Scanning laser polarimetry, retinal nerve fiber layer photography, and perimetry in the diagnosis of glaucomatous nerve fiber defects

A Narrative Review of the Association between Obstructive Sleep Apnea and Glaucoma in Adults

BACKGROUND

Obstructive sleep apnea (OSA) is a sleep disorder, primarily of the upper airway, which not only has a significant impact on quality of life but is also associated with various systemic diseases. Several ophthalmological diseases are also associated with OSA, especially glaucoma. The purpose of this review is to take a closer look at the causality and mutual influence.

METHODS

A systematic literature search was conducted using PubMed. A total of 19 studies with 316,178 adult participants were included.

RESULTS

Eleven of the sixteen studies concentrating on the prevalence of glaucoma in patients with OSA showed an association of both entities. One paper found a higher risk for progression of glaucoma in OSA patients. Five of the sixteen included studies failed to show a correlation between OSA and glaucoma. One study out of three surveying specific ophthalmological parameters showed an influence of OSA therapy on retinal nerve fiber layer (RNFL) thinning and vision. One study showed a rise in intraocular pressure (IOP), while two other studies showed no increase under continuous positive airway pressure (CPAP).

CONCLUSIONS

Our findings suggest an association between OSA and glaucoma and, especially, between OSA and thinning of RNFL. CPAP therapy appears to be also suitable for patients with comorbid glaucoma.

Retinal nerve fiber layer thickness changes in obstructive sleep apnea syndrome: one year follow-up results

AIM

To investigate the retinal nerve fiber layer (RNFL) thickness changes in patients with obstructive sleep apnea syndrome (OSAS) for one year follow-up. To discuss the possibility of detecting tendency of glaucoma in this population by using spectral domain optical coherence tomography (3D-OCT-2000 Spectral domain).

METHODS

After polysomnographic study, all subjects (64 OSAS patients and 40 controls) underwent detailed ophthalmological examination. After these examinations, patients with glaucoma and patients who had ophthalmological and/or systemic disease were excluded from the study. Totally, 20 patients in OSAS group and five patients in controls were excluded from the study in the first examination and follow-up period. The RNFL thickness was assessed with OCT. Forty-four OSAS patients and 35 control subjects were followed up 12mo. RNFL thickness change and OSAS patients were evaluated for severity of disease by Apnea-Hypopnea Index (AHI).

RESULTS

Forty-four OSAS patients and 35 controls were enrolled in the study. Statistically significance was found between OSAS patients and controls at the 12(th) mo. Average RNFL thickness was found to be significantly lower in last measurements in OSAS patients when compared with first measurements and control subjects (P<0.001, 0.002, respectively). There was a statistically significant correlation among AHI, and RNFL thickness (P<0.05).

CONCLUSION

The results suggest that the patients with OSAS were related with a proportional decrease in the RNFL thickness. These patients should be followed up regularly for glaucomatous changes. Detecting more RNFL thinning in severe OSAS was important.

Scanning laser topography and scanning laser polarimetry: comparing both imaging methods at same distances from the optic nerve head

Purpose:

To compare the performance of scanning laser topography (SLT) and scanning laser polarimetry (SLP) on the rim of the optic nerve head and its surrounding area and thereby to evaluate whether these imaging technologies are influenced by other factors beyond the thickness of the retinal nerve fiber layer (RNFL).

Materials and Methodology:

A total of 154 eyes from 5 different groups were examined: young healthy subjects (YNorm), old healthy subjects (ONorm), patients with normal tension glaucoma (NTG), patients with open-angle glaucoma and early glaucomatous damage (OAGE) and patients with open-angle glaucoma and advanced glaucomatous damage (OAGA). SLT and SLP measurements were taken. Four concentric circles were superimposed on each of the images: the first one measuring at the rim of the optic nerve head (1.0 ONHD), the next measuring at 1.25 optic nerve head diameters (ONHD), at 1.5 ONHD and at 1.75 ONHD. The aligned images were analyzed using GDx/NFA software.

Results:

Both methods showed peaks of RNFL thickness in the superior and inferior segments of the ONH. The maximum thickness, registered by the SLT device was at the ONH rim where the SLP device tended to measure the lowest values. SLT measurements at the ONH were influenced by other tissues besides the RNFL like blood vessels and glial tissues. SLT and SLP were most strongly correlated at distances of 1.25 and 1.5 ONHD.

Conclusions:

While both imaging technologies are valuable tools in detecting glaucoma, measurements at the ONH rim should be interpreted critically since both methods might provide misleading results. For the assessment of the retinal nerve fiber layer we would like to recommend for both imaging technologies, SLT and SLP, measurements in 1.25 and 1.5 ONHD distance of the rim of the optic nerve head.

