Stereoacuity in mild, moderate and severe glaucoma

Correlation between Central Visual Field Defects and Stereopsis in Patients with Early-to-Moderate Visual Field Loss

PURPOSE

To investigate the association between stereoacuity and the presence of central visual field defects (CVFDs) due to glaucoma.

DESIGN

A prospective, cross-sectional cohort study.

PARTICIPANTS

Participants with early-to-moderate glaucoma with a visual acuity better than 20/40, less than a 2-line difference in visual acuity between eyes, and 2 reliable Humphrey visual fields (VFs) (24-2 SITA standard) with mean deviation (MD) in the worse eye better than - 12 dB.

METHODS

Stereoacuity was measured using the Titmus stereo test. Participants with a significant field defect (P < 0.005) in any 1 of the central 4 points in the 24-2 SITA standard total deviation map in either eye were classified as having a CVFD. Vision-related quality of life (VR-QOL) was measured using 25-item National Eye Institute Visual Function Questionnaire scores. Logistic regression was used to determine the associations between the level of stereoacuity and age, sex, race, glaucoma type, presence of CVFDs, visual acuity, contrast sensitivity, and VF MD.

MAIN OUTCOME MEASURES

Stereoacuity in the CVFD and non-CVFD groups.

RESULTS

Sixty-five participants met the inclusion criteria. The mean age of the participants was 64.3 ± 8.0 years, and 64.6% were women. The median stereoacuity was 60 arc seconds (interquartile range [IQR], 40-120 arc seconds). Forty-two (65%) patients had CVFDs, and 23 (35%) patients did not. The median stereoacuity of the CVFD group was worse than that of the non-CVFD group (60 arc seconds [IQR, 50-140 arc seconds] vs. 40 arc seconds [IQR, 40-80 arc seconds], respectively; P = 0.001). The non-CVFD group had a higher percentage of participants with normal stereopsis than the non-CVFD group (61% vs. 21%, respectively; P = 0.001). A multivariable analysis found that the presence of CVFDs was associated with worse stereopsis levels (odds ratio, 4.49; P = 0.021). The CVFD group had a lower Visual Functioning Questionnaire-25 (VFQ-25) composite score (84.0 vs. 91.4; P = 0.004) and lower VFQ-25 subscale scores for general vision, near activities, and mental health (P < 0.05).

CONCLUSIONS

Central visual field defects were associated with increased odds of poor stereoacuity in patients with early-to-moderate glaucomatous VF loss. Specifically, patients without CVFDs are more likely to have normal stereopsis and higher VR-QOL than those with CVFDs. Patients with CVFDs should be counseled regarding how depth perception difficulties may affect daily living.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Approaching rehabilitation in patients with advanced glaucoma

Vision loss from advanced glaucoma is currently irreversible and impairs functional visual ability to effectively perform everyday tasks in a number of distinct functional domains. Vision rehabilitation strategies have been demonstrated to be effective in low vision populations and should be utilized in persons with advanced glaucoma to reduce disability and improve quality of life. Initial challenges to rehabilitation include an incomplete understanding of vision rehabilitation by the physician and patient, motivation to integrate rehabilitation into the plan of care, and availability of suitable providers to deliver this care. Physicians, working with well-trained vision rehabilitation providers can maximize function in important visual domains customized to the patient based on their needs, specific complaints, severity/pattern of visual damage, and comorbidities. Potential rehabilitative strategies to be considered for reading impairment include spectacle correction, visual assistive equipment, and sensory substitution, while potential strategies to facilitate driving in those deemed safe to do so include refractive correction, lens design, building confidence, restriction of driving to safer conditions, and avoiding situations where cognitive load is high. Mobility is frequently disrupted in advanced glaucoma, and can be addressed through careful distance refraction, behavior modification, home modification, mobility aids, walking assistance (i.e., sighted guide techniques), and smartphone/wearable technologies. Visual motor complaints are best addressed through optimization of lighting/contrast, sensory substitution, IADL training, and education. Special rehabilitative concerns may arise in children, where plans must be coordinated with schools, and working adults, where patients should be aware of their rights to accommodations to facilitate specific job tasks.

