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Orthokeratology (ortho-k) is the process of deliberately reshaping the anterior cornea by utilising specialty contact lenses to temporarily and reversibly reduce refractive error after lens removal. Modern ortho-k utilises reverse geometry lens designs, made with highly oxygen permeable rigid materials, worn overnight to reshape the anterior cornea and provide temporary correction of refractive error. More recently, ortho-k has been extensively used to slow the progression of myopia in children. This report reviews the practice of ortho-k, including its history, mechanisms of refractive and ocular changes, current use in the correction of myopia, astigmatism, hyperopia, and presbyopia, and standard of care. Suitable candidates for ortho-k are described, along with the fitting process, factors impacting success, and the potential options for using newer lens designs. Ocular changes associated with ortho-k, such as alterations in corneal thickness, development of microcysts, pigmented arcs, and fibrillary lines are reviewed. The safety of ortho-k is extensively reviewed, along with an overview of non-compliant behaviours and appropriate disinfection regimens. Finally, the role of ortho-k in myopia management for children is discussed in terms of efficacy, safety, and potential mechanisms of myopia control, including the impact of factors such as initial fitting age, baseline refractive error, the role of peripheral defocus, higher order aberrations, pupil size, and treatment zone size., (Copyright © 2021. Published by Elsevier Ltd.)

Purpose: To examine the choroidal thickness (ChT) response to short-term with-the-rule (WTR) and against-the-rule (ATR) simple myopic astigmatic defocus, with the response to spherical myopic defocus and clear vision used as control conditions., Methods: The left eye of 18 healthy adults aged 28 ± 6 years was exposed to clear vision, +3 D spherical myopic defocus, +3 D × 180 WTR, or +3 D × 90 ATR astigmatic defocus for 60 minutes, over four randomly ordered visits, while their right eye was optimally corrected. The macular ChT was measured with optical coherence tomography along the vertical and horizontal meridians before and after 20, 40, and 60 minutes of defocus., Results: After 60 minutes of defocus, ChT increased by +8 ± 5 µm (P < 0.001) with spherical myopic defocus, but varied with simple myopic astigmatic defocus, depending on the axis of astigmatism (P < 0.001), increasing by +5 ± 6 µm (P = 0.037) with WTR and decreasing by -4 ± 5 µm (P = 0.011) with ATR astigmatic defocus. These changes were similar across the vertical and horizontal meridians (P = 0.22). The ChT changes were greater than the change during the clear vision control condition (-1 ± 4 µm) for WTR (+5 ± 5 µm, P = 0.002) but not ATR (-4 ± 6 µm, P = 0.09) astigmatic defocus., Conclusions: These results provide insights into the human ChT response to short-term astigmatic defocus and highlight a potential difference in the myopiagenic signal associated with the orientation of astigmatic blur.

Purpose: Visual rehabilitation following penetrating keratoplasty is the primary indication for approximately 15% of all scleral lens fittings. Since corneal biomechanics are altered following penetrating keratoplasty, the aim of this study was to quantify changes in anterior corneal optics following short-term scleral lens wear in eyes with corneal grafts., Methods: Scheimpflug images were obtained before and after a period of scleral lens wear (mean 6.3 ± 1.4 h), from eyes that had previously undergone penetrating keratoplasty (10 eyes of nine participants, mean age 31 ± 9 years). Corneal power and thickness data were examined over the central 6 mm, including regional analyses of the central (0-3 mm) and the mid-peripheral cornea (3-6 mm annulus) using customised software to deterime corneal power vectors M (best fit sphere), J 0 (90/180 astigmatism) and J 45 (45/135 astigmatism). Anterior corneal aberrations were extracted using corneal elevation data., Results: Corneal power vector J 45 increased following lens wear (by 0.22 ± 0.05 D, p = 0.003) across the central 6 mm, while M displayed regional variations following lens wear indicating larger changes further from the corneal centre (p = 0.004). The change in corneal power vector M was also correlated with the magnitude of central corneal swelling (r = 0.65, p = 0.04). The anterior corneal aberration terms of oblique astigmatism, hoirzontal coma, and spherical aberration also varied following lens wear (all p ≤ 0.01). The mean change in the corneal spherocylinder derived from the elevation data following lens wear was +0.14/-0.54 × 44 for a 6 mm corneal diameter., Conclusions: Clinically significant alterations in anterior corneal topography and higher order aberrations were observed following short-term scleral lens wear in eyes that had undergone penetrating keratoplasty. Spherocylindrical changes were approximately double the magnitude and more oblique in orientation compared to previous reports of healthy eyes. Changes in corneal power vector M may be related to epithelial corneal oedema., (© 2020 The Authors Ophthalmic & Physiological Optics © 2020 The College of Optometrists.)