Decreased retinal nerve fiber layer thickness in patients with obstructive sleep apnea/hypopnea syndrome

BACKGROUND

To compare parameters for retinal nerve fiber layer (RNFL) thickness, optic nerve head (ONH) measurements, and macular thickness in patients with different severities of obstructive sleep apnea/hypopnea syndrome (OSAHS) versus normal controls.

METHODS

Patients presenting with snoring and daytime sleepiness who underwent overnight polysomnography to determine OSAHS severity were recruited, and subsequently referred for ophthalmologic evaluation. Optical coherence tomography was used to evaluate the retinal nerve fiber layer (RNFL), optic nerve head topography, and macular thickness for early detection of glaucoma. Patients determined not to have OSAHS were included as controls.

RESULTS

A total of 127 subjects were recruited, including 105 patients with OSAHS and 22 normal control subjects. RNFL thickness was significantly lower for the severe OSAHS group than for the control and mild OSAHS groups in the average (p < 0.0001) and in the superior quadrant (p = 0.0007). When subjects without OSAHS or with mild disease (AHI < 15) were grouped together and compared with patients with moderate/severe OSAHS (AHI ≧ 15), RNFL thickness measurements for the latter group were significantly lower in the average (p < 0.0001), and in the superior (p = 0.001), inferior (p = 0.029), and temporal (p = 0.007) quadrants. Positive correlations were identified between lowest oxygenation saturation on PSG and RNFL thickness in the average (r = 0.260), superior (r = 0.200) and nasal (r = 0.156) quadrants.

CONCLUSIONS

Compared to patients without OSAHS or those with mild disease, RNFL thickness was lower in patients with moderate/severe OSAHS. Lowest saturation of oxygen in the moderate/severe OSAHS group correlated with decreased RNFL thickness. Patients with moderate and severe OSAHS are at increased risk for glaucoma.

Snapshot polarimeter fundus camera

A snapshot imaging polarimeter utilizing Savart plates is integrated into a fundus camera for retinal imaging. Acquired retinal images can be processed to reconstruct Stokes vector images, giving insight into the polarization properties of the retina. Results for images from a normal healthy retina and retinas with pathology are examined and compared.

Association between localized visual field losses and thickness deviation of the nerve fiber layer in glaucoma

PURPOSE

To perform a correlation between morphology and function by studying local perimetric field losses and thickness reduction of the nerve layer in corresponding areas.

METHOD

Forty-seven patients with "preperimetric" open-angle glaucoma, 95 patients with "perimetric" open-angle glaucoma, and 75 control subjects had perimetric (Octopus) and polarimetric measurements. Criteria for exclusion: optic discs larger than 4 mm, media opacities, polarimetric hourglass pattern in the macular image. Thickness values of the retinal nerve fiber layer were determined in 14 upper and 14 lower sectors (10 degrees each) as well as nasally and temporally (40 degrees each) as provided from the GDx (software version 4000). The healthy control subjects served to determine age-corrected thickness deviation in all sectors. Analyses were calculated in eight nerve fiber bundle related areas. Due to non-linear relationships between perimetric defects and corresponding thickness deviation non-parametric tests were used.

RESULTS

Localized visual field defects in the present perimetric patients were highest in upper and lower visual field areas abutting the nasal meridian. Thickness loss of nerve fiber layer however was highest in more circumferential upper and lower nerve fiber bundles. Correlations between local mean defects and deviation of the retinal nerve fiber layer thickness from normals showed a clear association for corresponding areas. The correlation coefficients were significant (P < 0.01) for all arcuate superior and inferior visual field zones except horizontally and not for the area of the lower nasal step.

CONCLUSION

The present correspondence map indicates that focal perimetric defects can be identified best polarimetrically if they occur in the arcuate bundles of the visual field. A lack of correspondence was observed in the area of the papillo-macular bundle.

Influence of optic disc size on parameters of retinal nerve fiber analysis with laser scanning polarimetry

PURPOSE

The aim of the study was to evaluate the influence of optic disc size on the variables of laser scanning polarimetry (GDx).

PATIENTS AND METHODS

One hundred and nineteen healthy controls and 161 patients with ocular hypertension (OHT) received detailed ophthalmologic investigation with respect to glaucoma including retinal nerve fiber analysis with GDx (Version 3.0.05x1; Laser Diagnostic Technologies Europe). Optic disc size was measured with planimetry using 15 degrees optic disc photographs. With respect to frequency of optic disc size in the normal population patients were divided in quartiles of equal sample size.

