Effects of change in intraocular pressure on axial eye length and lens position

Refractive outcomes after immediate primary phacoemulsification for acute primary angle closure

This study investigated the refractive outcomes of 64 eyes overall including 32 immediate primary phacoemulsification in acute primary angle closure (APAC) eyes and 32 of their fellow eyes. We investigated best-corrected visual acuity, intraocular pressure (IOP), average keratometric diopter (K), spherical equivalent, axial length (AL), central corneal thickness, and anterior chamber depth (ACD) at preoperative examination (Pre) and more than 1-month post-phacoemulsification (1 m), and changes in values. Using SRK/T, Barrett Universal II (Barrett), Hill-Radial Basis Function Version 3.0 (RBF 3.0), and Kane formulas, we calculated and compared refractive prediction error (PE), absolute value of PE (AE), and changes in K, AL, and ACD from Pre to 1 m between APAC and fellow eyes. From Pre to 1 m, K remained similar in APAC and fellow eyes (p = 0.069 and p = 0.082); AL significantly decreased in APAC and in fellow eyes (both p < 0.001); and ACD significantly increased in APAC and in fellow eyes (both p < 0.001). The change in AL differed significantly between the two groups (p = 0.007). Compared to the fellow eyes, PE with SRK/T and Barret formulas (p = 0.0496 and p = 0.039) and AE with Barrett and RBF 3.0 formula (p = 0.001 and p = 0.024) were significantly larger in the APAC eyes. Thus, attention should be paid to refractive prediction error in immediate primary phacoemulsification for APAC eyes caused by preoperative AL elongation due to high IOP.

Opto-mechanical self-adjustment model of the human eye

The eye has specific optical and biomechanical properties that jointly regulate the eye's quality of vision, shape, and elasticity. These two characteristics are interdependent and correlated. Contrary to most currently available computational models of the human eye that only focus on biomechanical or optical aspects, the current study explores the inter-relationships between biomechanics, structure, and optical properties. Possible combinations of mechanical properties, boundary conditions, and biometrics were specified to ensure the opto-mechanical (OM) integrity to compensate for physiological changes in intraocular pressure (IOP) without compromising image acuity. This study evaluated the quality of the vision by analyzing the minimum spot diameters formed on the retina and drew how the self-adjustment mechanism affects the eye globe shape by adopting a finite element (FE) model of the eyeball. The model was verified by a water drinking test with biometric measurement (OCT Revo NX, Optopol) and tonometry (Corvis ST, Oculus).

Changes in Ocular Biometric Parameters Over a 24-Hour Period in Ocular Hypertensive Patients

Purpose: To identify 24-h changes in ocular biometric parameters in subjects with ocular hypertension (OHT), and to determine if an intraocular pressure (IOP)-lowering drug alters these parameters. Methods: Thirty volunteers with OHT (58.6 ± 9.2 years of age) were enrolled in this randomized, double-masked, placebo-controlled, crossover study. Participants self-administered 0.2% brimonidine or placebo 3 times daily for 6 weeks. Measurements of seated and supine IOP, central cornea thickness (CCT), anterior chamber depth (ACD), axial length (AXL), and lens thickness were made at 8 am, 3 pm, 8 pm, and 3 am. Statistical tests were Student's 2-tailed paired t-tests or 2-way analysis of variance (ANOVA) followed by one-way ANOVA and post hoc testing. Results: Time of day had a significant effect on IOP, CCT, ACD, and AXL. In placebo-treated eyes, CCT was greater at 3 am than at any other time (P < 0.01), ACD and AXL were greater at 3 am and 8 pm than at 3 pm (P < 0.01). Daytime IOPs were higher than nighttime (seated, P = 0.007; supine, P = 0.018), and supine IOP at night was higher than seated IOP during the day (P < 0.001). Brimonidine did not lower IOP at night nor did it alter the 24-h patterns of CCT, ACD, and AXL. Conclusions: Ocular biometric parameters exhibit characteristic 24-h fluctuations in patients with OHT. At night compared with day, the supine IOP increases, the cornea thickens, the anterior chamber deepens, and the AXL increases. Brimonidine does not alter these parameters at times when it lowers IOP (day) nor when it does not (night). Clinical Trial Registration number: NCT0132419.

A Review of Intraocular Pressure (IOP) and Axial Myopia

The pathogenesis of myopia is driven by genetic and environmental risk factors. Accommodation not only alters the curvature and shape of the lens but also involves contraction of the ciliary and extraocular muscles, which influences intraocular pressure (IOP). Scleral matrix remodeling has been shown to contribute to the biomechanical susceptibility of the sclera to accommodation-induced IOP fluctuations, resulting in reduced scleral thickness, axial length (AL) elongation, and axial myopia. The rise in IOP can increase the burden of scleral stretching and cause axial lengthening. Although the accommodation and IOP hypotheses were proposed long ago, they have not been validated. This review provides a brief and updated overview on studies investigating the potential role of accommodation and IOP in myopia progression.

Accuracy of different lens power calculation formulas in patients with phacomorphic glaucoma

PURPOSE:

The purpose of the study was to determine the most accurate formula for intraocular lens (IOL) power calculation among five currently used formulas in eyes with phacomorphic glaucoma (PG) undergoing cataract extraction surgery.

MATERIALS AND METHODS:

In this prospective interventional case series Patients diagnosed with PG were undergone uneventful phacoemulsification and IOL implantation. After 3 months, the refractive outcome for each formula was evaluated with mean prediction error (PE), mean absolute error (MAE), and the percentages of eyes within 0.25 D and 0.5 D of predicted error.

RESULTS:

Twenty-three patients completed the study. PEs were significantly different among the 5 formulas (P = 0.019), and Holladay I had the least error (−0.02 ± 1.11). Haigis formula had the highest hyperopic shift (0.37 ± 1.22), highest MAE (0.99 ± 0.78) and the lowest percentages of desired PEs, while the SRK II produced the greatest percentages. The overall differences in MAE between the 5 formulas were statistically insignificant (P = 0.547).

CONCLUSION:

In some extreme situations like patients with PG, lower generation of IOL power calculation formulas may still produce more acceptable refractive outcomes.

Gonioscopy-assisted transluminal trabeculotomy versus goniotomy with Kahook dual blade in patients with uncontrolled juvenile open-angle glaucoma: a retrospective study

Background

To compare the efficacy and safety of gonioscopy-assisted transluminal trabeculotomy (GATT) and Kahook Dual Blade (KDB) excisional goniotomy in patients with uncontrolled juvenile open-angle glaucoma (JOAG).

Methods

Thirty-three patients (46 eyes) were included in this single-center, retrospective, comparative study and treated with GATT (36 eyes) or KDB goniotomy (13 eyes). Intraocular pressure (IOP), number of glaucoma medications, adverse events, and additional anti-glaucoma procedures were collected during pre- and postoperative visits. Surgical success was defined as 6 mmHg ≤ IOP ≤ 18 mmHg and ≥ 20% IOP reduction from baseline with (partial success) or without (complete success) IOP-lowering medications.