Purpose: Astigmatism is an important refractive condition in children. However, the functional impact of uncorrected astigmatism in this population is not well established, particularly with regard to academic performance. This study investigated the impact of simulated bilateral astigmatism on academic-related tasks before and after sustained near work in children., Methods: Twenty visually normal children (mean age: 10.8 ± 0.7 years; six males and 14 females) completed a range of standardised academic-related tests with and without 1.50 D of simulated bilateral astigmatism (with both academic-related tests and the visual condition administered in a randomised order). The simulated astigmatism was induced using a positive cylindrical lens while maintaining a plano spherical equivalent. Performance was assessed before and after 20 min of sustained near work, during two separate testing sessions. Academic-related measures included a standardised reading test (the Neale Analysis of Reading Ability), visual information processing tests (Coding and Symbol Search subtests from the Wechsler Intelligence Scale for Children) and a reading-related eye movement test (the Developmental Eye Movement test). Each participant was systematically assigned either with-the-rule (WTR, axis 180°) or against-the-rule (ATR, axis 90°) simulated astigmatism to evaluate the influence of axis orientation on any decrements in performance., Results: Reading, visual information processing and reading-related eye movement performance were all significantly impaired by both simulated bilateral astigmatism (p < 0.001) and sustained near work (p < 0.001), however, there was no significant interaction between these factors (p > 0.05). Simulated astigmatism led to a reduction of between 5% and 12% in performance across the academic-related outcome measures, but there was no significant effect of the axis (WTR or ATR) of astigmatism (p > 0.05)., Conclusion: Simulated bilateral astigmatism impaired children's performance on a range of academic-related outcome measures irrespective of the orientation of the astigmatism. These findings have implications for the clinical management of non-amblyogenic levels of astigmatism in relation to academic performance in children. Correction of low to moderate levels of astigmatism may improve the functional performance of children in the classroom., (© 2014 The Authors Ophthalmic & Physiological Optics © 2014 The College of Optometrists.)

Purpose: To provide a comprehensive overview of research examining the impact of astigmatism on clinical and functional measures of vision, the short and longer term adaptations to astigmatism that occur in the visual system, and the currently available clinical options for the management of patients with astigmatism., Recent Findings: The presence of astigmatism can lead to substantial reductions in visual performance in a variety of clinical vision measures and functional visual tasks. Recent evidence demonstrates that astigmatic blur results in short-term adaptations in the visual system that appear to reduce the perceived impact of astigmatism on vision. In the longer term, uncorrected astigmatism in childhood can also significantly impact on visual development, resulting in amblyopia. Astigmatism is also associated with the development of spherical refractive errors. Although the clinical correction of small magnitudes of astigmatism is relatively straightforward, the precise, reliable correction of astigmatism (particularly high astigmatism) can be challenging. A wide variety of refractive corrections are now available for the patient with astigmatism, including spectacle, contact lens and surgical options., Conclusion: Astigmatism is one of the most common refractive errors managed in clinical ophthalmic practice. The significant visual and functional impacts of astigmatism emphasise the importance of its reliable clinical management. With continued improvements in ocular measurement techniques and developments in a range of different refractive correction technologies, the future promises the potential for more precise and comprehensive correction options for astigmatic patients., (© 2014 The Authors Ophthalmic & Physiological Optics © 2014 The College of Optometrists.)

John Lennon has an enduring, instantly recognisable, iconic, spectacle look. However, prior to 1966, he was rarely seen wearing glasses in public. From ages 7 to 26, he effectively hid his myopia away, including a period of unsuccessful contact lens wear during Beatlemania. This narrative review examines John's experience with contact lenses from 1963 to 1966 when he wore corneal rigid lenses made from polymethylmethacrylate, which regularly fell out. This frequent lens ejection was most likely due to the interaction between his upper eyelid and a spherical back surface rigid lens fitted to his right eye, which had a moderate degree of with‐the‐rule corneal astigmatism. John's recollection that his contact lenses stayed in place while 'stoned' supports this hypothesis, as a cannabis‐induced upper eyelid ptosis would reduce the likelihood of lens ejection. [ABSTRACT FROM AUTHOR]

