Mm In Axial Length Research Articles

Significant Axial Elongation with Minimal Change in Refraction in 3- to 6-Year-Old Chinese Preschoolers: The Shenzhen Kindergarten Eye Study

To document the distribution of ocular biometry and to evaluate its associations with refraction in a group of Chinese preschoolers. Population-based cross-sectional study. A total of 1133 preschoolers 3 to 6 years of age from 8 representative kindergartens. Biometric measurements including axial length (AL), anterior chamber depth (ACD), and corneal radius of curvature (CR) were obtained from partial-coherence laser interferometry (IOL Master; Carl Zeiss Meditec, Oberkochen, Germany) before cycloplegia. Lens power (LP) and AL-to-CR ratio were calculated. Cycloplegic refraction (3 drops of 1% cyclopentolate) was measured using an autorefractor (KR8800; Topcon Corp., Tokyo, Japan), and spherical equivalent refraction (SER) was calculated. Biometric and refractive parameters were assessed as a function of age and gender. Multiple regression analysis was performed to explore the associations between refraction and ocular biometry. Ocular biometric distributions and their relationships to refraction. Among the 1127 children (99.5%) with successful cycloplegic refraction, mean SER was 1.37±0.63 diopters (D). Prevalence of myopia increased from 0% at 3 years of age to 3.7% (95% confidence interval, 1.0%-6.5%) at 6 years of age. Biometric parameters followed Gaussian distributions with means of 22.39±0.68 mm for AL, 7.79±0.25 mm for CR, and 24.61±1.42 D for calculated LP; and non-Gaussian distributions with means of 3.34±0.24 mm for ACD and 2.88±0.06 for AL-to-CR ratio. Axial length, ACD, and AL-to-CR ratio increased from 3 to 6 years of age, CR remained stable, whereas LP declined. Overall, SER declined slightly. For the SER variance, AL explained 18.6% and AL-to-CR ratio explained 39.8%, whereas AL, CR, and LP accounted for 80.0% after adjusting for age and gender. Young Chinese children are predominantly mildly hyperopic, with a low prevalence of myopia by the age of 6 years. An increase of 1 mm in AL was associated with only 0.45 D of myopic change. Decreases in LP reduce the myopic shifts that normally would be associated with increases in AL, and thus play a key role in refractive development in this age group.

Is high myopia a risk factor for visual field progression or disk hemorrhage in primary open-angle glaucoma?

PurposeThe purpose of this study was to clarify differences between highly myopic and non-myopic primary open-angle glaucoma (POAG) patients, including normal-tension glaucoma patients.Patients and methodsA total of 269 POAG patients were divided into two groups: patients with ≥26.5 mm of axial length (highly myopic group) and patients with <24.0 mm of axial length (non-myopic group).ResultsWe analyzed 53 highly myopic and 93 non-myopic POAG patients. Age at first visit of the highly myopic group was significantly less than that of the non-myopic group (P<0.0001). Baseline intraocular pressures (IOPs) showed no significant differences. Follow-up IOPs of the non-myopic group were significantly lower than those of the highly myopic group (P=0.0009). According to the mean deviation definition of progression, the cumulative probability of non-progression of visual field (VF) loss was significantly greater in the highly myopic group (10-year survival rate, 73.7%±6.8%) than in the non-myopic group (10-year survival rate, 46.3%±5.8%; log-rank test, P=0.0142). The occurrence of disk hemorrhage (DH) in the non-myopic group (1.60±3.04) was significantly greater than that in the highly myopic group (0.93±2.13, P=0.0311). The cumulative probability of DH was significantly lower in the highly myopic group (10-year survival rate, 26.4%±5.4%) than in the non-myopic group (10-year survival rate, 47.2%±6.6%, P=0.0413).ConclusionHighly myopic POAG is considered as a combination of myopic optic neuropathy and glaucomatous optic neuropathy (GON). If GON is predominant, it has frequent DH and more progressive VF loss. However, when the myopic optic neuropathy is predominant, it has less DH and less progressive VF loss.

