the Tono-Pen XL(®) (r = -0.446) and AccuPen(®) (r = -0.427). The AccuPen(®) measurements were slightly but significantly lower than the Tono-Pen XL(®) measurements in both normal and diseased canine eyes. The CCT affected the results of neither tonometer regardless of disease, while both IOP and CCT tended to decrease with age in normal eyes.

Twenty‐four‐hour rhythm of ocular perfusion pressure in non‐arteritic anterior ischaemic optic neuropathy

In non-arteritic anterior ischaemic optic neuropathy (NAAION) patients, circulatory insufficiency within the optic nerve has previously been hypothesized to be related to nocturnal systemic hypotension. The main objective of this prospective cohort study was to investigate the nyctohemeral variations in ocular perfusion pressure (OPP) in NAAION patients. In 20 patients with NAAION, the intraocular pressure (IOP) was measured using the Tono-Pen XL(™) electronic tonometer every hour for 24 hr. Blood pressure (BP) was evaluated over 24 hr. Mean OPP was calculated with the following formula: OPP sitting position = (0.74 × mean BP) - IOP and OPP lying position = (0.84 × mean BP) - IOP. A nonlinear least squares dual-harmonic regression analysis approach was used to model the 24-hr rhythms of OPP data. On average, a 24-hr amplitude of 4.7 ± 2.6 mmHg was found for OPP. The patients were classified as either having a diurnal OPP rhythm (i.e. with a diurnal acrophase, 10% of the cases), a nocturnal OPP rhythm (45%) or absence of OPP rhythm (45%). Four patients had a nocturnal reduction in OPP (mean, -11%). The physiological nocturnal rhythm of OPP was maintained in 45% of the NAAION patients. The nocturnal reduction in OPP seen in 20% of the patients was within the range of OPP where optic nerve blood flow autoregulation is still fully operative. A high prevalence of obstructive sleep apnoea syndrome in our population (71%) may explain the low frequency of systemic nocturnal hypotension.

Validation of glaucoma-like features in the rat episcleral vein cauterization model

Background Glaucoma, an irreversible optic nerve neuropathy, always results in blindness. This study aimed to evaluate glaucoma-like features in the rat episcleral vein cauterization (EVC) model by multiple in vivo and in vitro evidences. Methods Wistar rat was used in this study. The elevated intraocular pressure (IOP) was induced by cauterization of three episcleral veins. IOP was monitored with Tono-Pen XL tonometer. Time-dependent changes to the neuronal retinal layers were quantified by Fourier domain-optical coherence tomography. The function of retina was evaluated by electroretinogram (ERG). Survival of retinal ganglion cells (RGCs) was quantified by retrograde labeling. Histology study was performed with retinal sections stained with hematoxylin-eosin, glial fibrillary acidic protein, and neuronal nuclear antigen. Retina and aqueous humor protein were extracted and cytotoxic protein tumor necrosis factor alpha (TNF-α) and alpha-2 macroglobulin (α2m) were measured with Western blotting. Results EVC is a relatively facile intervention, with low failure rates (<5%). After surgical intervention, chronic mild IOP elevation (about 1.6-fold over normal, P <0.05) was induced for at least 6 weeks without requiring a second intervention. High IOP causes chronic and progressive loss of RGCs (averaging about 4% per week), progressive thinning of neuronal retinal layers (3-5 μm per week), and reduction of a- and b-wave in ERG. EVC method can also induce glial cell activation and alterations of inflammation proteins, such as TNF-α and α2m. Conclusion EVC method can establish a robust, reliable, economic and highly reproducible glaucomatous animal model.

Effect of Topical Calcium Channel Blockers on Intraocular Pressure in Steroid-induced Glaucoma.

