Amir Samsudin

Effect of haemodialysis on intraocular pressure

AimsTo study the effect of haemodialysis on intraocular pressure (IOP) of patients at the University Malaya Medical Centre, Kuala Lumpur, and the influence of anterior chamber angles, surgery, and diabetes on the change in IOP after haemodialysis.MethodsProspective, single centre study on patients undergoing haemodialysis with a sample size of 98 eyes (49 patients). Ocular examination was performed before haemodialysis. Pre- and post-haemodialysis IOP measurements were taken. Plasma osmolarity changes and volume of fluid removed were noted. Patients on antiglaucoma treatment or who have had earlier laser or surgical procedures for it were excluded. Students t-test and Pearsons coefficient test were used to determine the statistical significance.ResultsPlasma osmolarity decreased significantly (−11.6±10.0mOsm/l, P<0.001). In eyes with occludable angles (8% of cases), IOP decreased significantly (−3.63±1.92 mmHg, P<0.001). In non-occludable angle eyes (92% of cases), no significant changes (P>0.05) in all subgroups of non-operated/operated and diabetic/non-diabetic eyes were seen.ConclusionsHaemodialysis does not cause significant changes in IOP in non-glaucomatous and non-occludable angle eyes.

Corneal changes in type II diabetes mellitus in Malaysia.

AIM To compare corneal endothelial structure and central corneal thickness (CCT) between type II diabetics and non-diabetic control patients. To look for correlations between diabetic status and corneal findings. METHODS Hospital-based, observational study. 200 eyes (from 100 type II diabetic patients and 100 controls) were included. Specular microscopy and pachymetry were used to measure endothelial cell density, size, coefficient of variation in cell area, hexagonality as well as corneal thickness. Independent t-tests were used to compare variables between diabetics and controls. Pearson correlation tests were used to evaluate correlations between corneal findings and diabetic status such as duration of diabetes, haemoglobin A1c (HbA1c) level and severity of diabetic retinopathy. RESULTS Endothelial cell density in the diabetic group (2541.6±516.4 cells/mm(2)) was significantly lower than that in the control group (2660.1±515.5 cells/mm(2), P<0.05). The average size of endothelial cells, standard deviation (SD) of cell size and coefficient of variation (CV) of cell area were all significantly higher in diabetics. Hexagonality was significantly lower in diabetics (41.1%±19.6%) compared to non-diabetics (45.2%±20.6%). CCT was higher in diabetics but not significant (P>0.05). Duration of diabetes, HbA1c level and severity of diabetic retinopathy were not significantly correlated with corneal endothelial findings. CONCLUSION Type II diabetes causes a significant alteration in the state of the cornea including reduction in endothelial cell density and increased pleomorphism and polymegathism. Central corneal thickness is unaffected.

Ocular Surface Disease in Glaucoma: Effect of Polypharmacy and Preservatives.

Purpose To evaluate the prevalence of ocular surface disease (OSD) in glaucoma and nonglaucoma subjects using different clinical tests and to determine the effect of number of antiglaucoma medications and preservatives on OSD. Methods This is a cross-sectional, case-comparison study at the Eye Clinic of the University of Malaya Medical Centre, Malaysia, between June 2012 and January 2013. Glaucoma subjects (n = 105) using topical antiglaucoma medications were compared with control subjects (n = 102) who were not on any topical medications. The presence of OSD was assessed using the tear film breakup time (TBUT) test, corneal staining, Schirmer test, and Ocular Surface Disease Index (OSDI) questionnaire grading. Results The prevalence of OSD varied from 37 to 91% in the glaucoma group, depending on the type of clinical test. More subjects in the glaucoma group had corneal staining (63% vs. 36%, p = 0.004), abnormal Schirmer tests (39% vs. 25%, p = 0.049), and moderate OSDI symptoms (17% vs. 7%, p = 0.028). The percentage with abnormal TBUT increased with higher numbers of topical medications and was high with both benzalkonium chloride–containing and preservative-free eye drops (90% and 94%, respectively, both p < 0.001). Benzalkonium chloride was associated with a nearly three times higher odds ratio of showing abnormal OSDI. Conclusions Ocular surface disease is common in those using topical antiglaucoma medications. Abnormal TBUT is associated with increasing number of eye drops and benzalkonium chloride–containing eye drops, although this also occurs with the use of preservative-free eye drops.

