Prevalence of strabismus and its risk factors among school aged children: The Hong Kong Children Eye Study.

The study aims to determine the prevalence of strabismus and its risk factors among school children in Hong Kong. This is a cross-sectional study involving 6-8 year old children from different districts in Hong Kong. 4273 children received comprehensive ophthalmological examination, cycloplegic auto-refraction, best corrected visual acuity (BCVA), anterior segment examination, cover/uncover test, ocular motility, and fundus examination. Demographic information, pre- and post- natal background, parental smoking status, and family history of strabismus were obtained through questionnaires. Strabismus was found among 133 children (3.11%, 95% CI 2.59-3.63%), including 117 (2.74%) exotropia and 12 (0.28%) esotropia cases (exotropia-esotropia ratio: 9.75:1). There was no significant difference in prevalence across age (6-8 years) and gender. Multivariate analysis revealed associations of strabismus with myopia (≤ - 1.00D; OR 1.61; 95% CI 1.03-2.52; P = 0.037) hyperopia (≥ + 2.00D; OR 2.49; 95% CI 1.42-4.39; P = 0.002), astigmatism (≥ + 2.00D; OR 2.32; 95% CI 1.36-3.94; P = 0.002), and anisometropia (≥ 2.00D; OR 3.21; 95% CI 1.36-7.55; P = 0.008). Other risk factors for strabismus included maternal smoking during pregnancy (OR 4.21; 95% CI 1.80-9.81; P = 0.001), family history of strabismus (OR 6.36; 95% CI 2.78-14.50, P < 0.0001) and advanced maternal age at childbirth (> 35 years; OR 1.65; CI 1.09-2.49, P = 0.018). The prevalence of strabismus among children aged 6-8 years in Hong Kong is 3.11%. Refractive errors, family history of strabismus and maternal smoking history during pregnancy are risk factors. Early correction of refractive errors and avoidance of maternal smoking during pregnancy are potentially helpful in preventing strabismus.

Correcting Higher Order Aberrations Using Image Processing.

Higher Order Aberrations (HOAs) are complex refractive errors in the human eye that cannot be corrected by regular lens systems. Researchers have developed numerous approaches to analyze the effect of these refractive errors; the most popular among these approaches use Zernike polynomial approximation to describe the shape of the wavefront of light exiting the pupil after it has been altered by the refractive errors. We use this wavefront shape to create a linear imaging system that simulates how the eye perceives source images at the retina. With phase information from this system, we create a second linear imaging system to modify source images so that they would be perceived by the retina without distortion. By modifying source images, the visual process cascades two optical systems before the light reaches the retina, a technique that counteracts the effect of the refractive errors. While our method effectively compensates for distortions induced by HOAs, it also introduces blurring and loss of contrast; a problem that we address with Total Variation Regularization. With this technique, we optimize source images so that they are perceived at the retina as close as possible to the original source image. To measure the effectiveness of our methods, we compute the Euclidean error between the source images and the images perceived at the retina. When comparing our results with existing corrective methods that use deconvolution and total variation regularization, we achieve an average of 50% reduction in error with lower computational costs.

Focal Structure-Function Relationships in Primary Open-Angle Glaucoma Using OCT and OCT-A Measurements.

Purpose: To evaluate the focal structure-function associations among visual field (VF) loss, optical coherence tomography angiography (OCT-A) vascular measurements, and optical coherence tomography (OCT) structural measurements in glaucoma. Methods: In this cross-sectional study, subjects underwent standard automated perimetry, OCT-based nerve fiber thickness measurements, and OCT-A imaging. Mappings of focal VF test locations with OCT and OCT-A measurements were defined using anatomically adjusted nerve fiber trajectories and were studied using multivariate mixed-effects analysis. Segmented regression analysis was used to determine the presence of breakpoints in the structure-function associations. Results: The study included 119 eyes from 86 Chinese subjects with primary open-angle glaucoma (POAG). VF mean deviation was significantly associated with global capillary perfusion density (ß = 0.13 ± 0.08) and global retinal nerve fiber layer thickness (ß = 0.09 ± 0.02). Focal capillary density (FCD) was significantly associated with VF losses at 34 VF test locations (66.7% of 24-2 VF), with 24 of the 34 locations being within 20° of retinal eccentricity. Focal nerve layer (FNL) thickness was significantly associated with 16 VF test locations (31.4% of 24-2 VF; eight locations within 20° eccentricity). For VF test locations in the central 10° VF, VF losses below the breakpoint were significantly associated with FCD (slope, 0.89 ± 0.12, P < 0.001), but not with FNL thickness (slope, 0.57 ± 0.39, P = 0.15). Conclusions: Focal capillary densities were significantly associated with a wider range of visual field losses and in a larger proportion of the visual field compared to nerve fiber thickness.

