Visual electrophysiology in congenital nystagmus with normal fundus.

OBJECTIVE: To identify the ophthalmic causes of congenital nystagmus with normal eye examination by visual electrophysiologic tests. MATERIAL AND METHOD: Medical records of patients who presented with nystagmus and no other neurological sign before 6 months of age with normal eye examination, between February 2004 and February 2005, were reviewed Complete ophthalmic examination and visual electrophysiologic tests were performed to identify the ophthalmic causes of congenital nystagmus. RESULTS: Thirty-four patients had met the criteria. Leber's congenital amaurosis was diagnosed in 13 patients (38.2%) by non-recordable electroretinography (ERG) and normal visual evoked potential (VEP). Idiopathic infantile nystagmus was diagnosed in 12 patients (35.3%) by normal ERG and VEP. Achromatopsia was diagnosed in 8 patients (23.5%) by flat retinal cone ERG but normal rod ERG and VEP. Rod-cone dystrophy was diagnosed in one patient (3%) by abnormal rod and cone ERG CONCLUSION: Visual electrophysiologic study is helpful to identify the ophthalmic causes of congenital nystagmus. Leber's congenital amaurosis is a common cause in congenital nystagmus.

Normative data of optic nerve head in Thai population by laser scanning tomography: Siriraj study.

OBJECTIVE: To study the normative values of topographic optic disc parameters in a Thai population. MATERIAL AND METHOD: Two hundred and six eyes of 103 normal subjects aging from 30-80 years were studied Thirteen topographic disc parameters were analyzed by confocal scanning laser ophthalmoscope using Heidelburg retina tomography (HRT II). The average value of two eyes in the same subject was used as the unit of statistical analysis, and then the normal values and means were statistically calculated at 95% reference interval (95% RI). Ethnic differences of the calculated optic nerve topography were compared with previous studies. The relationship of age, intraocular pressure (IOP), central corneal thickness (CCT), and optic disc parameters were assessed by Pearson correlation. RESULTS: Mean values with 95% RI of all 13 parameters were analyzed Whole parameters except cup volume demonstrated normal distribution. Mean value (95% RI) of disc area in normal Thai people was 2.67 mm2 (1.96, 3.71) which was larger than Caucasian people. Ethnic differences in topographic optic disc parameters were found among Thai and other races including Asians, Caucasians, African-Americans, and Hispanics. The results also revealed that age, IOP, and CCT had no significant relation to all optic disc parameters. CONCLUSION: Thai people had a larger optic disc area than Caucasians. There are marked differences of topographic optic nerve parameters among different ethnic groups. These differences need to be taken into account when evaluating glaucomatous optic neuropathy and when comparing results of studies completed among population of different ethnic and racial origins.

Normative data of electroretinogram and visual evoked potential in Thai population.

Objective : To define normal values of Electroretinogram [ERG] and Visual Evoked Potential [VEP] in different age groups using Viking Select Master Software V7.1. Methods: ERG and VEP values were measured using Viking Select Master Software V7.1 in selected subjects without history of ocular and/or systemic diseases that affect ERG and VEP values. Results were studied in three groups of age: less than 10 years old, 11 to 40 years old and over 40 years old. Results: There were 26 eyes in the first group with age range from 6-10 years old [mean 7.8 + 1.52 years old]. In ERG : the normal values of photopic amplitude of ; a-wave was> 18.57 microvoltage [ตV] and b-wave was> 23.82 ตV, flickering amplitude of b-wave was > 21.93 ตV, scotopic amplitude of b-wave was> 39.12 ตV, mesopic amplitude of ; a-wave was > 60.44 ตV and b-wave was > 96.84 ตV. In VEP : transient flash amplitude was> 20.58 ตV and latency was < 94.10 millisecond[ms], transient pattern size 2 amplitude was > 8.61 ตV and latency was < 100.00 ms. There were 75 eyes in the second group with age range from 11-38 years old [mean 26.8 + 7.35 years old]. The values of photopic amplitude of ; a-wave was > 22.56 ตV and b-wave was > 20.14 ตV, flickering amplitude of b-wave was > 19.35 ตV, scotopic amplitude of b-wave was > 32.29 ตV, mesopic amplitude of ; a-wave was > 45.05 ตV and b-wave was> 78.97 ตV, VEP- transient flash amplitude was > 11.64 ตV and latency was < 96.78 ms, transient pattern size 2 amplitude was > 4.82 ตV and latency was < 88.49 ms. There were 77 eyes in the third group with age range from 41-81 years old [mean 60.1 + 11.54 years old]. The values of photopic amplitude of; a-wave was > 19.12 ตV and b-wave was > 24.59 ตV, flickering amplitude of b-wave was > 18.76 ตV, scotopic amplitude of b-wave was > 35.60 ตV, mesopic amplitude of ; a-wave was > 40.90 ตV and b-wave was > 94.09 ตV, VEP- transient flash amplitude was > 10.07 ตV and latency was < 102.10 ms, transient pattern size 2 amplitude was > 5.34 ตV and latency was < 96.00 ms. Conclusion: We established normal ERG and VEP values in different age group using Viking Select Master Software V7.1 at Siriraj Hospital to distinguish between normal and pathological patients. The values are affected in relation to machine and environmental setting in different laboratory. It is essential for individual laboratories to set their own normal values.

A comparative study of visual evoked potentials in optic neuritis and optic neuritis with multiple sclerosis.

