Structure-function relationship comparison between retinal nerve fibre layer and Bruch's membrane opening-minimum rim width in glaucoma

AIM：To evaluate and compare structural optical coherence tomography（OCT）-based parameters,such as Bruch’s membrane opening-minimum rim width（BMO-MRW）,and retinal nerve fiber layer（RNFL）thickness in glaucoma patients with visual field（VF）defects,and to correlate both to mean deviation（MD）values of obtained standard achromatic perimetry（SAP）examinations.METHODS：Patients with glaucoma and glaucomatous VF defects were enrolled in this prospective study and compared to age-matched healthy individuals.All study participants underwent a full ophthalmic examination and VF testing with SAP.Peripapillary RNFL thickness and BMO-MRW were acquired with SD-OCT.Correlation analyses between obtained global functional and global as well as sectorial structural parameters were calculated.RESULTS：A consecutive series of 30 glaucomatous right eyes of 30 patients were included and compared to 36healthy right eyes of 36 individuals in the control group.Global MD of values correlated significantly with global RNFL（Pearson corr.coeff：0.632,P=0.001）and global BMO-MRW（Pearson corr.coeff：0.746,P〈0.001）values in the glaucoma group.Global MD and sectorial RNFL or BMO-MRW values correlated less significantly.In the control group,MD values did not correlate with RNFL or BMO-MRW measurements.A subgroup analysis of myopic patients（〉4 diopters）within the glaucoma group（n=6）revealed a tendency for higher correlations between MD and BMO-MRW than MD and RNFL measurements.CONCLUSION：In a clinical setting,RNFL thickness and BMO-MRW correlate similarly with global VF sensitivity in glaucoma patients with BMO-MRW showing higher correlations in myopic glaucoma patients.

Sensory innervation around immediately vs. delayed loaded implants: a pilot study

Although neurophysiological and psychophysical proof of osseoperception is accumulating, histomorphometric evidence for the neural mechanisms of functional compensation following immediate and delayed implant loading is still lacking. For this randomized split-mouth study, six mongrel dogs randomly received one of four treatment protocols at 36 implant-recipient sites over 16 weeks （third maxillary incisor, third and fourth mandibular premolar）： immediate implant placement and immediate loading （liP＋ IL）; delayed implant placement and delayed loading （DIP＋DL）; delayed implant placement and immediate loading （DIP＋IL）; and natural extraction socket healing （control）. Histomorphometry was performed in the peri-implant bone and soft tissues within 300 pm around the implants. Immunocytochemistry and transmission electron microscopy were used to confirm the presence of neural structures and to reveal their ultrastructural characteristics, respectively. Myelinated nerve fibres densely populated the peri-implant crestal gingival and apical regions, although they were also identified in the woven bone and in the osteons near the implant threads. Compared with the control group in the mandible, the group that received IIP＋IL showed a higher innervation （in N.mm^-2, 5.94±1.12 vs. 3.15±0.63, P〈0.001） and smaller fibre diameter （in pm, 1.37±0.05 vs. 1.64±0.13, P=0.016）, smaller axon diameter （in pm, 0.89±0.05 vs. 1.24±0,10, P=0.009） and g-ratio （0.64±0.04 vs. 0.76±0.05, P〈0.001） in the middle region around the implants. Compared with DIP＋IL in the mandible, IIP＋IL had a higher nerve density （in N.mm^-2, 13.23±2.54 vs. 9.64±1.86, P=0.027）, greater fibre diameter （in pm, 1.32±0.02 vs. 1.20±0.04, P=0.021）, greater axon diameter （in μm, 0.92±0.01 vs. 0.89±0.03, P=-0.035） and lower g-ratio （0.69±0.01 vs. 0.74±0.01, P=-0.033） in the apical region around the implants. It may be assumed that the treatment protocol with liP＋ IL is the preferred method to allow optimized peri-implant re-innervation, but further functional measurements are still required.