ABSTRACTPurpose: To evaluate the effect of 0.125% verapamil and 0.5% diltiazem eye drops on intraocular pressure (IOP) in steroid-induced glaucoma in rabbit eyes.Methods: A total of 18 rabbits with steroid-induced glaucoma were divided into three groups (A, B and C; n = 6 each). Right eyes in groups A, B and C received 0.5% diltiazem, 0.125% verapamil and 0.5% timolol eye drops twice daily for 12 days, respectively; whereas, left eyes received distilled water. IOP was measured with Tono-pen XL at baseline, day 4, day 8, and day 12 of treatment.Results: Both 0.5% diltiazem and 0.125% verapamil eye drops significantly reduced IOP compared to control eyes (p < 0.05). Reduction of IOP by 0.5% diltiazem, 0.125% verapamil eye drops were comparable to 0.5% timolol. No surface toxicity or systemic side effects were noted during the study period.Conclusion: Calcium channel blockers, verapamil, and diltia-zem significantly reduced IOP in rabbiteyes. This group of drugs may have a potential role in treatment of glaucomaHow to cite this article: Ganekal S, Dorairaj S, Jhanji V, Kudlu K. Effect of Topical Calcium Channel Blockers on Intraocular Pressure in Steroid-induced Glaucoma. J Current Glau Prac 2014;8(1):15-19.

Measurement of the difference in intraocular pressure between the sitting and lying body positions in healthy subjects: direct comparison of the Icare Pro with the Goldmann applanation tonometer, Pneumatonometer and Tonopen XL

Change in intraocular pressure is known to occur with body posture. Previously, markedly different estimations of this change were reported. The Icare Pro (Icare; Tiolat Oy, Helsinki, Finland) is designed to measure intraocular pressure with the subject supine. We compared the measurement of postural change in intraocular pressure obtained with this and 3 other tonometers: Goldmann applanation tonometer (CSO, Firenze, Italy), Pneumatonometer (Model 30, Reichert, Depew, NY, USA) and the Tonopen XL (Reichert). Prospective comparative study. Twenty-one healthy subjects. Intraocular pressure was measured in random order with four tonometers, first sitting then after 10 min of lying. Average postural intraocular pressure change (mmHg) and the 95% limits of agreement for measuring postural intraocular pressure change between tonometers. Average postural intraocular pressure change (lying minus sitting, mmHg) was measured highest with the Goldmann applanation tonometer (4.1 ± 2.6) and Pneumatonometer (3.9 ± 2.1), significantly lower with the Tonopen (0.9 ± 1.7) and was negative with the Icare (-0.9 ± 3.3). The 95% limits of agreement for measuring postural intraocular pressure change between Goldmann applanation tonometer and Icare, Pneumatonometer and Tonopen were -3.2-13.3, -6.4-6.9 and -2.8-9.4 mmHg, respectively. Postural change in intraocular pressure was measured similarly, on average, with Goldmann applanation tonometer and Pneumatonometer, and much lower with Tonopen and Icare Pro. There was poor interdevice agreement in measuring this parameter. We observed high intersubject variability, suggesting the clinical importance of this measurement in the diagnosis and management of glaucoma.

Dynamic Contour Tonometry, Tono-Pen XL&amp;lt;sup&amp;gt;&amp;#174;&amp;lt;/sup&amp;gt;, and Goldmann Applanation Tonometry in Comparison to Intracameral Intraocular Pressure (IOP) Measurements in Patients with Corneal Pathologies

