Análisis biomecánico del disco óptico bajo la variación de presión intraocular y rigidez escleral / Biomechanical analysis of the optic disc under variations in intraocular pressure and scleral rigidity

INTRODUCCIÓN: el incremento de la presión intraocular y las alteraciones detectadas en la apariencia de la cabeza del nervio óptico constituyen factores importantes en la determinación de la progresión del daño glaucomatoso. OBJETIVO: analizar el comportamiento del disco óptico bajo el efecto de la variación de la presión intraocular y de la rigidez escleral, a través de un modelo biomecánico. MÉTODOS: se emplea el método de los elementos finitos. Se definieron varios módulos de rigidez para la esclerótica de 3, 6 y 9 MPa y para la lámina cribosa 0,3 y 0,6 MPa. Todos los tejidos modelados fueron asumidos como materiales isotrópicos con comportamiento elástico e incompresible. RESULTADOS: la mayor concentración de tensiones se localizó en las zonas de la esclerótica peripapilar y en las paredes del canal escleral. Los máximos de tensión (97,523 kPa) y desplazamiento (95,64 µm) se obtuvieron cuando la esclerótica y la lámina cribosa fueron menos rígidas y con la mayor presión intraocular. CONCLUSIONES: la biomecánica del disco óptico influye en el desarrollo de la neuropatía óptica glaucomatosa. El mayor desplazamiento se encuentra en la zona central del disco óptico y está asociado a la pérdida de fibras nerviosas de la retina o al incremento de la excavación papilar en el mecanismo de daño glaucomatoso.

INTRODUCTION: Increase in intraocular pressure and alterations in the appearance of the optic nerve head are important factors in determining the progress of glaucomatous damage. OBJECTIVE: Analyze the behavior of the optic disc under the effect of variations in intraocular pressure and scleral rigidity using a biomechanical model. METHODS: The finite element method was used to define several rigidity modules for the sclera at 3.6 and 9 MPa and for the lamina cribosa at 0.3 and 0.6 MPa. All the tissues modeled were assumed to be isotropic materials with elastic, incompressible behavior. RESULTS: The highest concentration of tensions was located in areas of the peripapillary sclera and scleral canal walls. Tension and displacement peaks (97.523 kPa and 95.64 µm, respectively) were obtained when the sclera and the lamina cribosa were less rigid and intraocular pressure was highest. CONCLUSIONS: The biomechanical characteristics of the optic disc influence the development of glaucomatous optic neuropathy. The greatest displacement is found in the central area of the optic disc, and it is associated with the loss of retinal nerve fibers or an increase in papillary excavation in the mechanism of glaucomatous damage.

Ability of spectral domain optical coherence tomography peripapillary retinal nerve fiber layer thickness measurements to identify early glaucoma.

Purpose: To evaluate the ability of spectral domain optical coherence tomography (OCT) peripapillary retinal nerve fiber layer thickness (RNFLT) parameters to distinguish normal eyes from those with early glaucoma in Asian Indian eyes. Design: Observational cross-sectional study. Materials and Methods: One hundred and seventy eight eyes (83 glaucoma patients and 95 age matched healthy subjects) of subjects more than 40 years of age were included in the study. All subjects underwent RNFLT measurement with spectral OCT/ scanning laser ophthalmoscope (SLO) after dilatation. Sensitivity, specificity and area under the receiving operating characteristic curve (AROC) were calculated for various OCT peripapillary RNFL parameters. Results: The mean RNFLT in healthy subjects and patients with early glaucoma were 105.7 ± 5.1 μm and 90.7 ± 7.5 μm, respectively. The largest AROC was found for 12 o’clock- hour (0.98), average (0.96) and superior quadrant RNFLT (0.9). When target specificity was set at ≥ 90% and ≥ 80%, the parameters with highest sensitivity were 12 o’clock -hour (91.6%), average RNFLT (85.3%) and 12 o’ clock- hour (96.8 %), average RNFLT (94.7%) respectively. Conclusion: Our study showed good ability of spectral OCT/ SLO to differentiate normal eyes from patients with early glaucoma and hence it may serve as an useful adjunct for early diagnosis of glaucoma.