Results

The mean ± SD preoperative IOP was 30.48 ± 12.9 mmHg and 26.08 ± 13.1 mmHg (P = 0.164) on 3.71 ± 0.46 and 3.08 ± 0.86 (P = 0.023) glaucoma medications in GATT and KDB group, respectively. At 3 months, the mean ± SD IOP was 15.48 ± 5.93 mmHg and 20.0 ± 10.8 mmHg after GATT and KDB, respectively (P = 0.072). The percentage of IOP lowering from baseline was 44.4 in the GATT group and 14.1 in the KDB group (P = 0.011). The mean reduction in medications was 2.6 ± 1.7 and 0.8 ± 1.2 three months after GATT and KDB, respectively (P < 0.001). Cumulative proportion of partial and complete success were 65.6 and 44.7% in the GATT group, 30.8 and 15.4% in the KDB group at 6 months. Additional procedures were required in 13.9% of cases after GATT and in 61.5% after KDB (P = 0.001). Patients in the GATT group with prior anti-glaucoma procedures and postoperative IOP spikes were more likely to fail, while those with complete trabeculotomy had a better prognosis.

Conclusions

Reduction of IOP and medications were greater after GATT in uncontrolled JOAG eyes. Whereas, more additional IOP-lowering procedures were required after KDB goniotomy.

Trial registration

This study was registered under the Chinese Clinical Trial Registry (ChiCTR2000034172, 27/06/2020).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-02159-z.

Lowering Intraocular Pressure: A Potential Approach for Controlling High Myopia Progression

High myopia is among the most common causes of vision impairment, and it is mainly characterized by abnormal elongation of the axial length, leading to pathologic changes in the ocular structures. Owing to the close relationship between high myopia and glaucoma, the association between intraocular pressure (IOP) and high myopia progression has garnered attention. However, whether lowering IOP can retard the progression of high myopia is unclear. On reviewing previous studies, we suggest that lowering IOP plays a role in progressive axial length elongation in high myopia, particularly in pathologic myopia, wherein the sclera is more remodeled. Based on the responses of the ocular layers, we further proposed the potential mechanisms. For the sclera, lowering the IOP could inhibit the activation of scleral fibroblasts and then reduce scleral remodeling, and a decrease in the scleral distending force would retard the ocular expansion like a balloon. For the choroid, lowering IOP results in an increase in choroidal blood perfusion, thereby reducing scleral hypoxia and slowing down scleral remodeling. The final effect of these pathways is slowing axial elongation and the development of scleral staphyloma. Further animal and clinical studies regarding high myopia with varied degree of IOP and the changes of choroid and sclera during IOP fluctuation in high myopia are needed to verify the role of IOP in the pathogenesis and progression of high myopia. It is hoped that this may lead to the development of a prospective treatment option to prevent and control high myopia progression.

How a dynamic optical system maintains image quality: Self-adjustment of the human eye

The eyeball is continually subjected to forces that cause alterations to its shape and dimensions, as well as to its optical components. Forces that induce accommodation result in an intentional change in focus; others, such as the effect of intraocular pressure fluctuations, are more subtle. Although the mechanical properties of the eyeball and its components permit mediation of such subtle forces, the concomitant optical changes are not detected by the visual system. Optical self-adjustment is postulated as the mechanism that maintains image quality. The purpose of this study was to investigate how self-adjustment occurs by using an optical model of the eyeball and to test the requisite optical and biometric conditions.

The effect of intraocular pressure elevation and related ocular biometry changes on corneal OCT speckle distribution in porcine eyes

The aim of this study was to evaluate the influence of increase in intraocular pressure (IOP) and cooccurring changes in ocular biometry parameters on the corneal optical coherence tomography (OCT) speckle distribution in ex-vivo experiments on porcine intact eyes. Twenty-three eyeballs were used in the inflation test where IOP in the anterior chamber was precisely set from 10 mmHg to 40 mmHg in steps of 5 mmHg and where eye biometry was utilized (IOL Master 700). To assess the influence of the duration of the experiment on the OCT speckle statistics, the second experiment was performed with 10 eyeballs at the constant IOP of 15 mmHg. Based on the OCT scans of central cornea (Copernicus REVO), spatial maps of the scale parameter (a) and the shape parameter (v) of the gamma distribution speckle model were estimated. The means of both parameters for each spatial map were computed within the 2 mm of the central stroma. Both distributional parameters statistically significantly varied with IOP and time (one way repeated measures ANOVA, all p-values < 0.001). The a parameter revealed a faster statistically significant increase in IOP up to 25 mmHg, regardless of time. Central corneal thickness (CCT), the anterior chamber depth, and the mean equivalent spherical power varied significantly with IOP, whereas CCT and axial length changed statistically significantly with time. Statistically significant correlation was found between CCT and the a parameter, after removing IOP as a confounding factor (r = −0.576, p < 0.001). The parameters of the gamma distribution can be used not only for identifying IOP induced changes in the optical scattering within the corneal stroma, but also in corneal geometry. The approach of corneal speckle analysis could be potentially utilized for an indirect and noninvasive assessment of some properties of corneal stroma.

Repeatability of corneal biomechanics waveform signal parameters derived from Ocular Response Analyzer in children

PURPOSE

To investigate the repeatability of waveform signal parameters, measured with the Ocular Response Analyzer (ORA), in children.

METHODS

Two sets of ORA measurements, with a 10-min break between them, were performed on children, aged six to <11 years old, either wearing single-vision spectacles (SVS) or orthokeratology (ortho-k) lenses. Intraclass correlation coefficients (ICCs) were used to assess agreements between two sets of measurements (37 waveform signal parameters). Bland-Altman (BA) plots were used to further analyse waveform signal parameters which had ICC 95 % confidence interval (95 % CI) between 0.50 to >0.90 (regarded as moderate to excellent agreement).

RESULTS

A total of 30 participants [15 SVS, 15 ortho-k (3.6 ± 2.4 months)] completed the study. Since no significant between-group differences were detected in demographic data (p > 0.28) and all waveform signal parameters (p > 0.05), data from the two groups of participants were pooled for the analysis of repeatability. Six parameters, h2, h21, p1area, p1area1, p2area, and p2area1, achieved ICCs (95 % CI) of 0.82-0.85 (0.61-0.93). The mean (SD) of these six parameters were 372 (91), 248 (61), 4077 (854), 1762 (399), 2359 (670), and 1020 (300), respectively. Bland-Altman plots and 95 % limits of agreement (95 % LoA) showed considerable agreement for all six parameters, the mean difference (95 % LoA) were -3 (-101 to 94), -2 (-67.56-62.70), 111 (-723 to 946), 102 (-334 to 539), 25 (-718 to 768), and -3 (-350 to 343), respectively.

