Intraocular Pressure In Normal Eyes Research Articles

Changes to Outflow Structures After Pilocarpine in Primary Open Angle Glaucoma Compared With Healthy Individuals Using Optical Coherence Tomography.

Lower response of aqueous outflow pathway structures after pilocarpine could be observed in primary open angle glaucoma (POAG) patients, which is likely to be helpful for understanding intraocular pressure (IOP) evaluation in glaucoma. To evaluate the morphologic changes in the trabecular meshwork (TM), Schlemm canal (SC), scleral spur (SS), and ciliary muscle after miosis in patients with POAG and healthy individuals. A total of 30 patients with POAG and 26 healthy controls were recruited. All participants underwent complete ophthalmologic examinations, including IOP and swept-source optical coherence tomography (OCT), before and 1 hour after the local administration of pilocarpine (2%). OCT measurements included TM thickness and width, SC diameter and area, SS length, ciliary muscle thickness, and ciliary muscle angle (CMA). Pilocarpine administration induced a decline in IOP (15.6±2.3-14.6±2.2mmHg), decrease in nasal SS length (196.31±47.75-171.52±33.93μm), decrease in TM thickness (90.18±16.43-83.02±13.74μm), and increase in SC diameter (134.84±32.28-162.08±48.67μm) and SC area (3851.37±1455.07-4801.39±1762.37μm 2 ) among healthy controls. In contrast, no significant changes in IOP and OCT measurements were found in patients with POAG. At baseline, CMA was independently correlated with IOP in normal eyes. After miosis, the change in TM thickness was independently correlated with changes in IOP in normal eyes; in eyes with POAG, changes in SS length and CMA were independently associated with changes in IOP. Topical pilocarpine-induced morphologic changes to outflow pathway structures in healthy individuals without significant changes in POAG. The lower response observed in patients with glaucoma may be relevant to understanding IOP changes.

The effect of body position on intraocular pressure in anesthetized horses.

To evaluate the effect of four recumbent body positions on intraocular pressure (IOP) in anesthetized normal horses. Ten nonglaucomatous adult horses. Intraocular pressure was measured with a rebound tonometer in both eyes of standing sedated horses (baseline), then under general anesthesia during four randomized recumbent body positions, including Trendelenburg (Tr; 15-degree head down), reverse Trendelenburg (RTr; 15-degree head up), dorsal, and lateral; only the superior eye was measured in lateral positions. The mean of 3 IOP readings was taken at each position, allowing a minimum of 2minutes of acclimatization after each position change before obtaining measurements. Repeated Measures Analysis with Newman-Keuls Multiple Comparison Post hoc was used to compare IOPs in different positions, and linear regression was used to compare IOP with age and weight cofactors. When compared to baseline, the greatest change in IOP occurred in Tr (increase of 25.63±8.12mmHg). When comparing all recumbent positions to baseline, IOP significantly increased in 3 of 4 body positions (P<.001), with no significant difference identified between RTr and baseline. When comparing all body positions to each other, the greatest IOP difference occurred between the Tr and the RTr positions (increase of 26.95±5.41mmHg). Age and weight were not correlated with IOP in any position. Recumbent body position significantly increases IOP in normal eyes of horses under injectable anesthesia.

High myopes have lower normalised corneal tangent moduli (less ‘stiff’ corneas) than low myopes

To compare corneal tangent moduli between low and high myopes. Corneal hysteresis (CH) and corneal resistance factor (CRF) of 32 low and 32 high myopes were obtained using an Ocular Response Analyzer, followed by a corneal indentation device that measured corneal stiffness. Corneal topography, pachymetry, Goldmann applanation tonometry intraocular pressure (GAT-IOP), and corneal compensated intraocular pressure (IOPcc) were also obtained. Corneal tangent modulus was calculated on the basis of corneal stiffness, central corneal thickness and corneal radius. Comparisons between groups and associations between corneal biomechanical and ocular parameters were performed. Corneal tangent moduli were positively correlated with GAT-IOP (R2 = 0.078, p = 0.025), and IOPcc (R2 = 0.12, p = 0.006). Despite similarity in corneal thickness and radius, high myopes exhibited a significantly higher IOPcc (16.4 ± 2.51 mmHg) than low myopes (13.1 ± 1.96 mmHg; t(62) = -5.57, p < 0.0001). Both groups had similar corneal stiffness (0.063 ± 0.0085 and 0.063 ± 0.0079 N mm-1 for low and high myopes, respectively) and CRF (9.6 ± 1.58 and 9.5 ± 1.90 mmHg for low and high myopes, respectively). Moreover, high myopes exhibited a significantly lower CH (9.5 ± 1.51 mmHg) than low myopes (10.6 ± 1.38 mmHg; t(62) = 2.92, p = 0.005). After normalising corneal tangent moduli to the mean intraocular pressure in normal eyes (15.5 mmHg) using IOPcc, high myopes showed a significantly lower corneal tangent moduli (0.47 ± 0.087 MPa) than low myopes (0.57 ± 0.099 MPa; t(62) = 4.17, p < 0.0001). High myopes had lower normalised corneal tangent moduli than low myopes, which indicated that their corneas were less stiff. This is the first in vivo study comparing elastic moduli of the cornea in different refractive groups. Further studies are warranted to understand whether a less stiff cornea is a cause for or an outcome from myopia development.

