Structural and thermal characterizations of silica nanoparticles grafted with pendant maleimide and epoxide groups.

Grafting of free maleimide and epoxide pendant groups onto the surface of approximately 7-nm silica nanoparticles was investigated. Glycidyloxypropyl groups (3-glycidyloxypropyltrimethoxysilane and 3-aminopropyltrimethoxysilane) that carried epoxide groups and aminopropyl groups were grafted to the silica surface with the help of condensation reactions. Maleimide groups [1,1(')-(methylenedi-4,1-phenelene) bismaleimide] were introduced to the silica surface via nucleophilic addition reaction with the aminopropyl groups pre-grafted onto the surface. The grafted silica samples were characterized using CHN, FTIR, DSC, TGA-FTIR, and 13C and 29Si CP/MAS NMR spectroscopy. NMR analyses revealed that all the functional groups were covalently bonded to the silica surface and most of the maleimide and epoxide rings remained intact on surface. DSC analysis showed that the epoxide groups were more reactive than the maleimide groups.

A two-stage approach identifies a Q344X mutation in the rhodopsin gene of a Chinese Singaporean family with autosomal dominant retinitis pigmentosa.

INTRODUCTION: Retinitis pigmentosa (RP) is a group of hereditary retinal diseases in which photoreceptor cells degenerate. It is both clinically and genetically heterogenous. Using a two-stage approach by combining linkage analysis with mutation detection, we have rapidly identified the gene locus and the mutation site of a Chinese Singaporean family with autosomal dominant RP. MATERIALS AND METHODS: Three Chinese Singaporean families were tested. One family showed autosomal dominant inheritance pattern, while the other two could be recessive or sporadic. Twelve di-nucleotide markers tightly linked to 6 genes known to be responsible for either autosomal dominant or recessive RP were selected for linkage analysis. Cosegregation of marker and disease inheritance pattern permits identification of the target candidate gene. RFLP (restriction fragment length polymorphism) markers were added to confirm the linkage result prior to the detailed mutation detection study. RESULTS: With this two-stage strategy, the autosomal dominant RP family showed the rhodopsin locus segregating concordantly with the disease. Mutation screening later identified a nonsense mutation 5261C>T in the last exon of rhodopsin gene. It predicted a Q344X changes at the C-terminus of the gene product, truncating it by 5 amino acids. CONCLUSION: This systematic approach facilitates molecular diagnosis of a genetically heterogenous disease like RP. This is the first report of an RP mutation in Singapore. This 5261C>T mutation has been reported in the Caucasian, but not the Chinese population. The relatively milder phenotype in this family showed similarity to the reported US family, indicating the correlation of mutation site to severity of disease regardless of ethnicity.

Indocyanine green anterior segment angiography for studying conjunctival vascular changes after trabeculectomy.

BACKGROUND: The aim of the study was to evaluate the use of indocyanine green (ICG) for angiography of the anterior segment to characterize conjunctival and episcleral vasculature changes after trabeculectomy. METHODS: This was a prospective evaluation of anterior segment ICG angiography in 10 eyes of 10 patients undergoing trabeculectomy for the first time. Trabeculectomy was performed with intraoperative sponge application of 5-fluorouracil (5 cases) or mitomycin C (5 cases). Anterior segment ICG angiography was performed prior to surgery, then at 2 weeks and 2 months after surgery. RESULTS: With ICG, the anterior segment vessels were well delineated, including deep episcleral veins, which have not been clearly shown in previous angiographic techniques. Late phases of the angiogram could also be studied. The vascular alterations after trabeculectomy noted included oss of vascularity over the bleb area and vascular anastomoses along the perimeter of the avascular bleb. CONCLUSIONS: Angiography using ICG has potential as an investigative tool to study the conjunctival and episcleral vasculature changes after trabeculectomy.

Corneal transmissibility of diode versus argon lasers and their photothermal effects on the cornea and iris.