Biometry measurements using a new large-coherence–length swept-source optical coherence tomographer

To evaluate the repeatability and reproducibility of the measurements obtained with the Argos, a new biometer with swept-source optical coherence tomography (SS-OCT), and to compare them with the results obtained with the IOLMaster 500 (partial-coherence interferometry [PCI]) and the Lenstar LS 900 (optical low-coherence reflectometry [OLCR]) biometers. Private practice, Lynwood, California, USA. Prospective observational study. All measurements were performed with the SS-OCT tomographer, the PCI biometer, and the OLCR biometer. Eyes (n = 107) were measured to evaluate the axial length (AL), central corneal thickness (CCT), aqueous depth, anterior chamber depth (ACD), lens thickness, pupil size, corneal diameter, and anterior corneal radius of curvature (RAV). Repeatability and reproducibility of the SS-OCT measurements showed comparable values and a low variation rate, with an interset mean difference of 0.01 mm for AL, 0.01 mm for CCT, 0.01 mm for aqueous depth and ACD, 0.03 mm for lens thickness, 0.10 mm for pupil size, 0.14 mm for corneal diameter, and 0.02 mm for RAV. The SS-OCT device correctly measured the AL in 96% of the cases compared with 79% for the OLCR device and 77% for the PCI device. Comparisons between the PCI device and SS-OCT device were -0.01 ± 0.05 mm for AL, -0.17 ± 0.20 mm for ACD, and -0.01 ± 0.05 mm for RAV. Comparison between the OLCR device and the SS-OCT device was 0.01 ± 0.06 mm for AL, 0.08 ± 0.15 mm for ACD, 0.00 ± 0.05 mm for RAV, 0.00 ± 0.01 mm for CCT, 0.07 ± 0.14 mm for aqueous depth, -0.23 ± 0.22 mm for lens thickness, -0.29 ± 0.53 mm for pupil size, and -0.34 ± 0.76 mm for corneal diameter. Axial length measurements with the new SS-OCT biometer were comparable to the PCI and OLCR measurements with a higher AL acquisition rate. Dr. Shammas is a consultant to Movu, Inc. Drs. Ortiz, Kim, and Chong have proprietary interest in the new technology.

The Retina of Ansorge's Cusimanse (Crossarchus ansorgei): Number, Topography and Convergence of Photoreceptors and Ganglion Cells in Relation to Ecology and Behavior

The family Herpestidae (cusimanses and mongooses) is a monophyletic radiation of carnivores with remarkable variation in microhabitat occupation and diel activity, but virtually nothing is known about how they use vision in the context of their behavioral ecology. In this paper, we measured the number and topographic distribution of neurons (rods, cones and retinal ganglion cells) and estimated the spatial resolving power of the eye of the diurnal, forest-dwelling Ansorge's cusimanse (Crossarchus ansorgei). Using retinal wholemounts and stereology, we found that rods are more numerous (42,500,000; 92%) than cones (3,900,000; 8%). Rod densities form a concentric and dorsotemporally asymmetric plateau that matches the location and shape of a bright yellow tapetum lucidum located within the dorsal aspect of the eye. Maximum rod density (340,300 cells/mm²) occurs within an elongated plateau below the optic disc that corresponds to a transitional region between the tapetum lucidum and the pigmented choroid. Cone densities form a temporal area with a peak density of 44,500 cells/mm² embedded in a weak horizontal streak that matches the topographic distribution of retinal ganglion cells. Convergence ratios of cones to retinal ganglion cells vary from 50:1 in the far periphery to 3:1 in the temporal area. With a ganglion cell peak density of 13,400 cells/mm² and an eye size of 11 mm in axial length, we estimated upper limits of spatial resolution of 7.5-8 cycles/degree, which is comparable to other carnivores such as hyenas. In conclusion, we suggest that the topographic retinal traits described for Ansorge's cusimanse conform to a presumed carnivore retinal blueprint but also show variations that reflect its specific ecological needs.