Study of long term structural and functional changes in medically controlled glaucoma

AIM: Prospectively analyze the long term structural and functional changes in patients of primary open angle glaucoma(POAG) receiving medical therapy(beta blockers and non beta blockers). In this study an attempt has been made to evaluate whether medical reduction of IOP prevents or delays the progression of glaucomatous visual field loss and/or optic nerve damage in patients with open angle glaucoma. · METHODS: Study conducted over a period of 27 months,at a tertiary eye care hospital including both eyes of 40 patients with POAG. Group 1(20 patients,40 eyes) received beta-blockers,and Group 2(20 patients,40 eyes) received non-beta-blockers. Each patient underwent intraocular pressure measurement,best corrected visual acuity,slit-lamp,fundus examination,gonioscopy,central corneal thickness,visual field assessment by Humphrey automated perimetry and retinal nerve fibre layer thickness by Stratus optical coherence tomography at baseline and at two subsequent visits. The average time interval between each visit was 10-11 months. The statistical analysis was done using one-way analysis of variance(ANOVA). Post-hoc test,using tukey’ method were adopted. Probablity(P) value of 0.05 or less was considered to be statistically significant. ·RESULTS: A total of 80 eyes of 40 patients of POAG were enrolled,24 males,16 females,age group 50-80 years. In both beta and non beta blocker group,reduction(improvement) in mean IOP from initial levels to the levels achieved at the 2nd and 3rd visits was statistically significant. One way ANOVA(df=2),fisher f value =11.64,P =0.000,one way ANOVA(df =3),fisher f value =35.61,P =0.000. Both mean deviation(MD) and pattern standard deviation(PSD) in both beta and nonbeta blockers at different visits were not statistically significant. Retinal nerve fibre layer thickness(RNFL)-only mean inferior retinal nerve fibre layer,the difference between the mean value in beta and non beta blocker groupwere statistically significant. [unpaired t test value(df =78) =2.27,P =0.03]. Side effects with beta blocker were conjunctival hyperemia(10%),burning(5%),and conjunctival hyperemia(5%) in non beta blockers. ·CONCLUSION: Non-beta-blockers are as effective as beta-blockers in bringing about a significant lowering of intraocular pressure to the normal range,and in preventing progressive damage to the visual fields and retinal nerve fibre layer. The absence of systemic side effects and superior IOP lowering efficacy has made non beta-blockers attractive for first line therapy for the treatment of glaucoma worldwide.

Diagnostic evaluation of optical coherence tomography parameters in normal, preperimetric and perimetric glaucoma patients

AIM: To compare the diagnostic ability of glaucoma parameters measured by the optical coherence tomography(OCT) in normal, preperimetric glaucoma(PPG) and perimetric glaucoma(PG) patients. METHODS: This cross-sectional observational study includes 127 eyes of 127 subjects. Patients were divided into PPG(51 eyes), PG(46 eyes), and normal controls(30 eyes) based on clinical optic disc assessment and Humphrey visual field changes. The Heidelberg Spectralis OCT machine using Glaucoma Module Premium Edition software was used to measure the retinal nerve fiber layer(RNFL) and Bruch’s membrane opening-minimum rim width(BMO-MRW) to assess the optic nerve head and ganglion cell layer(GCL) thickness in the macula. RESULTS: RNFL, MRW, and GCL thickness were all significantly thinner in PG compared to PPG and the normal group. The BMO-MRW parameters showed better specificity(>70%) at 90% specificity compared to both RNFL and GCL parameters to discriminate normal, PPG, and PG patients. All BMO-MRW parameters showed higher area under curves(AUC) compared to RNFL and GCL parameters with the highest AUC observed in the superotemporal sector of the BMO-MRW(AUC=0.819 and and 0.897 between normal and PPG and PG groups respectively).CONCLUSION: While the BMO-MRW best discriminates PPG and PG against normal eyes, GCL parameters poorly differentiate the three groups.

Biomechanics of human optic chiasmal compression: ex vivo experiment and finite element modelling

The mechanism of bitemporal hemianopia arising as a result of chiasmal compression is unknown.In this study,we combined an ex vivo experiment and finite element modelling(FEM)to investigate its potential mechanism.A cadaveric human optic chiasm was scanned using micro-CT before and after deformation by inflation of Foley catheter,to simulate tumour growth from beneath.The geometry of the same chiasm was reconstructed and simulated using finite element analysis.Chiasmal deformations were extracted from the simulation and compared with those observed during micro-CT scanning.In addition,nerve fibre models examining variation in local fibre distribution patterns of the chiasm were incorporated to investigate the strain(deformation)distributions of the chiasm at an axonal level.The FEM model matched the micro-CT scans well both qualitatively and quantitatively.Compression of the chiasm induced high strains in the paracentral portions of the chiasm where the crossing optic nerve fibres are located.At an axonal level,the magnitude of strains affecting crossed fibres were greater than those affecting uncrossed fibres.The high strains in the paracentral portions of the chiasm,combined with the differences in strain between crossed and uncrossed nerve fibres,are consistent with a biomechanical explanation for the pattern of visual field loss seen in chiasmal compression.