A Comparison of Three Techniques for Measurement of Intraocular Pressure in Normal Eyes

Objectives: To compare the precision of intraocular pressure (IOP) measurements acquired using an ocular response analyser (ORA), Auto Kerato-Refracto-Tonometer (TRK-1P), and Goldmann applanation tonometer (GAT) in healthy eyes. Methods: In this prospective study, one eye of each of 57 normal subjects was randomly selected for analysis. Measurements of the IOP were performed using ORA, TRK-1P, and GAT, and measurements of corneal hysteresis (CH), corneal resistance factor (CRF), and central corneal thickness (CCT) were performed using ORA. Repeatability was assessed by the coefficient of variation (CV) and interclass correlation coefficients (ICCs). Agreement among tonometers was assessed by Bland–Altman plots and one-way ANOVA. Results: The average IOPs measured using Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), TRK-1P, and GAT (± SDs) were 15.13 ± 2.76, 14.39 ± 2.59, 16.54 ± 2.93, and 15.21 ± 2.54 mmHg, respectively. Intra-observer agreement across all tonometers was strong and slightly higher for GAT and IOPg than for TRK-1P. The intra-observer CVs for GAT IOPg, and TRK-1P, were 4.22 (ICC=0.94), 4.99 (ICC=0.93), and 6.69 (ICC=0.86), respectively. Inter-observer agreement between various measurement methods was evaluated with Bland-Altman plots with multiple measurements per subject and ICCs. Results indicated fairly poor agreement across measurement methods, as supported by large limits of agreement and ICCs. Conclusion: GAT, ORA, and TRK-1P are highly reliable methods for measurement of the IOP; however, the instruments cannot be used interchangeably.

Home assessment of diurnal intraocular pressure in healthy children using the Icare rebound tonometer

Although intraocular pressure (IOP) is known to vary with the circadian cycle in nonglaucomatous and glaucomatous eyes of adults, the clinical assessment of IOP often relies on periodic measurements obtained at office visits during daytime hours. Little has been reported on diurnal IOP patterns in healthy children. The purpose of this study was to evaluate diurnal IOP in normal eyes of healthy children with the Icare rebound tonometer and when recorded by a parent at home. This was a prospective study of IOP in normal eyes of healthy children. Children were recruited from a pediatric eye clinic. A parent was instructed on the use of the Icare rebound tonometer by a study physician and demonstrated proficiency its use in the clinic, at which time a masked IOP reading was also made with Goldmann applanation by a different study clinician. Home IOPs were then obtained and recorded 6 times daily at 2- to 3-hours intervals during 2 consecutive days by a parent. A total of 22 normal eyes (of 11 children) were included. We found that children without glaucoma demonstrate mean diurnal IOP fluctuation of 4-6 mm Hg, with similar IOP between right and left eyes, fair repeatability between consecutive days, and a tendency for higher early morning and lower late evening IOP. Healthy children without glaucoma demonstrate some diurnal fluctuation in IOP, comparable with that reported in nonglaucomatous eyes of adults. This information should prove as comparative for assessment of IOP fluctuation in children with known or suspected glaucoma.