Purpose: The accuracy of Goldmann applanation tonometry (GAT) has been shown to depend on several biomechanical properties of the cornea. Newer tonometry devices (e.g., the Dynamic Contour Tonometer PASCAL? [DCT] and the Tono-Pen? XL [TP]) have been designed to accurately measure intraocular pressure (IOP) independent of corneal thickness (CCT) and pathology. This study investigates the influence of corneal pathologies on the accuracy of these IOP measuring devices, and compares this accuracy to that of direct intracameral IOP measurement. Methods: 8 eyes of 8 patients suffering from corneal pathologies scheduled for penetrating keratoplasty, and 10 eyes of 10 patients scheduled for cataract surgery (control group) were examined. Before surgery, the anterior chamber was cannulated at the temporal corneal limbus. In a closed system, the intraocular pressure (IOP) was directly set to 10, 20, and 30 mmHg with a manometric water column. Intraocular pressure measurements taken by GAT, DCT, and TP were compared to intracameral measurements obtained by a precision reference pressure sensor. Results: Control group: All three methods showed good agreement with the intracameral readings (mean deviation of all three devices, -0.9 mmHg). Group with corneal pathologies: The TP yielded the most exact IOP values in the group with corneal pathologies when taking all diagnoses into account. The mean deviations from the intracameral IOP measurements were -0.9 mmHg ± 3.2 mmHg (mean ± SD) for TP, -2.9 mmHg ± 3.3 mmHg for GAT, and -5.0 mmHg ± 7.9 mmHg for DCT. For bullous keratopathy, the most exact IOP readings were obtained by the TP (mean deviation -0.2 mmHg ± 3.5 mmHg). The TP and GAT devices underestimated IOP in the patients with Fuchs’ endothelial dystrophy; all 3 devices underestimated adjusted IOP after keratoplasty. DCT showed the greatest deviations from adjusted IOP in the case of non-herpetic scars. In the control group, none of the devices showed a statistically relevant dependency on CCT. Nevertheless, in the group with corneal pathologies, only TP showed no dependency on CCT. Conclusion: Our results suggest that the Tono-Pen XL? is the most accurate measurement device to determine IOP in patients with corneal pathologies, especially in patients suffering from corneal edema (bullous keratopathy). GAT yielded surprisingly exact IOP values in patients suffering from irregular corneal surface. DCT showed a high degree of deviation from the adjusted IOP, and should not be used to determine IOP in corneas with the disorders listed here.

Postural Change in Intraocular Pressure

To compare directly the results of 4 tonometers in measuring postural change in the intraocular pressure (IOP) between sitting and lying body positions. In 19 healthy subjects, the IOP was measured both eyes with a Goldmann applanation tonometer (GAT) while sitting, then using the same GAT with the subject in the left lateral decubitus position after lying for 15 minutes, using a novel system comprising a motorized bed and a modified slit-lamp table. On the next day, the sitting IOP was measured in 1 eye using GAT, and additionally in random order Tonopen XL and pneumatonometer. Then subjects were asked to lie down, and the IOP was measured with these tonometers and also with a hand-held applanation tonometer (HA-2) after lying for 15 minutes and for 45 minutes; measurements were made with subjects in the supine position except with GAT. There were 10 male and 9 female subjects, with a mean age of 33.0±12.4 years. On day 1, the sitting GAT IOP (mm Hg) was 13.7±3.0 right eye and 13.6±2.8 left eye (P=0.7) and the lying GAT IOP was 17.8±3.5 right eye and 18.1±3.2 left eye (P=0.3 for inter-eye postural IOP change). Postural change in the right and the left eyes was moderately correlated, with a coefficient of 0.453. On day 2, postural changes after lying for 15 minutes as measured with a GAT, a Tonopen, a pneumatonometer, and a HA-2 were 4.9±2.6, 1.6±1.8, 4.2±2.0, and 3.1±2.7, respectively. After lying for 45 minutes, it decreased to 3.3±2.1, 1.1±4.3, 3.1±2.5, and 2.6±3.3, respectively; this IOP decrease was statistically significant for the GAT and the pneumatonometer. The inter-subject variability was large, as in some subjects there was nearly no postural change in the IOP, whereas in some the IOP increased by 8 to 10 mm Hg. Ninety-five percent limits of agreement showed a poor agreement between GAT and the other 3 tonometers in the sitting and lying IOPs and postural IOP changes measured. The average postural IOP change was similar when measured with GAT and a pneumatonometer, smaller with a hand-held GAT, and much smaller with a Tonopen XL. This change decreased significantly when lying between the 15- and 45-minute time points. The inter-subject variability in postural IOP was remarkable, consistent with previous reports, suggesting the importance of this parameter in clinical glaucoma practice. Inter-device agreement was poor and similar to previous reports.