CONCLUSIONS

Six waveform signal parameters (h2, h21, p1area, p1area1, p2area, and p2area1), which represent or are related to the areas under the waveform at the peaks in the signal, had moderate to excellent agreement in children. Results of the current study provides fundamental information for further studies on the potential clinical application of these waveform signal parameters in children.

The acute effects of single cup of coffee on ocular biometric parameters in healthy subjects

Purpose

To evaluate ocular biometric changes in healthy subjects after caffeine consumption from a cup of coffee.

Methods

A total of 36 subjects were included in this prospective observational study. Axial length (AL) and anterior segment parameters including aqueous depth (AD), anterior chamber depth (ACD), lens thickness (LT), and central corneal thickness (CCT) were measured with optic biometry, Lenstar LS 900 (Haag-Streit, Inc., Koeniz, Switzerland) before and 1 and 4 h after ingesting a cup of coffee (60 mg caffeine/100 mL).

Results

Mean age of the participants was 30.05 ± 7.43 years (range, 19–45). At baseline, 1st, and 4th hour, AL values were 23.9 ± 1.04 mm, 23.91 ± 1.04 mm, and 23.89 ± 1.04 mm, respectively, and no significant difference was observed (P>0.05). At baseline, 1st, and 4th hour, AD values were 3.06 ± 0.3 mm, 3.11 ± 0.3 mm, and 3.09 ± 0.3 mm, and ACD values were 3.6 ± 0.32, 3.66 ± 0.31, and 3.64 ± 0.31, respectively. AD and ACD values were significantly greater than baseline at 1st and 4th hours following coffee ingestion. Coffee intake caused a significant reduction in LT, compared with baseline and at the 1st and 4th hours which were 3.76 ± 0.28 mm, 3.69 ± 0.32 mm, and 3.72 ± 0.27 mm, respectively. No statistically significant difference was determined in between the 3 measurements in terms of CCT (P>0.05).

Conclusion

Caffeine causes a significant increase in AD and ACD and a significant decrease in LT following oral intake, for at least 4 h.

Morphological prediction of glaucoma by quantitative analyses of ocular shape and volume using 3-dimensional T2-weighted MR images

Elongated axial length of the eye increases the morbidity of glaucoma. Myopia also associates with elongated axial length, and such ellipsoid shape of the eyeball strongly contributes its pathogenesis. Morphological features of the eyeballs, which could be important factors for developing glaucoma, have not been well described. The aim of this study was to investigate the three-dimensional (3D) topographic features of glaucomatous eyeballs with/without myopia to evaluate the potential of those features for predicting glaucoma. Using a 3.0-tesla MRI, volume-isotropic turbo-spin-echo acquisition T2-weighted images were obtained from 55 patients with glaucoma and 22 controls to delineate the eyeballs. Eyeball volumes, axial lengths and transverse lengths were semi-automatically calculated and compared between four groups: normal, myopia, glaucoma, and glaucoma with myopia. Both glaucoma and myopia increased the eyeball volume compared to the normal eyes. An increased anisotropy ratio (axial/transversus length) was observed in myopic eyes compared to normal, whereas in the glaucomatous eyes, with or without myopia, no increase in anisotropy ratio was observed. Increasing volume of eyes can be caused by myopia and glaucoma. Myopic eyes were ellipsoid in shape, but there was less anisotropy and a near-spherical shape in glaucomatous eyes, even in glaucomatous myopic eyes.

Air-Puff-Induced Dynamics of Ocular Components Measured with Optical Biometry

Purpose

To analyze the dynamics of all optical components of the eye and the behavior of the eyeball under air-puff conditions in vivo. To determine the impact of the intraocular pressure (IOP) on the air-puff-induced deformation of the eye.

Methods

Twenty eyes of 20 healthy subjects were included in this study. The dynamics of the ocular components, such as the cornea, the crystalline lens, and the retina, was measured by a prototype swept source optical coherence tomography biometer integrated with the air-puff system. The system allows to acquire a series of axial scans at the same location as a function of time with no transverse scanning. Several parameters were extracted from optical coherence tomography data. The IOP was measured using a Goldmann applanation tonometry. The measurements of the eyes were performed before and 2 hours after administration of IOP-reducing drops, namely, 0.2 % brimonidine tartrate.

Results

There is a statistically significant correlation of corneal thickness, vitreous depth, and eye length with IOP. The deformation amplitudes of the cornea and the crystalline lens are inversely proportional to the IOP, but statistical significance is achieved only for the cornea. The crystalline lens is displaced without compression, and the return has the form of wobbling. The reduction of IOP level induces corresponding changes in the extracted parameters.

Conclusions

Optical biometry combined with air puff provides comprehensive information on the in vivo behavior of all ocular components, including the crystalline lens. Measurement of the axial length dynamics of during deformation enables correcting the deformation for eye retraction.

IMI - Clinical Myopia Control Trials and Instrumentation Report

The evidence-basis based on existing myopia control trials along with the supporting academic literature were reviewed; this informed recommendations on the outcomes suggested from clinical trials aimed at slowing myopia progression to show the effectiveness of treatments and the impact on patients. These outcomes were classified as primary (refractive error and/or axial length), secondary (patient reported outcomes and treatment compliance), and exploratory (peripheral refraction, accommodative changes, ocular alignment, pupil size, outdoor activity/lighting levels, anterior and posterior segment imaging, and tissue biomechanics). The currently available instrumentation, which the literature has shown to best achieve the primary and secondary outcomes, was reviewed and critiqued. Issues relating to study design and patient selection were also identified. These findings and consensus from the International Myopia Institute members led to final recommendations to inform future instrumentation development and to guide clinical trial protocols.

Twenty-four hour ocular and systemic diurnal rhythms in children

PURPOSE

Ocular diurnal rhythms have been implicated in myopia, glaucoma, diabetes, and other ocular pathologies. Ocular rhythms have been well described in adults; however, they have not yet been fully examined in children. The goal of this study was to investigate ocular and systemic diurnal rhythms over 24 h in children.

METHODS

Subjects, ages 5 to 14 years (n = 18), wore a light, sleep, and activity monitor for one week to assess habitual sleep/wake patterns, then underwent diurnal measurements every 4 h for 24 h. Measurements included blood pressure, heart rate, body temperature, intraocular pressure (IOP), ocular biometry, and optical coherence tomography imaging. Saliva was collected for melatonin and cortisol analysis. Mean ocular perfusion pressure was calculated from IOP and blood pressure. Central corneal thickness, corneal power, anterior chamber depth, lens thickness, vitreous chamber depth, and axial length were determined from biometry. Total retinal thickness, retinal pigment epithelium (RPE) + photoreceptor outer segment thickness, photoreceptor inner segment thickness, and choroidal thickness were determined for a 1 mm diameter centred on the fovea. Subjects' amplitude and acrophase of diurnal variation for each parameter were determined using Fourier analysis, and mean acrophase was calculated using unit vector averaging.