Topical Piperacillin/Tazobactam for Recalcitrant Pseudomonas Aeruginosa Keratitis

PURPOSE To report the treatment of therapy-resistant Pseudomonas aeruginosa keratitis with topical piperacillin/tazobactam. METHODS Retrospective report of 3 cases. RESULTS Three patients with P. aeruginosa keratitis were unresponsive to various antimicrobials. Resolution of all 3 cases of keratitis occurred upon commencement of topical piperacillin/tazobactam. CONCLUSION Therapy-resistant P. aeruginosa keratitis acquired from the community is becoming an increasing problem. Topical piperacillin/tazobactam is an option for the treatment of therapy-resistant P. aeruginosa keratitis.

Proptosis—Correlation and Agreement between Hertel Exophthalmometry and Computed Tomography

ABSTRACT Aim: To determine the correlation and agreement between Hertel exophthalmometry and computed tomography (CT) of the orbits in measuring proptosis. Materials and Methods: 80 patients (40 normal and 40 with proptosis) were recruited for this study. Exophthalmometry were performed on all of them using the Hertel exophthalmometer and CT. Values and correlations between the modalities were analysed with unpaired t-tests, intraclass correlation coefficients (ICC), and Pearson correlation coefficients (PCC). The Bland–Altman method was used to analyse the agreement between the two modalities. Results: Hertel exophthalmometer and CT measurements did not differ significantly (p > 0.05), although exophthalmometry measurements of the normal (14.5 ± 2.2 mm) and proptosis groups (20.5 ± 3.9 mm) were higher than those obtained from CT (13.9 ± 2.4 mm and 20.0 ± 3.7 mm, respectively). ICC for both the Hertel exophthalmometer and CT measurements were both 0.99, indicating high intra-observer reliability and reproducibility. PCC between Hertel exophthalmometer and CT measurements in both normal and proptosis groups were strongly correlated (r = 0.96 and 0.93, respectively, p = 0.01). The 95% limits of agreement (LOA) between Hertel exophthalmometer and CT measurements for the normal and proptosis groups were −0.70 to 1.78 mm and −2.36 to 3.33 mm, respectively. Conclusion: Although Hertel exophthalmometer and CT measurements are similar and strongly correlated, they do not agree well with each other in the presence of proptosis. The measurements should not be used interchangeably as the differences between them may lead to errors in clinical interpretation.

Allometry and Scaling of the Intraocular Pressure and Aqueous Humour Flow Rate in Vertebrate Eyes

In vertebrates, intraocular pressure (IOP) is required to maintain the eye into a shape allowing it to function as an optical instrument. It is sustained by the balance between the production of aqueous humour by the ciliary body and the resistance to its outflow from the eye. Dysregulation of the IOP is often pathological to vision. High IOP may lead to glaucoma, which is in man the second most prevalent cause of blindness. Here, we examine the importance of the IOP and rate of formation of aqueous humour in the development of vertebrate eyes by performing allometric and scaling analyses of the forces acting on the eye during head movement and the energy demands of the cornea, and testing the predictions of the models against a list of measurements in vertebrates collated through a systematic review. We show that the IOP has a weak dependence on body mass, and that in order to maintain the focal length of the eye, it needs to be an order of magnitude greater than the pressure drop across the eye resulting from gravity or head movement. This constitutes an evolutionary constraint that is common to all vertebrates. In animals with cornea-based optics, this constraint also represents a condition to maintain visual acuity. Estimated IOPs were found to increase with the evolution of terrestrial animals. The rate of formation of aqueous humour was found to be adjusted to the metabolic requirements of the cornea, scaling as Vac0.67, where Vac is the volume of the anterior chamber. The present work highlights an interdependence between IOP and aqueous flow rate crucial to ocular function that must be considered to understand the evolution of the dioptric apparatus. It should also be taken into consideration in the prevention and treatment of glaucoma.

The Influence of Scleral Flap Thickness, Shape, and Sutures on Intraocular Pressure (IOP) and Aqueous Humor Flow Direction in a Trabeculectomy Model.

Purpose:Intraocular pressure and aqueous humor flow direction determined by the scleral flap immediately after trabeculectomy are critical determinants of the surgical outcome. We used a large-scale model to objectively measure the influence of flap thickness and shape, and suture number and position on pressure difference across the flap and flow of fluid underneath it. Methods:The model exploits the principle of dynamic and geometric similarity, so while dimensions were up to 30× greater than actual, the flow had similar properties. Scleral flaps were represented by transparent 0.8- and 1.6-mm-thick silicone sheets on an acrylic plate. Dyed 98% glycerin, representing the aqueous humor was pumped between the sheet and plate, and the equilibrium pressure measured with a pressure transducer. Image analysis based on the principle of dye dilution was performed using MATLAB software. Results:The pressure drop across the flap was larger with thinner flaps, due to reduced rigidity and resistance. Doubling the surface area of flaps and reducing the number of sutures from 5 to 3 or 2 also resulted in larger pressure drops. Flow direction was affected mainly by suture number and position, it was less toward the sutures and more toward the nearest free edge of the flap. Posterior flow of aqueous humor was promoted by placing sutures along the sides while leaving the posterior edge free. Conclusion:We demonstrate a new physical model which shows how changes in scleral flap thickness and shape, and suture number and position affect pressure and flow in a trabeculectomy.