Radius of curvature changes in spontaneous improvement of foveoschisis in highly myopic eyes

BackgroundMyopic foveoschisis is the splitting of retinal layers overlying staphyloma in highly myopic patients that can lead to vision loss. We assess possible contributing mechanisms to the formation of foveoschisis...

Refractive errors in high myopic eyes after phacovitrectomy for macular hole.

To examine the refractive prediction error in high myopic eyes after phacovitrectomy. This retrospective comparative case series included 91 eyes (18 high myopic eyes and 73 non-high myopic eyes) of 91 patients who underwent successful phacovitrectomy (phacoemulsification, intraocular lens implantation, and pars plana vitrectomy). The high myopic eyes were defined as the eye with more than 26.0 mm of axial length. The postoperative prediction error of mean error and mean absolute error were evaluated at 4mo postoperatively. Axial length and keratometry measurement were performed preoperatively and 4mo postoperatively using the IOL Master. The refractive outcome after phacovitrectomy showed significantly greater myopic shift in the high myopic eyes [-1.08±0.87 diopters (D)] than that in the non-high myopic eyes (-0.43±0.63 D, P=0.004). Axial length and keratometric value in the high myopic eyes were significantly increased (P=0.043, 0.037 respectively), whereas those in the non-high myopic group were not significantly increased (P=0.135, 0.347 respectively). The change of the axial length in the myopic eye (0.46±0.28 mm) was greater than that in the non-high myopic eye (0.11 ± 0.34 mm; P<0.001). High myopic eyes showed more myopic shift than non-high myopic eyes after phacovitrectomy. The cause of myopic shift in high myopic eyes seems to be attributed to actual elongation of the axial length in high myopia.

Optical coherence tomography measurements of choroidal thickness in healthy eyes: correlation with age and axial length.

To evaluate subfoveal choroidal thickness (CT) in healthy eyes using spectral-domain optical coherence tomography (SD-OCT) and provide correlations between age and axial length. Enhanced depth SD-OCT imaging was performed with Cirrus (Carl Zeiss Meditec, Dublin, CA) and Spectralis (Heidelberg Engineering, Heidelberg, Germany) instruments. CT was measured from the outer limit of the retinal pigment epithelium to the inner surface of the sclera. The study enrolled 155 patients, with at least 20 in each decade between 22 and 89 years old. Mean axial length was 23.6 mm. Mean Heidelberg subfoveal CT was 286 µm. The correlation between Heidelberg and Zeiss subfoveal CT measurements was strong (r = .978) and significant (P < .001). Mean subfoveal CT was 7.7 µm thinner by Heidelberg versus Cirrus (P < .001). Multiple linear regression analysis revealed that age (P < .001), axial length (P = .001), and sex (P = .025) were significantly related to Heidelberg subfoveal CT. There is a strong negative correlation between CT and age (P <.001), with a 25 µm decrease in CT for each decade of life. Increasing axial length demonstrated a negative correlation with CT, decreasing 24.9 µm for each mm of axial length. Future studies of CT measurements can be performed on either instrument and must account for axial length, age, and sex to make appropriate conclusions.

Choroidal thickness in relation to sex, age, refractive error, and axial length in healthy Turkish subjects.