RESULTS

Repeated measures analysis of variance (ANOVA) showed that all parameters except anterior chamber depth exhibited significant variations over 24 h (p ≤ 0.005 for all). Axial length underwent diurnal variation of 45.25 ± 6.30 μm with an acrophase at 12.92 h, and choroidal thickness underwent diurnal variation of 26.25 ± 2.67 μm with an acrophase at 1.90 h. IOP was approximately in phase with axial length, with a diurnal variation of 4.19 ± 0.50 mmHg and acrophase at 11.37 h. Total retinal thickness underwent a significant diurnal variation of 4.09 ± 0.39 μm with an acrophase at 15.04 h. The RPE + outer segment layer was thickest at 3.25 h, while the inner segment layer was thickest at 14.95 h. Melatonin peaked during the dark period at 2.36 h, and cortisol peaked after light onset at 9.22 h.

CONCLUSIONS

Ocular and systemic diurnal rhythms were robust in children and similar to those previously reported in adult populations. Axial length and IOP were approximately in phase with each other, and in antiphase to choroidal thickness. These findings may have important implications in myopia development in children.

Role of corneal biomechanical properties in predicting of speed of myopic progression in children wearing orthokeratology lenses or single-vision spectacles

Objective

To determine the characteristics of children who were likely to progress rapidly and gain the greatest benefit from orthokeratology (ortho-k) treatment.

Methods and analysis

The files of 113 children who participated in two myopia control studies and wore either ortho-k lenses (n=62) or single-vision spectacles (SVS) (n=51) were reviewed. Baseline cycloplegic subjective refraction, central corneal thickness, axial length, keratometry, intraocular pressure, corneal biomechanical properties and 24-month axial length data were retrieved and analysed.

Results

Multivariate analysis showed that there was significant negative correlation between axial elongation and baseline age and corneal hysteresis (p<0.05) in the SVS group. In the ortho-k group, only baseline age was significantly and negatively associated with axial elongation (p<0.01).

Conclusion

Corneal biomechanical properties and baseline age can predict the rate of axial elongation in myopic children. It may be beneficial for younger myopic children with low corneal hysteresis to commence ortho-k treatment as early as possible.

Refractive outcomes of cataract surgery in primary congenital glaucoma

AIM

To evaluate refractive outcomes of cataract surgery with intraocular lens (IOL) implantation in operated eyes of primary congenital glaucoma (PCG).

DESIGN

A retrospective case-control study.

METHODS

Patients of PCG who developed cataract following trabeculectomy with trabeculotomy were recruited. Preoperative biometry was recorded and refractive outcomes of the patients in terms of spherical equivalent (SE) and prediction error were noted at 3 and at 12 months following surgery. The refractive outcomes were compared with non-glaucomatous eyes of children in similar age group who underwent lens aspiration with IOL implantation (controls).

RESULTS

The median age of the children with PCG (n = 31) at the time of cataract surgery was 60 months, similar to controls (n = 29); 48 months (p = 0.3). The SE in PCG eyes at 12 months was comparable to controls (p = 0.18). The prediction error (postoperative SE - predicted SE) at 3 months (p = 0.018) and at 12 months (p = 0.03) among PCG eyes was higher and more myopic compared with controls. The range of prediction error at 12 months in PCG eyes was - 8.6 to + 5.8 D (median - 2.0 D), whereas in controls it was - 4.2 to + 6.3 D (median + 0.5 D). For each mmHg intraocular pressure (IOP) increase there was 0.42 mm increase in axial length among PCG eyes and a 0.24 mm increase among controls (p < 0.001).

CONCLUSIONS

After IOL implantation there was a greater prediction error and a greater myopic shift among PCG eyes. Eyes of children with PCG are more prone to refractive surprises as their axial length changes are more sensitive to IOP fluctuation.

Excessive scleral shrinkage, rather than choroidal thickening, is a major contributor to the development of hypotony maculopathy after trabeculectomy

Purpose

We previously reported that eyes with hypotony maculopathy (HM) after trabeculectomy (TLE) exhibited more reduction of axial length (AL) than those without HM, suggesting that inward collapse of the scleral wall may contribute to the development of HM after TLE. However, we did not evaluate change in choroidal thickness (CT), which could influence AL measures. We compared the magnitude and rate of AL and CT changes in eyes with and without HM by simultaneously measuring these parameters before and after TLE.

Methods

We enrolled 77 eyes of 77consecutive patients with glaucoma, who underwent TLE between March 2014 and March 2016. Intraocular pressure (IOP), central corneal thickness, keratometry, AL, and CT were measured pre- and postoperatively, up to 6 months. These biometrics were compared in eyes with and without HM.

Results

The 14 patients who developed HM were significantly younger than those who did not. The eyes with HM exhibited significantly reduced AL (2.8%) compared to those without HM (0.7%). There was no significant difference in CT change between the two groups. The rate of AL reduction was significantly correlated with age, postoperative IOP, and preoperative AL. Post-adjustment logistic regression analysis revealed that eyes with AL reduction rate ≥ 2% had 11.67 higher risk for developing HM (95% confidence interval, 1.28–106.6; P = 0.03).

Conclusions

AL reduction rates ≥ 2% were significantly associated with HM. Excessive reduction in AL, which was seen in eyes with HM, was not an artificial measure resulting from choroidal thickening but rather reflected reductions in the anterior-posterior diameter of the eyeball. Inward collapse of the scleral wall leads to redundancy of the chorioretinal tissue, contributing to the development of HM after TLE.

Intraocular Pressure, Axial Length, and Refractive Changes after Phacoemulsification and Trabeculectomy for Open-Angle Glaucoma

PURPOSE

To compare changes in intraocular pressure (IOP), axial eye length (AEL), and refractive outcome in primary open-angle glaucoma patients undergoing cataract surgery and trabeculectomy in dependence of the sequence of surgeries.

MATERIALS AND METHODS

We retrospectively analysed 48 eyes. The changes in refraction, intraocular pressure, and axial eye length were analysed after surgery. In group A (21 subjects), phacoemulsification was performed before trabeculectomy, and in group B (27 subjects), trabeculectomy was performed before phacoemulsification with a minimum time span between interventions of 6 months.

RESULTS

The reduction in IOP and the decrease in AEL after trabeculectomy were significant after 6 and 12 months postsurgery (p < 0.001 each). The decrease in AEL was 0.42 ± 0.11% at 6 months after surgery and 0.40 ± 0.13% after 12 months from surgery; this decrease in AEL was comparable between the groups. The refractive outcome was significantly different between the groups (group A: 0.35 ± 0.75 dpt, group B: -0.05 ± 0.36 dpt, p = 0.018); in group A, trabeculectomy caused a hyperopic shift of 0.34 ± 0.44 dpt (p = 0.002) at 12 months postsurgery.

