Prediction error and accuracy of intraocular lens power calculation in pediatric patient comparing SRK II and Pediatric IOL Calculator

<p>Abstract</p> <p>Background</p> <p>Despite growing number of intraocular lens power calculation formulas, there is no evidence that these formulas have good predictive accuracy in pediatric, whose eyes are still undergoing rapid growth and refractive changes. This study is intended to compare the prediction error and the accuracy of predictability of intraocular lens power calculation in pediatric patients at 3 month post cataract surgery with primary implantation of an intraocular lens using SRK II versus Pediatric IOL Calculator for pediatric intraocular lens calculation. Pediatric IOL Calculator is a modification of SRK II using Holladay algorithm. This program attempts to predict the refraction of a pseudophakic child as he grows, using a Holladay algorithm model. This model is based on refraction measurements of pediatric aphakic eyes. Pediatric IOL Calculator uses computer software for intraocular lens calculation.</p> <p>Methods</p> <p>This comparative study consists of 31 eyes (24 patients) that successfully underwent cataract surgery and intraocular lens implantations. All patients were 12 years old and below (range: 4 months to 12 years old). Patients were randomized into 2 groups; SRK II group and Pediatric IOL Calculator group using envelope technique sampling procedure. Intraocular lens power calculations were made using either SRK II or Pediatric IOL Calculator for pediatric intraocular lens calculation based on the printed technique selected for every patient. Thirteen patients were assigned for SRK II group and another 11 patients for Pediatric IOL Calculator group. For SRK II group, the predicted postoperative refraction is based on the patient's axial length and is aimed for emmetropic at the time of surgery. However for Pediatric IOL Calculator group, the predicted postoperative refraction is aimed for emmetropic spherical equivalent at age 2 years old. The postoperative refractive outcome was taken as the spherical equivalent of the refraction at 3 month postoperative follow-up. The data were analysed to compare the mean prediction error and the accuracy of predictability of intraocular lens power calculation between SRK II and Pediatric IOL Calculator.</p> <p>Results</p> <p>There were 16 eyes in SRK II group and 15 eyes in Pediatric IOL Calculator group. The mean prediction error in the SRK II group was 1.03 D (SD, 0.69 D) while in Pediatric IOL Calculator group was 1.14 D (SD, 1.19 D). The SRK II group showed lower prediction error of 0.11 D compared to Pediatric IOL Calculator group, but this was not statistically significant (p = 0.74). There were 3 eyes (18.75%) in SRK II group achieved acccurate predictability where the refraction postoperatively was within ± 0.5 D from predicted refraction compared to 7 eyes (46.67%) in the Pediatric IOL Calculator group. However the difference of the accuracy of predictability of postoperative refraction between the two formulas was also not statistically significant (p = 0.097).</p> <p>Conclusions</p> <p>The prediction error and the accuracy of predictability of postoperative refraction in pediatric cataract surgery are comparable between SRK II and Pediatric IOL Calculator. The existence of the Pediatric IOL Calculator provides an alternative to the ophthalmologist for intraocular lens calculation in pediatric patients. Relatively small sample size and unequal distribution of patients especially the younger children (less than 3 years) with a short time follow-up (3 months), considering spherical equivalent only.</p

Thermal degredation study of kenaf fibre/epoxy composites using thermo gravimetric analysis

Kenaf fibres are receiving much attention in the natural fibre composite industry due to its potential as polymer reinforcements. However, like all natural fibres, kenaf fibres have lower thermal resistance as compared to synthetic fibres. In this current work, the characteristics of kenaf fibre/epoxy composites, both treated and untreated using alkalization process, exposed to high temperature were studied. Thermo gravimetric analysis (TGA) was used to study the thermal decomposition behaviour of treated and untreated kenaf fibre/epoxy composites, glass fibre/epoxy composite as well as neat epoxy from room temperature up to 600ºC. Surface morphology of both kenaf fibre/epoxy composites after exposure at 100ºC was observed using scanning electron microscopy (SEM). The results from the TGA showed that the addition of kenaf fibres into the epoxy slightly improves both the charring and thermal stability of the samples. However, it was observed that alkalization of fibres causes reduction in these behaviours. At 100ºC, the SEMs show more voids in the untreated composites than the treated ones, suggesting higher moisture content within the voids which influences the higher weight loss of untreated composite at this temperature