Intraocular Pressure Is Not Associated with Acute Mountain Sickness

Acute mountain sickness (AMS) is common at high altitude and may lead to high altitude cerebral edema (HACE) if not properly recognized. Previous studies have suggested that AMS is associated with increases in intracranial pressure (ICP). Increased ICP has been associated with increased intra-ocular pressure (IOP). This study was designed to determine the association between IOP and AMS. Subjects were recruited from a convenience sample of travelers in the Khumbu region of Nepal, elevation 14,410 ft (4392 m). Study participation involved completion of a questionnaire to assess for AMS by the Lake Louise Score (LLS), followed by three IOP measurements in each eye. Investigators were blinded to the LLS. Subjects with a history of ocular surgery were excluded. Three IOP measurements per eye were made using an applanation tonometer (Tono-Pen XL(®), Reichart Technologies) and averaged across both eyes. Multivariable logistic regression analysis was used to estimate the association between IOP and AMS while adjusting for age, ascent or descent, and use of acetazolamide. IOP and blood O2 saturation were compared using a Spearman correlation coefficient. 161 subjects were enrolled with a median age of 36 (IQR: 29-45) years; 60% were male, 75% were ascending, and 64% were taking acetazolamide; additionally, 38%, (95% CI: 31%-47%) were diagnosed with AMS (LLS ≥3). The median IOP was 21 (IQR 18-24) mmHg. The logistic regression model demonstrated no association between IOP and AMS as measured by LLS (odds ratio [OR] 1.0, 95% CI: 0.9-1.1),age (OR 1.0, 95% CI: 0.9-1.0) or with use of acetazolamide (OR 1.4, 95% CI: 0.6-2.6). Ascent (OR 0.4, 95% CI: 0.2-0.9) was negatively associated with IOP but not significantly so. IOP and O2 saturation were not correlated (p=0.93). IOP measured at high altitude is not associated with the diagnosis of AMS. Other approaches to diagnose AMS easily and accurately are needed.

The Impact of Corneal Edema on Intraocular Pressure Measurements Using Goldmann Applanation Tonometry, Tono-Pen XL, iCare, and ORA

Among other corneal biomechanical properties, Goldmann applanation tonometry (GAT) has been shown to depend on corneal edema. New tonometry devices have been designed, such as the Tono-Pen XL, iCare, and ocular response analyzer (ORA), to measure the intraocular pressure (IOP) accurately. This study aims to investigate the influence of corneal edema on the accuracy of these IOP-measuring devices in an in vitro model. A model of an artificial anterior chamber was developed using a guided trephination system. Eight donor corneas not suitable for keratoplasty were clamped into this artificial anterior chamber. All corneas showed signs of stromal edema. Intracameral pressure (ICP) was adjusted manometrically to 10, 20, 30, 40, and 50 mm Hg. The central corneal thickness (CCT) was determined by ultrasonic pachymetry. For each manometrically defined ICP, tonometry was performed using the iCare, Tono-Pen XL, GAT, and ORA. The mean CCT increased from 616.1±29.6 µm to 626.9±36.1 µm. At 10 mm Hg, GAT yielded a higher ICP than those manometrically adjusted (10.4±3.3 mm Hg); at all other ICP levels, GAT yielded lower ICP levels than those adjusted. The Tono-Pen XL and iCare showed the greatest difference at 10 mm Hg, with the Tono-Pen XL yielding a value of 14.0±4.0 mm Hg and the iCare yielding a value of 12.5±2.6 mm Hg. All other results of the 2 devices fell within a range of ±2 mm Hg from the adjusted ICP. The ORA provided accurate results only at "physiological" ICP levels with a maximum difference of 2.6 mm Hg at 30 mm Hg. At higher ICP levels, corneal hysteresis decreased significantly with increasing ICP. None of the measurement devices revealed a statistically relevant dependence on CCT in this experimental setting. The Tono-Pen XL and the iCare yielded the most accurate ICP values across all the adjusted ICP values. This may be because of their relatively small contact area with the cornea and, consequently, greater independence from corneal biomechanical properties. The ORA yielded accurate measurement results only at physiological ICP levels. As anticipated, GAT underestimated ICP. The Tono-Pen XL and the iCare should therefore be used to determine IOP in patients suffering from corneal edema, such as bullous keratopathy or Fuchs endothelial dystrophy.