RESULTS

The ratio between retinal nerve fiber layer thickness in the superior and inferior areas in relation to the nasal and temporal regions decreases significantly with increasing optic disc size and the difference between the highest and lowest retinal nerve fiber layer thickness decreases significantly with increasing optic disc size. The results of multivariate neural network analysis increased with larger optic disc size in controls as well as in patients with OHT. Linear regression analysis showed an increase of 9 units (the Number) per 1 mm(2) of optic disc size. A Number above 30, which indicates suspected glaucoma, was detected in more than a third of the normal population investigated if the optic disc area was larger than 3.5 mm(2). Overall, patients with OHT had a higher Number than controls (20.5+/-11.5 vs. 18.1+/-10.4; p>0.05), but the difference between the two groups did not reach a significant level.

CONCLUSIONS

Retinal nerve fiber analysis in patients with an optic disc size larger than 3.5 mm(2) should be interpreted carefully; the Number in particular requires corrections for optic disc size.

Retinal nerve fibre layer measurements are reduced in patients with obstructive sleep apnoea syndrome

PURPOSE

To determine the retinal nerve fibre layer (RNFL) thickness in patients with obstructive sleep apnoea syndrome (OSAS) in order to investigate the possibility of detecting early signs of glaucoma in this population.

METHODS

A total of 66 consecutive patients admitted for polysomnographic evaluation of suspected OSAS. Patients underwent an overnight sleep study in an effort to diagnose and determine the severity of OSAS. Patients who had the disease were classified as having mild and severe OSAS, while patients who did not have the disease were classified as controls. All patients received physical, neurological, and ophthalmological evaluation including visual acuity, slit-lamp examination, Goldmann applanation tonometry, gonioscopy with a three mirror contact lens, and fundus examination. After these examinations, patients with glaucoma and patients who had ophthalmological and/or systemic disease known to affect RNFL thickness were excluded from the study. The RNFL thickness was assessed with a scanning laser polarimeter (Nerve Fiber Analyzer GDx, Laser Diagnostic Technologies Inc., San Diego, CA, USA).

RESULTS

A total of 34 patients with obstructive sleep apnoea (19 mild, 15 severe) and 20 age-matched controls were included in the study. The thickness of RNFL was reduced in patients with OSAS compared to controls. The decrease in RNFL was found to be correlated with the severity of sleep apnoea (r=0.78, P=0.01).

CONCLUSIONS

The sleep apnoea syndrome is correlated with a proportional decrease in the RNFL. Decreased ocular perfusion related to hypoxia and vasospasm associated with OSAS may cause RNFL thinning, which may precede clinically detectable glaucoma.

[Analysis of optic nerve head by confocal scanning laser ophthalmoscope in ocular hypertension]

PURPOSE

To analyze optic nerve head topography using confocal the scanning laser ophthalmoscope (CSLO) in ocular hypertension in comparison to normal eyes.

PATIENTS AND METHODS

We examined 25 patients with ocular hypertension and 27 normal controls. All of them had a complete ophthalmic examination. Optic nerve head analysis was performed by using a CSLO-type Heidelberg retina tomograph (HRT). The following stereometric parameters were evaluated: disc area, area and volume of cup, cup/disc ratio, area and volume of neuroretinal rim, mean and maximal cup depth, cup shape measure, height variation contour, mean retinal nerve fiber layer thickness, and retinal nerve fiber layer (RNFL) cross-section area.

RESULTS

In ocular hypertension eyes, rim volume, height variation contour and RNFL thickness showed a statistically significant reduction compared to normal eyes.

CONCLUSION

HRT appears to be an important tool in detecting early damage of retinal nerve fiber layer in ocular hypertension.

Scanning laser polarimetry in myopic and hyperopic subjects

PURPOSE

To investigate the effect of refraction error and axial length on retinal nerve fiber layer (RNFL) measurements as obtained by scanning laser polarimetry (SLP).

METHODS

Besides ophthalmological standard examination (refractive error, keratometry, visual acuity, slit-lamp examination, applanation tonometry, funduscopy), perimetry, axial length measurement by means of ultrasound, and SLP were performed. Seventy-five myopic eyes (between -0.75 D and -8.5 D), 24 hyperopic eyes (0.75 D-6.5 D) and 40 emmetropic eyes were investigated. SLP parameters were compared in the different groups.

