Acute Ocular Manifestations after an Accidental Hydrofluoric Acid Release

PURPOSE: To report the ocular health of a community after an accidental release of hydrofluoric acid (HF). METHODS: The hospital records of 327 patients that were exposed to HF between Sep 9, 2012 and Oct 31, 2012 were reviewed. Demographic characteristics, subjective ocular symptoms, and the ophthalmologic examination results of the patients were analyzed retrospectively. RESULTS: Among the 327 patients, 203 patients (62.1%) were exposed to hydrofluoric acid (HF) within 1,000 m of the site of the accident. A total of 131 patients (40.1%) were exposed to HF over 3 days. The most frequently reported ocular symptoms after HF exposure were ocular pain (49.5%) and conjunctival hyperemia (37.9%). Conjunctival hyperemia (43.4%), corneal erosion (23.9%), conjunctiva papilla, and follicles (24.2% and 14.4%, respectively) were noted during ophthalmologic examinations, but 46.2% of patients were normal on examination. None of the patients had vision-threatening damages. CONCLUSIONS: In this study, severe ocular surface changes, which can affect vision, were not identified. This result could be explained by the low atmospheric HF concentration after the accident.

Study for Analysis of the Multifocal Visual Evoked Potential

PURPOSE: To introduce the clinical utility of the absolute value of the reconstructed waveform method in the analysis of multifocal visual evoked potential (mfVEP). METHODS: The mfVEP with 4-channel recording was performed using RETIscan(R) on 10 eyes of 10 normal subjects. Amplitudes were obtained from ring-shaped 6 areas and 4 sectors. The best visual evoked potential (VEP) response method and the absolute value of the reconstructed waveform method were compared in terms of analysis of the amplitudes. In order to assess the false positive rate of the examination, stimuli were administered with one-half of the cathode ray tube (CRT) monitor completely covered and the results were compared using 2 methods. RESULTS: The amplitudes in 6 areas and 4 sectors analyzed with the best VEP response method and the absolute value of the reconstructed waveform method showed no statistical difference (p > 0.05). The amplitude in the stimuli-blocked area of the absolute value of the reconstructed waveform method was smaller than that of the best VEP response method (p 0.05). CONCLUSIONS: The absolute value of the reconstructed waveform method has similar reproducibility and lower level of false positives relative to the best VEP response method. Therefore, it can be considered as a useful method in the analysis of the mfVEP.

Study for Analysis of the Multifocal Visual Evoked Potential

PURPOSE: To introduce the clinical utility of the absolute value of the reconstructed waveform method in the analysis of multifocal visual evoked potential (mfVEP). METHODS: The mfVEP with 4-channel recording was performed using RETIscan(R) on 10 eyes of 10 normal subjects. Amplitudes were obtained from ring-shaped 6 areas and 4 sectors. The best visual evoked potential (VEP) response method and the absolute value of the reconstructed waveform method were compared in terms of analysis of the amplitudes. In order to assess the false positive rate of the examination, stimuli were administered with one-half of the cathode ray tube (CRT) monitor completely covered and the results were compared using 2 methods. RESULTS: The amplitudes in 6 areas and 4 sectors analyzed with the best VEP response method and the absolute value of the reconstructed waveform method showed no statistical difference (p > 0.05). The amplitude in the stimuli-blocked area of the absolute value of the reconstructed waveform method was smaller than that of the best VEP response method (p 0.05). CONCLUSIONS: The absolute value of the reconstructed waveform method has similar reproducibility and lower level of false positives relative to the best VEP response method. Therefore, it can be considered as a useful method in the analysis of the mfVEP.

Multifocal Visual Evoked Potential in Normal Subjects

PURPOSE: To introduce the clinical utility of multifocal visual evoked potential (mfVEP) and to assess the waveform from normal Korean subjects. METHODS: mfVEP with 4 channel recording was performed using the RETIscan(R) system (Roland Consult, Wiesbaden, Germany) for 25 eyes of 25 normal subjects. Amplitudes and implicit times were obtained from ring-shaped 6 areas and 4 sectors. To investigate the false-positive ratio of the examination, stimuli were given with one-half of the CRT monitor completely covered and the results were compared. RESULTS: Amplitudes of P1, N2 were larger in the central 10degrees area than other areas (p<0.001). Amplitudes were reduced and implicit times were prolonged on peripheral areas. P1 amplitudes were larger in the inferior field. Waves with large amplitudes by noise were recorded in 13.7% of covered areas. CONCLUSIONS: mfVEP is useful tool to detect local optic nerve damage and rule out the non-organic cause of visual field defect. However, mfVEP results are difficult to interpret due to noise and poor patient cooperation. Standardization of mfVEP is necessary for its application.

