Biometric Parameters Of Eye Research Articles

Comment on: Influence of ocular biometric parameters such as effective lens position, keratometry, and axial length on near add power of multifocal intraocular lens.

We read with interest the manuscript by Wu et al.1 The authors conduced a review about the variability of multifocal intraocular lens (mIOL) addition depending on biometric eye parameters, compiling the theoretical background provided in the scientific literature. The main clinical implication is that this variability should be considered in surgical planning, as the authors remark in the conclusion. Beyond the theoretical background, which was already described by Savini et al.,2 the review missed some important clinical evidence for translation to real practice in mIOL selection. We would like to give our point of view about some important messages for clinical practice and comment on the possible corrections needed. “In clinic, myopic patients with steep cornea often have longer effective lens position (ELP), which reduces near focal point of mIOLs, whereas hyperopic patients with flat cornea have the opposite situation.” This situation is not commonly observed in clinical practice. Patients with a longer axial length (AXL) have a longer ELP, and corneal power is inversely correlated with AXL, which means that eyes with a longer AXL usually have flatter corneas, contrary to the authors' sentence. Thus, the formula considering all the parameters should be used for a correct estimation of the addition (EA) because the higher EA due to lower corneal power is usually dominated by a lower EA due to a longer ELP in longer eyes.3 Wu et al. state: “A larger ELP should be more suitable for a higher near add power of mIOLs and a lower ELP should be more suitable for a higher near add power of mIOLs.”1 We assume the authors based this recommendation on the study by Savini et al., but there is a mistake in the second half of the sentence, which we believe should read: “…lower ELP should be more suitable for a lower near add power of mIOLs.”2 Wu et al. state: “They also found that variations in ELP had a greater effect on the position of the near focal point than K.”1 This is true, the ELP dominates the EA in comparison with keratometry (K), but other factors should be considered beyond the EA calculation. According to clinical evidence, near vision goes beyond the EA. Keratometry has demonstrated frequent relationships with near vision performance, whereas relationships between EA and near visual performance could depend on mIOL design.4 Wu et al. state: “Considering that the defocusing curve can roughly reflect the real near addition of mIOLs,….”1 Clinical evidence supports that EA could underestimate the effective addition calculated from defocus curves.5 In conclusion, beyond the EA calculation for mIOL selection, near vision could be influenced by other eye biometric parameters and mIOL optical characteristics (such as light distribution). Some clinical evidence has demonstrated that eyes with higher corneal power (steeper corneas related to short eyes) have lower areas under the visual acuity defocus curve in the near range.4 Therefore, although the theoretical basis of EA recommends low-addition mIOLs for short eyes, our clinical studies suggest that caution should be exercised when selecting low-addition mIOLs in short eyes in patients with higher expectations of spectacle independence. The theory of EA for mIOL selection is more valid if the same optical design is used for different additions; however, different additions come from different manufacturers and optical designs. Surgeons should consider that EA theory might not always be accomplished. In addition, it should not be forgotten that selecting a higher EA for improving near vision might also lead to poorer intermediate vision, and nowadays, decisions should be made considering patient needs throughout the entire range of vision.

Ocular biometric dimensions according to gender. Are they different?

AbstractPurpose: To analyse ocular biometric parameters in men and women in a population of cataract surgery candidates and determine whether statistically significant differences exist.Methods: A cross‐sectional study of 5034 eyes of 2671 patients was performed. Biometric parameters of the eyes were measured by Zeiss IOLMaster 700. The axial length (AL), mean anterior radio (aR), mean posterior radio (pR), central corneal thickness (CCT), anterior chamber depth (ACD) (epithelium to lens), lens thickness (LT), and White to White corneal diameter (W2W) were evaluated. These data represent normative biometric values for the Valencian population.Results: The mean age in the male group was 73 ± 9.6 years, the mean age in the female group was 73.8 ± 8.3 years. The male/female ratio was 0.84. The male–female difference, with a 95% confidence interval (CI) in AL, ACD, and LT were 0.65 mm [0.57; 0.73] (p < 0.01), 0.17 mm [0.14; 0.2] (p < 0.01), and 0.031 mm [0.005; 0.5] (p < 0.05), respectively. Differences (95% CI) in W2W and CCT were 0.18 mm [0.15; 0.20] (p < 0.01), and 4.89 μm [2.55; 7.23] (p < 0.01). Differences (95% CI) in aR and pR were 0.137 mm [0.12; 0.153] (p < 0.01) and 0.122 mm [0.106; 0.139] (p < 0.01). All biometric eye parameters (AL, aR, pR, CCT, ACD, LT, W2W) measured, were lower in females than in males, with a statistically significant difference.Conclusions: Statistically significant differences between genders were found in all the biometric parameters evaluated. In our population, women's eyes are smaller than men's in all biometric parameters that shape them. Gender must be taken into account in the biometric evaluation of the eye. These results may be relevant in intraocular lens power calculation and in the evaluation of refractive error.

