Interocular Asymmetry Research Articles

Inter-ocular asymmetry of retinal parameters as measured with Ocular Coherence Tomography (OCT) in a sample of healthy young adults

Inter-ocular asymmetry of retinal parameters as measured with Ocular Coherence Tomography (OCT) in a sample of healthy young adults

Normal Value Ranges for Central Retinal Thickness Asymmetry in Healthy Caucasian Adults Measured by SPECTRALIS SD-OCT Posterior Pole Asymmetry Analysis.

To determine the normal variation in central retinal thickness asymmetry in healthy Caucasian adults using the posterior pole asymmetry analysis (PPAA) of a SPECTRALIS spectral-domain optical coherence tomography (SD-OCT) device. Healthy Caucasian individuals aged between 18 and 45 years with a visual acuity of minimum 20/20 and a spherical equivalent between -1.5 and +1.5 diopters were recruited. Retinal thickness and retinal nerve fiber layer thickness (RNFL) were using measured SPECTRALIS SD-OCT. Inter- and intraocular differences in central retinal thickness were calculated using the PPAA. The association between age, sex, and interocular asymmetry was evaluated by a linear model with Gaussian correlation structure. A total of 105 individuals, 30 men and 75 women, were studied. The mean age ± SD was 28.8 ± 7.87 years. The grand mean interocular retinal thickness asymmetry was 5.6 μm (95% confidence interval [CI]: 4.6-6.5) and the grand mean intraocular retinal thickness asymmetry was 8.3 μm (95% CI: 6.8-9.9) in the right eye and 8.4 μm (95% CI: 6.7-10.0) in the left eye. The highest local asymmetries were found in the nasal corners of macula were the posterior pole thickness map overlaps the temporal vascular arches. A slight general age and sex effect on the mean interocular retinal thickness asymmetry was found to be respectively 0.04 μm/year (95% CI: 0.02-0.06 μm) and 0.54 μm (95% CI: 0.19-0.88 μm) for men compared with women. Statistically significant physiological asymmetries in inter- and intraocular central retinal thickness exist. This must be considered when early signs of glaucoma or other pathologies are evaluated based on the retinal thickness asymmetry. (http://www.controlled-trials.com/isrctn/ number, ISRCTN09017572.).

Role of ocular pulse amplitude in glaucoma

The ocular pulse amplitude is defined as the difference between diastolic and systolic intraocular pressure. The ocular pulse is generated by the pulsatile ocular blood flow in the choroid. It is dependent on the dynamics of the cardiovascular system, the rigidity of the ocular vessels on one side and the biomechanical properties of the eye on the other side. In addition the influence of outflow facility of the aqueous humor, the level of the intraocular pressure itself and last but not least the rigidity of the sclera on the ocular pulse amplitude is until now not clear. Dynamic contour tonometry (Pascal®) does not only measure intraocular pressure almost independent of corneal thickness and curvature but also allows easy and fast measurement of ocular pulse amplitude on the slit lamp. The ocular pulse amplitude in healthy subjects is between 1.2 and 4 mmHg. If the ocular pulse amplitude is larger than 1.2 mmHg spontaneous pulsations of the central retinal vein are visible on fundoscopy. In patients with ocular hypertension the ocular pulse amplitude is larger than in normal subjects but this is mainly due to higher IOP levels. In patients with manifest open-angle glaucoma the ocular pulse amplitude stays initially within the normal range. In more advanced stages of the disease and especially in patients with ocular perfusion pressure dependent optic neuropathy the ocular pulse amplitude is gradually reduced. Due to the various factors influencing ocular pulse amplitude a direct correlation between reduced ocular pulse amplitude and reduced ocular perfusion pressure has not been established as yet. New approaches investigating the variations of the ocular pressure Fourier spectral analysis are promising, especially when simultaneous analysis of the arterial blood pressure is performed. These techniques may allow a fast and easy discrimination between healthy and glaucomatous patients in the near future. If ocular pulse amplitude exhibits a massive inter-ocular asymmetry in the presence of symmetrical ocular findings of extraocular vascular pathologies (i.e. carotid stenosis) are the most likely cause and therefore should be excluded.