The aim of this study was to investigate the association between choroidal thickness (CT) and sex, age, refractive error (RE), and axial length in healthy subjects. This is a study of 154 eyes in 154 healthy subjects. CT measurements were performed by the same experienced technician using a spectral domain optical coherence tomography device. CT was measured perpendicularly from the outer edge of the retinal pigment epithelium to the choroid-sclera boundary at the fovea and at six more points which are located at, respectively, 500 µm nasal to the fovea, 1,000 µm nasal to the fovea, and 1,500 μm nasal to the fovea, 500 μm temporal to the fovea, 1,000 μm temporal to the fovea, and 1,500 μm temporal to the fovea. The RE was measured by autorefractometry, and the axial length was measured by interferometry. Statistical analysis was performed to evaluate CT at each location, and to the correlations of CT with sex, age, RE, and axial length. The mean subfoveal CT was 265.86 ± 60.32 µm, the mean age was 49.01 ± 19.19 years, the mean RE was -0.17 ± 1.20 diopters (D), and the mean axial length was 23.39 ± 0.76 mm. CT profile indicated that the choroid was thicker at the fovea than at temporal and nasal locations. Univariable linear regression analysis showed that subfoveal CT decreased 3.14 µm for each year of age and decreased 79.33 µm for each mm of axial length (P = 0.000, R(2) = 0.249; P = 0.000, R(2) = 0.487, respectively). In a similar analysis, subfoveal CT was found to decrease by 50.24 µm/D myopia-shifted change in refraction (P = 0.000, R (2) = 0.201). The subfoveal choroid was 99.16 µm (39.22 %) thicker in men than women when adjusting for age and axial length (P = 0.000, R(2) = 0.249). CT decreases with increasing myopia, age, and axial length. Men had thicker choroid than women, and CT varies depending on location.

Épaisseur choroïdienne fovéolaire au SD-OCT dans la myopie forte avec macula bombée

To measure macular choroidal thickness (CT) using spectral-domain optical coherence tomography (SD-OCT) in highly myopic eyes with dome-shaped macula (DSM), and to investigate whether the choroid is thicker in these eyes compared to highly myopic eyes without MB. A cross-sectional study of 200 eyes was performed between January 2010 and June 2012. Twenty-four highly myopic eyes (12%) had a dome-shaped macula. All patients underwent a complete ophthalmological examination, SD-OCT (TOPCON 2000), and B-scan ultrasonography. OCT scans were analyzed in 7 sections, and subfoveal CT was measured manually between the Bruch's membrane and the internal aspect of the sclera. The 20 eyes with isolated dome-shaped macular were paired by age and axial length (AL) with 20 eyes without macular involvement. In the subgroup with isolated MB, the mean subfoveal CT was 101.86 μm (± 21.35 μm). A statistically significant negative correlation was found between CT and AL (r=-0.623, P=0.0001). The regression equation demonstrated a decrease of 8.3 μm per mm of AL. In the subgroup without MB, matched with the subgroup with MB by age (P=0.591), and AL (P=0.815), the mean subfoveal CT was 89.54 μm (± 20.12 μm). The comparison between the two subgroups found a statistically significant difference in subfoveal CT (P<10-4). In our study, choroidal thickness is increased in highly myopic eyes with dome-shaped macula compared to highly myopic eyes without dome-shaped macula. These findings suggest that abnormalities of the choroid may play a role in the pathogenesis of dome-shaped macula.

Relationship of lifestyle and body stature growth with the development of myopia and axial length elongation in Taiwanese elementary school children.

Context:The development of myopia and growth of the eye, occur at a time when body stature is increasing.Aims:To investigate the relationship of lifestyle and body growth with axial elongation and myopia development among schoolchildren aged 7 to 9 years.Settings and Design:Prospective study.Materials and Methods:Children in elementary schools without serious eye disorders were invited to participate. We measured cycloplegic refraction, corneal curvature, intraocular pressure, axial length, body height, and weight. Questionnaires about the children's daily lifestyles, family members’ myopia and parents’ socio-demographic status were completed. The children were followed up every 6 months in a 3-year period.Statistical Analysis Used:Bivariate correlations, simple and multiple regression.Results:Eighty-eight children participated in this study. Forty-eight were myopic at the beginning of the study, and their myopia correlated with longer axial length and parental myopia (P = 0.015, 0.012). Sixty-five children (74%) completed the study, and the rates of change per year were -0.43 ± 0.58 (mean + standard deviation) diopters in spherical equivalence, 0.32 ± 0.25 mm in axial length (AL), 5.73 ± 2.71 cm in body height, and 3.84 ± 2.23 kg in weight. The axial length change was positively correlated with the height change (P < 0.001). The myopia shift was correlated to axial length change (P = 0.000) but not correlated to height change. Using multiple regression test, near work was the only significant risk factor for myopia progression (P = 0.022).Conclusions:Our study showed that body height increment was correlated to axial length elongation but not to myopia shift in children aged 7-9 years. Genetic factors such as parental myopia and body height had a possible influence on myopia development, and the environment factor as near work intensity was related to myopia progression.