Influence of ocular biometric parameters such as effective lens position, keratometry, and axial length on near add power of multifocal intraocular lens.

Visual quality after multifocal intraocular lens (mIOL) implantation has received increased attention. Postoperative residual ametropia, posterior capsule opacification, dry eye, IOL decentration, pupil size, and other factors can affect patient visual acuity. In addition, patient dissatisfaction after mIOL implantation has a relationship with the near add power of mIOLs, which is correlated with vision habits of different patients. Indeed, the actual spectacle plane add power of mIOLs is incompletely consistent with the near add power given by the manufacturers. Ocular biometric parameters such as effective lens position, keratometry, and axial length have effect on the near add power of mIOLs in the lens plane. In this article, the influence of ocular biometric eye parameters on the actual near add power of mIOLs in the lens plane was reviewed.

Do Gender, Age, Body Mass and Height Influence Eye Biometrical Properties in Young Adults? A Pilot Study.

Background: Do gender, age, body mass and height influence eye biometrical properties in young adults? Methods: A total of 155 eyes (92 female, 63 male) of healthy subjects between the ages of 18 and 39 years were included in the study. The subjects’ gender and age were recorded, and their body mass, height and biometrical properties of the eyes were measured. Results: The male subjects had significantly thicker and flatter corneas and lower minimal rim-to-disk ratios than the female subjects did. In both genders, age showed strong, negative correlations with anterior chamber depth and pupil diameter and a positive correlation with lens thickness. We also found significant, negative correlations between body height and mass with keratometry measurements, negative correlations between body height and optic disk rim area and rim volume, and positive correlations between body mass and axial length in both genders. Conclusions: Biometric eye parameters differ among people. In addition to age and gender, which are usually taken into consideration when interpreting ocular biometry findings, we strongly suggest that body height and mass should be also routinely considered when interpreting eye biometry data, as these factors have an impact on ocular biometry.

Adaptive finite element eye model for the compensation of biometric influences on acoustic tonometry

Background and objectiveGlaucoma is currently a major cause for irreversible blindness worldwide. A risk factor and the only therapeutic control parameter is the intraocular pressure (IOP). The IOP is determined with tonometers, whose measurements are inevitably influenced by the geometry of the eye. Even though the corneal mechanics have been investigated to improve accuracy of Goldmann and air pulse tonometry, influences of geometric properties of the eye on an acoustic self-tonometer approach are still unresolved. MethodsIn order to understand and compensate for measurement deviations resulting from the geometric uniqueness of eyes, a finite element eye model is designed that considers all relevant eye components and is adjustable to all physiological shapes of the human eye. ResultsThe general IOP-dependent behavior of the eye model is validated by laboratory measurements on porcine eyes. The difference between simulation and measurement is below 8 µm for IOP levels from 5 to 40 mmHg. The adaptive eye model is then used to quantify systematic uncertainty contributions of a variation of eye length and central corneal thickness based on input statistics of a clinical trial series. The adaptive eye model provides the required relation between biometric eye parameters and the corneal deflection amplitude, which here is the measured quantity to trace back to the IOP. Implementing the relations provided by the eye model in a Gaussian uncertainty propagation calculation now allows the quantification of the uncertainty contributions of the biometric parameters on the overall measurement uncertainty of the acoustic self-tonometer. As a result, a systematic uncertainty contribution resulting from deviations in eye length dominate stochastic deviations of the sensor equipment by a factor of 3.5. ConclusionAs perspective, the proposed adaptive eye model provides the basis to compensate for systematic deviations of (but not only) the acoustic self-tonometer.

Results of First In Vivo Trial of an Acoustic Self-Tonometer.

PurposeGlaucoma is the world's most common cause of irreversible blindness, which makes early diagnosis, with the goal of preserving vision, essential. The current medical intervention is to reduce intraocular pressure (IOP) to slow down progression of the disease. The main goal of this study was to test a novel handheld acoustic self-tonometer on humans.MethodsA sound pressure pulse generated by a loudspeaker causes the eye to vibrate. A pressure chamber is placed on the human orbit to form a coupled system comprised of the patient's eye, the enclosed air, and the loudspeaker. A displacement sensor in front of the loudspeaker membrane allows the dynamic behavior of the entire system to be detected.ResultsFor this clinical trial series, a prototype of the acoustic self-tonometer principle was applied. The resulting membrane oscillation data showed sensitivity of patient IOP, but direct allocation of the measured damping and frequency to the IOP was not significant. For this reason, an artificial neural network was used to find relationships among the subjects’ biometric eye parameters in combination with the self-tonometer data for the IOP reference. An expanded measurement uncertainty (kp = 2) equal to 6.53 mm Hg was determined for the self-tonometer in a Bland–Altman analysis using Goldmann applanation tonometer reference measurements.ConclusionsThe usability and success rate of producing valid measurement values with the device during self-measurements by test subjects was nearly 92%. The cross-sensitivities observed require compensation in a possible redesign phase to reduce the measurement uncertainty by at least 25% to the maximum of 5 mm Hg required to seek medical device approval.Translational RelevanceBuilding on successful laboratory experiments with pig eyes, this article reports the results of testing the acoustic tonometer on humans.

