The effect of age on ocular blood supply determined by pulsatile ocular blood flow and color Doppler ultrasonography

Retinal nerve fiber layer and ophthalmic artery blood flow parameters in pseudoexfoliation syndrome and pseudoexfoliative glaucoma

OBJECTIVES

To investigate the relationship between ophthalmic artery (OA) blood flow parameters and retinal nerve fiber layer (RNFL) thickness in eyes with pseudoexfoliation (PEX).

METHODS

We compared PEX eyes without glaucoma (group A, n=53) and those with glaucoma (group B, n=18) with control eyes (group C, n=44). Subsequently, eyes in groups A and B were compared. Finally, OA color Doppler imaging measurements were recorded, and peripapillary RNFL analysis was performed.

RESULTS

The total RNFL measurements differed significantly among the groups (P=0.012), being thicker in group C than in group A (P=0.010) and significantly different between group B and groups A and C (both P=0.001). The peak systolic velocity (PSV) and end diastolic velocity (EDV) measurements of groups A and B were lower than those of group C (PSV: P=0.001 and P=0.001, respectively; EDV: P=0.001 and P=0.001, respectively). No significant difference was noted in resistive index (RI) measurements (P=0.370). In group B, significant negative correlations were noted between total RNFL and PSV (r=-0.743; P=0.001) and between total RNFL and EDV (r=-0.691; P=0.001), but not between total RNFL and RI measurements (P=0.548).

CONCLUSIONS

Pseudoexfoliation syndrome (PXS) with or without glaucoma was associated with a decrease in the PSV and EDV values of the OA. An extensive study may be needed to further explore the role of PXS in OA blood flow parameters. Total RNFL thickness values were lower in eyes with PEX than in those without.

The versatile roles of lumican in eye diseases: A review

Lumican is a keratan sulfate proteoglycan that belongs to the small leucine-rich proteoglycan family. Research has lifted the veil on the versatile roles of lumican in the pathogenesis of eye diseases. Lumican has pivotal roles in the maintenance of physiological tissue homogenesis and is often upregulated in pathological conditions, e.g., fibrosis, scar tissue formation in injured tissues, persistent inflammatory responses and immune anomaly, etc. Herein, we will review literature regarding the role of lumican in pathogenesis of inherited congenital and acquired eye diseases, e.g., cornea dystrophy, cataract, glaucoma and chorioretinal diseases, etc.

Deficits in mitochondrial TCA cycle and OXPHOS precede rod photoreceptor degeneration during chronic HIF activation

BACKGROUND

Major retinal degenerative diseases, including age-related macular degeneration, diabetic retinopathy and retinal detachment, are associated with a local decrease in oxygen availability causing the formation of hypoxic areas affecting the photoreceptor (PR) cells. Here, we addressed the underlying pathological mechanisms of PR degeneration by focusing on energy metabolism during chronic activation of hypoxia-inducible factors (HIFs) in rod PR.

METHODS

We used two-photon laser scanning microscopy (TPLSM) of genetically encoded biosensors delivered by adeno-associated viruses (AAV) to determine lactate and glucose dynamics in PR and inner retinal cells. Retinal layer-specific proteomics, in situ enzymatic assays and immunofluorescence studies were used to analyse mitochondrial metabolism in rod PRs during chronic HIF activation.

RESULTS

PRs exhibited remarkably higher glycolytic flux through the hexokinases than neurons of the inner retina. Chronic HIF activation in rods did not cause overt change in glucose dynamics but an increase in lactate production nonetheless. Furthermore, dysregulation of the oxidative phosphorylation pathway (OXPHOS) and tricarboxylic acid (TCA) cycle in rods with an activated hypoxic response decelerated cellular anabolism causing shortening of rod photoreceptor outer segments (OS) before onset of cell degeneration. Interestingly, rods with deficient OXPHOS but an intact TCA cycle did not exhibit these early signs of anabolic dysregulation and showed a slower course of degeneration.

CONCLUSION

Together, these data indicate an exceeding high glycolytic flux in rods and highlight the importance of mitochondrial metabolism and especially of the TCA cycle for PR survival in conditions of increased HIF activity.

Association of Ambulatory Blood Pressure and Other Factors With Intraocular Pressure-Related 24-Hour Contact Lens Sensor Profile in Untreated Glaucoma

Purpose

To investigate the association of diurnal blood pressure (BP) and other factors with the intraocular pressure (IOP)–related 24-hour contact lens sensor (CLS) profile of patients with untreated glaucoma.

Methods

The prospective study included 82 patients with untreated normal-tension glaucoma. CLS measurements and ambulatory BP monitoring were performed simultaneously for 24 hours. The association between the mean arterial pressure (MAP) and CLS profile was examined for the daytime and nocturnal periods using linear regression analysis. The associations between other factors and the CLS profile were also examined.

Results

Multivariate analysis of data from 63 eligible patients showed that higher average MAPs were significantly associated with larger average nocturnal CLS values (β coefficient = 0.273; P = 0.023); a larger increase in the last CLS value (β coefficient = 0.366; P = 0.003); larger standard deviations (SDs) of CLS values for the daytime, nocturnal, and 24-hour periods (β coefficient = 0.407, 0.293, and 0.375; P < 0.001, P = 0.032 and 0.002, respectively); and higher average ocular pulse frequencies for the daytime, nocturnal, and 24-hour periods (β coefficient = 0.268, 0.380, and 0.403; P = 0.029, 0.002, and 0.001, respectively). Thicker subfoveal choroids and shorter axial length were significantly associated with larger SDs and larger average CLS values, respectively. Smaller anterior chamber volume and lower corneal hysteresis were associated with larger SDs or larger average ocular pulse amplitude.

Conclusions

Ambulatory BP and several ocular parameters were significantly associated with various parameters of the 24-hour CLS profile.