New approach to corneal nerve fibers morphometry in diabetes mellitus on the basis of confocal biomicroscopy

to develop a new approach to morphometric analysis of corneal nerve fibers (CNF) and to evaluate their age-related changes in type 1 and type 2 diabetes mellitus patients. The study enrolled 150 participants (300 eyes) aged from 13 to 83 years, of them 37 type 1 diabetes patients (74 eyes), 51 type 2 diabetes patients (102 eyes), and 62 healthy volunteers (124 eyes). All participants were examined with HRT III Rostock Corneal Module (Heidelberg Engineering GmbH). Digital images thus obtained were analyzed with specially developed original software that automatically computes coefficients of CNF orientation symmetry and anisotropy. A strong inverse correlation has been found between the coefficient of CNF orientation anisotropy and glycated hemoglobin levels (r = -0.83, p < 0.001 and r = -0.79, p < 0.005 in patients with type 1 and type 2 diabetes respectively) as well as the duration of the disease (r = -0,7, p < 0.005 and r = -0.72, p < 0.001, type 1 and type 2 diabetes respectively). On the contrary, the coefficient of CNF orientation symmetry has been shown to be directly correlated with both glycated hemoglobin levels (r = 0.64, p < 0.005 and r = 0.78, p < 0.05, type 1 and type 2 diabetes respectively) and the duration of the disease (r = 0.62, p < 0.05 and r = 0.73, p < 0.05, type 1 and type 2 diabetes respectively). Interocular asymmetry in both coefficients was found in diabetic patients but not in the controls. On the basis of the proposed coefficients, age-related changes in corneal nerve fibers orientation have been determined. Normally, the degree of CNF tortuosity increases with age. The rate of this increase is the highest before the age of 35-40. As shown, type 1 diabetes is associated with low coefficients of CNF orientation anisotropy and high coefficients of CNF orientation symmetry as compared to type 2 diabetes in the same age group. As suggested by the results, the two proposed coefficients that describe the state of corneal nerve fibers can possibly be used for diagnosis and monitoring of diabetic peripheral neuropathy (DPN). However, to produce enough evidence, further studies should be conducted.

Interocular Asymmetries in Axial Length and Refractive Error in 4 Cohorts

Interocular Asymmetries in Axial Length and Refractive Error in 4 Cohorts

Interocular nystagmus asymmetry and motion sickness

Binocular videonystagmography (VNG) was used to study the vestibulo-ocular response to a double rotation test as a pre-flight medical examination (PFME) for assessing an aircrew’s vestibulo-autonomic stability. The objective of our study was to identify the relationship between the degree of the nystagmus response to rotation and the severity of motion sickness (MS). The investigated cohort included 135 subjects selected from flight crews aged 23 to 47 years, who were qualified healthy according to the PFME criteria. The test used was based on the intermittent cumulation of Coriolis accelerations by Bryanov’s method. The post-testing vestibular reactivity was assessed using criteria for determining the level of autonomic reactivity and protection movements. Binocular videonystagmography (VNG) with a mask cover was performed during and after rotation. The degree of interocular asymmetry of nystagmus velocity was shown to be directly associated with the severity of MS. We suggested the following asymmetry coefficients: the asymmetry coefficient of unidirectional nystagmus during flexions (ACf) and extensions (ACe); and the duration of convergence rotatory nystagmus during flexions (DCNf) and extensions (DCNe). It has been found that ACf and DCNf are correlated with the severity of MS (p < 0.05). On the basis of our data, we formulated the idea of the mechanism for MS development due to double rotation, which was understood as the occurrence in these conditions of intravestibular interlabyrinth conflict.