The prevalence of refractive error and visual impairment among New Zealand children in a community with significant socioeconomic disadvantage: is current preschool vision screening effective?

AIM: To examine the prevalence of refractive error and visual impairment and evaluate the efficacy of B4 School Check (B4SC) vision screening, in a cohort of predominantly New Zealand Maori and Pacific children from a community with socioeconomic disadvantage. METHOD: A cross-sectional investigation of children in the Welcome-to-School study. Participants received a comprehensive eye examination at six to seven years of age. Refractive error and amblyopia were identified and compared with B4SC vision screening results. RESULTS: One-hundred and fourteen children were assessed: 21.9% Maori, 57.9% Pacific and 20.2% Other. Over 30% of children had significant refractive error. Eighty-nine percent received a B4SC; 26.3% of children who passed the B4SC had significant refractive error. Seven children (6.1%) had amblyopia risk factors: none passed the B4SC, four were referred, one was identified for rescreening and two were not screened. CONCLUSION: Refractive errors were common in this cohort. For those screened, the B4SC was effective at identifying children with amblyopia risk factors but poor at detecting refractive errors potentially affecting academic performance. The efficacy of the programme was limited by the number of children screened, inequity of screening and the mismatch between the aims of the vision screening test and the overall rationale for the B4SC.

Comparison of Chinese and North American Tomographic Parameters and the Implications for Refractive Surgery Screening.

PURPOSE: The aim of this study was to determine whether there are significant clinical variations in the Belin/Ambrosio Enhanced Ectasia Display (BAD display) parameters between Chinese and North American eyes and whether any variations are related to differences in corneal diameter. DESIGN: Retrospective observational study. METHODS: Files were generated from patients seeking refractive surgical correction. Patients with previous surgery, evidence of corneal ectasia, or scans representing a non-normal cornea were excluded. Unpaired t tests were performed for all variables. Regression analyses were performed for all variables with respect to corneal diameter, and compared to evaluate the influence of corneal diameter between populations. Data were graphed as standard scores (z scores) to compare different parameters. RESULTS: 127 North American and 49 Chinese patients met study criteria. Statistically significant differences existed for corneal diameter (P < 0.01), anterior elevation at the thinnest point (P < 0.01), and Df (P < 0.01). In both populations, statistically significant correlations existed between corneal diameter and most indices, and most profoundly on pachymetric progression and final D. Regression slopes revealed a statistically significant difference for the influence of corneal diameter on ARTmax (P = 0.04) and was nearly significant for final D (P = 0.06). CONCLUSIONS: Corneal diameter had the greatest influence on pachymetric progression and final D, and more profoundly in the Chinese. This suggests that incorporating corneal diameter as an additional variable may make the BAD display more universally applicable. Also, the differences in anterior elevation parameters suggest that specific ethnic/geographic normative values may be beneficial for the BAD display.

Clinical Evaluation of a New Swept-Source Optical Coherence Biometer That Uses Individual Refractive Indices to Measure Axial Length in Cataract Patients.