Effects of corneal thickness on intraocular pressure measured with three different tonometers

To compare intraocular pressure (IOP) measured by a Goldmann applanation tonometer (GAT), a noncontact tonometer (NCT), and a portable noncontact tonometer (PNCT) in eyes of healthy volunteers, and to determine if a significant correlation exists between the IOP and the central corneal thickness (CCT). A total of 144 healthy participants were randomly assigned to one of two groups; in the first group, IOP was measured first with the NCT and then with the GAT. In the second group, IOP was measured first with the PNCT and then with the GAT. Subsequently, the CCT of all subjects was measured with an ultrasonic pachymeter. The IOPs determined by the GAT and NCT and were strongly correlated, as were those determined by the GAT and PNCT, in both groups. However, a Bland-Altman plot showed that the correlations between the GAT and NCT and between the GAT and the PNCT measurements were not significant. With all three instruments, the IOP readings varied with the CCT. The mean IOPs obtained with the GAT increased by 0.23 mmHg with each 10-microm increase in CCT (0.23 mmHg/10 microm). The comparable value for the NCT was 0.29 mmHg/10 microm, and that for the PNCT was 0.31 mmHg/10 microm. For measurements of IOP in normal eyes, the GAT is the tonometer least affected by the CCT, compared with the PNCT and NCT. A PNCT is more likely to be affected by variations in CCT than the GAT.

The Circadian Rhythm in Intraocular Pressure and its Relation to Diurnal Ocular Growth Changes in Chicks

Recent investigations have shown that growing chicken eyes elongate during the day and shorten during the night. We asked whether the chick, like a number of other animals, exhibits a rhythm in intraocular pressure (IOP) and whether this rhythm might be associated with this rhythm in elongation. We find that the intraocular pressure in normal eyes is high during the day and low in the middle of the night, similar to the rhythm in ocular elongation. The amplitude of this rhythm in IOP is approximately 8 mm Hg; it persists in constant darkness, albeit with a reduced amplitude, implying that the rhythm has a circadian component. Form deprivation by translucent diffusers does not affect the amplitude of the rhythm in IOP, but makes the phase of the rhythm more variable, such that the trough no longer consistently occurs at night.We find that the magnitude of the ocular compliance (the change in length induced by change in intraocular pressure) is consistent with the possibility that the diurnal changes in IOP might, through mechanical stretch, account for much of the diurnal changes in length. However, in individual eyes, we find consistent phase differences between the rhythms in IOP and ocular elongation. Therefore, we propose that the rhythm in IOP influences ocular elongation in ways other than by simply inflating the eye, for example, by influencing underlying rhythms in scleral extracellular matrix production. We conclude that the rhythm in IOP plays a role in the regulation of the growth of the eye.

Tonometry of normal eyes in raptors

Summary An applanation tonometer was used to estimate intraocular pressure in normal eyes of several species of raptors. No bird had active injury or illness, though some were nonreleasable to the Wild because of previous injury. Mean (± sd) intraocular pressure was 20.6 (± 3.4) mm of Hg in red-tailed hawks (Buteo jamaicensis, n = 10), 20.8 (± 2.3) mm of Hg in Swainson's hawks (Buteo swainsoni, n = 6), 21.5 (± 3.0) mm of Hg in golden eagles (Aquila chrysaetos, n = 7), 20.6 (± 2.0) mm of Hg in bald eagles (Haliaeetus leucocephalus, n = 3), and 10.8 (± 3.6) mm of Hg in great horned owls (Bubo virginianus, n = 6). There was no significant difference in intraocular pressure between hawks and eagles. Mean pressure in great horned owls was significantly (P &lt; 0.01) lower than pressure in hawks or eagles. Reliable intraocular pressure readings could not be obtained in barn owls (Tyto alba).

Three-dimensional confocal laser microscopy of fibronectin in normal and glaucomatous eyes

Aqueous humor exits the anterior chamber of the eye through the trabecular meshwork into Schlemm's canal, a vessel which drains into the systemic circulatory system. The aqueous humor crosses the endothelial lining of Schlemm's canal by means of focal invaginations which form pores and allow digress of fluid into the canal. The trabecular meshwork provides a resistance to fluid flow resulting in a physiologic intraocular pressure in normal eyes. The region adjacent to Schlemm's canal appears to be the site of highest resistance to fluid flow in both normal and glaucomatous eyes. In eyes with primary open angle glaucoma (POAG) the resistance to fluid flow through the trabecular meshwork is abnormally high, causing an elevated intraocular pressure (IOP), which can lead to irreversible damage of the optic nerve and blindness. A definitive morphologic correlate of this disease has not been discovered. Immunohistochemical studies localizing fibronectin in unfixed frozen sections of human eyes have shown elevated levels of fibronectin in the eyes with glaucoma, however the specific distribution of this protein has not been determined due to poor tissue preservation.

