Anterior eye surface changes following miniscleral contact lens wear

Purpose To quantify the effect of short-term miniscleral contact lens wear on the anterior eye surface of healthy eyes, including cornea, corneo-scleral junction and sclero-conjuctival area. Methods Twelve healthy subjects (29.9 ± 5.7 years) wore a highly gas-permeable miniscleral contact lens of 16.5 mm diameter during a 5-hour period. Corneo-scleral height profilometry was captured before, immediately following lens removal and 3 h after lens removal. Topography based corneo-scleral limbal radius estimates were derived from height measurements. In addition, elevation differences in corneal and scleral region were calculated with custom-written software. Sclero-conjuctival flattening within different sectors was analysed. Results Short-term miniscleral lens wear significantly modifies the anterior eye surface. Significant limbal radius increment (mean ± standard deviation) of 146 ± 80 μm, (p = 0.004) and flattening of −122 ± 90 μm in the sclero-conjuctival area, (p << 0.001) were observed immediately following lens removal. These changes did not recede to baseline levels 3 h after lens removal. The greatest anterior eye surface flattening was observed in the superior sector. No statistically significant corneal shape change was observed immediately following lens removal or during the recovery period. Conclusions Short-term miniscleral contact lens wear in healthy eyes does not produce significant corneal shape changes measured with profilometry but alters sclero-conjuctival topography. In addition, sclero-conjuctival flattening was not uniformly distributed across the anterior eye

IMI-Onset and Progression of Myopia in Young Adults

Myopia typically starts and progresses during childhood, but onset and progression can occur during adulthood. The goals of this review are to summarize published data on myopia onset and progression in young adults, aged 18 to 40 years, to characterize myopia in this age group, to assess what is currently known, and to highlight the gaps in the current understanding. Specifically, the peer-reviewed literature was reviewed to: characterize the timeline and age of stabilization of juvenile-onset myopia; estimate the frequency of adult-onset myopia; evaluate the rate of myopia progression in adults, regardless of age of onset, both during the college years and later; describe the rate of axial elongation in myopic adults; identify risk factors for adult onset and progression; report myopia progression and axial elongation in adults who have undergone refractive surgery; and discuss myopia management and research study design. Adult-onset myopia is common, representing a third or more of all myopia in western populations, but less in East Asia, where onset during childhood is high. Clinically meaningful myopia progression continues in early adulthood and may average 1.00 diopters (D) between 20 and 30 years. Higher levels of myopia are associated with greater absolute risk of myopia-related ocular disease and visual impairment, and thus myopia in this age group requires ongoing management. Modalities established for myopia control in children would be options for adults, but it is difficult to predict their efficacy. The feasibility of studies of myopia control in adults is limited by the long duration required.</p

Eyes grow towards mild hyperopia rather than emmetropia in Chinese preschool children

Purpose: To document one-year changes in refraction and refractive components in preschool children. Methods: Children, 3–5 years old, in the Jiading District, Shanghai, were followed for one year. At each visit, axial length (AL), refraction under cycloplegia (1% cyclopentolate), spherical dioptres (DS), cylinder dioptres (DC), spherical equivalent refraction (SER) and corneal curvature radius (CR) were measured. Results: The study included 458 right eyes of 458 children. The mean changes in DS, DC and SER were 0.02 ± 0.35 D, −0.02 ± 0.33 D and 0.01 ± 0.37 D, while the mean changes in AL, CR and lens power (LP) were 0.27 ± 0.10 mm, 0.00 ± 0.04 mm and − 0.93 ± 0.49 D. The change in the SER was linearly correlated with the baseline SER (coefficient = −0.147, p < 0.001). When the baseline SER was at 1.05 D (95% CI = 0.21 to 2.16), the change in SER was 0 D. The baseline SER was also linearly associated with the change in LP (coefficient = 0.104, p = 0.013), but not with the change in AL (p = 0.957) or with the change in CR (p = 0.263). Conclusion: In eyes with a baseline SER less than +1.00 D, LP loss was higher compared to axial elongation, leading to hyperopic shifts in refraction, whereas for those with baseline SER over this range, loss of LP compared to axial elongation was reduced, leading to myopic shifts. This model indicated the homeostasis of human refraction and explained how refractive development leads to a preferred state of mild hyperopia.The study was funded by Chinese National NatureScience Foundation (No. 81670898), Chinese Nat-ural Science Foundation for Young Staff (No.81800881), The Shanghai Three Year Public HealthAction Program (No. GWIV-3.3), The ShanghaiHigh-level Oversea Training Team Program on EyePublic Health (No. GWTD2015S08), The ShanghaiOutstanding Academic Leader Program (No.16XD1402300), Shanghai Nature Science Founda-tion (NO. 15ZR1438400), Three-year Action Pro-gram of Shanghai Municipality for Strengtheningthe Construction of the Public Health System(NO.GWIV-13.2), Key Discipline of PublicHealth-Eye health in Shanghai (No.15GWZK0601), Municipal Human ResourcesDevelopment Program for Outstanding YoungTalents in Medical and Health Sciences in Shanghai(Grant No. 2017YQ019), Shanghai Sailing Program(No. 17YF1416100), Foundation of ShanghaiMunicipal Commission of Health and FamilyPlanning (No. 20184Y0217), National Key R&DProgramofChina(2016YFC0904800,2019YFC0840607), National Science and Technol-ogy Major Project of China (2017ZX09304010) andSongjiang Science Foundation (No. 19SJKJGG30)