Translational Relevance

Ambulatory BP and ocular parameters may be modifiers of the 24-hour IOP-related profile of CLS.

Correlation of optical coherence tomography and Doppler ultrasonography findings in pseudoexfoliation syndrome

PURPOSE

We aimed to investigate the correlation between the color Doppler imaging (CDI) results and parameters determined by spectral domain optical coherence tomography (SD-OCT) in cases with pseudoexfoliation syndrome (XFS).

METHODS

99 participants were included in this prospective study. Retinal nerve fiber layer (RNFL), ganglion cell complex (GCC), optic nerve head (ONH) measurements were recorded. Perfusions of the ophthalmic artery (OA) and central retinal artery (CRA) were determined and resistivity indices (RI) were calculated.

RESULTS

No statistically significant differences were determined between the groups regarding the RNFL and ONH parameters. Only the minimum GCC thickness value was determined to be reduced in XFS group (n = 49) when compared to the controls (n = 50) (p = 0.018). The OA-RI and CRA-RI values of XFS group were significantly higher than the control group (p < 0.001 and p = 0.001). In XFSs, negative correlations were present between OA-RI and the minimum, average, inferior and inferotemporal regions of GCC thickness (r = - 0.448 p = 0.001, r = - 0.275 p = 0.040, r = - 0.295 p = 0.027, r = - 0.304 p = 0.024, respectively), and also between CRA-RI and minimum GCC values (r = - 0.317, p = 0.017). While a significant relationship was present between age and OA-RI and CRA-RI values in controls, no such correlation was present in XFSs.

CONCLUSIONS

The vascular resistance increased with age in controls, whereas it was independent of age in XFS group. In XFSs, RIs correlated significantly with certain GCC values, but not with RNFL and ONH parameters. It would be beneficial to follow the XFS with CDI as it provides supportive parameters to GCC in order to recognize early changes in XFS.

Transcriptomic analysis of the mouse retina after acute and chronic normobaric and hypobaric hypoxia

Oxygen delivery to the retinal pigment epithelium and the outer retina is essential for metabolism, function, and survival of photoreceptors. Chronically reduced oxygen supply leads to retinal pathologies in patients and causes age-dependent retinal degeneration in mice. Hypoxia can result from decreased levels of inspired oxygen (normobaric hypoxia) or reduced barometric pressure (hypobaric hypoxia). Since the response of retinal cells to chronic normobaric or hypobaric hypoxia is mostly unknown, we examined the effect of six hypoxic conditions on the retinal transcriptome and photoreceptor morphology. Mice were exposed to short- and long-term normobaric hypoxia at 400 m or hypobaric hypoxia at 3450 m above sea level. Longitudinal studies over 11 weeks in normobaric hypoxia revealed four classes of genes that adapted differentially to the hypoxic condition. Seventeen genes were specifically regulated in hypobaric hypoxia and may affect the structural integrity of the retina, resulting in the shortening of photoreceptor segment length detected in various hypoxic groups. This study shows that retinal cells have the capacity to adapt to long-term hypoxia and that consequences of hypobaric hypoxia differ from those of normobaric hypoxia. Our datasets can be used as references to validate and compare retinal disease models associated with hypoxia.

Effects of age on the peak ratio of ophthalmic artery Doppler

This study aimed to investigate the effects of age on the peak ratio (PR) of ophthalmic artery (OA) Doppler.The initial peak velocity (P1), second peak velocity (P2) and PR of OA were detected by color Doppler ultrasonography in 147 healthy subjects. All of the subjects were divided into 6 groups (G1-G6) according to the age. (G1, 20-29 years; G2, 30-39 years; G3, 40-49 years; G4, 50-59 years; G5, 60-69 years; and G6, 70 years or older). The blood pressure and heart rate were also examined before ultrasonography. The influences of age, blood pressure and heart rate on the P1, P2, and PR were further evaluated.There were significant differences in the P2 and PR among different age groups except for P1. There were no significant differences in the P2 and PR between the first 2 groups, neither among the latter 4 groups. Nevertheless, P2 and PR in the first 2 groups were significantly different from those in the latter 4 groups. In addition, both P2 and PR (not P1) increased significantly with age, systolic and diastolic blood pressure. P1, P2 and PR were not related to heart rate. Both P2 and PR were closely related to the age. PR also had a weak relationship with systolic blood pressure.Both P2 and PR of OA Doppler increase with age. Concern should be raised when P2 and PR are used to evaluate the hemodynamic change of OA.

Age-related changes in retrobulbar circulation: a literature review

Introduction

The advances in research methods used in ophthalmology allow for an increasingly accurate examination of the eyes, as well as the morphology and function of the vessels. Colour Doppler imaging is still the first-line method for the analysis of parameters of retrobulbar circulation. Therefore, the aim of this work was to present the current state of knowledge about anatomical and functional age-related changes in retrobulbar arteries.

Methods

A literature search was performed mainly based on the PubMed database.

Results

The anatomy of retrobulbar arteries, histological background of age-related vascular changes, age-related changes in retrobulbar blood flow in the ophthalmic artery, central retinal artery, short posterior ciliary arteries, and the reference values for the age-dependent retrobulbar circulation parameters measured by colour Doppler imaging are discussed in this review.

Conclusion

The age of the subject should always be taken into account when interpreting the parameters of retrobulbar blood flow measured by colour Doppler imaging.

Relationship Between the Parameters of Corneal and Fundus Pulse Signals Acquired With a Combined Ultrasound and Laser Interferometry Technique

Purpose

To estimate the relationship between the characteristics of the corneal pulse (CP) signal and those of the fundus pulse (FP) signal measured with a combined noncontact ultrasonic and laser interferometry technique in healthy subjects.