Dimensional and Flow Properties of the EX-PRESS Glaucoma Drainage Device

We read with interest the article by Sheybani et al. demonstrating the assessment of fluid dynamics and flow control between the XEN 45 microfistula implant (AqueSys, Aliso Viejo, CA, USA), EX-PRESS implant (Alcon Laboratories, Inc., Fort Worth, TX, USA), and silicone tubing from a Baerveldt implant (Abbott Medical Optics, Abbott Park, IL, USA). The authors demonstrated that the Hagen-Poiseuille equation can be used to calculate the required dimensions of a tube that would prevent hypotony at average aqueous humour production and that the EX-PRESS device, when placed without a sclera flap, results in hypotony. The article describes the EX-PRESS device to have an opening of 200 lm in inner diameter that tapers to a 50-lm inner lumen. Our group has previously reported our evaluation of the EX-PRESS device. Two device models are available, the P50 and P200, with advertised 50and 200-lm luminal internal diameters (ID), respectively. Esterman et al. previously reported that the resistance to the flow with the EX-PRESS device would decrease by 256 times if the luminal diameter were increased by 4 times, as expected from the HagenPoiseuille equation. However, they only observed a resistance value obtained with the P200 device in the order of 6 to 7 times lower than the P50 device, a finding we previously corroborated in our own study. The reduction in resistance with increased lumen ID cannot be explained with the Hagen-Poiseuille equation on the basis of the lumen ID criteria alone. On scanning electron microscopy, we observed that the internal diameters of the lumen of the P50 and P200 were in the region of 200 lm at the subconjunctival space and anterior chamber end. We confirmed with Alcon, Inc. that the P50 differs from the P200 only in having a 150-lm diameter bar lying across its lumen in the middle of the device. The P50 and P200 devices also have a side orifice at the anterior chamber end of their bodies, which means they do not have a constant circular cross section. This, together with the presence of the bar lying across the lumen of the P50 device, means that Poiseuille’s Law is not applicable. Sheybani et al. also state that the EX-PRESS does not provide significant outflow resistance. We too observed that there were minimal differences in pressures between the EXPRESS device and a typical trabeculectomy. However, we observed that device implantation resulted in less variability in pressure readings. This may be due to more consistent lumen sizes with small tolerances, compared to making a sclerostomy with a punching device or knife. We also observed that more manipulation was required subjectively with a smaller 27-gauge (G) versus 25-G needle stab on device insertion. This may result in a poorer fit around the body of the device, resulting in leakage. We agree with Sheybani et al. that use of the EX-PRESS device without a scleral flap carries significant risk of hypotony and has similar equilibrium pressures as the trabeculectomy procedure. We would highlight that the effective luminal diameter of the P50 is much larger than 50 lm and that intraoperative surgical technique may reduce tissue manipulation and, therefore, reduce postoperative pressure fluctuations.

Numerical Study on the Effects of Segmental Aqueous Humour Outflow on Ocular Drug Delivery

The present study develops a 3D model of the human eye to investigate the effects of segmental aqueous humour outflow on ocular drug delivery. Segmental outflow is modelled by prescribing the permeability of the trabecular meshwork (TM) as a spatially-varying heterogeneous function that follows a rectangular profile. The choice of the rectangular profile is decided based on a recent experimental study on segmental outflow. Results from the numerical simulations showed that segmental outflow causes the majority of the drugs to egress through the active part of the TM. In the context of glaucoma treatment, this can be detrimental to the treatment efficacy, since it is the non-active region is the primary target site of the drugs.

The Correlation Between Central Corneal Thickness and Glaucomatous Optic Nerve Damage in a Human Eye

Results from clinical studies suggest a strong correlation between central corneal thickness (CCT) and glaucomatous optic nerve damage. A 3D model is developed to carry out structural investigation of the IOP-induced posterior displacement of the lamina cribrosa (LC), under the influence of CCT. The cornea, the sclera and the LC are assumed to exhibit nonlinear material properties. The numerical results suggest a higher glaucoma progression rate with a lower CCT, which supports the clinical trend. The low influential rate of CCT towards optic nerve damage suggests that CCT may not be a dominant factor in structural injury of the nerve bundles. The results indicate that CCT measurement can be significant in the diagnostic system of glaucoma.