RESULTS

The statistical analysis of the absolute thickness values of SLP revealed highly significant ( P< 0.01) reductions in average thickness, ellipse average, superior average, inferior average, and superior integral in both myopic and hyperopic eyes in comparison with the emmetropic control eyes. The amount of reduction was between 12.9% (inferior average; myopia) and 30.2% (superior integral; hyperopia). There were no significant differences between myopes and hyperopes. A significant linear correlation for many of the SLP parameters with the refractive error (spherical equivalent) but not with axial length was found in both the hyperopic and the myopic group.

CONCLUSIONS

Despite a wide interindividual range, SLP measurement values decrease with increasing myopia and hyperopia. In clinical practice, such reduced RNFL thickness values should be viewed with the necessary caution and additional polarimetric signs for glaucomatous damage should be taken into consideration.

Influence of cataract surgery with implantation of different intraocular lenses on scanning laser tomography and polarimetry

PURPOSE

To describe the influence of cataract surgery with implantation of different intraocular lenses on scanning laser tomography (SLT) and scanning laser polarimetry (SLP) and to measure the birefringent properties of intraocular lenses in a laboratory setting.

DESIGN

Prospective cohort study.

METHODS

The influence of phacoemulsification cataract surgery with intraocular lens implantation (56 polymethylmethacrylate [PMMA; 31 Pharmacia/Upjohn 811 B and 25 Domilens Flex 60]; 25 hydroxyethylmethacrylate/methylmethacrylate (HEMA/MMA) [Technomed, Memory Lens]; 32 silicone [Allergan Si40]; 25 acrylic [Storz Hydroview]) on SLP and SLT measurements was evaluated preoperatively and 3 to 4 weeks postoperatively in 138 eyes of otherwise healthy patients. Lens opacities were classified according to the Lens Opacities Classification System III (LOCS III). Imaging was performed with TopSS and GDx (Laser Diagnostic Technologies, San Diego, California, USA) for SLT and SLP, respectively. Additionally, birefringent properties of intraocular lenses were measured in a laboratory setting.

RESULTS

Our results show that imaging with SLT and SLP is possible with lens opacity-induced visual acuity reductions down to 0.2 and 0.16, respectively. There were no significant differences in the topographic parameters assessed before and after cataract surgery with SLT. However, standard deviations between three within-session single measurements were smaller postoperatively. Nerve fiber layer patterns were similar before and after cataract surgery with SLP, whereas certain total nerve fiber layer thickness values were significantly higher postoperatively. As a consequence, "the number" is significantly lower in the Domilens Flex 60 group (P =.01) and in the Storz Hydroview group (P =.02), and with a tendency also in the other groups as well. Measurements with a high-resolution optical bench revealed no birefringent properties of the implanted lenses.

CONCLUSIONS

Our results indicate that after cataract surgery with intraocular lens implantation some SLP values are altered significantly, whereas SLT parameters are not influenced. These findings are of clinical interest, especially in the follow-up of glaucoma patients.

Visualization of localized retinal nerve fiber layer defects with the GDx with individualized and with fixed compensation of anterior segment birefringence

PURPOSE

To compare the visualization of localized retinal nerve fiber layer (RNFL) defects in GDx images with fixed and with individualized compensation of anterior segment birefringence (FC and IC, respectively) with their visualization in red-free fundus photographs.

DESIGN

Observational case series.

PARTICIPANTS

Eight eyes of six glaucoma patients with localized, wedge-shaped RNFL defects in red-free fundus photographs with matching visual field defects.

METHODS

We imaged all eyes with a GDx equipped with a variable corneal compensator (VCC). The VCC replaced the standard fixed compensator and could be set to compensate for birefringence of up to 120 nm at any axis. Individual anterior segment birefringence was estimated from a macular retardation profile that resulted from the interaction between birefringence of the anterior segment and that of Henle's fiber layer. Measurements of RNFL retardation were made with the GDx with FC (60 nm of retardation with a slow axis of 15 degrees nasally downward) and with IC. Maps of retardation measurements with FC and IC were superimposed on red-free fundus photographs.

MAIN OUTCOME MEASURES

Visualization of localized RNFL defects.

RESULTS

Localized RNFL defects were visible in GDx retardation maps obtained with IC. The defects closely matched those observed in red-free fundus photographs. With FC, however, the GDx retardation images did not correlate well with red-free fundus photography.

CONCLUSIONS

An individualized anterior segment compensation in the GDx improves the visualization of localized glaucomatous loss.

Combined use of frequency doubling perimetry and polarimetric measurements of retinal nerve fiber layer in glaucoma detection

PURPOSE

The aim of this study was to evaluate the diagnostic usefulness of the combined use of frequency-doubling technology (FDT) perimetry and polarimetry of the retinal nerve fiber layer.