PURPOSE: Diode laser (810 nm) may possess theoretical advantages over the argon blue-green laser (488 nm) for iridotomy/iridoplasty in an eye with oedematous cornea, such as the acute angle-closure glaucoma (AACG) patient, because of better diode laser tissue penetration in opaque media. We assessed the transmissibility of diode and argon lasers through corneas of varying clarity and evaluated the histopathological features of cornea and iris burns produced by these lasers. METHODS: The transmission of diode and argon lasers through human donor corneal buttons of three grades of clarity--clear, intermediate, and hazy--were compared. Corneal buttons of these varying levels of clarity were also treated with argon and diode lasers, with the beams deliberately focused onto the mid-stroma to assess their photothermal effects. Exposed pigmented irides from whole human eyes were treated directly with argon and diode lasers. The lasers were delivered via slit-lamp systems and the energy settings used were 1000 mW for argon and 980 mW for diode; spot sizes for both lasers were 100 microm, with exposure durations of 0.1 s. Light microscopy studies of these tissues were performed. RESULTS: Transmissibility of diode laser in clear, intermediate, and hazy corneas were 89, 87 and 85% respectively and was significantly superior to argon laser (78, 73 and 70% respectively; P < 0.001, paired Student's t-test). Diode laser did not produce morphological changes in all three grades of corneas whereas argon-laser-treated hazy corneas showed photothermal damage. Both lasers produced deep iris burns, with the diode laser tending to produce deeper burns. CONCLUSION: Our findings suggest that diode laser may be the ideal laser for iridotomy/iridoplasty in the AACG patient with hazy cornea.

Diode laser contact transscleral cyclophotocoagulation for refractory glaucoma in Asian patients.

PURPOSE: To evaluate the effectiveness and safety of diode laser contact transscleral cyclophotocoagulation in Asian patients with refractory glaucoma by lower energy settings with an innovative probe featuring a glass ball tip that focused the laser beam onto the ciliary body. METHODS: This prospective clinical study included consecutive Asian patients with dark irides and confirmed for glaucoma. Only one eye of each patient was treated. Diode laser contact transscleral cyclophotocoagulation treatment was performed with the center of the probe placed 1.5 mm behind the limbus. About 30 pulses of 810-mm laser radiation (power, 1.8 to 2.0 W; duration, 0.3 to 0.5 second) were applied around the eye. Patients were examined at fixed postoperative intervals. Intraocular pressure levels and postoperative complications were recorded. The relation between patient and disease characteristics, total laser energy delivered, and intraocular pressure effects were analyzed. RESULTS: Thirty-three patients were studied, with a mean follow-up period of 9.4 months. An average 56% of patients showed a 30% or greater drop in intraocular pressure. About 38% of patients achieved sustained intraocular pressure lowering to below 22 mm Hg at 18 months. Complications were few and included transient hypotony and iritis. CONCLUSIONS: In Asian patients with refractory glaucoma or painful glaucomatous eyes with poor visual acuity (defined for this study as worse than 20/200), low-energy-setting diode laser contact transscleral cyclophotocoagulation by means of the glass ball probe is relatively effective and safe.

Molecular studies of loss of heterozygosity in retinoblastoma.

Retinoblastoma (Rb) is a paediatric intraocular tumour in which predisposition can be inherited. Cases of Rb tumours can be divided into three types: familial cases, sporadic bilateral cases and sporadic unilateral cases. Familial and sporadic bilateral cases are usually categorised as hereditary while sporadic unilateral cases as non-hereditary. In both familial and non-familial forms of Rb, loss of heterozygosity of the Rb locus has been reported although its frequency in tumours has not so far been accurately determined. The cloning of the gene responsible for retinoblastoma (Rb1) has facilitated DNA studies and genetic counselling of patients. We have examined forty-five cases of retinoblastoma at five intragenic sites of the Rb1 locus, namely intron 1/BamH1, intron 17/Xba1, intron 24/TthIII1, intron 25/Dra1 and Rb1.20 VNTR. Thirty-six out of the forty-five cases (80%) were informative for these markers. Comparison of results between genomic DNA from peripheral blood and from tumours revealed that loss of heterozygosity of alleles could be detected in 50% of cases studied in which tumour samples were available. Investigation of parental origin of retained alleles showed that in all these cases, the paternal alleles were preferentially retained. The analysis of the genetic origin of mutations predisposing to retinoblastoma can facilitate new approaches for identifying recessive mutant genes that lead to cancer as well as to provide a conceptual basis for accurate prenatal predictions of cancer predisposition.

