Intraocular lens explantation technique for one-piece acrylic lenses.

PURPOSE: To present a simple technique to remove a one-piece, acrylic AcrySof (Alcon Laboratories Inc) intraocular lens (IOL) via the original incision. METHODS: The AcrySof IOL is removed via the original (2.75-mm) incision, without cutting or folding the IOL or widening the incision. After the IOL is viscodissected from the capsular bag and brought into the anterior chamber, toothed forceps hold the optic through the incision while the manipulator enters the side-port incision and hooks onto the optic 180° away. RESULTS: With the forceps pulling and the lens manipulator pushing the IOL toward the incision, the IOL will fold and be delivered. CONCLUSIONS: A one-piece, acrylic (Acrysof) IOL can be removed without cutting or folding the lens and without widening the original 2.75-mm incision.

Improvement in conduction velocity after optic neuritis measured with the multifocal VEP.

PURPOSE: To test the efficacy of the multifocal visual evoked potential (mfVEP) technique after long-term latency changes in optic neuritis (ON)/multiple sclerosis (MS), mfVEPs were recorded in 12 patients with ON/MS. METHODS: Sixty local VEP responses were recorded simultaneously. mfVEP was recorded from both eyes of 12 patients with ON/MS. Patients were tested twice after recovery from acute ON episodes, which occurred in 14 of the 24 eyes. After recovery, all eyes had 20/20 or better visual acuity and normal visual fields as measured with static automated perimetry (SAP). The time between the two postrecovery tests varied from 6 to 56 months. Between test days, the visual fields obtained with SAP remained normal. RESULTS: Ten of the 14 affected eyes showed improvement in median latency on the mfVEP. Six of these eyes fell at or below (improved latency) the 96% confidence interval for the control eyes. None of the 10 initially unaffected eyes fell below the 96% lower limit. Although the improvement was widespread across the field, it did not include all regions. For the six eyes showing clear improvement, on average, 78% of the points had latencies that were shorter on test 2 than on test 1. CONCLUSIONS: A substantial percentage of ON/MS patients show a long-term improvement in conduction velocity. Because this improvement can be local, the mfVEP should allow these improvements to be monitored in patients with ON/MS.

Multifocal visual-evoked potential in unilateral compressive optic neuropathy.

AIM: To evaluate the effects of unilateral compressive optic neuropathy on amplitude and latency of multifocal visual evoked potentials (mfVEPs). METHODS: Static automated perimetry and mfVEP recordings were obtained from six patients with presumed meningiomas affecting one optic nerve. Monocular and interocular amplitude and latency analyses were performed and compared with normal control subjects. RESULTS: The change in the mfVEP amplitude agreed with visual field findings with regard to topography and severity of deviation from normal. The delay in recordable responses from affected eyes ranged from 7.6 to 20.7 ms (interocular analysis) and 7.9 to 13.9 ms (monocular analysis). CONCLUSIONS: Compressive optic neuropathy decreases the amplitude and increases the latency of the mfVEP. The changes in latency were similar to those seen in optic neuritis but larger than those in ischaemic optic neuropathy and glaucoma.

The role of the multifocal visual evoked potential (mfVEP) latency in understanding optic nerve and retinal diseases.

PURPOSE: To examine the extent to which changes in the latency of the multifocal visual evoked potential (mfVEP) overlap in patients with glaucoma, recovered optic neuritis/multiple sclerosis (ON/MS), and retinal disease. METHODS: Monocular mfVEPs were obtained for both eyes of all subjects. Latencies and amplitudes of individual mfVEP responses were measured using custom software and expressed relative to a normative group (n = 100). Recordings were obtained from patients with ON/MS (n = 12), glaucoma (n = 50), and retinal disease (n = 15), as well as control subjects (n = 50). All subjects had 24-2 visual fields; patients with retinal disease had multifocal electroretinograms (mfERGs). The patients with retinal disease were examined by a neuro-ophthalmologist to rule out optic nerve disease and, in general, had relatively subtle or unremarkable fundus examinations but abnormal mfERG amplitudes. RESULTS: There was considerable overlap in the latencies for the patient groups for both monocular and interocular measures of mfVEP latency. This was particularly true for the patients with retinal disease and ON/MS, for whom the range of latencies was almost identical, as was the percentage of points in the field showing significant delays. CONCLUSION: The mfVEP delays seen in patients with retinal disease are similar in magnitude and prevalence to those seen in patients with a history of ON/MS. In general, this does not present a problem when using the mfVEP in the clinic. However, a retinal problem can be confused with ON/MS or, in fact, dismissed as functional, especially if the fundus appears normal.

