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Alvin K H Kwok

Publications and source records attributed to Alvin K H Kwok.

At least 19 recordsLinked to original sources
PubMed2006

Assessment of macular function by multifocal electroretinography following epiretinal membrane surgery with indocyanine green-assisted internal limiting membrane peeling.

PURPOSE: To evaluate the changes in macular function and potential retinal toxicity in epiretinal membrane (ERM) surgery with indocyanine green (ICG)-assisted internal limiting membrane (ILM) peeling using multifocal electroretinography (mfERG). METHODS: Thirteen eyes of 13 patients were randomly assigned to have ERM surgery with ILM peeling using 0.5 mg/ml or 1.25 mg/ml ICG staining. Patients were examined at baseline and at 3 and 6 months postoperatively. The postoperative mfERG N1 and P1 response amplitudes and peak latencies of various ring eccentricities were assessed and compared with baseline to determine any serial changes. RESULTS: After surgery, the median best-corrected visual acuity improved from 20/70 at baseline to 20/30 at 6 months postoperatively (Wilcoxon signed-ranks test, P=0.004). At 3 months postoperatively, the 0.5 mg/ml group showed no significant changes in N1 and P1 response amplitudes and peak latencies, whereas the 1.25 mg/ml ICG group showed significant reductions in N1 and P1 response amplitudes compared with baseline. No significant changes in mfERG responses were observed in either group at 6 months after surgery. CONCLUSIONS: Our mfERG findings suggested that the use of a higher concentration of ICG for ILM staining might result in transient retinal functional impairment postoperatively. The lowest possible concentration of ICG should be used intraoperatively to minimize potential retinal toxicity.

Aged↗
PubMed2006

Effect of application duration of 2% lidocaine jelly on aqueous lidocaine concentration for topical anesthesia in cataract surgery.

BACKGROUND: To evaluate the intraocular penetration of lidocaine 2% gel after different duration of application and to assess their effects on intraoperative pain. METHODS: Samples of aqueous humor were obtained in 41 eyes that had phacoemulsification under topical anesthesia with 2% lidocaine gel. The duration between lidocaine gel application and paracentesis was recorded. The aqueous concentration of lidocaine was measured using high performance liquid chromatography (HPLC). Patients were also asked to report the severity of intraoperative pain using a verbal analogue scale. Correlation analysis was performed to analyze the relationship between duration of lidocaine gel application, aqueous lidocaine concentration and intraoperative pain score. RESULTS: The mean duration of lidocaine gel application was 20.3+/-6.1 min and the mean aqueous lidocaine level was 14.2+/-8.5 micro g/ml. Longer duration of lidocaine gel application was significantly associated with higher aqueous concentration of lidocaine (Spearman's rho=0.58, P<0.001). Eyes in which lidocaine gel was applied for 20 minutes or more had significantly higher aqueous lidocaine level (two-tailed t-test, P=0.001) However, the duration of lidocaine gel application and the aqueous concentration of lidocaine showed no correlation with the patent's perceived pain score (P=0.20 and P=0.79, respectively). CONCLUSIONS: Increase in duration of lidocaine gel application resulted in higher aqueous concentration of lidocaine. Patients' level of perceived pain during phacoemulsification under lidocaine gel anesthesia was not related to the intraocular lidocaine absorption level after 10 min of gel application.

Adult↗
PubMed2005

Visual experiences during vitreous surgery under regional anesthesia: a multicenter study.

PURPOSE: To investigate patients' subjective intraoperative visual experiences during vitreous surgery performed under regional anesthesia, to ascertain if patients were frightened by their visual experiences, and to determine the risk factors associated with a frightening visual experience. DESIGN: Multicenter, prospective study. METHODS: Sixty-five patients who had vitreous surgery under regional (retrobulbar or peribulbar) anesthesia in five centers in Ireland, Singapore, and Hong Kong were interviewed within 2 hours of their operation using a standardized questionnaire. RESULTS: Thirty patients (46.2%) perceived light perception throughout the entire operation, 19 patients (29.2%) experienced transient loss of light perception, and 16 patients (24.6%) experienced no light perception throughout the entire duration of the surgery. Nine patients (13.8%) were frightened by their intraoperative visual experiences. Patients who were frightened by their visual experiences were more likely to see color (100%) than those who were not frightened (55.4%) (P = .010). The mean age of the patients who were frightened was lower (51.8 years) compared with those who were not frightened (64.6 years) (P = .003). The mean duration of surgery was longer for patients who were frightened (118.9 minutes) compared with those who were not frightened (91.2 minutes) (P = .047). CONCLUSIONS: Most patients undergoing vitreous surgery under regional anesthesia retained at least light perception intraoperatively. Importantly, 13.8% of patients were frightened by their visual experiences. A younger age, longer duration of surgery, and perception of color were risk factors for a frightening visual experience.