Interocular Asymmetry of the Visual Field Defects in Newly Diagnosed Normal-tension Glaucoma, Primary Open-angle Glaucoma, and Chronic Angle-closure Glaucoma

To compare the interocular asymmetry of visual field loss in newly diagnosed normal-tension glaucoma (NTG), primary open-angle glaucoma (POAG), and chronic angle-closure glaucoma (CACG) patients. Visual field results of 117 newly diagnosed, treatment-naive glaucoma patients (42 NTG, 38 POAG, and 37 CACG) were studied retrospectively. The following 3 visual field defect parameters were used to evaluate the interocular asymmetry: (1) global indices; (2) local mean deviations (MDs) of 6 predefined visual field areas; and (3) stage designated by glaucoma staging system 2. The differences of the above parameters between the trial eye (the eye with greater MDs) and the fellow eye in each subject were defined as interocular asymmetry scores. Interocular asymmetry of visual field loss was presented in all the 3 groups (all P<0.05). CACG group had greater total MD interocular asymmetry score compared with the NTG and POAG groups (among groups, P=0.008; NTG vs. CACG, P=0.005; POAG vs. CACG, P=0.009). CACG also presented with significantly higher local MD interocular asymmetry scores at central, inferior, and temporal areas compared with those of the POAG group and at inferior area compared with that of NTG group. No significant difference in either total or local MDs was detected between NTG and POAG (all P>0.05). Interocular asymmetry scores of glaucoma staging system 2 had no significant difference among the 3 groups (P=0.068). All CACG, POAG, and NTG groups presented with interocular asymmetric visual field loss at the time of diagnosis. CACG had greater interocular asymmetry compared with NTG and POAG. No significant interocular asymmetry difference was observed between NTG and POAG.

Hemifield pattern electroretinogram in ocular hypertension: comparison with frequency doubling technology and optical coherence tomography to detect early optic neuropathy.

BackgroundTo assess the sensitivity and specificity of hemifield pattern electroretinogram (HF-PERG) for detecting early retinal ganglion cell (RGC) damage in ocular hypertensive (OH) patients.MethodsFifty-two OH patients (mean age 56±9.6 years) with an intraocular pressure (IOP) .21 mmHg were assessed. All subjects underwent HF-PERG, optical coherence tomography (OCT), and frequency doubling technology (FDT) visual field.ResultsOH patients showed a significant increase of peak-time of the N95 (P=0.027) compared to controls. The amplitude of the N95 of the lower and upper HF-PERG showed significant differences (P=0.037 and P=0.023, respectively) between the two groups. A significant intraocular (P=0.006) and interocular (P=0.018) asymmetry of N95 amplitude was found. Receiver operating characteristic (ROC) curve analysis revealed a sensitivity of 93% for the N95 of the lower HF-PERG, whereas full-field pattern electroretinogram (PERG) N95 peak-time had a sensitivity of 88%. In OH patients, we found a thinning of OCT - retinal nerve fiber layer (RNFL), especially in the superior and inferior quadrant, although not statistically significant, and a significantly higher FDT pattern standard deviation (FDT-PSD; P=0.001). In the OCT-RNFL inferior quadrant, a sensitivity of 82% was recorded. Finally, the sensitivity of the FDT-PSD was 92%.ConclusionOur study shows that HF-PERG is a very sensitive test for detecting early damage of the RGC.

Robust Mouse Pattern Electroretinograms Derived Simultaneously From Each Eye Using a Common Snout Electrode

We recorded pattern electroretinograms (PERGs) simultaneously from each eye in mice using binocular stimulation and a common noncorneal electrode. The PERG was derived simultaneously from each eye in 71 ketamine/xylazine anesthetized mice (C57BL/6J, 4 months old) from subcutaneous needles (active, snout; reference, back of the head; ground, root of the tail) in response to contrast-reversal of gratings (0.05 cycles/deg, >95% contrast) generated on two custom-made light-emitting diode (LED) tablets alternating at slight different frequencies (OD, 0.984 Hz; OS, 0.992 Hz). Independent PERG signals from each eye were retrieved using one channel continuous acquisition and phase-locking average (OD, 369 epochs of 492 ms; OS, 372 epochs of 496 ms). The PERG was the average of three consecutive repetitions. Binocular snout PERGs had high amplitude (mean, 25.3 μV, SD 6.6) and no measurable interocular cross-talk. Responses were reliable (test-retest variability within-session, 14%, SD 7; between sessions, 25%, SD 9; interocular asymmetry within-session, 9%, SD 7; between sessions, 13%, SD 5). Retinal ganglion cells (RGCs) were the main source of the binocular snout PERG, as optic nerve crush in three mice abolished the signal. The PERG, a sensitive measure of RGC function, is used increasingly in mouse models of glaucoma and optic nerve disease. Compared to current methods, the binocular snout PERG represents a substantial improvement in terms of simplicity and speed. It also overcomes limitations of corneal electrodes that interfere with invasive procedures of the eye and facilitates experiments based on comparison between the responses of the two eyes.