Retinal image size in pseudophakia

Purpose: Approaches are developed to determine relative retinal magnifications in anisometropic patients undergoing cataract surgery; these can be used to balance between full spectacle corrections with equal intraocular lens (IOL) powers and a pure IOL power correction. Methods: The analysis started from the original and pseudophakic Navarro eye models, where in the latter case an IOL replaced the natural lens. A third model was a simplified Navarro-IOL model with a single surface cornea and a thin lens. These models were manipulated by altering vitreous length, corneal power and lens position. Retinal image sizes were determined for both full IOL corrections and full spectacle corrections by raytracing and approximate equations. Relative magnification (RM) was determined as the ratio of retinal image size of an eye to that of the appropriate standard eye. Results: For raytracing and full IOL correction, vitreous length led to RM change of 5%/mm, while for corneal power and IOL position this was −0.4%/D and 1.4%/mm, respectively. For raytracing and spectacle correction, effects were 0%/D (vitreous depth), −1.6%/D (corneal power) and +1.0%/mm (IOL position). For full IOL correction, the approximate RM calculations were highly accurate. For spectacle correction, the approximate RM calculations were exact for vitreous length changes, reasonably accurate for corneal power changes but very inaccurate for changes in anterior chamber depth. Conclusion: Relative magnification approximations may be useful to assess the risk of aniseikonia in anisometropic patients targeted for postoperative emmetropia. Some of these patients would be corrected best by a combination of spectacles and IOLs.</p

Modelling ocular ageing in adults with well-controlled type I diabetes

Purpose: To develop a paraxial eye model based on a previously collected cohort of adults with well-controlled type 1 diabetes mellitus (DM1) and a limited range of refractive errors. Methods: The study used the previously published biometric data of 72 participants (Age: 41.5 ​± ​12.4 years) with DM1. Measurements included objective refraction, anterior and posterior corneal radii of curvatures, and internal distances. Moreover, phakometry was used to determine the lens radii of curvature and lens equivalent indices, from which the lens powers were calculated. A multivariate linear regression was performed for each biometric parameter with respect to current age (Age), the time since the onset of diabetes (Tdb), and current levels of glycated hemoglobin (HbA1c). The vitreous chamber depth was determined from other distances, and lens equivalent index was chosen to balance the models. These were compared with an existing model for non-diabetic eyes. Results: Some dependent parameters were not affected by the independent variables (spherical equivalent, anterior corneal radius of curvature, central corneal thickness), some were affected by time since onset (the lens radii of curvatures, anterior chamber depth) and others were affected by both age and time since onset (posterior corneal radius of curvature, lens thickness, axial length). None of the dependent parameters were affected by current levels of HbA1c. Conclusions: The proposed model accurately describes the age-related changes in the eyes of people with DM1. In this description the age of diabetes onset plays an important role, especially if the diabetes onset occurred during childhood