BACKGROUNDS: Although the OCT biometer using individual refractive index is available, comparisons of measurement value and intraocular lens (IOL) power calculation error with other SS-OCT biometers are not known. OBJECTIVES: To compare the new SS-OCT biometer ARGOS (OCTB1), which uses individual refractive indices to measure axial length, with the IOLMaster 700 (OCTB2) and OA-2000 (OLCR), which use equivalent refractive index. METHOD: Six hundred and twenty-two eyes of 622 patients who had been diagnosed with cataract were enrolled in the study. Among the 158 eyes that had undergone cataract surgery, the postoperative refractive error was evaluated using the Haigis formula. RESULTS: The axial length measured by the OCTB1 showed a proportional bias in comparison with the other two biometers and a fixed bias in eyes with an axial length ≥26 mm. No significant difference was found in the median absolute refractive prediction error (p = 0.3278). However, in eyes with an axial length ≥26 mm, the OCTB1 showed myopic error compared with the other two biometers (p < 0.0001). CONCLUSIONS: In eyes with long axial length, when the conventional IOL calculation was optimized with the equivalent refractive index-based instrument, we need to consider that IOL calculation using OCTB1 tends to cause slightly myopic refractive prediction error.

OBSERVATION OF VITREOUS FEATURES USING ENHANCED VITREOUS IMAGING OPTICAL COHERENCE TOMOGRAPHY IN HIGHLY MYOPIC RETINOSCHISIS.

PURPOSE: To observe features of the posterior vitreous and vitreoretinal interface in highly myopic eyes with retinoschisis using enhanced vitreous imaging optical coherence tomography. METHODS: Comprehensive ophthalmologic examination and enhanced vitreous imaging optical coherence tomography were performed in 77 eyes of 63 patients with highly myopic retinoschisis. Two different modes of spectral domain optical coherence tomography were employed to estimate retinoschisis and the posterior vitreous features in optical coherence tomography images, respectively. The types and distribution of vitreoretinal interface abnormalities were also analyzed. RESULTS: Complete posterior vitreous detachment (PVD) was identified in 55 eyes (71.4%) with a Weiss ring. Residual cortex was found in 39 eyes (70.9%) with complete PVD. Vitreoretinal interface changes, including vitreoretinal adhesion and epiretinal membrane (ERM), most frequently appeared in the macular area (47.3%), followed by the inferior arched vessels region (34.5%). In partial PVD eyes, vitreoretinal traction, vitreoretinal adhesion, and epiretinal membrane tended to be observed in the inferior and superior arched vessels regions (54.5 and 40.9%, respectively). Among all types of vitreoretinal interface abnormalities, epiretinal membrane comprised the largest proportion (46.8%) despite the status of PVD. The presence of inner layers of retinoschisis connoted a relatively high possibility of vitreoretinal interface abnormalities occurring. CONCLUSION: Enhanced vitreous imaging optical coherence tomography reveals a high prevalence of vitreoretinal interface abnormalities in highly myopic eyes with retinoschisis. Vitreous cortex tends to remain on the macular area in eyes with complete PVD. Our findings may lead to better guidance for the surgical treatment of highly myopic retinoschisis.

Analysis between two optical biometric devices in patients with cataract / Análise entre dois dispositivos de biometria óptica em pacientes com catarata

ABSTRACT Objective: To evaluate the correlation of optical biometry and target with variable ages, anterior chamber depth, axial length, R1/K1 and R2/K2 established by two optical biometry devices in patients with cataract. Methods: The study included the analysis of 348 medical records, from which 503 cataract eyes were selected, which underwent evaluation by the optical biometric devices IOL Master 700 and Lenstar LS 900 in the period of April to July 2017. Data collected were: age, anterior chamber depth, axial length, R1/K1 and R2/K2. Results: The average of the biometrics obtained using Lenstar was 21.02, varying 3.46, more or less, with an average target of -0.02, varying 0.45. In relation to the IOL Master it was 21.19, with a variation of 3.40 and average target of -0.01, a variation of 0.11. It can be observed that despite close values in relation to the mean, there was significance (p<0.001). Axial length (p<0.001) and R1/K1 (p<0.001) had an influence on the difference of the biometric values between the devices. Conclusion: A high degree of clinical and statistical correspondence was observed between the results obtained by the biometry devices in patients with cataract.