Methods

Twenty-two healthy subjects participated in experiments that included measurements of intraocular pressure, ocular pulse amplitude, ocular biometry, blood pressure, and heart rate. Additionally, simultaneous recordings of CP and FP signals were acquired with a noncontact ultrasonic device combined with laser interferometry. Subsequently, ocular perfusion pressure (OPP) and the time and spectral parameters of CP and FP signals were computed. A system model was proposed to relate the FP signal to the CP signal.

Results

The system model revealed that the eye globe transfers information between signals of the posterior and anterior eye, relatively amplifying higher spectral harmonics. The amplitude of the second CP harmonic is predicted by FP_RMS and OPP (R² = 0.468, P = 0.002). Partial correlation analysis showed that the CP signal parameters are statistically significantly correlated with those of the FP signal and OPP, after correcting for age and sex.

Conclusions

The eye globe can be viewed as a high pass filter, in which the CP characteristic changes in relation to the fundus pulsation. The FP signal and OPP have an impact on the variations of the CP signal morphology.

Translational Relevance

Investigation of differences between the characteristics of the anterior and posterior tissue movements is a promising method for evaluating the role of circulatory and biomechanical components in the pathophysiology of ocular diseases.

Hif1a inactivation rescues photoreceptor degeneration induced by a chronic hypoxia-like stress

Reduced choroidal blood flow and tissue changes in the ageing human eye impair oxygen delivery to photoreceptors and the retinal pigment epithelium. As a consequence, mild but chronic hypoxia may develop and disturb cell metabolism, function and ultimately survival, potentially contributing to retinal pathologies such as age-related macular degeneration (AMD). Here, we show that several hypoxia-inducible genes were expressed at higher levels in the aged human retina suggesting increased activity of hypoxia-inducible transcription factors (HIFs) during the physiological ageing process. To model chronically elevated HIF activity and investigate ensuing consequences for photoreceptors, we generated mice lacking von Hippel Lindau (VHL) protein in rods. This activated HIF transcription factors and led to a slowly progressing retinal degeneration in the ageing mouse retina. Importantly, this process depended mainly on HIF1 with only a minor contribution of HIF2. A gene therapy approach using AAV-mediated RNA interference through an anti-Hif1a shRNA significantly mitigated the degeneration suggesting a potential intervention strategy that may be applicable to human patients.

Targeting Hif1a rescues cone degeneration and prevents subretinal neovascularization in a model of chronic hypoxia

Background

Degeneration of cone photoreceptors leads to loss of vision in patients suffering from age-related macular degeneration (AMD) and other cone dystrophies. Evidence, such as choroidal ischemia and decreased choroidal blood flow, implicates reduced tissue oxygenation in AMD pathology and suggests a role of the cellular response to hypoxia in disease onset and progression. Such a chronic hypoxic situation may promote several cellular responses including stabilization of hypoxia-inducible factors (HIFs).

Methods

To investigate the consequence of a chronic activation of the molecular response to hypoxia in cones, von Hippel Lindau protein (VHL) was specifically ablated in cones of the all-cone R91W;Nrl^-/- mouse. Retinal function and morphology was evaluated by ERG and light microscopy, while differential gene expression was tested by real-time PCR. Retinal vasculature was analyzed by immunostainings and fluorescein angiography. Two-way ANOVA with Šídák’s multiple comparison test was performed for statistical analysis.

Results

Cone-specific ablation of Vhl resulted in stabilization and activation of hypoxia-inducible factor 1A (HIF1A) which led to increased expression of genes associated with hypoxia and retinal stress. Our data demonstrate severe cone degeneration and pathologic vessel growth, features that are central to AMD pathology. Subretinal neovascularization was accompanied by vascular leakage and infiltration of microglia cells. Interestingly, we observed increased expression of tissue inhibitor of metalloproteinase 3 (Timp3) during the aging process, a gene associated with AMD and Bruch’s membrane integrity. Additional deletion of Hif1a protected cone cells, prevented pathological vessel growth and preserved vision.

Conclusions

Our data provide evidence for a HIF1A-mediated mechanism leading to pathological vessel growth and cone degeneration in response to a chronic hypoxia-like situation. Consequently, our results identify HIF1A as a potential therapeutic target to rescue hypoxia-related vision loss in patients.

Does transient increase in axial length during accommodation attenuate with age?

Background

The aim was to profile transient accommodative axial length changes from early adulthood to advanced presbyopia and to determine whether any differences exist between the responses of myopic and emmetropic individuals.

Methods

Ocular biometry was measured by the LenStar biometer (Haag‐Streit, Switzerland) in response to zero, 3.00 and 4.50 D accommodative stimuli in 35 emmetropes and 37 myopes, aged 18 to 60 years. All results were corrected to reduce errors arising from the increase in crystalline lens thickness with accommodation. Accommodative responses were measured sequentially by the WAM 5500 Auto Ref/Keratometer (Grand Seiko, Hiroshima, Japan).

Results

Axial length increased significantly with accommodation (p < 0.001), with a mean corrected increase in axial length of 2 ± 18 µm and 8 ± 16 µm observed at 3.00 and 4.50 D, respectively. The magnitude of accommodative change in axial length was not dependent on refractive error classification (p = 0.959); however, a significant reduction in the magnitude and variance of axial length change was evident after 43 to 44 years of age (p < 0.002).

Conclusion

The negative association between transient increase in axial length and age, in combination with reduced variance of data after age 43 to 44 years, is consistent with a significant increase in posterior ocular rigidity, which may be influential in the development of presbyopia.

[Intraocular pressure, ocular blood flow, and corneal biomechanics changes after LASIK surgery for myopia]

AIM

to study changes in intraocular pressure (IOP), volumetric ocular blood flow (OBF) rate, and biomechanical properties of the cornea after excimer laser ablation in patients with myopia of different degrees.