Intraocular Pressure of Supine Patients Using Four Portable Tonometers

To evaluate the congruity of intraocular pressure (IOP) measurements from supine patients, which were obtained using four portable tonometers. Intraocular pressure measurements were obtained from the right eye of 72 supine patients. We used the iCare (Tiolat Oy, Helsinki, Finland) rebound tonometer, the Diaton (BICOM Inc., Long Beach, NY) transpalpebral tonometer, the Tonopen XL (Reichert inc., Depew, NY), and a Kowa hand-held applanation tonometer (HAT; Kowa Company, Ltd., Nagoya, Japan). Relationships between mean IOPs were evaluated using Pearson correlation coefficients, and the mean differences between tonometers, using one-way analysis of variance followed by Tukey-Kramer post-hoc analysis. Levels of agreement were evaluated using Bland-Altman analysis. The mean IOPs (mean ± SD) were 18.2 ± 3.5 mm Hg for iCare, 14.8 ± 3.4 mm Hg for Diaton, 16.7 ± 3.7 mm Hg for Tonopen XL, and 16.8 ± 2.8 mm Hg for Kowa HAT. Pearson correlation coefficients between iCare, Tonopen XL, and Kowa HAT ranged from 0.382 to 0.577, whereas those between Diaton and other tonometers ranged from 0.041 to 0.286. Post-hoc analysis indicated significant differences between all pairs except Tonopen XL and Kowa HAT. The mean difference between measurements from iCare and Diaton was 3.39 ± 3.39 mm Hg; iCare and Tonopen XL, 1.47 ± 3.52 mm Hg; iCare and Kowa HAT, 1.49 ± 2.90 mm Hg; Diaton and Tonopen XL, -1.93 ± 4.90 mm Hg; Diaton and Kowa HAT, -1.90 ± 4.15 mm Hg; and Tonopen XL and Kowa HAT, 0.02 ± 3.61 mm Hg. Computation of the width of the 95% limits of agreement resulted in a wide bias range when comparing Diaton with all tonometers. Relatively good agreements were observed between iCare, Tonopen XL, and HAT. Intraocular pressure measurements obtained in a supine position by four portable tonometers were not interchangeable. Although iCare and Tonopen XL significantly overestimated IOP values in eyes with a higher IOP when compared with Kowa HAT, the agreements between iCare, Tonopen XL, and Kowa HAT were at clinically acceptable levels.

Biodegradable nanoparticles for controlled subconjunctival delivery of latanoprost acid: In vitro and in vivo evaluation. Preliminary results

Purpose of the study was to develop and assess a novel controlled drug delivery system of latanoprost acid (LA). Poly(lactide)/Monomethoxy-poly(ethyleneglycol) (PLA-PEG) nanoparticles (NPs) were prepared using an emulsification-solvent evaporation technique. NPs were characterized in vitro according to their size, ζ-potential, drug entrapment efficiency and LA release. LA-loaded NPs (equivalent to 8.5 μg LA) were administered into the subconjunctival space of normotensive rabbits (group A). A free LA solution of the same drug content was subconjunctivally injected in a second rabbit group (group B), while blank NPs were administered in a third group (group C). A group of untreated animals (group D) served as the control. Intraocular pressure (IOP) was monitored for 8 consecutive days, using the Tono-pen XL. Aqueous humor (AH) levels of LA were evaluated for 6 days post-administration, by means of HPLC. Mean nanoparticle size was 80 nm. The drug entrapment efficiency was 18.3%. NPs sustained the release of LA over several days in vitro. Non-significant differences in baseline IOP were found between groups (p = 0.22). LA-loaded NPs exerted a significant hypotensive effect on group A, while IOP values remained significantly lower compared to the rest groups, throughout the study (p = 0.04). LA AH concentrations in group B continuously decreased with time, while LA levels in group A steadily increased. On day 6, LA levels were higher in group A compared to group B (344 ± 73.5 ng/ml and 228 ± 41.01 ng/ml, respectively). No adverse effects were observed. In conclusion, after subconjunctival administration, the LA-loaded NPs provided sustained LA delivery in vivo. They appear to be a promising system for the controlled subconjunctival delivery of LA.