New method to assess the accuracy of intraocular lens power calculation formulas according to ocular biometric parameters.

To develop a new method that makes it easy to detect accuracy deficiencies of any intraocular lens (IOL) power calculation formulas and to test it on 9 different formulas. IOA, Madrid, Spain. Retrospective observational case series. This study's first stage included 3519 eyes from 3519 candidates for cataract surgery for which frequency distributions for the following biometric eye parameters were computed: axial length (AL), anterior chamber depth (ACD), lens thickness (LT), white-to-white (WTW), and mean corneal radius (Rm). The resulting data for each parameter were fifth, 25th, 75th and 95th percentiles, which allowed definition of the corresponding normality range. In a second stage, the new graphic-representation method was tested for 9 different formulas in a sample of 70 eyes undergoing cataract surgery with multifocal IOL (mIOL) implantation. Normality ranges (defined as the 25th to 75th percentile interval) were 22.84 to 24.42 mm for AL, 2.86 to 3.39 mm for ACD, 4.36 to 4.88 mm for LT, 11.64 to 12.19 mm for WTW, and 7.52 to 7.87 mm for Rm, with lower sizes in women. No significant differences were found among the 9 formulas for percentage of eyes in ±0.50 diopters (D) (P = .82) or ±1.00 D (P = .97). The graphical method showed less accuracy in ±0.50 D for ACDs from 2.46 to 2.85 mm (5th to 25th percentile) for several formulas (P < .05). Nine formulas showed nonsignificant differences in the general predictability for a sample of eyes that were candidates to mIOL implantation. Predictability in this sample decreased for short ACDs.

Biometric parameters and intra ocular lens power used for cataract eyes in Karnali, Nepal.

The biometric parameters of the eye are measured for the calculation of the intra ocular lens power to be used in cataract surgery. To report the keratometry reading, axial length and intra ocular lens power used for eyes operated for cataract in Karnali Zone, Nepal, and to compare these findings with those reported in other similar studies. The data for the study were retrospectively collected from the case files of patients who had undergone cataract surgery between January 2011 and July 2012 in Karnali Zone, Nepal. These surgeries were performed in an outreach surgical camp organized by the Himalaya Eye Hospital, Nepal, as a part of its annual program. The SPSS 16.0 and Microsoft Excel 2007 software were used for the data analysis. The total number of patients taken for the study was 1055 and the total number of eyes was 1055. There were 530 (50.23%) males and 525 (49.77%) females, with the mean age of 64.34±11.25, ranging from 8 to 98 years.The mean keratometry reading for the total sample was 44.11±1.6 (range, 34.00D to 49.00D). The mean axial length for the total sample was 22.68±0.88 (range, 17.75 to 26.17). The mean IOL power for the total sample was 21.60±1.74 (range, +15.00 to +30.00). The biometric eye parameters of keratometry, axial length and IOL power of this study required for cataract surgery in a Karnali population are similar to those presented in other similar studies from Nepal and abroad.

Optical analysis to predict outcomes after implantation of a double intraocular lens magnification device

To analyze the effect of different optical parameters of the eye on the outcomes of implantation of a double intraocular lens (IOL) magnification device in patients with low vision. Fundación Oftalmológica del Mediterráneo, Valencia, Spain. The eye's refraction and magnification before and after surgery were evaluated using a theoretical eye model based on paraxial optics approximation. Four parameters on which refraction and magnification are dependent were evaluated: anterior chamber depth (ACD), axial length (AL), mean keratometry (Km), and the distance between the 2 implanted IOLs. The 4 variables were analyzed separately in the first stage. Next, different combinations of ACD, AL, and Km values were studied. The goal was to predict what type of eye (in terms of ACD, AL, and Km values) is suitable for successful implantation of the double-IOL magnification device. Axial length had a significant influence on eye magnification. The Km value mainly affected refraction. The ACD did not influence the success of the procedure. The distance between the 2 IOLs was a decisive parameter in the analysis. Analysis of optical and biometric eye parameters could guide selection of patients for implantation of the double-IOL magnification device. Eyes with higher AL and Km values (myopic eyes) are the most suitable for this procedure.