Air-Gas Exchange Reevaluated: Clinically Important Results of a Computer Simulation

The primary aim of this study was to evaluate the efficiency of air-gas exchange techniques and the factors that influence the final concentration of an intraocular gas tamponade. Parameters were varied to find the optimum method of performing an air-gas exchange in ideal circumstances. A computer model of the eye was designed using 3D software with fluid flow analysis capabilities. Factors such as angular distance between ports, gas infusion gauge, exhaust vent gauge and depth were varied in the model. Flow rate and axial length were also modulated to simulate faster injections and more myopic eyes, respectively. The flush volume of gas required to achieve a 97% intraocular gas fraction concentration were compared. Modulating individual factors did not reveal any clinically significant difference in the angular distance between ports, exhaust vent size, and depth or rate of gas injection. In combination, however, there was a 28% increase in air-gas exchange efficiency comparing the most efficient with the least efficient studied parameters in this model. The gas flush volume required to achieve a 97% gas fill also increased proportionately at a ratio of 5.5 to 6.2 times the volume of the eye. A 35-mL flush is adequate for eyes up to 25 mm in axial length; however, eyes longer than this would require a much greater flush volume, and surgeons should consider using two separate 50-mL gas syringes to ensure optimal gas concentration for eyes greater than 25 mm in axial length.

Lenstar Versus Ultrasound for Ocular Biometry in a Pediatric Population

To compare the central corneal thickness (CCT), axial length (AL), anterior chamber depth (ACD), and lens thickness (LT) measured with Lenstar with those obtained with ultrasound pachymetry and A-scan contact ultrasound (ASU) in children. ODs of 565 school children were included. All measurements were obtained 30 min after instilling 1% tropicamide. For each instrument, three consecutive measurements per each child were performed. Initially, examiner 1 performed measurements with Lenstar to obtain CCT, AL, ACD, and LT. Later, examiner 2 performed measurements with corneal pachymetry to obtain CCT. Finally, ASU was used by examiner 2 to obtain AL, ACD, and LT. Four parameters obtained with Lenstar were compared with those obtained with pachymetry and ASU using Pearson correlation coefficients (r) and Bland-Altman analyses. Lenstar measurements were obtained in 557 of 565 subjects(mean age; 10.48 ± 2.11 years, mean spherical equivalent of the ODs; +0.47 ± 1.18 diopters) whereas ASU and pachymetry could be performed in 530 of 565. Four hundred seventy-nine subjects were statistically assessed after 41 subjects were extracted as outliers from 530 subjects in whom all instruments could be performed. Mean difference between pachymetry and Lenstar was 13.20 ± 13.13 μm [95% confidence interval (CI): 12.01 to 14.37]. Mean difference between ASU and Lenstar was -0.72 ± 0.35 mm (95% CI: -0.75 to -0.69) for AL, -0.27 ± 0.32 mm (95% CI: -0.30 to -0.24) for ACD, and 0.24 ± 0.28 mm (95% CI: 0.22 to 0.27) for LT. R values were 0.912 (p < 0.001), 0.904 (p < 0.001), 0.487 (p < 0.001), 0.369 (p < 0.001) for CCT, AL, ACD, and LT respectively. AL and ACD were found to be greater with Lenstar, whereas CCT and LT measures were smaller. It is concluded that there was agreement between instruments for CCT and ACD, because the small differences between measures were clinically insignificant. AL and LT values cannot be used interchangeably. If these differences are considered, Lenstar can replace ASU and pachymetry for the majority of children.

