Richard P. Hagan

The Kinematics and Kinetics of Slipknots for Arthroscopic Bankart Repair

An apparatus has been developed to enable the in vitro measurement of the kinematics and kinetics of a slipknot, both while the knot is being tightened and with the knot in place and the tension removed. During tightening, the apparatus provides a linearly increasing resistance, which may be considered analogous to the resistance experienced when the labrum is drawn toward and apposed to the edge of the glenoid cavity during a Bankart repair. The tension to close the knot is measured with a tensiometer, in tandem with the closure of the capsule model onto the bone anchor, which is measured with a datalogger. The tightening tension was limited to 25 N and intraoperator and interoperator comparisons were made for four knots tied by six participants. Failure of a knot was taken to be reverse slippage of 2 mm. A second criterion of ease of slide was used to assess each knot. We found wide interoperator variability with regard to slipknot tying. A methodology for quality control of slipknot tying is presented.

Early multifocal electroretinogram findings during intravitreal ranibizumab treatment for neovascular age-related macular degeneration.

PURPOSE To evaluate changes in the multifocal electroretinogram (mfERG) in patients with neovascular age-related macular degeneration (nAMD) undergoing ranibizumab treatment. METHODS This was an observational, longitudinal, prospective study. Treatment-naive patients with nAMD who met the inclusion and exclusion criteria underwent a course of monthly injections of ranibizumab over 3 months. At baseline and month 3, each subject was evaluated with best corrected visual acuity (BCVA), contrast sensitivity (CS), fluorescein and indocyanine green angiography, optical coherence tomography (OCT), and mfERG. Additional mfERGs were performed at weeks 1 and 4 and BCVA and OCT at weeks 4 and 8. RESULTS Eighteen patients were enrolled. Between baseline and week 12, median BCVA improved from 59 to 69 ETDRS letters (P = 0.001), median CS improved from 29 to 30 letters (P = 0.05), mean OCT central foveal subfield thickness (CFT) decreased from 294 to 199 μm (P = 0.005), mean P1 amplitude density of the mfERG central zone increased from 35.85 to 51.55 nV/deg(2) (P = 0.009). The mfERG response correlated positively with BCVA (F = 22; P < 0.0001) and negatively with CFT (F = 12.73; P = 0.00078). CONCLUSIONS Intravitreal ranibizumab therapy appears to induce an increase in mfERGs centrally in patients with nAMD at least in the short term. Longer term studies to investigate the prognostic value of mfERG responses to predict changes in visual acuity in nAMD and other diseases are warranted. (ClinicalTrials.gov number, NCT01023971.).

Removal of eye movement artefacts from single channel recordings of retinal evoked potentials using synchronous dynamical embedding and independent component analysis.

A system is described for the removal of eye movement and blink artefacts from single channel pattern reversal electroretinogram recordings of very poor signal-to-noise ratios. Artefacts are detected and removed by using a blind source separation technique based on the jadeR independent component analysis algorithm. The single channel data are arranged as a series of overlapping time-delayed vectors forming a dynamical embedding matrix. The structure of this matrix is constrained to the phase of the stimulation epoch: the term synchronous dynamical embedding is coined. A novel method using a marker channel with a non-independent synchronous feature is employed to identify the single most relevant source estimation for reconstruction and signal recovery. This method is non-lossy, all underlying signal being recovered. In synthetic datasets of defined noise content and in standardised real data recordings, the performance of this technique is compared to conventional fixed-threshold hard-limit rejection. The most significant relative improvements are achieved when movement and blink artefacts are greatest: no improvement is demonstrable for the random noise only situation.

Early diagnosis of Stargardt disease with multifocal electroretinogram in children

To present two pediatric cases where multifocal electroretinogram (mfERG) was able to establish an earlier diagnosis compared to full field electroretinogram (ERG) Case 1: an 11-year-old boy with reduced visual acuity, pale discs, macular pigmentation with white dots bilaterally. Case 2: a 12-year-old girl with reduced vision in her right eye, slight pallor of the right optic disc, intense pigmentation at both maculae and scattered punctate lesions throughout the peripheral fundi. Both had been investigated with electrodiagnostic tests according to the International Society of Clinical Electrophysiology for Vision protocol. Full-field ERGs for both children showed normal responses. Case 1: mfERG revealed a severe reduction in function in the inner 20°. Case 2: mfERG showed attenuated responses in each eye. Clinical examination and mfERG were consistent with Stargardt disease. mfERG is applicable to children and is a sensitive tool for early diagnosis of retinal dystrophies.

The role of visually evoked potentials in the management of hemispheric arachnoid cyst compressing the posterior visual pathways

We report a case of an occipital arachnoid cyst in an infant, managed on the basis of changes in visually evoked potentials (VEPs). A significant asymmetry of VEP responses prompted neurosurgical intervention, which improved visual behavior and electrical response to both pattern and flash stimuli.

