Biomedical subjects

John R Grigg

Publications and source records attributed to John R Grigg.

5 recordsLinked to original sources

PubMed2006

Multifocal visual evoked responses to dichoptic stimulation using virtual reality goggles: Multifocal VER to dichoptic stimulation.

Multifocal visual evoked potentials (mfVEPs) have demonstrated good diagnostic capabilities in glaucoma and optic neuritis. This study aimed at evaluating the possibility of simultaneously recording mfVEP for both eyes with dichoptic stimulation using virtual reality goggles and also to determine the stimulus characteristics that yield maximum amplitude. ten healthy volunteers were recruited and temporally sparse pattern pulse stimuli were presented dichoptically using virtual reality goggles. Experiment 1 involved recording responses to dichoptically presented checkerboard stimuli and also confirming true topographic representation by switching off specific segments. Experiment 2 involved monocular stimulation and comparison of amplitude with Experiment 1. In Experiment 3, orthogonally oriented gratings were dichoptically presented. Experiment 4 involved dichoptic presentation of checkerboard stimuli at different levels of sparseness (5.0 times/s, 2.5 times/s, 1.66 times/s and 1.25 times/s), where stimulation of corresponding segments of two eyes were separated by 16.7, 66.7,116.7 & 166.7 ms respectively. Experiment 1 demonstrated good traces in all regions and confirmed topographic representation. However, there was suppression of amplitude of responses to dichoptic stimulation by 17.9+/-5.4% compared to monocular stimulation. Experiment 3 demonstrated similar suppression between orthogonal and checkerboard stimuli (p = 0.08). Experiment 4 demonstrated maximum amplitude and least suppression (4.8%) with stimulation at 1.25 times/s with 166.7 ms separation between eyes. It is possible to record mfVEP for both eyes during dichoptic stimulation using virtual reality goggles, which present binocular simultaneous patterns driven by independent sequences. Interocular suppression can be almost eliminated by using a temporally sparse stimulus of 1.25 times/s with a separation of 166.7 ms between stimulation of corresponding segments of the two eyes.

Adult↗

PubMed2006

Multifocal visual evoked potential analysis of inflammatory or demyelinating optic neuritis.

OBJECTIVE: To determine the sensitivity of multifocal visual evoked potentials (mVEP) in optic neuritis of an inflammatory or demyelinating nature. DESIGN: Cross-sectional study. PARTICIPANTS: Sixty-four patients participated who had a confirmed diagnosis of optic neuritis (ON) (past and acute). Based on the McDonald multiple sclerosis (MS) criteria, 25 patients (27 eyes with ON) were deemed to have isolated optic neuritis and thus not have MS (i.e., the not-MS group), and 19 patients (24 eyes with ON) had a diagnosis of MS (i.e., the MS group). The remaining 20 patients (25 eyes with ON) were at a high risk of MS, but diagnostic evaluation was equivocal, and thus were classified as the possible MS group. A control group of 20 normal patients was enrolled. TESTING: The mVEP test was performed using the Accumap. All ON patients had recent magnetic resonance imaging scans of the brain and spinal cord. MAIN OUTCOME MEASURES: Multifocal visual evoked potentials amplitude and latency values were analyzed within each group and were compared with the normal controls. RESULTS: No abnormality was recorded on mVEP in the control group. Of all the ON eyes, 74 (97.3%) were abnormal on mVEP testing. Amplitude values were abnormal in 92.6% of not-MS eyes, 92.0% of possible MS eyes, and 100% of those with MS, and latency was abnormal in 33.3%, 76.0%, and 100%, respectively. There was a significant difference in the mVEP latency z-scores among all ON groups (P<0.01; Kruskal-Wallis test). Although distribution graphs of latency z-scores in the not-MS and MS groups had single peaks and were clearly separate from each other, the latency z-score distribution within the possible MS group in postacute patients was bimodal, with each peak corresponding to the distribution of the not-MS and MS group, respectively. The mVEP latency z-scores had a sensitivity and specificity of 100% in detecting patients with ON due to MS when compared with normal patients. CONCLUSIONS: The mVEP test is a sensitive and specific tool for detecting optic neuritis. There was a significant difference in latency analysis findings between patient groups as classified according to the McDonald MS criteria. Latency results suggest a role in identifying a patient's risk for future MS.

Acute Disease↗

PubMed2006

Nanophthalmos: ultrasound biomicroscopy and Pentacam assessment of angle structures before and after cataract surgery.

We report a case of nanophthalmos with intractable secondary glaucoma. Bilateral cataract extraction with intraocular lens implantation was used as definitive treatment for the chronic angle-closure glaucoma. The changes in angle and ciliary body anatomy were well documented with preoperative and postoperative Pentacam assessment (Oculus Optikgeräte GmbH) and ultrasound biomicroscopy (Paradigm Medical Industries) images. We believe these are the first diagnostic and prognostic images of this kind in a nanophthalmic eye.

Anterior Eye Segment↗

PubMed2004

Test-retest variability of multifocal visual evoked potential and SITA standard perimetry in glaucoma.

PURPOSE: To investigate the test-retest variability of multifocal visual evoked potential (mfVEP) and threshold perimetry in glaucoma, and to examine the relationship between the two techniques. METHODS: Data were recorded using the AccuMap mfVEP and SITA standard program of the Humphrey Field Analyzer. Data were obtained twice within a 4-week period from both eyes of 74 patients with varying amounts of glaucomatous visual field loss. The number of defective test locations (those falling beyond a given probability value of being normal) were calculated for mfVEP and SITA, using databases incorporated within the instruments software. Reliability measures and test times were recorded along with patient test preference. RESULTS: Both tests showed a large degree of test-retest variability in the number of defective test locations (95% limits of agreement for mfVEP and SITA being 13.39 and 9.88, respectively). A "fair to moderate" degree of spatial agreement was found between mfVEP and SITA. The number of mfVEP defective locations was dependent on the signal amplitude. No relationship was found between test-retest variability and the reliability indices for either test. The mean time taken to perform mfVEP and SITA standard was 33 and 20 minutes, respectively, and 73 of the 74 patients preferred the mfVEP test. CONCLUSIONS: Test-retest variability was found to be slightly greater for mfVEP. The processing of mfVEP signals needs to be changed to remove the relationship between the number of defective locations and signal amplitude. The majority of patients preferred mfVEP to conventional perimetry although mfVEP takes longer to perform.

Aged↗

PubMedDate not supplied

Complicated hyphaema: think sickle.

Two cases of complicated hyphaema associated with sickle cell trait are presented. The pathophysiology, diagnosis and management of raised intraocular pressure in sickle cell trait are discussed.

Adult↗