RESUMO Objetivos: Avaliar a correlação da biometria óptica e target com as variáveis idade, profundidade da câmara anterior, comprimento axial, R1/K1 e R2/K2 estabelecidos por dois dispositivos de biometria óptica em pacientes com catarata. Métodos: O trabalho abrangeu a análise de 348 prontuários dos quais foram selecionados 503 olhos com catarata ,que passaram pela avaliação nos dispositivos de biometria óptica IOL Master 700 e Lenstar LS 900 no período de abril a julho de 2017. Os dados colhidos foram: idade, profundidade da câmara anterior, comprimento axial, R1/K1 e R2/K2 . Resultados: A média da biometria obtida utilizando o Lenstar foi de 21,02, variando 3,46 para mais ou para menos, com target médio de -0,02, variando 0,45. Já em relação ao IOL Master foi de 21,19, com variação de 3,40 e target médio de -0,01, variação de 0,11. Pode-se observar que apesar de valores próximos em relação à média, houve significância (p < 0,001). Houve a concordância da biometria em relação ao comprimento axial (p < 0,001) e R1/K1(p < 0,001). Conclusão: Observou-se alto grau de correspondência clínica e estatística entre os resultados obtidos pelos dispositivos de biometria em pacientes com catarata.

Ganglion cell-inner plexiform layer thickness by swept-source optical coherence tomography in healthy Korean children: Normative data and biometric correlations.

The purpose of this study was to identify the normative values of ganglion cell-inner plexiform layer (GCIPL) thickness in healthy Korean children using swept-source optical coherence tomography (SS-OCT) and to investigate the correlations of age, refractive error, axial length (AL), retinal nerve fiber layer (RNFL) thickness and cup-to-disc (C/D) ratio with GCIPL thickness. Children aged between 3 and 17 who had visited our pediatric ophthalmology clinic were enrolled. Each subject underwent full ophthalmic examinations including RNFL thickness, C/D ratio and GCIPL thickness measurement by SS-OCT as well as AL measurement by partial-coherence interferometry. A total of 254 eyes of 127 children were included. The mean average GCIPL thickness was 71.5 ± 5.35 µm; the thickest sector was the superonasal and the thinnest the inferior. According to multivariate regression analysis, average GCIPL thickness was significantly associated with spherical equivalent and RNFL thickness (P < 0.0001 for both): the higher the myopia or the thinner the RNFL thickness, the thinner the GCIPL thickness. In conclusion, this study provides an SS-OCT-based pediatric normative database of GCIPL thickness that can serve as a reference for early detection and follow-up of glaucoma and optic nerve diseases in children.

Study of Vesicular Monoamine Transporter 2 in Myopic Retina Using [18F]FP-(+)-DTBZ.

PURPOSE: To investigate the relationship between expression level of vesicular monoamine transporter 2 (VMAT2) and myopia, as well as the feasibility of noninvasive myopia diagnosis through imaging VMAT2 in retina by using [18F]fluoropropyl-(+)-dihydrotetrabenazine ([18F]FP-(+)-DTBZ). PROCEDURES: The right eyes of ten guinea pigs were deprived of vision to establish form-deprived (FD) myopia and the left eyes were untreated as the self-control eyes. The location and expression level of VMAT2 in the eyes were detected by micro-positron emission tomography (PET)/X-ray computed tomography (CT) imaging through using [18F]FP-(+)-DTBZ. Immunofluorescence staining and Western blot were used to confirm the location and expression level of VMAT2 in the eyes. The concentrations of dopamine (DA) and its metabolites including 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were also investigated by high-performance liquid chromatography. RESULTS: The right eyes deprived of vision were obviously myopic (- 3.17 ± 1.33 D) after procedure, while the left eyes were hyperopic (4.60 ± 0.83 D, P < 0.0001). The main expressions of VMAT2 in the eyes were located in retina. VMAT2 was significantly reduced in the myopic retina compared to the normal one from PET/CT results (P = 0.0008), which could also be verified by Western blots (P = 0.029). The concentrations of DA, DOPAC, and HVA in the FD eyes were all significantly less than those in the control eyes (P = 0.024, P = 0.018, P = 0.008). As a role of storing and releasing DA in vesicles, VMAT2 was demonstrated positively correlating with the amounts of DA (P = 0.030), DOPAC (P = 0.038), and HVA (P = 0.025) through Pearson's correlation coefficient test. CONCLUSIONS: We demonstrate that [18F]FP-(+)-DTBZ can be used to noninvasively image VMAT2 in retina. The expression level of VMAT2 in retina may act as a new biomarker for myopia diagnosis. The decreasing of VMAT2 expression level may play an important role in the development of myopia through correspondingly reducing the amount of DA in retina.