MATERIAL AND METHODS

A total of 16 patients (32 eyes) with myopia ranging from 2.75 to 9.0 D were examined before and after LASIK. Ocular Blood Flow Analyzer (OBFA) was used to measure IOP and OBF as well as pulse amplitude and volume. Ocular Response Analyzer (ORA) was also employed to provide the following data: Goldmann-equivalent IOP, corneal compensated IOP, corneal hysteresis, and corneal resistance factor. The eyes were then divided into two groups: group 1 - 15 eyes with less than 70-µm deep ablation of the cornea and group 2 - 17 eyes with more than 70-µm deep ablation.

RESULTS

Group 1 demonstrated a statistically reliable decrease in IOP values provided by either method and biomechanical parameters of the cornea (p<0.005), but no difference in pre- and postoperative OBF, or pulse amplitude, or pulse volume (p>0.05). In group 2, all the parameters changed reliably, except for the pulse volume (p>0.05). In particular, a decrease was recorded for IOP (with no dependence to the method of measurement; p<0.001), pulse amplitude (p<0.01), corneal hysteresis (p<0.001), and corneal resistance factor (p<0.001); an increase - for OBF (p<0.05).

CONCLUSION

One should allow for possible mismeasurement of IOP and OBF as well as biomechanical parameters of the cornea in post-LASIK patients, keeping in mind that the extent of error depends on the depth of ablation. Shallow ablation (no more than 70-µm deep) has no statistically significant effect on OBF readings, while IOP seems to decrease considerably. In deep ablation (more than 70-µm deep), both parameters are reliably lower than at baseline.

Age-Related Changes in Ocular Blood Velocity in Suspects with Glaucomatous Optic Disc Appearance. Comparison with Healthy Subjects and Glaucoma Patients

Purpose

To evaluate retrobulbar blood flow characteristics of glaucoma suspects with glaucomatous optic disc appearance (GODA) in comparison to healthy control group (CG) and primary open angle glaucoma patients (POAG) and assess the effect of age.

Methods

145 patients from a single glaucoma clinic were enrolled and classified into two diagnostic groups (GODA and POAG). Third group of subjects consisted of 67 age matched individuals (CG). Retrobulbar blood velocity measurement in central retinal artery was performed using color Doppler imaging (CDI). CDI images were processed in custom software leading a range of parameter estimates from a continuous waveform signal. The effect of age on the estimated parameters was evaluated with the stepwise forward regression and ANCOVA in which age was used as a continuous factor. One-way ANOVA was used to test for the differences in the CDI parameters between the three considered groups. Correlation between restive index (RI) and pulsatility index (PI) was assessed with a bilinear fitting guaranteeing no discontinuities in RI intercept estimate. Fisher test was used to assess the applicability of a bilinear PI/RI relationship, while the statistics of the RI intercept estimate were evaluated using the bootstrap.

Results

ANCOVA showed significant interaction between age and group (p<0.05) for five out of nine considered CDI parameters. The RI intercept for CG and GODA groups was 0.602±0.047, and 0.574±0.044 respectively, while the RI intercept of 0.934±0.066 was found for the POAG.

Conclusions

The observed similarity of CG and GODA group and dissimilarity between GODA and POAG groups in terms of PI/RI relationship is remarkable. Age may play some role in the different mechanisms occurring in blood velocity dynamics in GODA and POAG subjects but it is not a strongly determining factor.

Glaucomatous and age-related changes in corneal pulsation shape. The ocular dicrotism

PURPOSE

To ascertain whether the incidence of ocular dicrotic pulse (ODP) increases with age, it is more pronounced in glaucomatous than in normal eyes and whether it is related to cardiovascular activity.

METHODS

261 subjects aged 47 to 78 years were included in the study and classified into four groups: primary open angle glaucoma (POAG), primary angle-closure glaucoma (PACG), glaucoma suspects with glaucomatous optic disc appearance (GODA) and the controls (CG). Additionally, in each group, subjects with ODP were divided into two age subgroups around the median age. A non-contact ultrasonic method was used to measure corneal indentation pulse (CIP) synchronically with the acquisition of electrocardiography (ECG) and blood pulse signals. ODP was assessed from the acquired signals that were numerically processed in a custom written program.

RESULTS

ODP incidence was about 78%, 66%, 66% and 84% for CG, GODA, POAG, and PACG group, respectively. With advancing age, the ODP incidence increased for all subjects (Δ = 12%), the highest being for the PACG and POAG groups (Δ = 30%). GODA group did not show an age-related increase in the incidence of ODP.

CONCLUSIONS

The ocular dicrotism, measured with non-contact ultrasonic method, was found to be a common phenomenon in elderly subjects. The increased ODP incidence in PACG and POAG group may correspond to either higher stiffness of glaucoma eyes, biochemical abnormalities in eye tissues, changes in ocular hemodynamics, may reflect the effect of medications or be a combination of all those factors. The results of GODA group suggest different mechanisms governing their ocular pulse that makes them less susceptible to generating ODP and having decreased predisposition to glaucoma.

Chronologic versus biologic aging of the human choroid

Several aspects of chronologic and biologic aging in the human choroid are reviewed from the literature. They often reveal methodological problems for age-dependent changes of the following parameters: choroidal thickness, choroidal pigmentation, choroidal vasculature and blood flow, and choroidal innervation. On reinterpreting some data of studies concerning Bruch's membrane, changes observed at different age points seem more likely to be nonlinear. Concluding from the data presented so far, chronologic aging should not be used as a factor for physiological changes in the human choroid. Longitudinal study designs are necessary to further establish the impact of age. Meanwhile, a more biologic oriented model of aging processes in the choroid should be established, including specified conditions (e.g., light exposure and refractory state). This would help to define more individual strategies for prevention and early stages of a certain defined disease.