Correlation of misfolded transthyretin in abnormal vitreous and high myopia related ocular pathologies

BackgroundHigh myopia is usually defined as eyes with −6 dioptres (D) of myopia, or >26.0mm in axial length. Progressive and excessive elongation of the eyeball leads to secondary ocular diseases such as macular detachment (MD) and macular hole (MH). Higher transthyretin (TTR) levels had been detected in abnormal serums, but the situation in vitreous humor and the mechanism are still unclear. MethodTransthyretin concentrations in vitreous of 80 high myopia patients and 20 healthy controls were determined by ELISA. After affinity purification, SDS-PAGE, Western-blot, and circular dichroism (CD) spectroscopy were employed for the secondary structure research. ResultsVitreous transthyretin concentration of MD patients was ~1.1 times higher than that of MH patients, and 4.1 times higher than that of healthy controls. TTR in MD patients' vitreous showed a much more stable tetrameric structure. In neutral condition, compared with the secondary structure of healthy TTR, purified TTR in MD and MH vitreous samples showed lower β-sheets content; ~50% of β-sheets of the TTR in MD vitreous samples were lost. ConclusionsThe results suggested that MD and MH patients had higher vitreous TTR concentrations; TTR in MD vitreous had an abnormally stable tetrameric structure, possibly due to misfolding.

Primary gas tamponade in the management of macular hole with retinal detachment in highly myopic eyes

Background We conducted a retrospective study to investigate the role of the primary gas tamponade on the final success rate of macular hole with retinal detachment (MHRD) in highly myopic eyes. Methods Retrospective chart review of the patients diagnosed as MHRD in highly myopic eyes between 1992 and 2008 was done. Fifty-three highly myopic eyes (>−6.0 diopter, >26 mm of axial length, or visible posterior staphyloma) with a retinal detachment resulting from a macular hole were included. The main outcome measures were anatomic reattachment and final visual acuity. Results Thirty-two of the 53 eyes received primary gas tamponade, and the reattachment of retina was achieved in 8 eyes (8/32, 25%). Twenty-one of the 53 eyes received primary pars plana vitrectomy (PPV) with or without scleral buckle, and the reattachment of retina was achieved in 12 eyes (12/21, 57.1%). The final success rate after adjunctive operations was 96.9% in the primary gas tamponade group, and 85.7% in the primary PPV group. Stability of vision (improved or maintained) was achieved in 78.1% of the primary gas group, and 66.7% in the primary PPV group. Conclusion Our results indicate that primary gas tamponade does not decrease the final success rate in the repair of MHRD in highly myopic patients. Since it is safe and time-saving, primary gas tamponade could be a good alternative for primary treatment in those who are not willing or eligible for more complicated surgeries.

Comparison of the biometric values obtained by two different A-mode ultrasound devices (Eye Cubed vs. PalmScan): A Transversal, descriptive, and comparative study

BackgroundTo assess the reliability of the measurements obtained with the PalmScan™, when compared with another standardized A-mode ultrasound device, and assess the consistency and correlation between the two methods.MethodsTransversal, descriptive, and comparative study. We recorded the axial length (AL), anterior chamber depth (ACD) and lens thickness (LT) obtained with two A-mode ultrasounds (PalmScan™ A2000 and Eye Cubed™) using an immersion technique. We compared the measurements with a two-sample t-test. Agreement between the two devices was assessed with Bland-Altman plots and 95% limits of agreement.Results70 eyes of 70 patients were enrolled in this study. The measurements with the Eye Cubed™ of AL and ACD were shorter than the measurements taken by the PalmScan™. The differences were not statistically significant regarding AL (p < 0.4) but significant regarding ACD (p < 0.001). The highest agreement between the two devices was obtained during LT measurement. The PalmScan™ measurements were shorter, but not statistically significantly (p < 0.2).ConclusionsThe values of AL and LT, obtained with both devices are not identical, but within the limits of agreement. The agreement is not affected by the magnitude of the ocular dimensions (but only between range of 20 mm to 27 mm of AL and 3.5 mm to 5.7 mm of LT). A correction of about 0.5 D could be considered if an intraocular lens is being calculated. However due to the large variability of the results, the authors recommend discretion in using this conversion factor, and to adjust the power of the intraocular lenses based upon the personal experience of the surgeon.