OBJECTIVE: To compare the visual evoked potentials (VEP) in patients with acute optic neuritis, recurrent optic neuritis, and optic neuritis with multiple sclerosis. MATERIAL AND METHOD: The authors retrospectively reviewed VEP latency records of the patients with optic neuritis in Siriraj Hospital from 1995 to 2005 and divided them into three groups, acute optic neuritis, recurrent optic neuritis, and optic neuritis with multiple sclerosis (ON/MS). The patients with non-recordable VEP in the analysis were excluded. Comparison of the mean latency of the VEP in affected eyes among the three groups was statistically analyzed by a nonparametric independent sample test. RESULTS: Twenty-two patients with acute optic neuritis, 8 patients with recurrent optic neuritis, and 22 patients with ON/MS participated in this study. The mean age among the three groups was not statistically significant. The median value of the latency of flash VEP (fVEP) and pattern reversal VEP (PRVEP) in the acute optic neuritis group was shorter than that of the recurrent optic neuritis group, and statistically significant (fVEP p = 0.012; PRVEP, p = 0.004). The median value of the latency of PRVEP in the acute optic neuritis group was shorter than that of the ON/MS group, and statistically significant (PRVEP p = 0.002). The median value of the latency of both fVEP and PRVEP in the recurrent optic neuritis group and ON/MS group were delayed with no statistical significance (fVEP p = 0.458; PRVEP, p = 0.403). CONCLUSION: The VEP can be used to demonstrate the demyelinating mechanism of optic neuritis and optic neuritis with multiple sclerosis, but cannot determine the susceptibility of the patients with acute ON to become MS. The significantly delayed latency of VEP in recurrent optic neuritis is possibly caused by severe damage of the optic nerve conduction from recurrent attacks.

Tonometry after laser in situ keratomileusis treatment: a preliminary study in Thai patients.

OBJECTIVE: To evaluate the change in intraocular pressure (IOP) measurement by Goldmann applanation tonometer after Laser in Situ Keratomileusis (LASIK) for myopia and myopic astigmatism, and to assess the correlation between the changes of lOP reading and the reduction of central corneal thickness (CCT) after LASIK in Thai patients. STUDY DESIGN: Prospective correlational study. MATERIAL AND METHOD: LASIK was performed on 65 eyes of 33 patients for correction of myopia and myopic astigmatism. IOP was measured by Goldmann applanation tonometer before and 3 months after LASIK. The correlation between the change in IOP reading and the change in central corneal thickness were evaluated. RESULTS: IOP reading was significantly reduced by mean of 2.9 +/- 2.5 mmHg (p = 0.0001). The authors used Pearson analysis to study the correlation between the change in IOP and the reduction of CCT. In subgroup analysis the patients were divided by degree of myopia: group 1, myopia less than -3 diopters (D) (n = 14); group 2, myopia -3 to -6 D (n = 31); group 3, myopia greater than -6 D (n = 20)). The result showed more correlation in higher myopia group (Pearson; r = 0.158 in group 3, r = -0.098 in group 2 and r = -0.102 in group 1). CONCLUSION: Goldmann applanation tonometry underestimates the IOP in thin cornea. Variability in CCT is a potent confounder of this tonometry technique. Therefore, it has important implications for considering CCT measurement incorporated with Goldmann applanation tonometry for glaucoma diagnosis especially in myopic patients who undergo LASIK surgery.

Efficacy of brimonidine 0.2 per cent as adjunctive therapy to beta-blockers: a comparative study between POAG and CACG in Asian eyes.

OBJECTIVE: To compare the efficacy and safety profile of brimonidine as adjunctive therapy to beta-blockers between primary open angle glaucoma (POAG) and chronic angle closure glaucoma (CACG) in Asian eyes. DESIGN: Three-months, open-label, prospective study. PARTICIPANTS: Twenty-three patients (35 eyes) with POAG and 25 patients (39 eyes) with CACG were enrolled in the study. INTERVENTION: Patients with POAG or CACG post iridectomy whose IOP was inadequately controlled with topical beta-blocker monotherapy were included. Then, brimonidine 0.2 per cent was added twice daily in both groups. Study visit occurred at weeks 2, 4, 8, and 12. Complete ophthalmic examinations were performed in all visits. MAIN OUTCOME MEASURES: Efficacy was determined by reduction in IOP from baseline and tolerability was assessed by reports of adverse events. RESULTS: After 3 months of brimonidine adjunctive treatment, the mean (+/- SEM) IOP reduction were 4.37+/-0.34 mmHg (19.4%) in POAG and 4.54+/-0.37 mmHg (20.1%) in CACG (p= 0.741). No serious ocular or systemic adverse event was reported. CONCLUSION: Brimonidine was well tolerated, efficacious and provided additive IOP reduction in POAG and CACG.

Evaluation of screening tests and prevalence of glaucoma: integrated health research program for the Thai elderly.

The purposes of this study were to evaluate the accuracy of glaucoma screening tests and to assess the prevalence of glaucoma in an elderly Thai population over 60 years of age. This was a cross-sectional study. 3706 subjects were recruited from 33 communities in the vicinity of Siriraj Hospital. All received an eye examination from ophthalmologists and general practitioners including visual acuity, Schiotz tonometry and optic disc evaluation in their residential communities. Subjects who were suspected of having glaucoma were re-examined at the Glaucoma Clinic, Siriraj Hospital. They were then classified as having definite glaucoma of a specific type or as not having glaucoma. The overall prevalence of glaucoma was 6.1 per cent (128/2092). The percentages of primary open angle glaucoma, primary angle closure glaucoma, normotension glaucoma and secondary glaucoma were 47.7 per cent, 41.4 per cent, 9.4 per cent, and 1.6 per cent respectively. The sensitivity and specificity of the screening tests performed by ophthalmologists were 100 per cent and 97.2 per cent and those performed by general practitioners were 21.7 per cent and 96.5 per cent.