Abnormal pattern visual evoked response in carotid-cavernous fistula

Abnormal pattern visual evoked response in carotid-cavernous fistula

Central Serous Chorioretinopathy Produces Macular Pigment Profile Changes

Macular pigment (MP) is the collective name for three isomeric carotenoids: lutein, zeaxanthin, and meso-zeaxanthin. Macular pigment density is greatest in the central retina, peaking at the fovea and falling to negligible levels at 7 degrees of eccentricity from the fovea. Several studies have documented the interocular symmetry of MP optical density (MPOD) spatial distribution. The ongoing University of Missouri-St. Louis study uses a novel, customized heterochromatic flicker photometer to map the spatial distribution of MPOD up to 8 degrees of eccentricity relative to the fovea. Here, we report the MPOD measurements in a subject with resolved central serous chorioretinopathy (CSC) in the right eye. Two subjects performed the full MPOD spatial mapping. The test subject (WK) had a history of central serous CSC of the right eye. The control subject (CP) had an unremarkable ocular health history. Comprehensive exams were performed on each subject including Cirrus optical coherence tomography imaging and fundus photographs. Subject CP showed highly symmetric interocular MPOD profiles at the fovea and 2, 4, and 6 degrees of eccentricity. Subject WK showed interocular asymmetry at the fovea and at 2 degrees with relative symmetry at 4 and 6 degrees. A paired sample t test identified nonsignificant interocular values for subject CP and statistically significant differences of at 2 degrees for subject WK. We hypothesize that subject WK's interocular MPOD spatial distribution asymmetry resulted from his history of resolved CSC. This asymmetry is statistically significant at 2 degrees of retinal eccentricity and corresponds to the extent of retinal pigment epithelium changes observed on the fundus photographs. These findings suggest that MP and retinal pigment epithelium changes after a CSC episode are comparable in the area of the retina affected. These disruptions may also be measureable in other macular conditions in which the sensory retina is affected (e.g., cystoid macular edema and clinically significant macular edema).

Retinal and Choroidal Thickness in Myopic Anisometropia

We compared the retinal thickness (RT) and choroidal thickness (ChT) between the fellow eyes of nonamblyopic myopic anisometropes. The eyes of 22 nonamblyopic myopic anisometropes (≥ 1 diopter [D] spherical equivalent refraction [SER] anisometropia) were examined using spectral domain optical coherence tomography (SD-OCT). Customized software was used to register, align, and average multiple foveal OCT B-scan images from each subject to enhance image quality. Two independent masked observers manually determined the RT and ChT from each SD-OCT image up to 2.5 mm nasal and temporal to the fovea. Axial length (AXL) was measured using optical low coherence biometry during relaxed accommodation. The mean SER anisometropia was 1.74 ± 0.95 D and the mean interocular AXL difference was 0.58 ± 0.41 mm. There was no significant difference in foveal RT between the fellow eyes (P > 0.05). Mean subfoveal ChT was significantly thinner in the more myopic eye (252 ± 46 μm) compared to the fellow, less myopic eye (286 ± 58 μm) (P < 0.001). There was a moderate correlation between the interocular difference in subfoveal ChT and the interocular difference in AXL (r = -0.50, P < 0.01). Asian anisometropes displayed more regionally symmetrical (nasal-temporal) interocular differences in ChT profile compared to Caucasians. RT was similar between the fellow eyes of myopic anisometropes; however, the subfoveal choroid was significantly thinner in the more myopic (longer) eye of this anisometropic cohort. The interocular asymmetry in ChT correlated with the interocular difference in AXL.