Behçet's disease: corneal perforation as an ocular manifestation.

PURPOSE: Although ocular manifestations are common among patients with Behçet's disease, corneal perforation has not been reported in the literature. We report an unusual case of Behçet's disease with corneal perforation as the main ocular involvement. METHODS/RESULTS: An elderly Chinese patient was referred for eye examination because of clinical suspicion of Behçet's disease. Eye examination showed evidence of long-standing autoimmune disease of the eye, mild iritis and a corneal perforation in the left eye. Despite evidence of chronicity and corneal perforation, the patient was asymptomatic. The perforation was successfully treated with cyanoacrylate glue. CONCLUSIONS: While anterior segment involvement is common in Behçet's disease, this case highlights an unusual and hitherto unreported ocular involvement.

Vascular changes over trabeculectomy blebs.

Low-dose anterior segment fluorescein angiography was performed on 10 eyes before and after trabeculectomy with a limbal-based conjunctival flap. Post-trabeculectomy angiography shows that all successful trabeculectomies have an area of decreased capillary vascular perfusion over the bleb site not coincidental with the area of the bleb and that there is delayed filling of vessels running over the bleb.

Cyclocryotherapy for chronic glaucoma after vitreoretinal surgery.

The case records were reviewed of 27 patients with chronic glaucoma after vitreoretinal surgery who underwent 28 cyclocryotherapy procedures between March 1987 and March 1992. The average intraocular pressure after 3 months was between 11.0 and 13.3 mmHg with an average fall of 24-26 mmHg. More than 85% had intraocular pressures of less than 21 mmHg after 3 months; 28% were hypotonic (IOP < 6 mmHg). Six months postoperatively, 68% maintained or had improved vision. The hypotonic eyes were found to have deterioration in vision more frequently than those with an intraocular pressure > 5 mmHg (57% compared with 24%). The odds of a hypotonic eye losing vision were 4.27 times greater than for a non-hypotonic eye. Cyclocryotherapy was successful in relief of pain in all 4 eyes which were painful pre-operatively.

Visual field loss with capillary non-perfusion in preproliferative and early proliferative diabetic retinopathy.

Thirty two eyes of 19 patients with capillary non-perfusion from preproliferative and early proliferative diabetic retinopathy underwent visual field testing on the 30-2 program of the Humphrey visual field analyser. The mean defect (MD) p value was < 5% in 30 (94%) eyes and the corrected pattern standard deviation (CPSD) was < 10% in 31 (97%) eyes. Areas of capillary non-perfusion demonstrated by fundal fluorescein angiography were closely associated with areas of reduced retinal sensitivity in these 31 eyes. More severe visual field defects were present in non-insulin dependent diabetics and in older patients. MD and CPSD p values of less than 0.5% and 1% respectively were found to be associated with non-insulin dependent diabetes (p < 0.05 and p < 0.01 respectively) and with the older age group (p < 0.05). There was no correlation between severity of field defects with hypertension and degree of retinopathy.

An overview of eye problems in Singapore's elderly.

Medical problems increase in frequency with advancing age. Ophthalmic problems are no exception, and add to disability in the elderly. Cataract, glaucoma, diabetic retinopathy, retinal detachment and age-related maculopathy are common blinding problems in middle-aged to elderly patients. If recognised early and properly managed, useful vision can be preserved in many cases. However, despite increasing awareness of conditions such as acute angle-closure glaucoma and diabetic retinopathy, patients are still presenting too late to the eye clinics. Successful management and rehabilitation of the patient depend upon greater awareness and early diagnosis, and requires cooperation between all medical personnel who deal with elderly patients.