Binocular Summation of Visual Acuity at High and Low Contrast in Early Glaucoma

PRCIS

This study examined the integrity of binocular summation function in patients with mild glaucoma. We found that binocular summation of visual acuity is preserved in these patients, despite their reduced monocular inputs.

PURPOSE

Binocular summation represents superiority of binocular to monocular performance. In this study we examined the integrity of binocular summation function in patients with early glaucoma who had structural glaucomatous changes but otherwise had no significant interocular acuity asymmetry or other functional deficit detected with standard clinical measures.

MATERIALS AND METHODS

Participants included 48 patients with early glaucoma according to Hodapp, Anderson, and Parrish 2 (HAP2) criteria (age 65±12 y) and 42 healthy controls (age 60±12 y), matched for stereoacuity. Visual acuity was assessed binocularly and monocularly at high (95%) and low (25%) contrast using the Early Treatment Diabetic Retinopathy Study (ETDRS) charts at 6 m. Binocular acuity summation was evaluated utilizing a binocular ratio (BR).

RESULTS

Overall, binocular and monocular visual acuity of the control group was better than that of the glaucoma group for both contrast levels, P =0.001. For the glaucoma group, there was a significant difference between BRs at high and low contrast, 0.01±0.05 and 0.04±0.06 ( P =0.003), respectively. For the control group, the difference between BR at high and low contrast was not statistically significant, 0.00±0.07 and 0.02±0.06 ( P =0.25), respectively.

CONCLUSION

For patients with early glaucoma, binocular summation function for visual acuity was preserved at both contrast levels. This suggests an adaptation of the visual system in early stages of glaucoma that allows for normal binocular summation in the presence of reduced monocular visual input.

Evaluation of depth perception and association of severity in Glaucoma patients and suspects

BACKGROUND

To evaluate depth perception in Primary open angle glaucoma (POAG), glaucoma suspects compared to controls and to determine the association between depth perception and severity of glaucoma.

METHODS

This was a hospital based, comparative, cross-sectional study. The ethical clearance was taken from institutional review committee of Institute of Medicine [Reference no.399 (6-11) E² 077-078]. Agematched, equal number of participants in each group (N=20) were evaluated with both Titmus and Frisby stereoacuity tests to measure depth perception as stereopsis threshold in seconds of arc. The participants were selected using the purposive sampling technique.

RESULTS

There was no differences in age, sex, or best corrected visual acuity, intraocular pressure, central corneal thickness (CCT), found among the three groups (POAG, Glaucoma Suspects and Control) respectively. However, there was significant difference in cup disc ratio (CDR) between the groups. Equal number of male and female were there in each group, while in POAG group male to female ratio was 3:2. The mean stereoacuity threshold in control group was 53.5±23.23 seconds of arc with Titmus test and 38.75±18.83 seconds of arc with Frisby stereoacuity test. The difference in threshold was significant between control and glaucoma suspect with Titmus (t=1.991, p=0.05) and with Frisby (t=2.114, p=0.04). The difference was also significant in POAG group by Titmus (t=3.135, p=0.0033) and by Frisby (t=3.014, p=0.004). More so, with increasing severity of glaucoma, the mean threshold of stereopsis increased as seen with both Titmus and Frisby Tests (ANOVA, p < 0.001) CONCLUSION: Primary open angle glaucoma patients and glaucoma suspects, showed significant reduction in depth perception. Decreased stereoacuity was associated with greater glaucomatous visual field loss.