CONCLUSION

IOP reduction after trabeculectomy causes AEL shortening. The effect on refractive outcome depends on the sequence of surgeries. Better refractive outcome is achieved if phacoemulsification is performed after trabeculectomy.

Ethnic differences in lens parameters measured by ocular biometry in a cataract surgery population

Purpose

To investigate whether differences exist in lens position and other lens parameters among major ethnic groups with cataractous eyes, which may help explain racial differences in angle closure risk.

Methods

This retrospective, cross-sectional study included 807 adult patients who had cataract surgery between years 2014 and 2016 at the University of California, San Francisco (UCSF). Adult patients of white, Asian, Hispanic and African-American ethnicity were included. Lens position (LP), defined as anterior chamber depth (ACD) + 1/2 lens thickness (LT), was assessed using measurements from optical biometry. Other assessed biometric parameters included axial length (AL), relative lens position (RLP) (defined as LP/AL), and anterior chamber depth (ACD).

Results

A total of 807 patients and 1361 eyes were included in this study from a database of patients having cataract surgery. Mean age was 69.2 years (age range from 18 to 101 years old), and 60.3% of patients were women. The mean LP measurements were 5.54±0.32 mm for white, 5.38±0.32 mm for Asian, 5.32±0.30 mm for Hispanic, and 5.40±0.28 mm for African-American participants. After adjusting for age, sex, and AL, significant differences were found when comparing LP in paired comparisons among White cohort with Asians (P<0.001), Hispanics (P<0.001) and African-Americans (P = 0.003). Additionally, when comparing RLP, similar significant results were found when comparing Whites with Asians (P<0.001), Hispanics (P<0.001) and African-Americans (P = 0.002). Lastly, pair-wise comparison of LT between ethnic groups showed significant differences while comparing Asians with Whites (P = 0.001) and Asians with African-Americans (P<0.001).

Conclusion

The results of this study suggest that the LP of Hispanic, Asian, and African-American patients are significantly smaller than that of White patients, and among all ethnic groups, Hispanics and after Asians have the smallest LP (P<0.001) and RLP (P<0.001). These findings may have implications for the relative risk of angle closure and the potential IOP response after cataract surgery among different ethnic groups.

Relationship between intraocular pressure, anterior chamber depth and lens thickness in primary open-angle glaucoma patients

INTRODUCTION

To investigate the relationship between intraocular pressure (IOP), anterior chamber depth (ACD) and lens thickness (LT) in primary open-angle glaucoma (POAG) patients and compare with age- and sex-matched controls.

METHODS

A cross-sectional analytical study of 62 newly diagnosed POAG patients compared with 62 age- and sex-matched control subjects in a tertiary eye clinic. Socio-demographic data and ocular examinations were documented. IOP was measured using the Goldmann applanation tonometer. LT and ACD were measured using A-scan ultrasonography and the IOLMaster, respectively. Data were analyzed using SPSS version 19.0 and level of significance set at p value <0.05.

RESULTS

In the glaucoma group and control groups, respectively, mean age was 60.3 ± 8.9 and 58.5 ± 8.1 years (p = 0.234), mean IOP was 28.27 ± 7.88 and 14.47 ± 2.60 mmHg (p < 0.001), mean ACD was 3.12 ± 0.27 and 3.15 ± 0.24 mm (p = 0.514), mean LT was 4.24 ± 0.46 and 4.23 ± 0.45 mm (p = 0.903), and mean ACD was shallower in females (p = 0.034) and (p = 0.001). In the glaucoma group, there was a positive correlation between IOP and ACD (r = 0.022, p = 0.864), but a negative correlation between IOP and LT (r = -0.04, p = 0.758) and ACD and LT (r = -0.058, p = 0.657). In the control group, there was a positive correlation between IOP and ACD (r = 0.141, p = 0.275), IOP and LT (r = 0.031, p = 0.811) and ACD and LT (r = 0.016, p = 0.901).

CONCLUSION

ACD is shallower in females. There is no significant correlation between IOP and ACD or between IOP and LT in POAG as well as normal individuals.

Changes in Axial Length and Refractive Error After Noninvasive Normalization of Intraocular Pressure From Elevated Levels

PURPOSE

To explore the changes in axial length and refractive error after noninvasive normalization of intraocular pressure (IOP) from elevated levels.

DESIGN

A prospective observational study.

METHODS

We enrolled 51 consecutive patients with abnormally elevated unilateral IOP (≥10 mm Hg compared with that of the fellow eye, in which the IOP was ≤21 mm Hg). In all patients, the keratometric value and axial length were obtained with the aid of an IOLMaster before and after IOP normalization (defined as attainment of an IOP difference of ≤3 mm Hg compared with the fellow eye, with or without topical application of ocular hypotensive therapy). We focused principally on IOP, axial length, the keratometric value, and the predicted refractive difference (the predicted refractive error after IOP normalization upon placement of an IOL with a power for emmetropia correction determined prior to IOP normalization).

RESULTS

The axial length was significantly reduced from 23.5 to 23.3 mm after IOP normalization, from 45.9 mm Hg to 14.3 mm Hg (P < .001). The change in IOP correlated with that of the axial length (r = 0.826, P < .001), but not with the change in the keratometric value (P = .618). The change in axial length per 10 mm Hg IOP decrease was -0.06 mm (P < .001). The IOP change was correlated with the predicted refractive difference (r = 0.693, P < .001); the predicted refractive difference per 10 mm Hg IOP decrease was +0.15 diopter (P < .001).

CONCLUSIONS

The axial length decreased and the predicted refractive difference increased (hyperopia) as IOP decreased. Therefore, a possible risk of postoperative hyperopic shift should be considered when biometric examination for IOL power calculation is performed in a patient with an abnormally elevated IOP.

An examination of the relation between intraocular pressure, fundal stretching and myopic pathology

Pathological myopia is one of the leading causes of visual impairment worldwide. Myopic development and progression is biomechanical and dominated by axial elongation. This clinical perspective examines some of the stretch-related fundal changes, which are associated with axial elongation and myopic pathology. The biomechanics of stretching of the fundus appears to depend on genetically and/or visual experience-based scleral changes, which reduce its thickness and elastic modulus so that it becomes more susceptible to the distending forces of intraocular pressure. These changes include reduced collagen synthesis, altered collagen fibres, tissue loss, altered proteoglycans and increased matrix metalloproteinase activity. Such changes are associated with reduced scleral rigidity and related increased potential to stretch in response to intraocular pressure. As axial elongation progresses, the sclera appears likely to continue to reduce in thickness and in its capacity to resist intraocular pressure, especially when pressure becomes elevated. Tessellation, lacquer cracks, myopic crescents, staphylomata, chorioretinal atrophy and retinal detachment are examined within a model for stretching of the fundus. Age, refractive error and axial length, for example, are associated with increased pathological progression. Myopic pathological progression can become dominated by vascular changes and include a greater risk of loss of acuity and blindness. Measures to control myopic pathology, which successfully slow or prevent stretching of the fundus, appear to be key factors in reducing or even avoiding permanent visual loss associated with this condition. For example, limiting axial elongation and related myopic fundus pathology by inhibiting changes which reduce the elastic modulus of scleral tissue is a desirable outcome from interventions to control myopia. Similarly, reducing exposure to the distending stress of elevated intraocular pressure appears to be a desirable form of intervention to control myopia, especially if myopic pathology can be reduced or prevented.