Background: To investigate the influence of compression factor upon changes in ocular higher‐order aberrations (HOAs) in young myopic children undergoing orthokeratology treatment. Methods: Subjects aged between six and < 11 years, with low myopia (0.50–4.00 D inclusive), low astigmatism (≤ 1.25 D), and anisometropia (≤ 1.00 D), were randomly assigned to wear orthokeratology lenses of different compression factors in each eye (one eye 0.75 D and the fellow eye 1.75 D). HOAs were measured weekly over one month of lens wear. Wavefront analysis was conducted over a 5‐mm pupil using a sixth order Zernike polynomial expansion. Linear mixed models were used to examine the individual Zernike co‐efficients and specific root‐mean‐square (RMS) error (spherical, comatic, total HOAs) metrics and their changes between the two eyes during the study period. Results: Twenty‐eight myopic (mean manifest spherical equivalent refraction: −2.10 ± 0.58 D) children (median [range] age: 9.3 [7.8–11.0] years) were analysed. Significant interocular differences in HOAs at baseline were observed for Z6−6 and Z6−4 only (both p < 0.05). During the lens wear period, eyes fitted with the increased compression factor showed greater changes in primary spherical aberration (Z40, p = 0.04) and RMS values for spherical and total HOAs (both p < 0.01). Considering data from both eyes together, after adjusting for the paired nature of the data, some other Zernike terms (Z31 and Z60, both p < 0.01) and the RMS value of comatic aberrations (p < 0.001) significantly increased after one month of orthokeratology treatment. The increase in primary spherical aberration (Z40) was positively correlated with the reduction in spherical equivalent refractive error, but only in eyes fitted with the increased compression factor (r = 0.69, p < 0.001). Conclusions: Increasing the orthokeratology compression factor by 1.00 D significantly altered some HOAs, particularly spherical aberration. Given the association between positive spherical aberration and eye growth in children, further research investigating the influence of orthokeratology compression factor on axial eye growth is warranted. [ABSTRACT FROM AUTHOR]

Scleral contact lenses have a range of therapeutic and optical applications. In recent years, scleral lens prescribing has increased due to significant advances in ocular imaging technology, lens manufacturing processes, and the widespread availability of scleral lenses globally. While the optical principles of scleral lenses are identical to those of corneal rigid lenses (i.e. the post-lens tear layer neutralises the majority of anterior corneal astigmatism and higher order aberrations), the nature of scleral lenses and their typical fitting characteristics means that many of the assumptions of 'thin lens' paraxial optics traditionally used for corneal rigid lens calculations may be inappropriate in certain clinical scenarios. This review provides a comprehensive overview of a variety of lens and fitting characteristics that are unique to scleral lenses, or not typically encountered with corneal rigid lenses, and how these factors may potentially influence optical performance based on theoretical modelling, in particular; scleral lens parameters, the post-lens tear layer, and dynamic changes during lens wear. Current front and back surface lens designs and future scleral lens applications are also discussed, along with lens modifications to improve visual outcomes and transient changes in corneal optics induced by appropriately fitted modern scleral lenses. [ABSTRACT FROM AUTHOR]

Purpose: To examine the influence of centre thickness upon miniscleral lens flexure and the association between the magnitude of in-vivo lens flexure and scleral toricity.Methods: In-vivo lens flexure was measured using a videokeratoscope in 9 healthy young participants (25 ± 4 years) with normal corneae fitted with ICD 16.5 miniscleral lenses (hexafocon B material) with centre thicknesses of 150, 250, and 350 μm. Scleral toricity was determined from sagittal height data over a 15 mm chord obtained from a corneo-scleral topographer.Results: On average, lens flexure increased with decreasing centre thickness, but remained <0.50 D (mean increase <0.25 D, p = 0.63). Scleral toricity was positively correlated with in-vivo flexure for the 150 μm (r = 0.77, p = 0.02) and 250 μm (r = 0.72, p = 0.03) lenses. Using a group mean split, eyes with >200 μm scleral toricity exhibited greater in-vivo flexure than eyes with <200 μm (0.40 D more, averaged across all lenses, p = 0.02), and this effect was greatest for the 150 μm lens (0.61 D more, p = 0.04).Conclusions: Decreasing the centre thickness from 350 μm to 150 μm resulted in <0.25 D increase in lens flexure for a high Dk and low modulus material. Scleral toricity >200 μm was associated with more in-vivo lens flexure. When intentionally reducing scleral lens centre thickness to enhance oxygen transmissibility, customised back surface designs may be required to minimise in-vivo flexure in eyes with >200 μm scleral toricity at a 15 mm chord. [ABSTRACT FROM AUTHOR]