Topical Review: Assessment of Binocular Sensory Processes in Low Vision

SIGNIFICANCE

This article summarizes the evidence for a higher prevalence of binocular vision dysfunctions in individuals with vision impairment. Assessment for and identification of binocular vision dysfunctions can detect individuals experiencing difficulties in activities including reading, object placement tasks, and mobility.Comprehensive vision assessment in low vision populations is necessary to identify the extent of remaining vision and to enable directed rehabilitation efforts. In patients with vision impairment, little attention is typically paid to assessments of binocular vision, including ocular vergence, stereopsis, and binocular summation characteristics. In addition, binocular measurements of threshold automated visual fields are not routinely performed in clinical practice, leading to an incomplete understanding of individuals' binocular visual field and may affect rehabilitation outcomes.First, this review summarizes the prevalence of dysfunctions in ocular vergence, stereopsis, and binocular summation characteristics across a variety of ocular pathologies causing vision impairment. Second, this review examines the links between clinical measurements of binocular visual functions and outcome measures including quality of life and performance in functional tasks. There is an increased prevalence of dysfunctions in ocular alignment, stereopsis, and binocular summation across low vision cohorts compared with those with normal vision. The identification of binocular vision dysfunctions during routine low vision assessments is especially important in patients experiencing difficulties in activities of daily living, including but not limited to reading, object placement tasks, and mobility. However, further research is required to determine whether addressing the identified deficits in binocular vision in low vision rehabilitative efforts directly impacts patient outcomes.

Study of correlation between stereopsis and retinal nerve fiber layer thickness in cases of glaucoma

Background

Glaucoma is an important and common optic neuropathy characterized by progressive loss of retinal ganglion cells and associated morphological changes to the optic nerve and retinal nerve fiber layer (RNFL). The most common assessment of visual function in glaucoma uses perimetric measurements of visual sensitivity. Only few studies have evaluated the binocular function in patients with glaucoma. This study was taken up to establish the correlation of RNFL thickness, in glaucoma, with near and distance stereopsis.

Methods

This pilot, cross-sectional observational study included 100 diagnosed cases of glaucoma and 100 normal participants as controls, studied over a period of one year. The records of all the participants were checked, and only established cases of glaucoma after fulfilling the inclusion and exclusion criteria were included. Analysis of the RNFL using spectral-domain optical coherence tomography was carried out. All the participants were thereafter evaluated for stereoacuity by near (at 40 inches) and distance (at 3 meter) Randot stereoacuity charts.

Results

There was a negative correlation between the RNFL thickness and the absolute value of streoacuity (-0.303 for distance versus -0.101 for near in cases and -0.308 for distance and -0.416 for near in control group), decreasing the actual functional stereoacuity, therefore the cases with lower RNFL thickness had lower stereoacuity both for distance and near, however it was statistically significant only for distance (p=0.002).

Conclusion

Functional aspects, such as stereoacuity, may also be affected in the glaucoma because of decrease in RNFL thickness. Therefore, binocular status should also be evaluated in cases of glaucoma.

Intra- and inter-hemispheric processing during binocular rivalry in mild glaucoma

Glaucoma is considered a progressive optic neuropathy because of the damage and death of the retinal ganglion cells. It is also a neurodegenerative disease because it affects neural structures in the visual system and beyond, including the corpus callosum–the largest white matter structure involved in inter-hemispheric transfer of information. In this study we probed the dysfunction of the inter-hemispheric processing in patients with mild glaucoma using the phenomenon of binocular rivalry. Patients with mild glaucoma and no measurable visual field defects and age-matched controls underwent a thorough visual assessment. Then they participated in a series of psychophysical tests designed to examine the binocular rivalry derived from intra- and inter-hemispheric processing. Static horizontal and vertical sinewave gratings were presented dichoptically using a double-mirror stereoscope in 3 locations: centrally, to probe inter-hemispheric processing, and peripherally to the left or to the right, to probe intra-hemispheric processing. Although the two groups were matched in functional measures, rivalry rate of the glaucoma group was significantly lower than that of the control group for the central location, but not for the peripheral location. These results were driven mainly by the patients with normal tension glaucoma whose average rivalry rate for the central location (from which information reaches the two hemispheres) was almost half (46% lower) that of the controls. These results indicate a dysfunction in inter-hemispheric transfer in mild glaucoma that can be detected behaviourally before any changes in standard functional measures.