Assessment of ocular hemodynamics after laser in situ keratomileusis using color Doppler imaging

To investigate ocular blood flow changes in healthy myopic patients following laser in situ keratomileusis (LASIK) using color Doppler imaging. Sixteen eyes of 16 myopic patients were studied. LASIK was performed and intraocular pressure was raised to levels ≥65 mmHg. Color Doppler images were obtained to study the ophthalmic and central retinal arteries preoperatively and postoperatively at 1 day, 1 week, and 1 month. There was no significant correlation between patient age and preoperative ocular blood flow parameters. A significant positive correlation between the degree of myopia and the peak systolic volume of the ophthalmic artery (r = 0.6, P = 0.01) was found. A highly significant decrease in the peak systolic volume and end-diastolic volume with an increase in the resistive index of both arteries (P < 0.005) was seen at 1 day and 1 week postoperatively. There was no significant difference between the preoperative and postoperative data 1 month after the procedure. The findings of this study show temporary alterations in ocular blood flow parameters after LASIK. LASIK is an increasingly common lifestyle procedure and further studies on larger groups are still recommended.

HTRA1 in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of severe visual impairment and irreversible blindness in most developed countries, affecting more than 50 million of elderly people worldwide. Current treatments, such as intravitreal injection of antiangiogenic agents, mitigate the effect of advanced AMD but cannot completely cure the disease. Comprehensive understanding of the AMD pathological mechanisms is important for the development of new therapies. Previously, we identified a single-nucleotide polymorphism (rs11200638) in the promoter region of the high temperature requirement factor A1 (HTRA1) gene on chromosome 10q26 to be associated with exudative AMD. In further biological studies, we have provided evidence that HTRA1 could be a potential disease-causing gene within the 10q26 locus. In this review, we summarize the pathology of AMD and the molecular function of the HtrA1 protein. Also evaluated are the genetic effects of HTRA1 polymorphism on AMD in different populations and interactions with other AMD-associated genes, especially with the complement factor H (CFH) gene, which was identified for nonexudative AMD. The biological roles of HtrA1 are exhaustively examined on its contribution to the multifactorial pathogenic mechanism of AMD. Although HtrA1 should play a part in AMD pathogenesis, a host of other genetic and environmental factors, known and unknown, is involved and warrants intensive future research.

In vivo measurement of regional variation in anterior scleral resistance to Schiotz indentation

PURPOSE

Recent studies indicate that ocular and scleral rigidity is pertinent to our understanding of glaucoma, age related macular degeneration and the development and pathogenesis of myopia. The principal method of measuring ocular rigidity is by extrapolation of data from corneal indentation tonometry (K(o) ) using Friedenwald's transformation algorithms. Using scleral indentation (Schiotz tonometry) we assess whether regional variations in resistance to indentation occur in vivo across the human anterior globe directly, with reference to the deflection of Schiotz scale readings.

METHODS

Data were collected from both eyes of 26 normal young adult subjects with a range of refractive error (mean spherical equivalent ± S.D. of -1.77 D ± 3.28 D, range -10.56 to +4.38 D). Schiotz tonometry (5.5 g & 7.5 g) was performed on the cornea and four scleral quadrants; supero-temporal (ST) and -nasal (SN), infero-temporal (IT) and -nasal (IN) approximately 8 mm posterior to the limbus.

RESULTS

Values of K(o) (mm(3) )(-1) were consistent with those previously reported (mean 0.0101 ± 0.0082, range 0.0019-0.0304). In regards to the sclera, significant differences (p < 0.001) were found across quadrants with indentation readings for both loads between means for the cornea and ST; ST and SN; ST and IT, ST and IN. Mean (±S.D.) scale readings for 5.5 g were: cornea 5.93 ± 1.14, ST 8.05 ± 1.58, IT 7.03 ± 1.86, SN 6.25 ± 1.10, IN 6.02 ± 1.49; and 7.5 g: cornea 9.26 ± 1.27, ST 11.56 ± 1.65, IT 10.31 ± 1.74, SN 9.91 ± 1.20, IN 9.50 ± 1.56.

CONCLUSIONS

Significant regional variation was found in the resistance of the anterior sclera to indentation produced by the Schiotz tonometer.

Correlation among choroidal, parapapillary, and retrobulbar vascular parameters in glaucoma

PURPOSE

To study and compare the correlation among choroidal, parapapillary, and retrobulbar vascular parameters in healthy subjects, glaucoma suspects, and open-angle glaucoma (OAG) patients.

DESIGN

Prospective observational clinical study.

METHODS

The study included one randomly selected eye from 21 normal subjects, 30 glaucoma suspects based on optic disc appearance, and 22 OAG patients. The pulsatile ocular blood flow (POBF), a measure of choroidal blood flow, was assessed using ocular blood flow analyzer whereas parapapillary blood flow and blood velocity of retrobulbar blood vessels were measured using scanning laser Doppler flowmetry and color Doppler imaging, respectively. All vascular parameters along with blood pressure and intraocular pressure measurements were obtained within a 2-hour period. Univariate regression analyses were used to evaluate the correlation of POBF values with parapapillary blood flow values, retrobulbar blood flow velocities, and resistive index, which represents vascular resistance, in each group. Two multiple linear regression models were created based on results of univariate analyses and included POBF, mean parapapillary blood flow, age, and mean ocular perfusion pressure; and POBF, temporal short posterior ciliary artery resistive index, age, and mean ocular perfusion pressure.

RESULTS

POBF was significantly associated with parapapillary blood flow (r2 = 0.54; P < .001, positive correlation) and temporal short posterior ciliary artery resistive index (r2 = 0.39; P < .001, negative correlation) in normal subjects. Results were consistent when corrected for age, intraocular pressure, and blood pressure parameters. POBF values did not correlate with parapapillary blood flow values or temporal short posterior ciliary artery resistive index in glaucoma suspects or OAG patients.

CONCLUSION

The relationships of POBF with parapapillary blood flow and calculated retrobulbar vascular resistance differs among normal subjects, glaucoma suspects, and OAG patients. This provides further evidence of vascular dysregulation in OAG.