Characteristics of kenaf fibre/epoxy composites subjected to thermal degradation

Kenaf fibres are receiving much attention in the natural fibre composite industry due to its potential as polymer reinforcements. However, like all natural fibres, kenaf fibres have lower thermal resistance as compared to synthetic fibres. In this current work, the characteristics of kenaf fibre/epoxy composites, both treated and untreated using alkalization process, exposed to high temperature were studied. Thermogravimetric analysis (TGA) was used to study the thermal decomposition behaviour of treated and untreated kenaf/epoxy composites as well as their components, kenaf fibre and neat epoxy from room temperature up to 600 °C. The weight loss and physical changes of these samples were observed through furnace pyrolysis. Surface morphology of the composites after degradation was observed using scanning electron microscopy (SEM). The results from the TGA showed that the addition of kenaf fibres into the epoxy slightly improves both the charring and thermal stability of the samples. However, it was observed that alkalization causes reduction in these behaviours for the kenaf/epoxy composite. Generally, increased exposure time causes higher weight loss of the composites only up to 150 °C. At higher temperature, duration of exposure has little influence on the weight loss. Fibre-matrix debondings were observed on degraded samples implying mechanical degradation of the composites had occurred

Physical and mechanical properties of bamboo fibre/polyester composites subjected to moisture and hygrothermal conditions

The widespread use of natural fibre reinforced composites is hindered by a few issues, some related to the durability of the natural fibre itself especially when exposed to certain environmental conditions. In this study, the moisture impact on the physical and mechanical behaviours of bamboo fibre/polyester composites was investigated. Composites fabricated using bamboo fibres and polyester resin were immersed in water at room temperature (25 ℃) for 60 days and at 80 ℃ for 2 days. The percentage of thickness swelling and surface expansion was recorded throughout the duration of the study, until apparent physical degradation was observed on the samples. At both temperatures, untreated and treated composites had similar swelling behaviour, with 8% NaOH-treated composite showing highest swelling rate. The surface area expansion for all composites was observed to be much lower than in the thickness direction and was relatively negligible. Since the percentage of final swelling was about the same for all composites, it was also found that the composites achieved similar maximum tensile strength for both conditions, with approximately 2% increment at room temperature and 13.6% reduction at 80 ℃

Characteristics of kenaf fibre immersed in different solutions

Nowadays, kenaf fibres are becoming extensively used as natural reinforcements for polymeric composites. The mechanical properties of the fibres are the most influential elements on the characteristics of the composites. In the current work, tensile property of kenaf fibre was studied at different aging conditions (immersed in water, salt water, diesel and engine oil). The tensile property of the fibre was tested in two different techniques as single fibre, and bundle (20-55 fibres). Surface morphology of the fibres, before and after aging, was observed using scanning electron microscopy. The results showed that engine oil highly influenced the mechanical properties of the fibre compared to the other solutions. A drop in the strength was about 70% for both untreated and treated fibres immersed in diesel solution followed by diesel, and then water. The reduction in tensile strength by salt water solutions was the least, at about 27.16% for untreated fibres. The damage on the fibre aged in salt water was less than the damages observed on the aged fibres in other solutions

Natural fibers and their characterization

To understand the contribution of bamboo fibers in a composite system, the characteristics of the fiber should be comprehensively evaluated. One of the major issues regarding the use of natural fibers in the polymer composite industry is the incompatibility between the hydrophilic fibers and the hydrophobic polymer resin, which renders weak the interfacial adhesion, leading to ineffectiveness of load transfer from the matrix resin to the reinforcing fibers. One of the most recent and effective technique for improving interfacial adhesion between natural fibers and polymer matrices is alkali treatment, which involves the immersion of fibers in sodium hydroxide (NaOH) solution. Although several studies have shown the potential of using bamboo fibers as reinforcement in natural composites, limited work is conducted to comprehensively study the influence of the NaOH on the structural, physical, and tensile characteristics of bamboo fiber. Such studies are essential to understand these important characteristics of bamboo fibers, leading to their mechanical improvement, producing compositeswith enhanced properties and, eventually, expanding the use of bamboo fibers in the polymer composite industry. This chapter aims at evaluating the effect of alkali treatment on the structural, physical, and tensile characteristics of bamboo fibers, as well as the interfacial and tensile properties of the corresponding bamboo fiber/polyester composites. The morphological changes of the fibers and the impact they have on the interfacial adhesion of the fiber/matrix interface were studied using scanning electron microscopy (SEM) to understand the mechanical behavior of the composites. Single fiber tensile test (SFTT) and single fiber fragmentation test (SFFT) were used to study the tensile and interfacial behaviors of the fibers, respectively