A Limited Comparison of Apraclonidine's Dose Response in Subjects with Normal or Increased Intraocular Pressure

We performed a multicentered, placebo-controlled, randomized, crossover study comparing the efficacy of 0.5% and 1.0% apraclonidine hydrochloride in 15 normal volunteers and 17 subjects with increased intraocular pressure. Apraclonidine 1% produced a maximum 30.4% +/- 14.0% (4.7 +/- 2.4 mm Hg) decrease in mean intraocular pressure in normal eyes and a 31.3% +/- 16.5% (7.6 +/- 4.2 mm Hg) decrease in eyes with increased pressure. Apraclonidine 0.5% produced a maximum 25.8% +/- 9.7% (4.0 +/- 1.7 mm Hg) decrease in mean intraocular pressure in normal eyes and a 27.4% +/- 16.0% (6.8 +/- 4.5 mm Hg) decrease in eyes with increased pressure. There was no statistically significant difference in mean percent intraocular pressure lowering effect between the 0.5% and 1.0% apraclonidine concentrations. Most subjects treated with apraclonidine had a greater than or equal to 20% reduction in intraocular pressure from baseline. Twelve hours after instillation of apraclonidine, nine of the normal volunteers had an intraocular pressure of 10 mm Hg or less. Apraclonidine produced the same percent intraocular pressure decrease regardless of the initial level of intraocular pressure.

Beeinflussung des Augeninnendruckes des Augengesunden nach Einnahme von Propranolol und Metoprolol

Oral doses of propranolol and metoprolol were tested on 24 patients without glaucoma. The aim of this study was to compare the decrease in intraocular pressure in normal eyes following a single oral dose of propranolol or metoprolol. A statistically significant decrease in IOP was noticed, but no difference was seen between propranolol and metoprolol.

Effect of ascorbic acid on intraocular pressure of normal and buphthalmic rabbits.

Compared with serum the aqueous humor of the eye is high in ascorbic acid. The administation of ascorbic acid appears to have a transient hypotonic effect on intraocular pressure in normal eyes. Its effect on glaucomatous eyes is not as well defined particularly in the case of the rabbit. In this communication we shown the ocular hypotensive effal (+/+) or have hereditary glaucoma (bu/bu). We also show that the transport of ascorbate from the serum to the aqueous is much slower in buphthalamic rabbits than in normal controls. Osmolarity is suggested as a possible hypotensive mechanism and a differential fluid transport rate between the blood and the aqueous for the different genotypes is suggested as a possible mechanism for the difference in duration.

Effect of indomethacin on the ocular hypotensive action of adrenaline in the rabbit

A two percent (2%) solution of adrenaline administered topically twice daily lowered ocular tension and this hypotension persisted during the entire three week period of treatment. Indomethacin, 0·25% and 0·125% inhibited the ocular hypotensive action of adrenaline but did not affect intraocular pressure in normal eyes. It is suggested that the antagonism of the ocular hypotensive action of adrenaline in rabbits by indomethacin may be due to either inhibition of prostaglandin biosynthesis or Ca ++ binding in ocular tissues.

Acquired cupping of the optic nerve head in normotensive eyes.

Clinical measurements of a horizontal cup/disc ratio were obtained among a sample of 160 normal twin subjects by stereoscopic biomicroscopy. Measurements of horizontal cup/disc ratio were normally distributed and theere was no significant association with sex, laterally, race, or refractive error in the mid-range. However, there was a significant association between size of the cup/disc ratio and age as well as intraocular pressure. After taking into account the correlation between age an intraocular pressure in normal eyes, the association between cup/disc ratio and each of these variable remained statistically significant. It is not always recoginized that the size of the normal physiological cup increases with age, and it was not previously observed that "normal" cupping occurs with age apart from the effect of pressure. The average effect of age on cup/disc ratio, amounting to an icrease of 0-0026 per year for this sample, is small. But, allowing for individual variation, some persons could show a recognizable acquired increase in cup/disc ration with age, even in the absence of glaucoma. The possibility of "normal"cupping occurring in association with age, pressure, or high myopia, alone or in combination, merits cosideration in the clinical evaluation of glaucoma suspects and serves to re-emphasize the importance of an adequate central visual field examination in the diagnosis of glaucoma. Studies are needed on the differentiatin between "normal" and "morbid" moulding of the optic nerve head.