Age-related macular degeneration and the aging eye

Age-related macular degeneration (AMD) is an ocular disease that causes damage to the retinal macula, mostly in the elderly. Normal aging processes can lead to structural and blood flow changes that can predispose patients to AMD, although advanced age does not inevitably cause AMD. In this review, we describe changes that occur in the macular structure, such as the retinal pigment epithelium and Bruch's membrane, with advancing age and in AMD. The role of genetics in AMD and age-related changes in ocular blood flow that may play a role in the pathogenesis of AMD are also discussed. Understanding the pathophysiology of AMD development can help guide future research to further comprehend this disease and to develop better treatments to prevent its irreversible central vision loss in the elderly.

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.

Color Doppler orbital hemodynamics in healthy individuals and patients with vascular disorders in Taiwan

The main purpose of this study was to establish a data bank of orbital vasculature hemodynamics as assessed by color Doppler imaging (CDI) for normal Taiwanese. In addition, we compared the hemodynamic variables in subjects with a healthy orbital vasculature and 10 patients with various orbital disorders. From 1994 to 1995, we collected data from 90 age-and gender-matched (43 males, 47 females) healthy individuals, with age stratified by decades (ranging from 4 to 79 years). Ten patients with various orbital lesions were also examined by CDI. Peak systolic velocity (PSV), end diastolic velocity (EDV), mean velocity (MV), pulsatility index (PI), and resistivity index (RI) were obtained for the ophthalmic, central retinal, and posterior ciliary arteries. The MV was also measured in the ophthalmic, central retinal, and vortex veins. The mean and standard deviation of the values were calculated for each decade of age. There was no correlation between the CDI-generated values and gender. Student's t-test showed that the flow velocity in the group below age 10, compared with that of the other groups, is significantly higher (p < 0.05). The CDI values in diseased orbits could be classified as hyper-, iso-, or hypovascular in comparison with healthy orbits. On linear regression, there was a correlation between age and the PSV, EDV, and MV of healthy ophthalmic arteries.

Pulsatile ocular blood flow: relationship with flow velocities in vessels supplying the retina and choroid

BACKGROUND

Although ocular tonography measures a pulsatile component of the ocular perfusion, the retinal and/or choroidal components of this pulsatile flow remain undefined.

AIM

To compare ocular tonography with the assessment of flow velocities in arteries supplying the retina, choroid and entire orbit.

METHODS

22 normal eyes from 11 subjects were studied. Pulsatile ocular blood flow (POBF) was measured using the ocular blood flow tonograph, and flow velocities in the ophthalmic, central retinal (CRA) and temporal short posterior ciliary arteries (TSPCA) using colour Doppler imaging. The correlation between POBF and retrobulbar flow velocities was determined.

RESULTS

POBF correlated significantly with peak systolic velocity (PSV) of the CRA (r = 0.56, p = 0.007) and the TSPCA (r = 0.48, p = 0.02), and with the resistive index of the TSPCA (r = 0.45, p = 0.04). Additionally, pulse amplitude (PSV-end diastolic velocity) in the CRA and the TSPCA correlated significantly with POBF measurements (each p<0.05). However, POBF did not correlate with any flow velocity indices in the ophthalmic artery.

CONCLUSION

POBF is associated with systolic and pulsatile components of blood flow velocities in both the CRA and the TSPCA. This result suggests that POBF determinations are influenced by the pulsatile components of both choroidal and retinal perfusion.

Technical note: How many readings are required for an acceptable accuracy in pulsatile ocular blood flow assessment?

PURPOSE

Pulsatile ocular blood flow (POBF) assessment aids the diagnosis of ocular diseases with defective ocular haemodynamics, such as glaucoma. Although each successful POBF measure given by the instrument represents five 'repeatable' pulses, there has been no study verifying how repeatable they are. There is also no report on the minimal number of measurements for an acceptable accuracy.

METHODS

Forty-three healthy young subjects were recruited and each subject had five consecutive POBF measurements obtained from one randomly selected eye. The coefficient of variation was calculated from the raw data of the five 'repeatable' pulses. The average from five consecutive measurements was considered as the standard for comparison with the first, average of the first two, the first three and the first four measurements. The 95% limits of agreement were determined using the Bland and Altman approach.

RESULTS

The coefficient of variation was greater than the manufacturer's claim of within 10%. The mean (+/-S.D.) POBF calculated from five consecutive measures was 732.5 +/- 243.2 microL min(-1). The mean (+/-S.D.) difference between the standard POBF and the first, average of the first two, the first three and the first four measurements was (in microL min(-1)): 12.5 +/- 59.8, 7.8 +/- 42.1, 9.6 +/- 32.5 and 3.7 +/- 19.6 respectively. The corresponding 95% limits of agreement were (in microL min(-1)): +/-117.2, +/-82.6, +/-63.8 and +/-38.4 respectively.

CONCLUSIONS

As the five 'repeatable' pulses were not as repeatable as the manufacturer claims, practitioners should not rely on one single POBF measure. An average of three consecutive measurements will be adequate to detect the minimum reported difference in POBF between glaucoma and normal patients.

Retrobulbar blood flow in patients with cataract

OBJECTIVE

To investigate retrobulbar haemodynamics in patients with cataract.

SUBJECTS AND METHODS

Colour Doppler imaging of the ophthalmic artery was carried out on the eye scheduled for surgery in 30 patients with cataract and in one randomly selected eye of 100 healthy controls. The peak systolic velocity, mean velocity, end diastolic velocity and resistivity index in the ophthalmic artery were computed and adjusted for the influence of age and mean arterial pressure. Cataract type was recorded and lens opacity was measured with an opacity lensmeter. Odds ratio (OR) for cataract was analysed in a logistic regression model, depending on the adjusted blood-flow parameters, age and smoking status.