Photopic Negative Response (PhNR) in Normal Subjects

PURPOSE: To evaluate the nature of photopic negative response (PhNR) in normal subjects. METHODS: The electroretinogram (ERG) waves were recorded in 52 eyes of 26 normal subjects with UTAS E-3000(R) (LKC Technologies Inc., Gaithersberg, MD, USA). Photopic cone response was obtained for analysis from a white flash with white background illumination (group 1) and a red flash with blue background illumination (group 2), after stimulations ranging from 0.007674 cd.s/m2 (-25dB) to 7.736 cd.s/m2 (5dB) with a 5dB interval. RESULTS: PhNRs were observed in all 52 eyes in group 1 stimulated with the white flash at 0.9933 cd.s/m2 (-4dB). PhNRs were also observed in all 52 eyes in group 2 at 2.4297 cd.s/m2 (0dB) after stimulation with the red flash. There was correlation between the amplitudes of PhNR and intensity of stimuli (p<0.001). Implicit times of PhNR were correlated with age in both groups, but amplitudes decreased with age in group 1. CONCLUSIONS: The amplitudes of PhNR were correlated with intensity of stimuli and age had an influence on PhNR. Standardization of examination conditions is necessary when recording PhNR.

Correlation of OCT and Hemifield Pattern VEP in Hemianopia

PURPOSE: To analyze the correlation between RNFL thickness changes measured by OCT and hemifield pattern VEP in hemianopic visual field loss. METHODS: Twelve eyes of six patients with hemianopia were studied. Two patients had bitemporal hemianopia caused by chiasmal tumor, one patient had inferior hemianopia caused by traumatic optic neuropathy, and three patients had homonymous hemianopia caused by occipital lobe lesions. The retinal nerve fiber layer thickness around the optic disc was measured by optical coherence tomography (OCT) and visual pattern evoked potentials were measured using hemifield stimulations. RESULTS: Normal eyes of traumatic optic neuropathy patients were excluded from the analysis. The retinal nerve fiber layer thickness as measured by OCT corresponded to the visual field defect in 9 of 11 eyes (81.8%) and the hemifield pattern VEP response corresponded to visual field defect in 7 of 11 eyes (63.6%). CONCLUSIONS: RNFL thickness measurement by OCT and hemifield PVEP are useful in evaluation of patients with hemianopia. However, they should be performed with caution, and compared with various clinical examinations because of their incomplete correlation with visual field defects.

The Results of B-scan Ultrasonography in Different Positions after Vitrectomy and Gas Tamponade

PURPOSE: To determine the proper time frame in which to assess retinal attachment status and to evaluate the superior retinal attachment status by performing B-scan ultrasonography in different positions on patients who have undergone pars plana vitrectomy and gas tamoponade. METHODS: In this prospective study, 23 patients (23 eyes) who had undergone pars plana vitrectomy and gas tamponade were investigated between June 2005 and February 2006. SF6 (18%) was injected into the vitreous cavity of 15 eyes, and C3F8 (14%) was injected into the vitreous cavity of 8 eyes. At postoperative day 1, day 3, week 1, week 2, and week 4, B-scan ultrasonography was performed in the supine, sitting, prone, right decubitus, and left decubitus positions. RESULTS: The proper time to evaluate the retinal attachment status was three days post-operatively in 10 eyes (66.7%) with SF6 (18%) injections and two weeks post-operatively in six eyes (75%) that had C3F8 (14%) injections. The superior retinal attachment status can be evaluated from the summation of B-scan ultrasonography results performed in the right decubitus and left ducubitus positions. CONCLUSIONS: The proper time to evaluate the retinal attachment status was related to the degree of the gas absorption when performing B-scan ultrasonography after pars plana vitrectomy and gas tamponade. To evaluate the entire retina, it is useful to perform B-scan ultrasonograhy in the prone, right decubitus and left decubitus positions.