Intraocular pressure measurements with the Tono-Pen XL® and Perkins® applanation tonometers in horses and cattle

The objective of this study was to compare the accuracy between two applanation tonometers, Tono-Pen XL® and Perkins®, in horses and cattle. The eyes of 20 horses and 20 cattle conscious and healthy were evaluated for the in vivo study and both eyes of 5 horses and 5 cattle were used as controls for the postmortem study. In conscious animals, the tonometry was performed with auriculopalpebral nerve block and then topical anesthesia for both tonometers and 1% fluorescein eye drops only for the Perkins tonometer. Readings of intraocular pressure (IOP) in the postmortem study were taken using manometry and tonometry by Tono-Pen XL® and Perkins®. The correlation coefficient (r²) between manometry and applanation tonometers Tono-Pen XL® and Perkins®, in horses, were 0.845 and 0.989, respectively, and in cattle, were 0.772 and 0.988, respectively. The mean IOP values in conscious horses with Tono-Pen XL® and Perkins® were 20.1±3.9mmHg and 20.9±3.2mmHg, respectively, and in conscious cattle, these values were 17.2±2.4mmHg and 17.9±1.4mmHg, respectively. There was a strong correlation between the IOP values obtained by direct ocular manometry and the Tono-Pen XL® and Perkins® tonometers in horses and cattle. There was no statistically significant difference between the mean IOPs obtained with both tonometers in conscious animals; however, there was a difference between the minimum values, which were on average 2-3 mmHg lower with the Tono-Pen XL® tonometer than with the Perkins® tonometer, which justifies a table of normal values differentiated for each tonometer.

Poor correlation between intracranial pressure and intraocular pressure by hand-held tonometry

PurposeThe aim of this study is to provide data on the controversial issue of whether handheld measurements of intraocular pressure (IOP) are capable of accurately predicting elevated intracranial pressure (ICP) in patients undergoing lumbar puncture (LP).MethodsAll patients over the age of 18 years who underwent an LP in the emergency or neurological departments at the Tel Aviv Medical Center for any reason between October 2007 and July 2010 were eligible to participate in this prospective observational pilot study. IOP was measured with the Tono-Pen XL while patients were in the supine position before undergoing LP. ICP was measured in the lateral recumbent position. ICP and bilateral IOP were measured, and the mean and maximum values of IOP were calculated. The association between ICP and each one of the four IOP measures was evaluated by the Pearson correlation coefficient.ResultsTwenty-four patients (mean age 37.8 ± 15.8 years, ten males and 14 females) were enrolled. The reasons for their requiring an LP were headache (19/24 patients), evaluation for hemiparesis (2/24), cognitive deterioration (1/24), and seizures (2/24). Nine had elevated mean opening pressure (>20 cm H2O), six had an elevated mean IOP (>20 mmHg), and four of these six also had an elevated opening pressure. There was no significant correlation between the ICP measurements and any of the IOP measurements.ConclusionHandheld ocular tonometry has poor sensitivity and specificity for the prediction of increased ICP and is not an effective tool for screening for ICP in the ED or in the neurology department.