The bigaussian nature of ocular biometry

To study how the leptokurtic shape of the refractive distribution can be derived from ocular biometry by means of a multivariate Gaussian model

Comparing Methods to Estimate the Human Lens Power

PURPOSE. To compare the accuracy of different methods of calculating human lens power when lens thickness is not available. METHODS. Lens power was calculated by four methods. Three methods were used with previously published biometry and refraction data of 184 emmetropic and myopic eyes of 184 subjects (age range, 18-63 years; spherical equivalent range, Ϫ12.38 to ϩ0.75 D). These three methods consist of the Bennett method, which uses lens thickness, a modification of the Stenström method and the BennettRabbetts method, both of which do not require knowledge of lens thickness. These methods include c constants, which represent distances from lens surfaces to principal planes. Lens powers calculated with these methods were compared with those calculated using phakometry data available for a subgroup of 66 emmetropic eyes (66 subjects). RESULTS. Lens powers obtained from the Bennett method corresponded well with those obtained by phakometry for emmetropic eyes, although individual differences up to 3.5 D occurred. Lens powers obtained from the modified-Stenström and BennettRabbetts methods deviated significantly from those obtained with either the Bennett method or phakometry. Customizing the c constants improved this agreement, but applying these constants to the entire group gave mean lens power differences of O cular refraction is determined by axial length, anterior chamber depth, corneal power ,and lens power. Although axial length and keratometry measurements have become routine clinically, determining lens power is problematic, as the lens radii of curvature and refractive index distribution are usually not available. Although techniques have been proposed in the literature to estimate the radii in vivo, 1-5 they are currently too complicated to be used in large-scale studies or clinical practice. Because of this impracticality, various methods have been proposed that use ocular biometry, such as keratometry, ocular axial length, anterior chamber depth, lens thickness, and ocular refraction, to estimate the power of an equivalent lens at a location near that of the lens. Since these biometric parameters are easily determined, such methods can provide a quick estimate of the equivalent lens power. The most well known of these methods was proposed by Bennett, 6 who used a thick-lens description that makes assumptions about the shape and refractive index distribution of the lens based on the Gullstrand-Emsley schematic eye. 7 From this, he could calculate the equivalent lens power in a way that has been shown to be accurate in comparison with phakometry. Other methods do not require this knowledge of the lens thickness, such as the approaches proposed by Stenström 11 These approaches might be useful in a clinical practice using biometry devices that do not provide lens thickness (e.g., IOL Master; Carl Zeiss Meditec, Dublin, CA), or in analysis of historical biometry data. The purposes of this study are (1) to verify the agreement that Dunne et al. 8 found between the Bennett method and phakometry; to (2) compare lens powers obtained with the Bennett method, our modification of the Stenström method, and the Bennett-Rabbetts method for previously published data of emmetropic and myopic eyes, and (3) to provide customized constants to optimize the performance of these three methods. The results allow improvement of our statistical eye model 12 by including a more reliable method to estimate lens power when lens thickness is not available. METHODS Subjects To estimate the accuracy of the lens power calculations with respect to phakometry, we need the biometry and phakometry data of a population of normal subjects. For this purpose, we used previously published data by Atchison et al. To compare the results of the three power calculation methods for a wider range of refractions, the first dataset was supplemented by a second set from the same research group. 14 This dataset contained 118 eyes of 118 emmetropic and myopic subjects (43 men, 75 women; 74 Caucasian, 44 non-Caucasian) with a mean spherical equivalent refraction of Ϫ2.69 Ϯ 2.79 D (range, Ϫ12.3 to ϩ0.75 D) and an average subject age of 25.4 Ϯ 5.1 years (range, 18 -36 years). No phakometry data were available for this second dataset. Inclusion criteria were stringent, to ensure that only healthy eyes were included. These entailed, among others, corrected visual acuity better than 6/6 on an ETDRS chart, an intraocular pressure below 21 mm Hg, and a Pelli-Robson contrast sensitivity of 1.65 or better for subjects of 40 years of age and younger and a contrast sensitivity of 1.50 or better for subjects older than 40 years of age. In the myopic dataset, eyes with astigmatism larger than 0.5 D were also excluded. The subjects&apos; eyes were not dilated or cyclopleged before testing, which might have caused some degree of accommodation in some of From th