Symmetry of Optic Nerve Head Parameters Measured by the Heidelberg Retina Tomograph 3 in Healthy Eyes: The Blue Mountains Eye Study

To assess the symmetry of optic nerve head parameters measured by the Heidelberg Retina Tomograph 3 (HRT 3) between fellow eyes in a normal elderly population. Cross-sectional population-based study. Participants of the Blue Mountains Eye Study 10-year follow-up who did not have optic disc disease, including glaucoma, were included. Optic nerve head parameters measured by HRT 3 were compared between fellow eyes. The normal range of interocular asymmetry (larger disc minus smaller disc) was determined by the 2.5th and 97.5th percentiles. A total of 1276 eligible participants had HRT scans of both eyes. HRT measurements in right eyes differed slightly in rim steepness and rim volume from those in left eyes (P < .05). The 2.5th and 97.5th percentile of interocular asymmetry limits were -0.41 and 0.45 for cup-to-disc ratio and -0.19 and 0.22 for cup-to-disc area ratio, respectively. The highest interocular correlation was found in disc area and cup area (r ranged from 0.74-0.76), whereas mean cup depth, cup volume, and retinal nerve fiber layer thickness had the poorest correlation (r ≤ 0.07). Greater optic disc area asymmetry was associated with a larger interocular difference in the other optic nerve head parameters. There was minimal interocular difference and substantial interocular correlation in optic nerve head parameters measured by HRT 3. Interocular asymmetry greater than 0.2 for cup-to-disc area ratio was considered outside the normal range.

Clinical and instrumental criteria in predicting the clinical course of chronic posttraumatic uveitis after penetrating ocular trauma

Aim. To identify the prognostic criteria for the recovery or transformation to chronic form in patients with prolonged clinical course of uveitis associated with penetrating ocular trauma basing on the results of clinical examination and instrumental methods. Methods. 120 patients with chronic clinical course of post-traumatic uveitis were examined 2-3 months after the penetrating ocular trauma using clinical examination and ultrasonography of eye and orbita. 1st group consisted of 60 convalescents, 2nd included 60 patients with chronic disease. The control group consisted of 40 healthy volunteers. Ultrasonography included measurement of innermost eye coat thickness and the retrobulbar part of the optic nerve thickness measured 10 mm behind the eyeball bilaterally. Results were statistically analyzed. Results. Prognostic criteria for recovery or chronic inflammation development in chronic post-traumatic uveitis were found. They are: G-index and interocular asymmetry coefficient of innermost eye coat and optic nerve thickness. At calculation of G-index, which characterizes inflammatory consequences of trauma, presence of cornea imbibition, rubeosis iridis, cataract, vitreous body fibrosis, pulled-in cornea and sclera scars, retinal and choroidal detachment, the eyeball subatrophy, decreased eye fluid pressure, optic nerve thickening. The value of all the parameters equaled 1. An interocular thickness asymmetry coefficient characterized innermost eye coat thickness or optic nerve thickness ratio in injured eye compared to other eye. 2-3 weeks after the trauma characteristic G-index value of G ≥4, an interocular asymmetry coefficient value of ≥1,3 for innermost eye coat thickness and ≥1,1 for optic nerve thickness are the indicators of a high risk of chronic development. Lesser values predict recovery. Conclusion. Use of the set of found prognostic criteria in patients with prolonged clinical course of uveitis provides high prognosis accuracy of 93,3% at predicting recovery or chronic uveitis development.