DESIGN

Cross-sectional study.

METHODS

Seventy ocular hypertensive patients (normal optic disk and standard perimetry, elevated intraocular pressure [>21 mm Hg]), 59 patients with "preperimetric" open-angle glaucoma (glaucomatous optic disk atrophy, elevated intraocular pressure [>21 mm Hg], no visual field defect in standard perimetry), 105 patients with "perimetric" open-angle glaucoma (glaucomatous optic disk atrophy and clearly marked visual field defect), and 73 control subjects had FDT screening (protocol: C-20-5) and polarimetric measurements (GDx). Criteria for exclusion: optic disks larger than 4 mm(2), media opacities, patients younger than 33 years or older than 66 years. None of the subjects had earlier FDT perimetry. One eye of each patient and control subject entered the statistical evaluation. Database and statistical software were used for case-wise recalculation of all missed localized probability levels to create a FDT screening score.

RESULTS

At a predefined specificity of 94.5% in control eyes, discrimination between "perimetric" glaucoma and normal subjects is superior using the FDT perimetry (sensitivity = 84.8%) in comparison to polarimetry (sensitivity = 63.8%), whereas sensitivity is similar with both methods in "preperimetric" patients (GDx, FDT: 25.4%). In several cases, patients classified as glaucomatous by the GDx are not the same patients as identified by the FDT perimetry. Therefore, a two-dimensional discrimination analysis can increase correct positive classification. Using a linear combination of the present FDT screening score and polarimetry ("the number"), 92.4% of "perimetric" glaucoma eyes and 44.1% of "preperimetric" glaucoma eyes have been classified as glaucomatous.

CONCLUSION

Joint usage of polarimetry and FDT perimetry indicate that a combination of different techniques which can uncover different glaucoma properties, might be helpful in early glaucoma detection.

Retinal nerve fiber layer analysis: relationship between optical coherence tomography and red-free photography

PURPOSE

Comparison of retinal nerve fiber layer (RNFL) thickness measurements using optical coherence tomography (OCT) to the clinical standard red-free photography (evaluated semiquantitatively), in relation to functional visual field damage in primary open-angle glaucoma (POAG) patients, ocular hypertensives, and POAG suspects.

METHODS

Concurrent, cross-sectional study. In four age-matched groups (42 patients with early to moderate POAG, 34 ocular hypertensives, 22 POAG suspects, and 25 normal controls), RNFL was assessed with OCT, standardized red-free photographic scoring method and standard achromatic perimetry.

RESULTS

OCT RNFL thickness decreases with increased RNFL damage (detected with red-free photography). The global average OCT RNFL thickness correlated significantly with the photographic total RNFL score (r = .650, P = .0001). Both OCT and photographic scoring system were able to find significantly thinner RNFL in the glaucoma group as compared with normals (P = .0001 for both), ocular hypertensives (P = .0001 for both), and suspects (P = .0001 for both). However, neither OCT nor photography could significantly differentiate between ocular hypertensives, suspects, and normals. Both OCT and photography were significantly correlated with VF loss. For the percentage of VF points depressed <5%, the correlation was highest for OCT (r = -0.615 for OCT and r = -0.476 for photography). OCT had a higher diagnostic accuracy than photography (86% and 77%, respectively).

CONCLUSION

For RNFL thickness measurements, the presence of high correlations between OCT, photographic scores, and functional visual field loss suggest the validity of OCT measurements. The higher diagnostic accuracy of OCT RNFL measurements suggests its potential advantage for detection of early cases of glaucoma.

Visual field defects and neural losses from experimental glaucoma

Glaucoma is a relatively common disease in which the death of retinal ganglion cells causes a progressive loss of sight, often leading to blindness. Typically, the degree of a patient's visual dysfunction is assessed by clinical perimetry, involving subjective measurements of light-sense thresholds across the visual field, but the relationship between visual and neural losses is inexact. Therefore, to better understand of the effects of glaucoma on the visual system, a series of investigations involving psychophysics, electrophysiology, anatomy, and histochemistry were conducted on experimental glaucoma in monkeys. The principal results of the studies showed that, (1) the depth of visual defects with standard clinical perimetry are predicted by a loss of probability summation among retinal detection mechanisms, (2) glaucomatous optic atrophy causes a non-selective reduction of metabolism of neurons in the afferent visual pathway, and (3) objective electrophysiological methods can be as sensitive as standard clinical perimetry in assessing the neural losses from glaucoma. These experimental findings from glaucoma in monkeys provide fundamental data that should be applicable to improving methods for assessing glaucomatous optic neuropathy in patients.