Meta-analysis of beta radiation augmentation for trabeculectomy - results in distinct ethnic groups / Meta-análise da trabeculectomia potencializada pela radiação beta - resultados em grupos étnicos distintos

PURPOSE: To conduct a systematic review with meta-analysis on the efficacy of trabeculectomy (TREC) followed by beta irradiation (BRT/TREC) compared to TREC alone for glaucoma in terms of intraocular pressure (IOP) control and adverse effects of treatment in different ethnic groups. METHODS: A meta-analysis of randomized controlled trials (RCT) was performed comparing adjunct BRT treatment for glaucoma with standard TREC after 12 months. The MEDLINE, EMBASE, LILACS, and Cochrane Library databases, Trial registers, bibliographic databases and recent studies of relevant journals were searched. Two reviewers independently reviewed relevant reports and the references from these reports were searched for additional trials, using guidelines set by QUOROM statement criteria. RESULTS: Of a total of 1,350 citations, eight studies (five cohorts, three randomized) were identified and only 3 RCT were included in this meta-analysis. Higher IOP reductions were verified in the BRT arm compared to the control arm (mean difference=1.68 mmHg, 95 percent CI= 0.61-2.68, P=0.002). Uncontrolled postoperative IOP (>21 mmHg) was less frequent when BRT was used (BRT/ TREC arm) compared to the control arm (38/218=17.4 percent versus 9/239=3.8 percent; OR=6.7; 95 percent CI 3.2-14.3, P<0.0001). Although better IOP control was observed in all patients treated with adjuvant BRT, only Black patients displayed a significant difference (P=0.005). There were no significant differences between the BRT and control arms regarding loss of visual acuity, postoperative complications and necessity of cataract surgery. CONCLUSION: Adjunct BRT increases the success rate of TREC, with better results in non Caucasian patients, and does not influence the occurrence of postoperative complications.

OBJETIVO: Realizar uma revisão sistemática com meta-análise sobre a eficácia da trabeculectomia (TREC), seguida ou não por irradiação beta (BRT/TREC) para o tratamento do glaucoma, em termos de controle da pressão intraocular (PIO) e de efeitos adversos, em diferentes grupos étnicos. MÉTODOS: Uma meta-análise de ensaios clínicos randomizados (RCT) foi realizada, comparando os resultados de 12 meses da TREC com o uso adjuvante de BRT, com aqueles da TREC padrão. Foram fontes de pesquisa as bases de dados MEDLINE, EMBASE, LILACS, Cochrane, além de sítios de registro de ensaios clínicos, estudos recentes em revistas da área e outras bases de dados bibliográficos. Dois revisores avaliaram independentemente publicações relevantes e as referências desses trabalhos foram pesquisadas para procura de ensaios adicionais, de acordo com as diretrizes estabelecidas pelos critérios do QUOROM. RESULTADOS: De um total de 1.350 citações, oito estudos (cinco coortes e três aleatorizados) foram identificados e apenas 3 RCT foram incluídos nesta meta-análise. Maiores reduções na PIO foram verificadas no braço de estudo da BRT, comparado com o braço controle (diferença média=1,68 mmHg, 95 por cento CI= 0,61-2,68, P=0,002). A frequência de PIO pós-operatória não controlada (>21 mmHg) foi menor quando utilizada a BRT (BRT/TREC) em relação ao grupo controle (38/218 =17,4 por cento versus 9/239 =3,8 por cento; OR= 6,7 IC 95 por cento 3,2 14,3, P<0,0001). Apesar do melhor controle da PIO ter sido observada em todos os pacientes do braço BRT, apenas os pacientes negros apresentaram uma diferença significativa (P=0,005). Não houve diferenças significativas entre os braços BRT e controle, em termos de perda da acuidade visual, complicações pós-operatórias e necessidade de cirurgia de catarata. CONCLUSÃO: O uso de BRT adjuvante aumenta a taxa de sucesso da TREC, com melhores resultados em pacientes não-caucasianos, não influenciando a ocorrência de complicações pós-operatórias.