Fixation control and eye alignment in children treated for dense congenital or developmental cataracts

Many children treated for cataracts develop strabismus and nystagmus; however, little is known about the critical period for adverse ocular motor outcomes with respect to age of onset and duration. Children who had undergone extraction of dense cataracts by the age of 5 years were enrolled postoperatively. Ocular alignment was assessed regularly throughout follow-up. Fixation stability and associated ocular oscillations were determined from eye movement recordings at ≥5 years old. Multivariate logistic regression was used to evaluate whether laterality (unilateral vs bilateral), age at onset, and/or duration of visual deprivation were associated with adverse ocular motor outcomes and to determine multivariate odds ratios (ORs). A total of 41 children were included. Of these, 27 (66%) developed strabismus; 29 (71%) developed nystagmus. Congenital onset was associated with significant risk for strabismus (OR, 5.3; 95% CI, 1.1-34.1); infantile onset was associated with significant risk for nystagmus (OR, 13.6; 95% CI, 1.6-302). Duration >6 weeks was associated with significant risk for both strabismus (OR, 9.1; 95% CI, 1.9-54.2) and nystagmus (OR, 46.2; 95% CI, 6.0-1005). Congenital onset was associated with significant risk for interocular asymmetry in severity of nystagmus (OR, 25.0; 95% CI, 2.6-649), as was unilateral cataract (OR, 58.9; 95% CI, 5.1-2318). Laterality (unilateral vs bilateral) and age at onset were significant nonmodifiable risk factors for adverse ocular motor outcomes. Duration of deprivation was a significant modifiable risk factor for adverse ocular motor outcomes. The current study demonstrated that reduced risk for nystagmus and strabismus was associated with deprivation ≤6 weeks.

Interocular asymmetry of foveal thickness in Parkinson disease.

Purpose. To quantify interocular asymmetry (IA) of foveal thickness in Parkinson disease (PD) versus that of controls. Design. Prospective case-control series. Methods. In vivo assessment of foveal thickness of 46 eyes of 23 PD patients and 36 eyes of 18 control subjects was studied using spectral domain optical coherence tomography (SD-OCT). Inner versus outer layer retinal segmentation and macular volumes were quantified using the manufacturer's software, while foveal thickness was measured using the raw data from each eye in a grid covering a 6 by 6 mm area centered on the foveola in 0.25 mm steps. Thickness data were entered into MATLAB software. Results. Macular volumes differed significantly at the largest (Zone 3) diameter centered on the foveola (ETDRS protocol). By segmenting inner from outer layers, we found that the IA in PD is mostly due to changes on the slope of the foveal pit at the radial distances of 0.5 and 0.75 mm (1.5 mm and 1 mm diameter). Conclusions. About half of the PD patients had IA of the slope of the foveal pit. IA is a potentially useful marker of PD and is expected to be comparable across different SD-OCT equipment. Data of larger groups may be developed in future multicenter studies.

Electroretinogram findings in unilateral optic neuritis

To report the electrophysiological findings in patients with unilateral optic neuritis (ON), with particular reference to the electroretinogram (ERG). A retrospective analysis of full-field ERG, pattern ERG (PERG) and pattern visual evoked potential findings from 46 patients with clinical and electrophysiological findings in keeping with unilateral ON. ISCEV standard ERGs did not significantly differ between the optic neuritis and fellow eyes, nor between patients with and without MS. Differences were present in the N95 component of the PERG, which was significantly lower in the affected eye, and the pattern reversal visual evoked potential, which showed significantly longer peak time (latency) in the affected eye. In addition, there was a significant difference between patients with and without multiple sclerosis (MS). No significant inter-ocular asymmetry in ISCEV standard ERGs was present in these cases of unilateral optic neuritis, either as a clinically isolated syndrome or as part of multiple sclerosis. All ERGs recorded were normal.

Extent of asymmetry and unilaterality among juvenile onset primary open angle glaucoma patients

Juvenile onset open angle glaucoma (JOAG) due to its rarity is not well characterized. We aimed to assess the extent of interocular asymmetry of baseline intraocular pressure (IOP), disc morphometry and visual field defects at presentation in patients with primary JOAG. Retrospective, single-centre, hospital-based study. Fifty-two consecutive JOAG patients who presented with glaucomatous optic neuropathy in at least one eye, without any secondary causes of glaucoma. Participants were evaluated for baseline clinical features. The optic disc parameters were measured using scanning laser ophthalmoscopy (Heidelberg Retina Tomograph). Reliable and reproducible visual field tests using standard 30-2 Humphrey automated perimetry were analysed. Interocular asymmetry of baseline IOP, vertical cup:disc ratio and mean deviation. Fourteen patients (27%) had glaucomatous optic neuropathy in only one eye at initial presentation; the fellow eyes of which had IOP <21 mmHg in eight whereas six had IOP >21 mmHg. In 20 out of 52 patients (39%) one eye remained perimetrically unaffected. Patients presenting with bilateral optic neuropathy were found to be significantly younger (24.4 ± 10.6 years) in age compared to those with unilateral optic neuropathy (32 ± 8.2 years) (P = 0.02). One-fourth of primary JOAG patients present as a unilateral optic neuropathy with 60% of these having normal IOP in the fellow eyes. Primary JOAG may present with considerable asymmetry with a small proportion presenting as a unilateral disease.