Adult↗
PubMed2005

Prevalence and characteristics of peripheral retinal degeneration in Chinese adults with high myopia: a cross-sectional prevalence survey.

PURPOSE: The purpose of this study was to study the prevalence of peripheral retinal findings in adult Chinese patients with high myopia (refraction < or = -6.00 D) and to investigate the correlation between the retinal lesions and the severity of myopia or axial length. METHODS: A cross-sectional prevalence survey screening was conducted in high ethnic Chinese myopes with refractions equal to or less than -6.00 D. The examinations included cycloplegic refraction, A and B scan ultrasonography, and retinal examinations by indirect ophthalmoscopy with scleral indentation and Goldmann three-mirror contact lens examination. RESULTS: Two hundred thirteen eyes in 213 patients with a mean refraction of -10.10 +/- 4.23 D (range = -6.00 to -27.00 D) were examined. The mean axial length was 26.69 +/- 1.68 mm (range = 25.18-33.62 mm) and the mean age was 33.5 +/- 10.6 years (range = 18-73 years). The most common peripheral retinal finding was pigmentary degeneration (51.2%), followed by lattice degeneration in 12.2% and retinal holes in 7.5% of eyes. A positive correlation was noted between axial length and the lesions of pigmentary degeneration and pavingstone degeneration. The prevalence of retinal holes was 6.4% and 30.0% in eyes with axial length of < 30 mm and > or = 30 mm, respectively (chi-squared test, p = 0.006). CONCLUSION: A high prevalence of peripheral retinal degenerations was found in adult Chinese high myopes. The presence of retinal holes was positively correlated with very high myopia of an axial length of > or = 30 mm.

Adult↗
PubMed2005

TIMP-1 production in human retinal pigment epithelial cells after laser exposure.

PURPOSE: To investigate changes in the production of tissue inhibitor of metalloproteinase type 1 (TIMP-1) by human retinal pigment epithelial (RPE) cells following argon laser exposure. METHODS: Human cultured ARPE19 cells were exposed to argon green laser at four different energy levels ranging from 60mW to 360mW. After laser exposure, the culture media were sampled at 0, 24, 72 and 144 hours for TIMP-1 concentration produced by the RPE cells. The levels of TIMP-1 in the cells treated with different laser energy levels were compared with a control group not exposed to laser application. Immunocytochemistry for proliferating cell nuclear antigen (PCNA) was performed to detect any adverse effects on the RPE cells caused by laser exposure. RESULTS: Immediately after laser exposure, the concentration of TIMP-1 was not detectable. At 24 hours after laser exposure, the concentration of TIMP-1 increased significantly in RPE cells treated with 120mW and 240mW at 24 hours (P=0.006 and P=0.001 respectively) compared with control cells. At 72 hours after treatment, RPE cells treated at 120mW, 240mW and 360mW demonstrated significantly increase in TIMP-1 production compared with control (P=0.003, P < 0.001 and P < 0.001, respectively). No significant reduction in cell viability was observed following laser application as detected by PCNA expression. CONCLUSIONS: Our results demonstrated that early TIMP-1 production by RPE cells in cell cultures was enhanced following laser exposure.

Cell Line↗
PubMed2004

Hemorrhagic complication in an unsuspected macular choroidal melanoma.

PURPOSE: To report a rare presentation of a hemorrhagic complication in a patient with unsuspected macular choroidal melanoma. DESIGN: Interventional case report. METHODS: A 32-year-old Chinese woman presented with disturbance of her left central vision. A hemorrhagic mass at the macula was noticed that was evacuated by submacular surgery. RESULTS: The mass expanded rapidly into a mushroom configuration after surgery. Fine-needle aspiration confirmed the diagnosis of malignant choroidal melanoma, and enucleation followed. Histology demonstrated moderately large epithelioid tumor cells with prominent nucleoli. The sclera was intact, and the optic nerve was not involved. The patient has been followed for 5 years without signs of local recurrence or metastasis. CONCLUSION: We should be alert for atypical presentations of choroidal melanoma. Unnecessary or inadvertent surgical intervention may induce tumor growth and subsequent local spread or metastasis.

Adult↗
PubMed2004

Indocyanine green-assisted internal limiting membrane removal in epiretinal membrane surgery: a clinical and histologic study.