Myopia Affects Retinal Nerve Fiber Layer Measurements as Determined by Optical Coherence Tomography

To determine whether increasing myopia is associated with thinner peripapillary retinal nerve fiber layer (RNFL) when measured by Stratus optical coherence tomography (OCT). Observational cross-sectional study. Normal subjects with myopia underwent refractometry, axial length measurement (IOL Master), optic nerve examination, and OCT (12 fast RNFL scans/eye). The more myopic eye was chosen as the study eye. Correlation coefficients were calculated for demographic and optic disk characteristics, and degree of myopia. Mean age (n=27) was 34+/-8 years (range: 23 to 54). Mean cup-to-disk ratio was 0.38 with 41% large and 59% medium disk size. Eight subjects had peripapillary atrophy and 6 had disk tilt. Mean spherical equivalent was -5.40 D (range: -1.25 to -11.25), with mean axial length of 25.65 mm (range: 22.63 to 27.92). No significant associations were found between RNFL thickness and age (P=0.20), sex, disk size, cup-to-disk ratio, tilt, or peripapillary atrophy. RNFL thickness decreased with higher axial length (overall R=-0.70, P<0.001, superior R=-0.60, P=0.001, and inferior R=-0.60, P=0.001), and higher spherical equivalent (overall R=-0.52, P=0.005, superior R=-0.41, P=0.03, and inferior R=-0.45, P=0.02). Overall RNFL thickness decreased 7 mum/1 mm of axial length, and 3 mum/1 D sphere. Moderately myopic subjects tend to have thin peripapillary RNFL, mainly at the superior and inferior poles, as measured by Stratus OCT. This phenomenon should be considered when interpreting a glaucoma suspect's Stratus OCT measurements compared with the normative database.

Intraocular lens power calculation in short eyes

To compare the accuracy of the Hoffer Q and SRK-T formulae in eyes below 22 mm in axial length, using biometry measured with partial coherence inferometry (PCI), without a customised ACD constant. Data were retrospectively and prospectively collected by identifying eyes of axial length below 22 mm in the records of the intraocular lens (IOL) master and in preoperative notes. Biometry was performed using PCI and IOL power was calculated using both SRK-T and Hoffer Q formulae. Refractive outcome was measured and the accuracy of the two formulae compared. Forty-one eyes of 41 patients were identified with an axial length <22 mm. Axial lengths ranged from 21.96 to 20.29 with a mean of 21.51 mm, and IOL power ranging from 23 dioptres (D) to 29 D. The Hoffer Q formula showed a mean prediction error of 0.61 D (SD 0.80) compared with the SRK-T, which showed a mean prediction error of 0.87 D (SD 0.829). A paired t-test found that the Hoffer Q was significantly more accurate than the SRK-T formula (P<0.001). Hoffer Q was found to be more accurate than the SRK-T formula in this series of eyes <22 mm axial length when customised ACD constants are not used. Royal College of Ophthalmologists guidelines may need to be adjusted in accordance with these findings. This study underlines the importance of monitoring outcomes, and suggests different customisations are needed for different formulae, with a higher correction if the SRK-T formula is used for short eyes.

Failure behavior of carbon steel pipe with local wall thinning near orifice

Monotonic four-point bending tests were conducted using pipe specimens having an orifice undergoing local wall thinning. The effects of local wall thinning on the fracture behaviors of pipe were investigated. Local wall thinning was machined on the inside of pipes in order to simulate erosion corrosion metal loss. The configurations of the eroded area were l = 100 mm in axial length, d/ t = 0.5 and 0.8 in thickness ratio, and 2 θ = 180° in angle. The area undergoing local wall thinning was subjected to either tensile or compressive stress. Failure type could be classified into ovalization, local buckling, and crack initiation, depending on thickness ratio, and stress at the eroded area. Three-dimensional elasto-plastic analyses were also carried out using the finite element method, which is able to accurately simulate fracture behaviors. Failure analysis map was constructed for pipes with or without orifice based on the results of finite element analyses in order to investigate the effect of orifice on the failure behaviors.