Intraocular Pressure Changes during Accommodation in Progressing Myopes, Stable Myopes and Emmetropes

Purpose

To investigate the changes of intraocular pressure (IOP) induced by 3-diopter (3 D) accommodation in progressing myopes, stable myopes and emmetropes.

Design

Cross-sectional study.

Participants

318 subjects including 270 myopes and 48 emmetropes.

Methods

195 progressing myopes, 75 stable myopes and 48 emmetropes participated in this study. All subjects had their IOP measured using iCare rebound tonometer while accommodative stimuli of 0 D and 3 D were presented.

Main Outcome Measures

IOP values without accommodation and with 3 D accommodation were measured in all subjects. Baseline IOPs and IOP changes were compared within and between groups.

Results

There was no significant difference in IOPs between progressing myopes, stable myopes and emmetropes when no accommodation was induced (17.47±3.46, 16.62±2.98 and 16.80±3.62 respectively, p>0.05). IOP experienced an insignificantly slight decrease after 3 D accommodation in three groups (mean change -0.19±2.16, -0.03±1.68 and -0.39±2.65 respectively, p>0.05). Subgroup analysis showed in progressing myopic group, IOP of children (<18 years old) declined with accommodation while IOP of adults (≥18 years) increased, and the difference was statistically significant (p = 0.008). However, after excluding the age factor, accommodation induced IOP changes of high progressing myopes (≤-6 D), low, moderate and non-myopes (>-6 D) was not significantly different after Bonferroni correction (p = 0.838).

Conclusions

Although no difference was detected between the baseline IOPs and accommodation induced IOP changes in progressing myopes, stable myopes and emmetropes, this study found accommodation could cause transient IOP elevation in adult progressing myopes.

Diurnal Alterations of Refraction, Anterior Segment Biometrics, and Intraocular Pressure in Long-Time Dehydration due to Religious Fasting

PURPOSE

To investigate the effects of dehydration due to fasting on diurnal changes of intraocular pressure, anterior segment biometrics, and refraction.

SUBJECTS AND METHODS

The intraocular pressures, anterior segment biometrics (axial length: AL; Central corneal thickness: CCT; Lens thickness: LT; Anterior chamber depth: ACD), and refractive measurements of 30 eyes of 15 fasting healthy male volunteers were recorded at 8:00 in the morning and 17:00 in the evening in the Ramadan of 2013 and two months later. The results were compared and the statistical analyses were performed using the Rstudio software version 0.98.501. The variables were investigated using visual (histograms, probability plots) and analytical methods (Kolmogorov-Smirnov/Shapiro-Wilk test) to determine whether or not they were normally distributed.

RESULTS

The refractive values remained stable in the fasting as well as in the control period (p = 0.384). The axial length measured slightly shorter in the fasting period (p = 0.001). The corneal thickness presented a diurnal variation, in which the cornea measured thinner in the evening. The difference between the fasting and control period was not statistically significant (p = 0.359). The major differences were observed in the anterior chamber depth and IOP. The ACD was shallower in the evening during the fasting period, where it was deeper in the control period. The diurnal IOP difference was greater in the fasting period than the control period. Both were statistically significant (p = 0.001). The LT remained unchanged in both periods.

CONCLUSIONS

The major difference was shown in the anterior chamber shallowing in the evening hours and IOP. Our study contributes the hypothesis that the posterior segment of the eye is more responsible for the axial length alterations and normovolemia has a more dominant influence on diurnal IOP changes.

Accommodation-induced intraocular pressure changes in progressing myopes and emmetropes

PURPOSE

To investigate the changes of intraocular pressure (IOP) and anterior eye segment biometric parameters under different accommodative statuses in progressing myopes and emmetropes.

METHODS

Forty-six progressing myopes and 40 emmetropes participated in this study. All the subjects had their IOP and anterior eye segment biometric parameters (including corneal thickness, anterior chamber depth, anterior chamber angle width, and lens thickness) measured using iCare rebound tonometer and VisanteTM anterior segment-optical coherence tomography while accommodative stimuli of 0, 3, and 6D were presented.

RESULTS

There was no significant difference in IOP between progressing myopes and emmetropes when no accommodation was induced (16.22±4.11 vs 17.01±3.72, respectively, t=-0.93, P>0.05). However, IOP significantly increased with accommodation in progressing myopes (mean change +1.02±2.07 mm Hg from 0D to 6D, F=5.35, P<0.01), but remained unchanged (mean change -0.76±3.22 mm Hg from 0D to 6D, F=1.46, P>0.05) in emmetropes. Meanwhile, we found that their anterior chamber depth decreased (P<0.01), anterior chamber angle narrowed (P<0.01), and lens thickened (P<0.01) significantly with accommodation, both in progressing myopes and emmetropes.

CONCLUSIONS

Although no difference was detected between the IOPs of progressing myopes and emmetropes without accommodation, accommodation could induce transient IOP elevation in progressing myopes. Simultaneously, we found that their anterior chamber depth decreased, anterior chamber angle narrowed, and lens thickened with accommodation. Although emmetropes showed the similar anterior eye segment structure changes, their IOPs did not increase with accommodation. Our study indicated that IOP elevation with accommodation in progressing myopes might be related to myopia progression.

The short-term effects of exercise on intraocular pressure, choroidal thickness and axial length

Purpose

To explore ocular changes in healthy people after exercise.

Methods

Twenty five volunteers underwent exercise for 15 minutes on a treadmill. Measurements of choroidal thickness, intraocular pressure (IOP), ocular biometry, and blood pressure were taken before and after exercise. Enhanced Depth Imaging optical coherence tomography (EDI-OCT) was used to measure choroidal thickness at the fovea. Intraocular pressure (IOP) was measured by Goldmann applanation tonometry. Ocular biometric measures were collected using A scan ultrasound. Blood pressure was measured concurrently with the acquisition of the scans.

Results

Twenty five volunteers (25 eyes) with a mean age of 25.44±3.25 years were measured. There was a significant increase in systolic and diastolic pressure after exercise (P<0.05). The IOP showed a significant decrease after exercise (P<0.05). However there was no significant difference in the mean choroidal thickness, ocular axial length, anterior chamber depth, lens thickness, or vitreous length before and after exercise measurements (P>0.05).