PURPOSE: To evaluate the clinical outcome and quantify histologically the amount of microscopic internal limiting membrane (ILM) and epiretinal membrane (ERM) present in ILM and ERM specimens obtained from ERM surgery. DESIGN: Interventional consecutive case series. METHODS: Patients scheduled for ERM surgery were recruited prospectively. Pars plana vitrectomy, removal of ERM, and ILM peeling with indocyanine green (ICG) staining were performed in all patients. Epiretinal membrane and ILM specimens were sent for histologic examination. The amount of ERM present in ILM specimens and the amount of ILM present in ERM specimens were quantified by manual counting. Outcome measures include change in best-corrected visual acuity (BCVA), proportion of cases with 2 or more lines of visual improvement, anatomic outcome, proportions of microscopic ERM within ILM, and microscopic ILM within ERM. RESULTS: Eighteen eyes in 18 patients were operated with a mean follow-up of 19.3 months. There were 13 primary ERMs and five secondary ERMs. The mean logMAR BCVA improved from 0.83 preoperatively to 0.49 postoperatively (P <.001). The mean lines of improvement in BCVA was 3.3 lines with 14 patients (77.8%) who had 2 or more lines of BCVA improvement. Histologic evaluation of the specimens showed no significant correlation with the final BCVA of 20/50 or better. Eleven (61.1%) of the ILM specimens showed various amount of microscopic ERM and 16 (88.9%) of the ERM specimens showed various amount of ILM fragments. The mean proportion of ERM within ILM specimens was 4.69% and that of ILM within ERM specimens was 51.5%. No significant recurrence of ERM was found. CONCLUSION: Recurrence of ERM may be minimized by removing residual microscopic ERM present on the ILM. Indocyanine green-assisted ILM peeling in ERM surgery appears to have favorable visual and anatomic outcomes.

Aged↗
PubMed2003

Internal limiting membrane staining with various concentrations of indocyanine green dye under air in macular surgeries.

PURPOSE: To determine the effective minimal concentration of indocyanine green (ICG) for staining the internal limiting membrane (ILM) under air in macular surgeries and to report the clinical outcome of these patients. DESIGN: Prospective, randomized clinical trial. METHODS: Consecutive cases of macular hole (17 cases) and epiretinal membrane (ERM) (11 cases) undergoing primary surgery with ICG-stained ILM peeling were randomized to receive one of the three concentrations (mg/ml) of ICG (1): 0.25, (2) 0.5, and (3) 1.25. The number of ICG injections, visual quality of the stained ILM, and time used for ILM peeling were recorded. Internal limiting membrane specimens were subsequently examined under electron microscopy. Preoperative and postoperative clinical data with fluorescein angiography were recorded. RESULTS: There was a significantly smaller number of eyes with poor ILM staining in the 1.25-mg/ml group compared with the 0.25- to 0.5-mg/ml group (Fisher exact test, P =.04). The mean time required for ILM peeling was 4.2 minutes (range, 2.0-8.1 minutes). There was no significant difference in the time required for ILM peeling among the three concentration groups (one-way analysis of variance, P =.18) or between the macular hole and ERM group (two-tailed t test, P =.34). No ICG toxicity was found clinically or angiographically, except in one suspected case with ERM formation at the edge of ILM peeling. Electron microscopy of ILM specimens did not reveal any retinal elements. CONCLUSIONS: 1.25-mg/ml ICG under air stains the macular ILM consistently well for its removal in macular surgeries. The safety of ICG-stained ILM peeling needs further evaluation.

Adult↗
PubMed2003

Epiretinal membrane formation with internal limiting membrane wrinkling after Nd:YAG laser membranotomy in valsalva retinopathy.

PURPOSE: To report the location of premacular hemorrhage in Valsalva retinopathy and epiretinal membrane formation with internal limiting membrane (ILM) wrinkling after neodymium;yttrium-aluminum-garnet (Nd:YAG) laser membranotomy. DESIGN: Interventional case report. METHODS: A 35-year-old man with a massive premacular hemorrhage due to Valsalva retinopathy underwent Nd:YAG laser membranotomy. After membranotomy, his visual acuity improved from 20/200 to 20/25. Ten months later, he developed metamorphopsia with visual acuity of 20/30. A semiopacified membrane with radiating striae was found, and pars plana vitrectomy was performed for membrane removal. RESULTS: Histologic examination of the membrane showed hemosiderin deposits within macrophages on the retinal side of the ILM. One year later, the patient was asymptomatic with visual acuity of 20/20. CONCLUSIONS: To our knowledge, histopathologic confirmation of the sub-ILM hemorrhage in Valsalva retinopathy and epiretinal membrane formation with ILM wrinkling as a complication after Nd:YAG laser membranotomy have not been previously reported.