Automatic positioning of cursors in the transient pattern electroretinogram (PERG) with very poor SNR using an Expert System

An expert system is described which automatically cursors PERG waveforms of very poor signal-to-noise ratio. The training data-set is derived from shape-perturbated PERG waveforms based on the ISCEV Standard and a series of clinically-normal waveforms. In validation trials, the Expert System is clearly shown to out-perform the Human Expert in the presence of noise. All software was written in MatLab®. It is proposed that this system is generic and similarly applicable to other transient recordings. A comprehensive Internet demonstration (SPoC: Smart Positioning of Cursors) is maintained at www.liverpooleye.org

Multifocal Choroiditis with Panuveitis in an 8-Year-Old Boy with Long-Standing Idiopathic Acute Anterior Uveitis:

Purpose To report successful treatment of a rare case of sight-threatening pediatric multifocal choroiditis with panuveitis (MFCPU) and the use of electrophysiology to confirm return of macular function. Methods Case report. Results An 8-year-old boy with a history of bilateral recurrent non-juvenile idiopathic arthritis acute anterior uveitis (AAU) presented with new-onset blurry vision and floaters in both eyes. Visual acuity had deteriorated to 20/200 right eye and 20/100 left eye. Cells were observed in the anterior chamber and vitreous of both eyes. Ophthalmoscopy showed multiple active small cream-colored chorioretinal lesions and cystoid macular edema (CME) in both eyes in the absence of systemic disease, suggestive of idiopathic MFCPU. Successful rapid visual recovery and resolution of CME confirmed by spectral-domain optical coherence tomography (SD-OCT) was achieved with prompt intensive systemic steroid therapy followed by early introduction of methotrexate. After 9 months, his visual acuities improved to 20/32, and pattern reversal visual evoked potentials and 19 hexagon multifocal electroretinography posttreatment were normal, showing recovery of macular function. Conclusions Multifocal choroiditis with panuveitis is rare in children and has not been documented in the presence of previous longstanding recurrent AAU. Onset of floaters in children should alert the clinician to early stages of posterior pole involvement and progression to reduction in vision due to CME requires prompt aggressive steroid therapy monitored by clinical examination, SD-OCT, and electrophysiology, followed by early introduction of immunosuppressive drugs for long-term stability and to avoid steroid-induced adverse effects in children.

Relatively spared central multifocal electroretinogram responses in acute quinine toxicity.

A 71-year-old man was investigated with electrodiagnostic testing 4 months after a deliberate quinine overdose. Initially he was admitted to intensive care unit with visual acuity (VA) of perception of light in both eyes. VA recovered to 6/6 right eye and 6/12 left eye, though severely constricted fields were noted. Slow stimulus (base period of 83 ms) multifocal electroretinogram (ERG) showed electronegative responses outside the inner 5 degrees, with a reduced but electropositive response seen in this central area. It appears that in this case of bilaterally negative ERGs that the macula/fovea (which has a vascular supply through the choroid) is relatively spared as is seen in bilateral vascular electronegative ERGs. This may indicate that quinine toxicity to the retina may be secondary to effects similar to vascular occlusion or severe ischemia during the acute phase of quinine poisoning.

Automated Post Hoc Removal of Power-Line and CRT Frame Pulse Contamination from Retinal and Cortical Evoked Potentials (EPs)

Recordings of the ERG, PERG, VEP and their multi-focal variants are occasionally contaminated with harmonic noise arising from the mains supply and CRT monitors. These noise contributions can be modelled as distorted sinusoids and identified by means of non-linear multiple regression and removed: no a priori estimates of number or frequency of noise sources are required. This approach is termed noise cancellation and does not constitute any form of notch filter: the fidelity of the underlying waveform is preserved. Here the simple theory is illustrated in artificial datasets and then applied to clinical examples of PERG and VEP. The programming language used throughout is MatLab R13SP3 (Mathworks UK Ltd.).

Keratoconus associated with CSNB1.

A 35-year-old man with best corrected visual acuities of −18.00/+10.00×180 (6/60) OD and −10.00/+8.00×5 (6/36) OS. Bilateral steep central corneal thinning, paracentral ectasia and Vogts striae were present; normal fundi. Corneal topography disclosed 7.4 dioptres of irregular astigmatism in the central 3 mm with thinning (335 &mgr;m). Electroretinography (ERG) showed no response. There were no medical or environmental influences for his keratoconus. Occurrence of keratoconus and CSNB in the patient may represent a chance association, but keratoconus has not been previously linked with CSNB1 either as a chance or true association though both show genetic predisposition.