Near and Distance Stereoacuity in Patients With Primary Open-angle Glaucoma

PURPOSE

To compare near and distance stereoacuity between patients with primary open-angle glaucoma (POAG) and a control group, and to analyze the associations between stereoacuity and POAG severity.

METHODS

This cross-sectional study compared near and distance stereoacuity between the POAG and control groups. The data from the POAG group were used to assess the associations between stereoacuity (both near and distance) and the severity of visual field (VF) defects (based on Hodapp-Anderson-Parrish classification and the VF index).

RESULTS

The study included 94 eyes of 47 patients with POAG and 80 eyes of 40 control subjects. Near and distance stereoacuity were significantly lower in the POAG group than in the control group (both P<0.001). Near stereoacuity worsened with POAG severity in terms of both the Hodapp-Anderson-Parrish classification and VF index (P=0.007 and P=0.049, respectively). However, distance stereoacuity was not associated with POAG severity for either categorization (P=0.12 and P=0.57, respectively). The proportions of patients with reduced near stereoacuity and those with a lack of distance stereoacuity were higher in the POAG group than in the control group.

CONCLUSIONS

Near and distance stereoacuity were significantly lower among patients with POAG than among control subjects. Near stereoacuity worsened with increasing POAG severity but distance stereoacuity did not. However, the proportion of patients with a lack of distance stereoacuity was higher in the POAG group than in the control group.

The prevalence and diagnosis of 'stereoblindness' in adults less than 60 years of age: a best evidence synthesis

PURPOSE

Stereoscopic vision (or stereopsis) is the ability to perceive depth from binocular disparity - the difference of viewpoints between the two eyes. Interestingly, there are large individual differences as to how well one can appreciate depth from such a cue. The total absence of stereoscopic vision, called 'stereoblindness', has been associated with negative behavioural outcomes such as poor distance estimation. Surprisingly, the prevalence of stereoblindness remains unclear, as it appears highly dependent on the way in which stereopsis is measured.

RECENT FINDINGS

This review highlights the fact that stereopsis is not a unitary construct, but rather implies different systems. The optimal conditions for measuring these varieties of stereoscopic information processing are discussed given the goal of detecting stereoblindness, using either psychophysical or clinical stereotests. In that light, we then discuss the estimates of stereoblindness prevalence of past studies.

SUMMARY

We identify four different approaches that all converge toward a prevalence of stereoblindness of 7% (median approach: 7%; unambiguous-stereoblindness-criteria approach: 7%; visual-defect-included approach: 7%; multiple-criteria approach: 7%). We note that these estimates were derived considering adults of age <60 years old. Older adults may have a higher prevalence. Finally, we make recommendations for a new ecological definition of stereoblindness and for efficient clinical methods for determining stereoblindness by adapting existing tools.

Quantitative MRI evaluation of glaucomatous changes in the visual pathway

Background

The aims of this study were to investigate glaucomatous morphological changes quantitatively in the visual cortex of the brain with voxel-based morphometry (VBM), a normalizing MRI technique, and to clarify the relationship between glaucomatous damage and regional changes in the visual cortex of patients with open-angle glaucoma (OAG).

Methods

Thirty-one patients with OAG (age: 55.9 ± 10.7, male: female = 9: 22) and 20 age-matched controls (age: 54.9 ± 9.8, male: female = 10: 10) were included in this study. The cross-sectional area (CSA) of the optic nerve was manually measured with T2-weighed MRI. Images of the visual cortex were acquired with T1-weighed 3D magnetization-prepared rapid acquisition with gradient echo (MPRAGE) sequencing, and the normalized regional visual cortex volume, i.e., gray matter density (GMD), in Brodmann areas (BA) 17, 18, and 19, was calculated with a normalizing technique based on statistic parametric mapping 8 (SPM8) analysis. We compared the regional GMD of the visual cortex in the control subjects and OAG patients. Spearman’s rank correlation analysis was used to determine the relationship between optic nerve CSA and GMD in BA 17, 18, and 19.