RESULTS

The mean (SD) age was 45.5 (17.7) and 67.6 (5.8) years in controls and patients with cataract, respectively (p<0.001). The female to male ratio was 54:46 and 13:17, respectively (p = 0.41). Significant predictors of cataract in a forward stepwise logistic regression analysis were age (OR = 1.194; 95% confidence interval (CI) = 1.103 to 1.292; p<0.001), smoking status (OR = 14.119; 95% CI = 2.753 to 72.398; p = 0.002) and mean blood-flow velocity in the ophthalmic artery (OR = 0.731; 95% CI = 0.607 to 0.881; p = 0.001). Adjusted mean velocity was significantly lower in patients with cataract, even when only age-matched (age >55 years) non-smokers (31 controls, 19 patients with cataract) were considered (p = 0.003). Lens opacity and the type of cataract had no influence on the present findings.

CONCLUSION

High mean velocity in the ophthalmic artery may be associated with a reduced risk of cataract.

Pulsatile ocular blood flow in patients with asymmetric internal carotid artery stenosis

BACKGROUND

The pulsatile ocular blood flow (POBF) of patients with asymmetric internal carotid artery (ICA) stenosis was measured bilaterally. The purpose of this study was to investigate the sensitivity of POBF assessments in screening for ICA stenosis.

METHODS

Seventeen subjects with asymmetric ICA stenosis confirmed with carotid duplex ultrasound were recruited. The diagnoses of ICA stenosis were categorised into less than 50 per cent, 50 to 69 per cent and 70 per cent or greater. Their POBF and ocular dimensions were measured after local anaesthesia. Twenty-three normal healthy subjects were recruited as the control. All of the subjects had an inter-ocular axial length difference of less than one millimetre.

RESULTS

There were 14 males and three females in the patient group with a median age of 74 years. Fourteen patients had reduced POBF to the eye ipsilateral on the side with greater ICA stenosis. The reduction in POBF ranged from 3.1 to 49.2 per cent. Two patients had reduced POBF contralateral to the side with greater ICA stenosis. One patient had similar POBF between the eyes. The control group included six males and 17 females with a median age of 65 years. The difference in their POBF between the eyes ranged from 0.3 to 13.0 per cent.

CONCLUSIONS

Stenosis of the internal carotid artery was found to reduce the POBF ipsilateral to the side with greater stenosis. The overlap in the difference in inter-ocular POBF between the patient and control groups led to a low sensitivity (calculated as 41.2 per cent) for screening ICA stenosis from an assessment of POBF. Therefore, POBF assessment is not a good diagnostic tool for screening for ICA stenosis.

Effects of changes in self-reported vision on cognitive, affective, and functional status and living arrangements among the elderly

PURPOSE

To study effects of changes in self-reported vision on functional status, cognition, depressive symptoms, and living arrangements.

DESIGN

Longitudinal analysis of household survey data.

METHODS

A total of 6234 sample persons observed in the study of Assets and Health Dynamics Among the Oldest Old (AHEAD) 1995 were followed in 1998, 2000, and 2002 or until death or sample attrition. Effects of changes in self-reported vision and other factors were assessed by means of ordinary least-squares and logistic regression with panel data methods. Main outcome measures were limitations of instrumental activities of daily living (IADLs), activities of daily living (ADLs), and other, cognition, depressive symptoms, and living arrangements.

RESULTS

A decline from excellent/good vision to fair/poor near and distance vision had statistically significant effects on several IADL limitations, and some ADL and other limitations. Largest effects were for driving (OR for no limitation: 0.55, P = .003), managing money (OR: 0.61, P < .001), and preparing hot meals (OR: 0.61, P < .001). Onset of fair-poor near vision increased the likelihood of onset of at least one IADL (OR for no limitation: 0.71, P < .01) and ADL (OR: 0.74, P = .003) limitation. Onset of legal blindness resulted in a 78% increase in the likelihood of an IADL limitation (OR for no limitation: 0.22, P < .001). Effects of vision declines on cognition and depressive symptoms were statistically significant but small. Decline in vision increased the probability of nursing home residence.

CONCLUSIONS

Visual impairment has major impacts on functional status. Preventing vision loss is likely to appreciably improve the functioning of elderly persons.

Duplex sonography of retro-orbital and carotid arteries in patients with normal-tension glaucoma

PURPOSE

To evaluate retrobulbar and carotid arterial hemodynamics in patients with normal-tension glaucoma using Doppler sonography.

MATERIALS AND METHODS

Duplex sonography was performed in 41 patients with normal-tension glaucoma and 30 control subjects to evaluate resistance indices (RIs) in retro-orbital and carotid arteries. Mean values were compared using the independent t-test. The ratios of the RI in retro-orbital to RIs in the carotid arteries (CCA and ICA) and interocular and intercarotid differences in RI (DeltaRI) were also calculated.

RESULTS

Is in the central retinal (CRA) and temporal and nasal posterior ciliary arteries (TPCA and NPCA) were statistically significantly greater in glaucomatous eyes (p < 0.001). Plaque formation in carotid arteries without significant stenosis was noted in 12% of patients and 10% of control subjects. Ratios of RI of CRA or TPCA or NPCA to that of CCA and the ratios of RI of CRA or NPCA to that of ophthalmic arteries (OA) were significantly greater in glaucomatous eyes. We also found that ratios of the RI of CRA or TPCA or NPCA to that of ICA and the ratio of the RI of OA to CCA were nearly equal to 1 in both patients and control subjects. We found no significant difference between interocular and intercarotid DeltaRIs in patients and control subjects.

CONCLUSIONS

In patients with symmetric normal-tension glaucoma, duplex sonography showed an elevated RI in CRA and PCA. The Doppler evaluation of carotid arteries was useful.