Kataraktoperation und kombinierte Katarakt-/Glaukomoperation als augeninnendrucksenkende Maßnahme in Augen mit relativem anterioren Mikrophthalmus

Eyes with relative anterior microphthalmos (RAM) (normal [> 20.0 mm] axial length but disproportionally small anterior segment [horizontal corneal diameter < 11 mm]) often present with increased intraocular pressure. Under these difficult conditions cataract surgery alone or in combination with a glaucoma filtering procedure is often required. We retrospectively reviewed the records of 71 patients (108 eyes) with RAM in whom cataract only (n = 72) or combined cataract/glaucoma surgery (n = 36) was performed. Preoperative clinical and biometric findings, intraoperative complications and postoperative results (visual acuity and intraocular pressure) were analysed. Median preoperative values were 7.46 mm for corneal curvature, 2.53 mm for anterior chamber depth and 22.44 mm for axial length. The implanted lens had a median 25.0 dioptric power. The IOP was reduced from 15.6 +/- 3.9 mm Hg to 13.5 +/- 3.1 mm Hg with cataract surgery alone and from 22.4 +/- 5.5 mm Hg to 15.4 +/- 4.0 mm Hg with combined surgery. Mean best corrected visual acuity improved from 0.4 +/- 0.2 to 0.79 +/- 0.25 with cataract surgery and from 0.5 +/- 0.3 to 0.81 +/- 0.24 with combined surgery. Intraoperatively only 3 eyes had a rupture of the posterior capsule and postoperatively 2 eyes developed malignant glaucoma in the combined group. The results show that, in eyes with RAM, cataract surgery alone or in combination with glaucoma surgery can be performed with excellent results and low complication rate if adequate precautions are taken (especially the use of hyperosmotic agents).

Is It in the Episcleral Space or in the Medial Canthal Extraconal Space?

Hauser-Ross Eye Institute, Sycamore, Illinois. glfanning@aol.comI was interested to see the article by Nouvellon et al. 1describing their results using the episcleral block technique that was described by Dr. Jacques Ripart. This is an excellent article, but I have a few comments.In my opinion, the block was not in the episcleral space in the majority of these patients. The authors report that the median depth of needle insertion was 15 mm, with the needle having been inserted posterior to the caruncle. The average eye is approximately 23.5 mm in axial length, which tells us that the tip of the needle was well beyond the equator of the eye (in the frontal plane) in more than half of the patients. With the needle inserted this deeply, I believe that it is anatomically impossible for the needle tip to have remained in the episcleral space. The injections were made into the medial canthal fat-filled space, not into the episcleral space. When the needle depth was only 5–10 mm, it is quite probable that the tip was in the episcleral space. The median volume of anesthetic injected provides further proof of my thesis. When 10 ml anesthetic is injected into the episcleral space, significant and noticeable chemosis occurs 100% of the time, but the authors describe chemosis in only 6 of 2,031 patients.I am especially worried about the range of needle depth insertion. The deepest reported insertion depth was 35 mm. In my opinion,2a needle longer than 25 mm should never be inserted into this part of the orbit. Even the 25-mm needle should not be inserted to its complete depth, the shoulder of the needle not being allowed to go beyond the plane of the iris. The reason for this is that the optic canal lies directly at the rear of the medial wall of the orbit. A needle placed aggressively along this wall can reach the optic canal in many patients, resulting in damage to the optic nerve, ophthalmic artery, or both.Finally, because the majority of injections were made into the medial canthal fat-filled space (in my opinion), why not use a safer route to that space? Hustead et al. 3described a much safer technique, in which the needle is inserted into the little tunnel that lies between the caruncle and the medial canthus and is advanced parallel and very close to the medial wall. With this technique, there is much less chance of endangering the globe or the medial rectus muscle, and the technique is easy to learn and easy to teach.Hauser-Ross Eye Institute, Sycamore, Illinois. glfanning@aol.com