Adult↗
PubMed2003

Photodynamic therapy with verteporfin for subfoveal idiopathic choroidal neovascularization: one-year results from a prospective case series.

OBJECTIVE: To study the safety and efficacy of photodynamic therapy (PDT) with verteporfin in treating subfoveal choroidal neovascularization (CNV) of idiopathic cause. DESIGN: A prospective, noncomparative, consecutive, open-label, two-center, interventional case series. PARTICIPANTS: Patients aged 50 years or younger with the diagnosis of idiopathic CNV by exclusion of other related causes together with the CNV extending under the geometric center of the foveal avascular zone. METHODS: Seventeen eyes from 17 patients received PDT with verteporfin according to a standardized protocol. Retreatment was considered if fluorescein leakage from the CNV was shown in fluorescein angiography at every 3-month follow-up. The visual, clinical, and angiographic responses were observed. Complications from treatment were monitored and documented. MAIN OUTCOMES MEASURES: The changes in the best-corrected visual acuity (BCVA) at the 1-year follow-up. The proportion of patients with improved (gained 2 lines or more), stable, and dropped (lost 2 lines or more) vision and the mean number of treatments required during the 1-year interval were measured. Complications were monitored and tabulated. RESULTS: Seventeen eyes with complete 1-year follow-up were analyzed. The mean logarithm of the minimum angle of resolution BCVA improved from 0.64 to 0.41 (Wilcoxon signed-ranks test, P = 0.007). Sixteen eyes (94%) had stable or improved vision. Only one patient (6%) had moderate loss of vision. The mean number of PDT treatment was 1.8 per eye over the 1-year period. Patients with smaller lesion size or active vascular CNV on presentation were more likely to have a final BCVA of 20/100 or better (Fisher's exact test, P = 0.006 and P = 0.015, respectively). No serious local or systemic complications were encountered. CONCLUSIONS: PDT seems to be a promising treatment strategy in achieving a stable or improved vision for subfoveal idiopathic CNV. The treatment was well tolerated. Further studies and longer follow-up are warranted to assess the long-term safety and efficacy of PDT compared with observation or other treatment modalities.

Adult↗
PubMed2003

Multiport-illumination-system-assisted phacoemulsification in eyes with dense vitreous hemorrhage during combined cataract and vitreous surgery.

We describe the use of a multiport illumination system to enhance the red reflex during combined phacoemulsification and pars plana vitrectomy in 10 patients with cataract and vitreous hemorrhage. This method improves illumination and visualization of the lens structures and the instruments, which may reduce the risk of complication. To our knowledge, this approach has not been reported.

Aged↗
PubMed2003

Macular hole surgery with or without indocyanine green stained internal limiting membrane peeling.

BACKGROUND: To compare the anatomical and visual outcome in primary idiopathic macular hole surgery with or without indocyanine green (ICG) stained internal limiting membrane (ILM) peeling. METHODS: The medical records of the last 40 consecutive eyes receiving primary idiopathic macular hole surgery with gas as internal tamponade performed by a single surgeon were retrospectively reviewed and analysed. All eyes had a follow-up period of at least 6 months. In the initial 22 consecutive eyes, no ILM peeling was performed (non-ILM peeling group). The subsequent 18 eyes underwent surgery with ICG-stained ILM peeling (ILM peeling group). RESULTS: The primary anatomical closure rates were 88.9% and 59.1% in the ILM peeling group and non-ILM peeling group, respectively. The difference was statistically significant (Fisher's exact test, P = 0.038). Improvement in visual acuity was more marked in the ILM peeling group than in the non-ILM peeling group, with a mean improvement of 3.6 and 1.3 lines, respectively (two-tailed t-test, P = 0.036). There were significantly more cases with improvement of two or more lines of visual acuity after surgery, with 66.7% in the ILM peeling group and 31.8% non-ILM peeling group (Chi-square test P = 0.028). However, there was no significant difference in the final postoperative logMAR best-corrected visual acuity between the two groups (two-tailed t-test, P = 0.073). CONCLUSIONS: Based on this study, ICG-stained ILM peeling seems to improve the anatomical and visual outcome in primary idiopathic macular hole surgery. Further studies in this aspect are warranted.

Adult↗