Conclusion

There was a significant decrease in IOP from exercise without a change in choroidal thickness and ocular biometric measures. IOP and choroidal thickness were not correlated, suggesting that the IOP decrease from exercise is not due to changes in choridal thickness.

Changes in axial length and choroidal thickness after intraocular pressure reduction resulting from trabeculectomy

Purpose

To evaluate changes in axial length and choroidal thickness after trabeculectomy.

Patients and methods

Fourteen patients under 80 years of age with glaucoma, were enrolled. The choroid was imaged using prototypical high-penetration optic coherence tomography (OCT) and the thickness was measured. Axial length, choroidal thickness, and intraocular pressure (IOP) were measured bilaterally at 3 pm 1 day before and 6 days after trabeculectomy. The choroidal thickness was measured at the fovea and four other locations (2 mm superior, temporal, inferior, and nasal to the center of the optic nerve head).

Results

The IOP and axial length significantly decreased in eyes that underwent trabeculectomy (P < 0.0001 for the IOP; P < 0.001 for axial length comparisons). The mean choroidal thicknesses significantly increased in eyes that underwent trabeculectomy compared to preoperatively (P < 0.0001 for the fovea; P < 0.01 for four locations around the optic disc). The mean magnitude of change in IOP was correlated positively with the mean magnitude of change in axial length, but not correlated with the mean magnitude of change in choroidal thickness at the fovea that underwent trabeculectomy. The sum of the axial length and subfoveal choroidal thickness in eyes decreased significantly postoperatively (P < 0.05).

Conclusion

The axial length shortened, the choroid thickened, and the sum of the axial length and subfoveal choroidal thickness decreased with IOP reduction early after trabeculectomy.

Changes in choroidal thickness, axial length, and ocular perfusion pressure accompanying successful glaucoma filtration surgery

PURPOSE

To investigate the changes in choroidal thickness (CT), axial length (AL), and ocular perfusion pressure (OPP) accompanying intraocular pressure (IOP) reduction after trabeculectomy. methods: Thirty-nine eyes of 39 patients with primary open-angle glaucoma uncontrolled by medical therapy were included in this prospective and interventional study. All patients underwent a fornix-based trabeculectomy. The CT was measured by enhanced depth imaging-optical coherence tomography. IOP, AL, and systolic/diastolic blood pressure were also measured, and OPP was calculated. All measurements were performed at baseline and 1 month after surgery.

RESULTS

The mean IOP was 25.0 ± 5.8 mm Hg at baseline and 11.7 ± 2.6 mm Hg after trabeculectomy (P<0.001), and the mean subfoveal CT was 295 ± 84 mm Hg at baseline and 331 ± 82 mm Hg after trabeculectomy (P<0.001). The mean AL was 23.64 ± 0.98 mm at baseline and 23.54 ± 0.96 mm after trabeculectomy (P<0.001), whereas the mean OPP was 38.8 ± 6.2 mm Hg preoperatively, and 51.1 ± 7.3 mm Hg postoperatively (P<0.001). The change in CT negatively correlated with the change in IOP (r=-0.785, P<0.001) and AL (r=-0.693, P<0.001), whereas it positively correlated with the change in OPP (r=0.418, P=0.008).

CONCLUSION

These results suggest that the large IOP decrease following trabeculectomy causes choroidal thickening. In addition, CT changes are associated with IOP and AL reduction as well as OPP increase.

Phacoemulsification and intraocular lens implantation after inadvertent intracapsular injection of intravitreal dexamethasone implant

In this interventional case series, two eyes of two patients with diabetic macular oedema and one eye of a patient with complicated cataract secondary to uveitis associated with juvenile idiopathic arthritis had inadvertent injection of dexamethasone implant into the capsular bag. This was followed by successful completion of phacoemulsification and intraocular lens implantation. At 1-year follow-up, all patients maintained visual acuity of ≥ 20/40 with absence of macular oedema.

Changes in choroidal thickness and optical axial length accompanying intraocular pressure increase

PURPOSE

To measure changes in choroidal thickness (CT), retinal thickness (RT), and axial length (AL) accompanying intraocular pressure (IOP) increase and to investigate the changes in axial eye dimensions induced by IOP increase.

METHODS

Thirty-four eyes of 34 patients undergoing a diagnostic provocative test for primary angle closure (PAC). Patients with other macular diseases were excluded. Patients underwent the darkroom prone provocative test (DR-PPT) for 1 h. We measured CT and RT at the fovea by optical coherence tomography with the enhanced depth imaging method and AL with noncontact, partial coherence laser interferometry before and after the DR-PPT.

RESULTS

There was a statistically significant increase in the mean (SD) IOP of 7.3 (9.2) mmHg and the mean (SD) AL of 0.06 (0.12) mm after the DR-PPT (P < 0.001 and P = 0.014, respectively). There was a statistically significant decrease in the mean (SD) subfoveal CT of 30.0 (36.8) μm (P < 0.001), while there was no significant change in the mean foveal RT. The change in subfoveal CT was negatively correlated with the changes in IOP (r = -0.71, P < 0.001) and AL (r = -0.54, P = 0.004).

CONCLUSIONS

In eyes suspected of having PAC, acutely increased IOP accompanies choroid thinning and corresponding elongation of the optical axis.

Manipulation of intraocular pressure for studying the effects on accommodation

A reliable experimental system in which IOP can be manipulated or a rapid IOP change can be induced while simultaneously and continuously measuring IOP and the ocular accommodative changes would be useful for understanding the physiological effect of intraocular pressure (IOP) on the accommodative mechanism. In this study, an IOP perfusion and recording system was developed and tested using 13 enucleated pig eyes. The vitreous chamber of the pig eyes was cannulated with a needle connected to two fluid reservoirs at different heights. One reservoir was set to achieve one of three baseline pressures of 5.5 mmHg, 13.0 mmHg and 20.5 mmHg. The other reservoir was moved to achieve pressures of 1.5 mmHg, 3.0 mmHg, 4.5 mmHg and 6.0 mmHg higher than the baseline pressure. The height differential between the reservoirs determined the amplitude of IOP changes. Rapid IOP changes were induced by switching the reservoirs with a solenoid pinch-valve. Two needles, one each attached to a pressure transducer were inserted into the anterior chamber and vitreous chamber respectively. Custom developed software was used to measure the anterior chamber pressure and vitreous chamber pressure at 80 Hz. A high-resolution continuous A-scan ultrasound biometer (CUB) was used to dynamically measure changes in ocular biometry including anterior chamber depth (ACD), lens thickness (LT) and vitreous chamber depth (VCD) while the vitreous chamber pressure was manipulated. The changes in ACD, LT and VCD were analyzed as a function of the pressure change. Perfusion-induced axial biometric changes were quantified by the slopes of linear regression relationships. Both anterior chamber pressure and vitreous chamber pressure changed relatively systematically with the induced vitreous chamber pressure changes (anterior chamber: y = 0.863x + 0.030, r(2) = 0.983; vitreous chamber: y = 0.883x + 0.009, r(2) = 0.981). At perfusion pressures of 5.5, 13.0 and 20.5 mmHg, the slopes for ACD were -5.72, -2.75 and -2.36 μm/mmHg, for LT were -3.31, -1.59 and -1.03 μm/mmHg and for VCD were 19.05, 8.63 and 5.18 μm/mmHg. The system was able to manipulate and monitor IOP while axial biometry changes were recorded. This system will allow the relationship between IOP and accommodation to be studied in non-human primate eyes.