Refractive error is associated with intracranial volume.

Myopia is part of the spectrum of refractive error. Myopia is associated with psychometric intelligence and, the link between brain anatomy and myopia has been hypothesized. Here we aimed to identify the associations between brain structures and refractive error in developed young adults. In a study cohort of 1,319 normal educated young adults, the refractive error showed a significant negative correlation with total intracranial volume and total cerebrospinal fluid (CSF) volume but not with total gray matter volume (GMV) or total white matter volume (WMV). Time spent studying was associated with refractive error but could not explain the aforementioned associations with brain volume parameters. The R2 values of the simple regression between spherical equivalent and outcome variables for each sex in non-whole brain imaging analyses were less than 0.05 in all cases and thus were weak. Psychometric intelligence was not associated with refractive error or total CSF volume, but it weakly positively correlated with total GMV and total WMV in this study population. Thus, refractive error appears to be primarily (weakly) associated with the volume of the cranium, whereas psychometric intelligence was associated with the volume of the brain.

Repeatability and agreement of central corneal thickness measurement with non-contact methods: a comparative study.

PURPOSE: To compare the central corneal thickness (CCT) measurements and reliability of RTVue XR-100 anterior segment optical coherence tomography (AS-OCT), AL-scan optical biometer and Schwind Sirius anterior segment analysis system. METHODS: The CCT was measured in one hundred and twenty-seven eyes of 127 healthy subjects with AS-OCT, AL-scan and Sirius system. Mean CCT was compared among the instruments, and the level of agreement was assessed using Bland-Altman plots. One eye each of 30 subjects was randomly assigned for intrasession intraoperator and interoperator repeatability which was assessed using coefficient of variation and intraclass correlation coefficient. RESULTS: Mean CCT with AS-OCT, AL-scan and Sirius system was 496.72 ± 32.75, 507.43 ± 33.54 and 512.08 ± 33.1 µm, respectively. There was no statistically significant difference between AL-scan and Sirius system (p = 0.26). Significant difference was found between AS-OCT/AL-scan (p = 0.01) and AS-OCT/Sirius system (p < 0.0001). Bland-Altman analysis showed a high level of agreement between AL-Scan/Sirius system (Mean difference -4.6 µm) and a low level of agreement between AS-OCT/AL-scan (Mean difference -10.7 µm) and OCT/Sirius system (Mean difference -15.4 µm). CONCLUSIONS: AS-OCT underestimated CCT measurements when compared to other two devices in healthy subjects. Hence, one must be cautious when analyzing the results from different machines and should be aware that the measurement values are not interchangeable.

Ametropia, retinal anatomy, and OCT abnormality patterns in glaucoma. 2. Impacts of optic nerve head parameters.

Clinicians use retinal nerve fiber layer thickness (RNFLT) measured by optical coherence tomography (OCT) as an adjunct to glaucoma diagnosis. Ametropia is accompanied by changes to the optic nerve head (ONH), which may affect how OCT machines mark RNFLT measurements as abnormal. These changes in abnormality patterns may bias glaucoma diagnosis. Here, we investigate the relationship between OCT abnormality patterns and the following ONH-related and ametropia-associated parameters on 421 eyes of glaucoma patients: optic disc tilt and torsion, central retinal vessel trunk location (CRVTL), and nasal and temporal retinal curvature adjacent to ONH, quantified as nasal/temporal slopes of the inner limiting membrane. We applied multivariate logistic regression with abnormality marks as regressands to 40,401 locations of the peripapillary region and generated spatial maps of locations of false positive/negative abnormality marks independent of glaucoma severity. Effects of torsion and temporal slope were negligible. The effect of tilt could be explained by covariation with ametropia. For CRVTL/nasal slope, abnormality pattern shifts at 7.2%/23.5% of the peripapillary region were detected, respectively, independent of glaucoma severity and ametropia. Therefore, CRVTL and nasal curvature should be included in OCT RNFLT norms. Our spatial location maps may aid clinicians to improve diagnostic accuracy.