Effect of breath-holding on pulsatile ocular blood flow measurement in normal subjects

BACKGROUND

The Valsalva maneuver is known to affect intraocular pressure (IOP). Simple breath-holding may cause IOP elevation. A recent study demonstrated a decrease in pulsatile ocular blood flow (POBF) during forcible exhalation. This study investigated whether breath-holding could affect POBF measurement.

METHODS

Thirty-eight healthy young adults were recruited. Their POBF's were measured with an ocular blood flow pneumatonometer. The first set of measurements was made using normal measurement protocol. Three consecutive readings were obtained, and the mean was used for analysis. The second set of measurements was taken after 5-min rest, and the subjects were required to hold their breath during the acquisition period.

RESULTS

As previously reported, POBF reduced with increasing myopia. There was no significant change in IOP, pulse rate, POBF, and pulse amplitude between normal protocol and breath-holding condition. POBF and pulse amplitude demonstrated a greater variation, shown by coefficient of variation, when subjects held their breath.

CONCLUSIONS

This study found a greater variation in consecutive POBF measurements during breath-holding condition. There was no significant difference in either POBF or pulse amplitude during breath-holding session, probably because of the use of three consecutive measurements, and averaged results were generated from them. It is advised to measure the POBF by taking consecutive readings, and subjects should not hold their breath.

Chromatic-Spatial Vision of the Aging Eye

The human visual system undergoes continuous anatomical, physiological and functional changes throughout the life span. There is also continuous change in the spectral distribution and intensity of light reaching the retina from infancy through senescence, primarily due to changes in the absorption of short-wave light by the lens. Despite these changes in the retinal stimulus and the signals leaving the retina for perceptual analysis, color appearance is relatively stable during aging as measured by broadband reflective or self-luminous samples, the wavelengths of unique blue and yellow, and the achromatic locus. Measures of ocular media density for younger and older observers show, indeed, that color appearance is independent of ocular media density. This may be explained by a renormalization process that was demonstrated by measuring the chromaticity of the achromatic point before and after cataract surgery. There was a shift following cataract surgery (removal of a brunescent lens) that was initially toward yellow in color space, but over the course of months, drifted back in the direction of the achromatic point before surgery. The spatial characteristics of color mechanisms were quantified for younger and older observers in terms of chromatic perceptive fields and the chromatic contrast sensitivity functions. Younger and older observers differed with small spots or with chromatic spatial gratings near threshold, but there were no significant differences with larger spots or suprathreshold spatial gratings.

Senescence of human multifocal electroretinogram components: a localized approach

BACKGROUND

Previous studies have shown significant age-related changes in the first-order kernel of multifocal ERG (mfERG) responses. All of these reports were based upon ring averages across the retinal field. This study was carried out to determine age-related changes in the localized response and localized variability in the mfERG parameters: N1P1 amplitude, scalar product and implicit time of P1.

METHODS

MfERG recordings from 70 normal phakic subjects (ages 9-80 years) were analyzed with VERIS 4.8. Scalar product values (for each hexagon based on ring average templates) were obtained and analyzed for age-related changes. Statistical measures such as coefficient of variation (CV) and parameters of a linear regression model were applied. Point-by-point comparisons were made across hemifields.

RESULTS

Each localized response showed a significant aging effect either in scalar product or in N1P1 amplitude. The average decline of the response was approximately 5% per decade, varying from 3.3% (peripherally) to 7.5% (perifoveally). The decline was significantly higher for the superior than for the inferior retina for amplitude parameters, corresponding to larger increases in P1 implicit time. The relative rate of change with age was similar for the nasal and the temporal retina. The average CV for all subjects at all locations was 29.4% (+/-4.1%).

CONCLUSIONS

The localized approach revealed patterns of age-related change that were not apparent in the ring averages. Information about changes in discrete retinal areas with age should make the mfERG more useful in quantitatively monitoring progression of retinal disease.

The effect of axial length on ocular blood flow assessment in anisometropes

BACKGROUND

Pulsatile ocular blood flow (POBF) assessment measures the choroidal circulation and therefore provides data with diagnostic value in certain ocular diseases, such as glaucoma. The technique assumes a constant pressure-volume relationship. The current study investigated the effect of axial length on POBF from subjects with axial anisometropia. Ocular blood supply in the ophthalmic artery was also determined using colour Doppler ultrasonography.

METHODS

Thirty-one normal, anisometropic subjects were recruited, whose ages ranged from 20 to 34 years. They had axial anisometropia (expressed by spherical equivalent) of at least 2 D. After Goldmann tonometry, the POBF of each eye was measured in a supine posture by one examiner, followed by a measurement of the blood flow velocity in the ophthalmic artery using colour Doppler ultrasonography in the same posture by another examiner. There was a 10 min rest between the two techniques. All the measurements were made at around the same time to eliminate any effect from diurnal variation.

RESULTS

The mean anisometropia (expressed by spherical equivalent) was 3.89 +/- 1.96 D and the mean inter-ocular axial length difference was 1.49 +/- 1.00 mm. The anisometropia and axial length were significantly different between the two eyes (paired t-tests: p < 0.001). However, the intra-ocular pressure was similar between the two eyes (paired t-test: p = 0.41). The POBF was significantly lower in the eye with the longer axial length (459.3 microL min-1) than the fellow eye (590.8 microL min-1), paired t-test: p < 0.001. The pulse amplitude was also significantly lower in the eye with the longer axial length (1.61 mmHg) than the fellow eye (1.89 mmHg), paired t-test: p < 0.001. However, the blood flow velocity from colour Doppler ultrasonography did not demonstrate any significant difference between the two eyes (paired t-test: p > 0.05).

CONCLUSIONS

The POBF and pulse amplitude were found to be reduced in the eye with the longer axial length but colour Doppler ultrasonography did not show any significant difference. This suggests that a new pressure-volume relation should be considered in deriving POBF. Practitioners should measure the axial length in POBF assessment.