Evaluation of intraocular pressure according to corneal thickness before and after excimer laser corneal ablation for myopia

Intraocular pressure is affected by corneal thickness and biomechanics. Following ablative corneal refractive surgery, corneal structural changes occur. The purpose of the study is to determine the relationship between the mean central corneal thickness (CCT) and the change in intraocular pressure measurements following various corneal ablation techniques, using different measurement methods. Two hundred myopic eyes undergoing laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) were enrolled into a prospective, non-randomized study. Corneal parameters examined included full ocular examination, measurement of CCT, corneal topography, corneal curvature and ocular refractivity. Intraocular pressure measurements were obtained using three different instruments-non-contact tonometer, Goldmann applanation tonometer and TonoPen XL (TonoPen-Central and TonoPen-Peripheral). All measurements were performed pre-operatively and 4months post-operatively. Post-operative intraocular pressure was significantly lower than pre-operative values, with all instruments (p value < 0.001, Student's t-test). The post-operative intraocular pressure decrease was smallest using the Tonopen-XL compared to the Goldmann applanation tonometer and non-contact tonometer (p value < 0.001, ANOVA). Intraocular pressure readings are significantly reduced following corneal ablation surgery. We determined in our myopic patient cohort that the TonoPen XL intraocular pressure measurement method is the least affected following PRK and LASIK as compared to other techniques.

The relationship between measurement method and corneal structure on apparent intraocular pressure in glaucoma and ocular hypertension

To analyse the relationship between measured intraocular pressure (IOP) and central corneal thickness (CCT), corneal hysteresis (CH) and corneal resistance factor (CRF) in ocular hypertension (OHT), primary open-angle (POAG) and normal tension glaucoma (NTG) eyes using multiple tonometry devices. Right eyes of patients diagnosed with OHT (n=47), normal tension glaucoma (n=17) and POAG (n=50) were assessed. IOP was measured in random order with four devices: Goldmann applanation tonometry (GAT); Pascal dynamic contour tonometer (DCT); Reichert ocular response analyser (ORA); and Tono-Pen XL. CCT was then measured using a hand-held ultrasonic pachymeter. CH and CRF were derived from the air pressure to corneal reflectance relationship of the ORA data. Compared to the GAT, the Tonopen and ORA Goldmann equivalent (IOPg) and corneal compensated (IOPcc) measured higher IOP readings (F=19.351, p<0.001), particularly in NTG (F=12.604, p<0.001). DCT was closest to Goldmann IOP and had the lowest variance. CCT was significantly different (F=8.305, p<0.001) between the 3 conditions as was CH (F=6.854, p=0.002) and CRF (F=19.653, p<0.001). IOPcc measures were not affected by CCT. The DCT was generally not affected by corneal biomechanical factors. This study suggests that as the true pressure of the eye cannot be determined non-invasively, measurements from any tonometer should be interpreted with care, particularly when alterations in the corneal tissue are suspected.

The effects of the modulus of the lens material on intraocular pressure measurement through soft contact lenses

To investigate the effects of the modulus of the lens material on the intraocular pressure measurement using the Tono-Pen XL applanation tonometer through soft contact lenses. Thirty eyes of 15 patients with myopia were evaluated. Intraocular pressure (IOP) measurements were performed using Tono-Pen XL directly over cornea, and subsequently through three soft contact lenses made up of different lens materials. All were -3.00 diopter soft contact lenses: lotrafilcon A with a low water content (24%) and high modulus (1.4 MPa) (CL-I), balafilcon A with a moderate water content (36%) and moderate modulus (1.1 MPa) (CL-II), and vifilcon A with a moderate water content (55%) and low modulus (0.79 MPa) (CL-III). IOP measurements through contact lenses were compared with each other, and with direct corneal measurements. The mean age of the patients (11 males and 4 females) was 26.86±5.62 years. All measurements obtained through CLs were significantly higher than the direct corneal measurements. The measurements through CLs differed by 4.61±0.54 mmHg (P=0,001), 2.9±0.46 mmHg (P=0.001), and 1.94±0.51 mmHg (P=0,003) for CL-I, CL-II and CL-III, respectively. In the paired comparisons of measurements through CLs, all comparisons were significant except the comparison of measurements through CL-II and CL-III (P=0.128). IOP measurements through silicone-hydrogel contact lenses with a high modulus and low water content were higher compared to the other contact lenses. While measuring IOP through CLs, the clinicians should consider the effect of the lens material and the features of the device used.