Results

We found that the normal and OAG patients differed significantly in optic nerve CSA (p < 0.001) and visual cortex GMD in BA 17 (p = 0.030), BA 18 (p = 0.003), and BA 19 (p = 0.005). In addition, we found a significant correlation between optic nerve CSA and visual cortex GMD in BA 19 (r = 0.33, p = 0.023), but not in BA 17 (r = 0.17, p = 0.237) or BA 18 (r = 0.24, p = 0.099).

Conclusion

Quantitative MRI parametric evaluation of GMD can detect glaucoma-associated anatomical atrophy of the visual cortex in BA 17, 18, and 19. Furthermore, GMD in BA 19 was significantly correlated to the damage level of the optic nerve, as well as the retina, in patients with OAG. This is the first demonstration of an association between the cortex of the brain responsible for higher-order visual function and glaucoma severity. Evaluation of the visual cortex with MRI is thus a very promising potential method for objective examination in OAG.

Strabismus surgery outcomes in eyes with glaucoma drainage devices

PURPOSE

To report strabismus surgery outcomes in eyes with prior implantation of glaucoma drainage devices (GDD).

METHODS

The medical records of patients who underwent strabismus surgery for ocular misalignment that developed after implantation of a GDD over a 13-year period at a single institution were examined retrospectively. Patient characteristics, deviation types, preoperative measurements, surgical procedures, and postoperative measurements were analyzed.

RESULTS

Of the 16 patients included, 14 had exotropia (34^Δ ± 16^Δ) and 11 had vertical deviations (15^Δ ± 7^Δ), of which 9 had concurrent exotropia and vertical deviations. Preoperatively, 9 patients had diplopia. The surgical approach was tailored to address the deviation most noticeable to the patient-horizontal, vertical, or both if the vertical component could be addressed by horizontal muscle supra- or infraplacement. Three patients underwent simultaneous horizontal and vertical surgery. All patients underwent strabismus surgery on an eye with a GDD. Surgical motor success (defined as horizontal deviation ≤10^Δ, vertical ≤4^Δ) was achieved in 42% of horizontal and 57% of vertical deviations. Postoperatively 74% of deviations decreased by ≥50% in magnitude. Diplopia resolved in 50% of patients who presented with preoperative diplopia. One patient had intraoperative bleb perforation, but none had postoperative hypotony at any follow-up visit. Only 2 required a second strabismus surgery.

CONCLUSIONS

Strabismus surgery with preservation of the filtering bleb following implantation of a glaucoma drainage device is a low risk procedure that can improve ocular alignment and related symptoms, despite a low motor success rate by standard criteria.

Manufacturer changes lead to clinically important differences between two editions of the TNO stereotest

PURPOSE

Stereoacuity tests used in clinical practice should be repeatable and reproducible. However, it has been observed in a clinical setting that new editions of the TNO stereotest appear to give different values from those obtained using previous versions. The purpose of the present research was to investigate this observation.

METHODS

One hundred and twenty-one Dutch subjects, 88 (73%) females and 33 (27%) males, with an average age of 34.0 years (range 18-55) had their stereoacuity measured using two different versions of the TNO stereoacuity test (TNO 13 and TNO 15). The TNO was tested in a counterbalanced order so that consecutive subjects started with alternate editions to avoid bias.

RESULTS

There was a significant difference (p < 0.001) between the median value for stereoacuity measured with TNO 13 (30 s of arc) and TNO 15 (60 s of arc). The bias between the two test versions was -0.23 Log arcseconds (95% limits of the differences: 0.15 to -0.60 Log arcseconds).

CONCLUSION

This study reveals that results obtained with two different editions of a commonplace stereoacuity test are not comparable. New versions come on the market at regular intervals and the assumption that they will give the same results as previous versions may not be valid. Besides the statistically significant difference between the TNO 13 and TNO 15, the Bland-Altman plot also showed a considerable bias and the 95% limits of the differences between the TNO 13 and TNO 15 are more than two steps on the Log arcsecond scale. This difference between two editions of the TNO stereotests is not clinically acceptable and therefore it is inappropriate to use the two versions of the test interchangeably. It is important in both research and clinical records to specify the edition of the TNO test used.