Determining abnormal interocular latencies of multifocal visual evoked potentials.

PURPOSE: To describe methods for measuring interocular latency differences of multifocal visual evoked potentials (mfVEP) and for determining regions with abnormal interocular latencies in patients. METHODS: The mfVEPs from 100 individuals with normal visual fields and normal fundus examinations were analyzed. Individuals ranged in age from 21.6 to 92.4 years. The stimulus was a 60 sector, pattern-reversing dartboard display. Each sector had 16 checks, 8 white (200 cd/m2) and 8 black (< 1 cd/m2). Interocular latency was measured as the temporal shift producing the best cross-correlation value between the corresponding responses of each eye. The 'corrected interocular latency' was defined as the difference between this shift and the mean interocular latency (shift) for a particular sector and recording channel. RESULTS: The variability of the corrected interocular latency decreased as the signal-to-noise ratio (SNR) of the mfVEP responses increased. For example, the 95% confidence intervals decreased from over 16 ms to under 4 ms as SNR increased. Grouping and summing the responses also lead to an increase in SNR and a decrease in the confidence interval. The results of various cluster criteria were also derived. A cluster criterion (e.g. two or more contiguous points within a hemisphere exceeding a given confidence interval), can serve to increase the specificity for detection of eyes or individuals with abnormal interocular latencies. For example, while 21% of the eyes had 3 or more points exceeding the 5% confidence interval, only 1.8% of the eyes had a cluster of 3 or more of these points. Finally, interocular latency was only weakly correlated with age (r = 0.26). CONCLUSION: In testing for abnormalities in interocular latencies, the confidence interval should be based upon the SNR of the response. Grouping and summing responses to increase SNR or employing a cluster test may also prove useful.

Determining abnormal latencies of multifocal visual evoked potentials: a monocular analysis.

PURPOSE: To describe a methodology for measuring abnormal timing of monocular multifocal visual evoked potentials (mfVEP). METHODS: The mfVEPs from 100 individuals with normal visual fields and normal fundus exams were analyzed. The stimulus was a 60 sector, pattern-reversing dartboard display. For each of the 60 locations of the dartboard and each channel and each eye, a template was derived based upon the average of the responses from the 100 normal individuals. In deriving this template, care was taken to exclude those responses reversed in polarity as compared to the average response. The best array of responses for each individual was compared to these templates. The relative latency of each response was measured as the temporal shift producing the best cross-correlation value. RESULTS: The 95% confidence interval (CI) decreased as the signal-to-noise ratio (SNR) of the mfVEP responses increased. For example, the 95% CI decreased from over 17 ms to under 9 ms as the SNR increased. Grouping and summing the responses also lead to an increase in SNR and a decrease in CI. Because the number of points exceeding the CI is not randomly distributed among normal individuals, a cluster criterion (e.g. two or more contiguous points within a hemisphere exceeding a given confidence interval) can be helpful. For example, while 18% of the eyes had 5 or more points exceeding the 5% confidence interval, only 6.5% of the eyes had a cluster of 5 of these points. The correlation between relative latency and age was relatively low (r = 0.46). CONCLUSION: For detecting abnormalities in the timing of monocular, mfVEP responses, a template method provides a reasonable approach. In devising a particular test for abnormal timing, the CI should be based upon the SNR of the response. In addition, grouping and summing responses to increase SNR or employing a cluster test may also prove useful.