The Brückner Transillumination Test: Limited Detection of Small-Angle Esotropia

To evaluate the sensitivity of the Brückner test in detecting esotropia of 2° to 10° by interocular asymmetry of the red fundus reflex.Single-blinded evaluation of the diagnostic test.Five blinded observers and 20 isometropic orthotropes.Set-up 1 included monocular evaluation of the Brückner reflex test for each eye of 10 subjects. The subjects alternated fixation between an ophthalmoscope light and an eccentric target (2.5°, 5°, 7.5°, and 10°). Set-up 2 comprised simulation of esotropia of 2° to 5°, 7.5°, and 10° by base-in prisms placed in front of both eyes of 20 subjects. The subjects fixated with either their right or left eye. As a control experiment, 0.5° base-in prisms were used.Set-up 1 tested the sensitivity in detecting a change in reflex between central and eccentric retinal illumination. Set-up 2 tested the sensitivity and specificity in detecting asymmetry of the Brückner reflex between the 2 eyes as a dimming of the reflex of the fixating eye in a 2° to 10° simulated esotropia.In set-up 1, fixation of the ophthalmoscope light owing to foveal dimming was discriminated from fixation of the eccentric target in 98.2% of the trials, regardless of target eccentricity. In set-up 2, esotropia of 2° to 5° was detected in 62% of 100 trials by red reflex asymmetry. Dimming of the reflex in the fixating eye was found in 48% of 100 trials. Esotropia of 7.5° and 10° was detected in 85% and 97% of the trials, respectively. Dimming in the fixating eye was present in 75% and 86% of the trials, respectively. Thirty-six percent of the 300 control tests were false-positives.When the eccentric fundus reflex was compared with the central reflex in the same eye, dimming owing to central fixation of the ophthalmoscope was reliably detected. However, comparison of the eccentric red reflex in the strabismic eye with the central reflex in the fixating eye showed that the Brückner red reflex test was not suitable for detecting small angles of squint.The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Static ocular counterroll reflex in skew deviation

The static ocular counterroll (OCR) reflex generates partially compensatory torsional eye movements during head roll. It is mediated by the utricle in the inner ear. Skew deviation is a vertical strabismus thought to be caused by imbalance in the utriculo-ocular pathway. We hypothesized that if skew deviation is indeed caused by damage to this reflex pathway, patients with skew deviation would show abnormal OCR. Eighteen patients with skew deviation caused by brainstem or cerebellar lesions and 18 normal participants viewed a target at 1 m. Ocular responses to static passive head roll-tilts of approximately 20° were recorded using search coils. Static OCR gain was calculated as the change in torsional eye position divided by the change in head position during sustained head roll. Perception of the subjective visual vertical (SVV) was also measured. Group mean OCR gain was reduced by 45% in patients. At an individual level, OCR gains were asymmetric between eyes and between torsional directions in 90% of patients. In addition, the hypotropic eye incyclotorting gain was lower than the hypertropic eye excyclotorting gain during head roll toward the hypotropic eye in 94% of patients. No consistent pattern of gain asymmetry was found during head roll toward the hypertropic eye. The SVV was tilted toward the hypotropic eye. Static OCR gain is significantly reduced in skew deviation. Interocular and directional gain asymmetries are also prevalent. The asymmetries provide further evidence that disruption of the utriculo-ocular pathway is a mechanism for skew deviation.