The short-term influence of exercise on axial length and intraocular pressure

PURPOSE

The aim of this study is to investigate the short-term influence of a period of dynamic exercise on axial length (AXL) and intraocular pressure (IOP) in young adult subjects.

PATIENTS AND METHODS

In all, 20 young adult subjects (10 myopes and 10 emmetropes) participated. Baseline measures of ocular biometrics, IOP and ocular pulse amplitude (OPA) were taken following a 20-min rest period. Subjects then performed 10 min of moderate intensity, low impact dynamic exercise (bicycle ergometry). Measures of ocular biometrics, IOP and OPA were repeated immediately after, and then 5 and 10 min after this exercise task. Systemic blood pressure and pulse rate were also monitored. A repeated measures analysis of variance was used to investigate the changes in the measured parameters.

RESULTS

Exercise resulted in significant changes in a range of ocular parameters. A small but significant decrease in AXL was observed following exercise (P<0.0001). The largest change in AXL was noted immediately following exercise (mean decrease -17±10 μm). IOP and OPA also decreased significantly following exercise (P<0.0001). A moderate but significant positive association was found between the changes in AXL and the changes in IOP (r(2)=0.36, P<0.0001). There were no significant differences found between the myopic and emmetropic subjects in the magnitude of changes observed in ocular parameters following exercise.

CONCLUSION

The physiological effects of dynamic exercise lead to changes in a range of ocular parameters, including significant reductions in IOP, OPA and decreases in AXL.

Deformation of the early glaucomatous monkey optic nerve head connective tissue after acute IOP elevation in 3-D histomorphometric reconstructions

PURPOSE

To retest the hypothesis that monkey ONH connective tissues become hypercompliant in early experimental glaucoma (EEG), by using 3-D histomorphometric reconstructions, and to expand the characterization of EEG connective tissue deformation to nine EEG eyes.

METHODS

Trephinated ONH and peripapillary sclera from both eyes of nine monkeys that were perfusion fixed, with one normal eye at IOP 10 mm Hg and the other EEG eye at 10 (n=3), 30 (n=3), or 45 (n=3) mm Hg were serial sectioned, 3-D reconstructed, 3-D delineated, and quantified with 3-D reconstruction techniques developed in prior studies by the authors. Overall, and for each monkey, intereye differences (EEG eye minus normal eye) for each parameter were calculated and compared by ANOVA. Hypercompliance in the EEG 30 and 45 eyes was assessed by ANOVA, and deformations in all nine EEG eyes were separately compared by region without regard for fixation IOP.

RESULTS

Hypercompliant deformation was not significant in the overall ANOVA, but was suggested in a subset of EEG 30/45 eyes. EEG eye deformations included posterior laminar deformation, neural canal expansion, lamina cribrosa thickening, and posterior (outward) bowing of the peripapillary sclera. Maximum posterior laminar deformation and scleral canal expansion co-localized to either the inferior nasal or superior temporal quadrants in the eyes with the least deformation and involved both quadrants in the eyes achieving the greatest deformation.

CONCLUSIONS

The data suggest that, in monkey EEG, ONH connective tissue hypercompliance may occur only in a subset of eyes and that early ONH connective tissue deformation is maximized in the superior temporal and/or inferior nasal quadrants.

Intraocular pressure spikes in keratectasia, axial myopia, and glaucoma

PURPOSE

To review a range of activities associated with intraocular pressure (IOP) spikes. To examine the possible significance of IOP spikes in conditions such as keratectasia, axial myopia, and glaucoma.

METHODS

Hypotheses concerning mechanisms for adverse responses to IOP spikes were examined.

RESULTS

Apart from the possibility that IOP spikes might cause susceptible corneal, posterior scleral, or optic nerve head tissue to yield to associated distending forces, there is the possibility that these tissues will be also be damaged by increased hydrostatic pressure.

CONCLUSIONS

In-office tonometry does not indicate the degree to which ocular tissues are exposed to IOP spikes. For eyes that are exposed to IOP spikes of longer duration, that occur frequently and which result in a larger IOP increment, the risk of an adverse response may be greater. Changes in ocular tissues because of increased hydrostatic pressure may include morphological cellular changes and alterations to enzyme function. Eye rubbing may be the most significant mechanism for creating IOP spikes because of the large IOP increments that may be involved, as well as the possibility that abnormal rubbing can become a chronic habit. As appears to be the case in keratoconus, asymmetric exposure to IOP spikes may help to explain some asymmetric presentations of post-laser-assisted in situ keratomileusis, glaucoma, or myopia. Ideally methods for the objective assessment of patient risk for adverse responses to IOP spikes will continue to be developed. A self-administered questionnaire may help identify patients who are significantly exposed to IOP spikes. Family history may indicate an increased risk of diseases for which IOP spikes may have significant implications. Patient counseling regarding the possibility that IOP spiking activities may contribute to the development and/or progression of conditions such as keratectasia, axial myopia, and glaucoma may be indicated.

Non-invasive biometric assessment of ocular rigidity in glaucoma patients and controls

PURPOSE

To determine in vivo whether a pharmacologically induced change in intraocular pressure (IOP) leads to measurable changes in axial eye length and whether there is a difference between glaucoma patients and control subjects.

METHODS

42 subjects (19 patients with primary open angle glaucoma and 23 control patients matched for age and gender) underwent axial eye length measurement using partial coherence laser interferometry and measurement of IOP using dynamic contour tonometry before and 2 h after oral intake of 500 mg acetazolamide. Student's t-test was used to compare differences in the means.

RESULTS

An identical drop in IOP was induced in both the glaucoma (mean+/-SEM: 2.90+/-0.44 mmHg, n=19) and the control group (mean+/-SEM: 3.17+/-0.32 mmHg, n=23). The change in axial eye length was significantly smaller (P=0.026) in the glaucoma group (mean+/-SEM: -14.2+/-3.2 microm, n=19) compared with the control group (mean+/-SEM: -23.0+/-2.98 microm, n=23).

CONCLUSIONS

Our results strongly suggest that the ocular rigidity is increased in patients with established glaucoma in comparison to control subjects. Ocular rigidity could play a role in the pathogenesis and pathophysiology of glaucoma. Determination of ocular rigidity could be helpful in detection of glaucoma.