Structural Changes of Inner and Outer Choroid in Central Serous Chorioretinopathy Determined by Optical Coherence Tomography.

PURPOSE: To determine the structural changes of the choroid in eyes with central serous chorioretinopathy (CSC) by enhanced depth imaging optical coherence tomography (EDI-OCT). METHODS: A retrospective comparative study was performed at two academic institutions. Forty eyes with CSC, their fellow eyes, and 40 eyes of age-matched controls were studied. Subfoveal cross sectional EDI-OCT images were recorded, and the hypo reflective and hyperreflective areas of the inner and outer choroid in the EDI-OCT images were separately measured. The images were analyzed by a binarization method to determine the sizes of the hyporeflective and hyperreflective areas. RESULTS: In the inner choroid, the hyperreflective area was significantly larger in the CSC eyes (35,640±10,229 µm2) than the fellow eyes (22,908±8,522 µm2) and the control eyes (20,630±8,128 µm2; P<0.01 vs control for both, Wilcoxon signed-rank test). In the outer choroid, the hyporeflective area was significantly larger in the CSC eyes (446,549±121,214 µm2) than the control eyes (235,680±97,352 µm2, P<0.01). The average ratio of the hyporeflective area to the total choroidal area was smaller in the CSC eyes (67.0%) than the fellow eyes (76.5%) and the control eyes (76.7%) in the inner choroid (P<0.01, both). However, the ratio was larger in the CSC eyes (75.2%) and fellow eyes (71.7%) than in the control eyes (64.7%) in the outer choroid (P<0.01, both). CONCLUSIONS: The larger hyperreflective area in the inner choroid is related to the inflammation and edema of the stroma of the choroid in the acute stage of CSC. The larger hyporeflective areas in the outer choroid is due to a dilatation of the vascular lumens of the larger blood vessels. These are the essential characteristics of eyes with CSC regardless of the onset.

Optical low-coherence reflectometry in the calculation of intraocular lens power in silicone oil-filled eyes.

PURPOSE: To evaluate the refractive outcome after combined surgery of silicone oil removal with phacoemulsification and intraocular lens implantation. We calculated ocular lens implantation power with optical low-coherence reflectometry (Lenstar LS900; Haag Streit, Koniz, Switzerland) in silicone oil-filled eyes. METHODS: Prospective, comparative study. The intraocular lens power of 35 silicone oil-filled eyes of 35 patients was calculated with a Lenstar LS900 laser biometer. In all cases we performed a combined procedure of pars plana vitrectomy with silicone oil removal and phacoemulsification with intraocular lens implantation. We analyzed the spherical equivalent of predicted and postoperative refractive error. A control group consisted of 25 cases of cataract extraction and intraocular lens implantation in non-vitrectomized eyes. RESULTS: The mean deviation of the final refraction was -0.03 ± 1.06 diopters and did not differ significantly from non-vitrectomized eyes (P < 0.05). 68.6% eyes had a deviation of ±1 diopter. There were no differences between high myopic and emmetropic silicone oil-filled eyes (-0.05 ±1.33 diopters vs. -0.03 ± 1.00 diopters; P < 0.05). CONCLUSIONS: Optical low-coherence reflectometry enables accurate intraocular lens power calculations in silicone oil-filled eyes. The refractive outcome is as accurate as in non-vitrectomized eyes.

Effect of ocular magnification on macular measurements made using spectral domain optical coherence tomography.

AIM: The aim of the present study was to study the effect of ocular magnification on macular measurements made using spectral domain optical coherence tomography (OCT). MATERIALS AND METHODS: One hundred and fifty-one subjects were included from the normative study of foveal morphology carried out at our hospital. Subjects underwent comprehensive eye examination and macular scanning using Cirrus high-definition OCT and axial length (AXL) measurement. Macular cube 512 × 128 scan protocol was used for scanning the macula. Automated measurements of the fovea namely foveal diameter, foveal slope (lateral measurements) and foveal depth (axial measurement) were taken. A correction factor for ocular magnification was done using the formula t = p × q × s, where "t0" is the corrected measurement, "p" is the magnification of OCT, "q0" is the ocular magnification, and "s" is the measurement on OCT without correction. The difference between corrected and uncorrected measurements was evaluated for statistical significance. RESULTS: Mean AXL was 22.95 ± 0.78 mm. Refractive error ranged from -3D to +4D. Mean difference between measured and corrected foveal diameter, slope and depth was 166.05 ± 95.37 ΅m (P < 0.001), 0.81° ± 0.53° (P < 0.001) and 0.05 ± 0.49 ΅m (P = 0.178) respectively. AXL lesser than the OCT calibrated value of 24.46 mm showed an increased foveal diameter (r = 0.961, P < 0.001) and a reduced foveal slope (r = -0.863, P < 0.001) than the corrected value. CONCLUSION: Lateral measurements made on OCT varied with AXL s other than the OCT calibrated value of 24.46 mm. Therefore, to estimate the actual dimensions of a retinal lesion using OCT, especially lateral dimensions, we recommend correction for the ocular magnification factor.

Refractive and topographic errors in topography-guided ablation produced by epithelial compensation predicted by 3D Artemis VHF digital ultrasound stromal and epithelial thickness mapping.

PURPOSE: To describe and quantify the errors inherent to topography-guided ablation of irregular corneas due to natural epithelial thickness compensatory remodeling. METHODS: Artemis very high-frequency (VHF) digital ultrasound scanning (ArcScan Inc) was performed on a cornea that had undergone radial keratotomy with inferior and superior trapezoidal keratotomies, resulting 27 years later in high irregular astigmatism (+6.50 -8.00 × 101) and severe loss of corrected distance visual acuity (CDVA) to 20/50. The epithelial thickness profile was highly irregular, masking a significant proportion of the true stromal irregularity from front corneal surface topography, which would have resulted in significant inaccuracies had a topography-guided ablation been performed. The stromal ablation pattern of a transepithelial phototherapeutic keratectomy (PTK) ablation was modeled, which appeared logically to reduce the areas of abnormal stromal surface elevation and resembled a hyperopic astigmatic ablation of approximately 3.50 diopters of cylinder. Artemis-assisted transepithelial PTK was performed to target the stromal irregularity masked by epithelium. RESULTS: Artemis-assisted transepithelial PTK induced a refractive change similar to that predicted (+2.24 -3.97 × 120), demonstrating the refractive shift produced by the epithelium. The epithelial thickness profile became relatively regular and CDVA returned to 20/20⁻². Two topography wavefront-guided ablations were performed to correct the remaining topographic irregularity and refractive error, resulting in a near plano refraction, significantly lower higher order aberrations, and CDVA of 20/20⁺². CONCLUSIONS: A knowledge of stromal surface shape and power shift produced by epithelial thickness profile alterations after corneal surgery has the potential of improving the efficacy and safety of custom corneal ablation.

Comparison of postoperative refractive outcomes: IOLMaster® versus immersion ultrasound.

BACKGROUND AND OBJECTIVE: To compare the postoperative refractive outcomes between IOLMaster biometry (Carl Zeiss Meditec, Inc., Dublin, CA) and immersion ultrasound biometry for axial length measurements. PATIENTS AND METHODS: Refractive outcomes in 354 eyes were compared using the IOLMaster and the immersion ultrasound biometry. Predicted refraction was determined using manual keratometry and the SRK-T formula with personalized A-constant. RESULTS: The axial lengths measured using the IOLMaster and immersion ultrasound were 24.49 ± 2.11 and 24.46 ± 2.11 mm, respectively, and the difference was significant (P < .05). The mean errors were 0.000 ± 0.578 D with the IOLMaster, and 0.000 ± 0.599 D with the immersion ultrasound, but the difference was not significant. The mean absolute error was smaller with the IOLMaster than with immersion ultrasound (0.463 ± 0.341 vs 0.479 ± 0.359 D), but the difference was not significant. CONCLUSION: IOLMaster biometry yields highly accurate results in cataract surgery. However, if the IOLMaster is unavailable, immersion ultrasound biometry with personalized intraocular lens constants is an acceptable alternative.