Purpose There have been only a limited number of studies examining the accommodative response that occurs when the two eyes are provided with disparate accommodative stimuli, and the results from these studies to date have been equivocal. In this study, we therefore aimed to examine the capacity of the visual system to aniso-accommodate by objectively measuring the interocular difference in the accommodation response between fellow dominant and non-dominant eyes under controlled monocular and binocular viewing conditions during short-term exposure to aniso-accommodative stimuli. Methods The accommodative response of each eye of 16 young isometropic adults (mean age 22 ± 2 years) with normal binocular vision was measured using an open-field autorefractor during a range of testing conditions; monocularly (accommodative demands ranging from 1.32 to 4.55 D) and binocularly while altering the accommodation demand for each eye (aniso-accommodative stimuli ranging from 0.24 to 2.05 D). Results Under monocular viewing conditions, the dominant and non-dominant eyes displayed a highly symmetric accommodative response; mean interocular difference in spherical equivalent 0.01 ± 0.06 D (relative) and 0.22 ± 0.06 D (absolute) ( p > 0.05). During binocular viewing, the dominant eye displayed a greater accommodative response (0.11 ± 0.34 D relative and 0.24 ± 0.26 D absolute) irrespective of whether the demand of the dominant or non-dominant eye was altered ( p = 0.01). Astigmatic power vectors J0 and J45 did not vary between eyes or with increasing accommodation demands under monocular or binocular viewing conditions ( p > 0.05). Conclusion The dominant and non-dominant eyes of young isometropic individuals display a similar consensual lag of accommodation under both monocular and binocular viewing conditions, with the dominant eye showing a small but significantly greater (by 0.12-0.25 D) accommodative response. Evidence of short-term aniso-accommodation in response to asymmetric accommodation demands was not observed. [ABSTRACT FROM AUTHOR]

Purpose To examine the influence of short-term miniscleral contact lens wear on corneal shape, thickness and anterior surface aberrations. Methods Scheimpflug imaging was captured before, immediately following and 3 h after a short period (3 h) of miniscleral contact lens wear for 10 young (mean 27 ± 5 years), healthy participants. Natural diurnal variations were considered by measuring baseline diurnal changes obtained on a separate control day without contact lens wear. Results Small but significant anterior corneal flattening was observed immediately following lens removal (overall mean 0.02 ± 0.03 mm, p < 0.001) which returned to baseline levels 3 h after lens removal. During the 3 h recovery period significant corneal thinning (−13.4 ± 10.5 μm) and posterior surface flattening (0.03 ± 0.02 mm) were also observed (both p < 0.01). The magnitude of posterior corneal flattening during recovery correlated with the amount of corneal thinning ( r = 0.69, p = 0.03). Central corneal clearance (maximum tear reservoir depth) was not associated with corneal swelling following lens removal ( r = −0.24, p > 0.05). An increase in lower-order corneal astigmatism Z (2,2) was also observed following lens wear (mean −0.144 ± 0.075 μm, p = 0.02). Conclusions Flattening of the anterior corneal surface was observed immediately following lens wear, while ‘rebound’ thinning and flattening of the posterior surface was evident following the recovery period. Modern miniscleral contact lenses that vault the cornea may slightly influence corneal shape and power but do not induce clinically significant corneal oedema during short-term wear. [ABSTRACT FROM AUTHOR]

Purpose To examine the symmetry of corneal changes following near work in the fellow eyes of non-amblyopic myopic anisometropes. Methods Thirty-four non-amblyopic, myopic anisometropes (minimum 1 D spherical equivalent anisometropia) had corneal topography measured before and after a controlled near work task. Subjects were positioned in a headrest to minimise head movements and read continuous text on a computer monitor for 10 min at an angle of 25 degrees downward gaze and an accommodation demand of 2.5 D. Measures of the morphology of the palpebral aperture during primary and downward gaze were also obtained. Results The more and less myopic eyes exhibited a high degree of interocular symmetry for measures of palpebral aperture morphology during both primary and downward gaze. Following the near work task, fellow eyes also displayed a symmetrical change in superior corneal topography (hyperopic defocus) which correlated with the position of the upper eyelid during downward gaze. Greater changes in the spherical corneal power vector (M) following reading were associated with a narrower palpebral aperture during downward gaze ( p = 0.07 for more myopic and p = 0.03 for less myopic eyes). A significantly greater change in J0 (an increase in against the rule astigmatism) was observed in the more myopic eyes (−0.04 ± 0.04 D) compared to the less myopic eyes (−0.02 ± 0.06 D) over a 6 mm corneal diameter ( p = 0.01). Conclusions Changes in corneal topography following near work are highly symmetrical between the fellow eyes of myopic anisometropes due to the interocular symmetry of the palpebral aperture. However, the more myopic eye exhibits changes in corneal astigmatism of greater magnitude compared to the less myopic eye. [ABSTRACT FROM AUTHOR]

Abstract: This study compared the corneal and total higher order aberrations between the fellow eyes in monocular amblyopia. Nineteen amblyopic subjects (8 refractive and 11 strabismic) (mean age 30±11years) were recruited. A range of biometric and optical measurements were collected from the amblyopic and non-amblyopic eye including; axial length, corneal topography and total higher order aberrations. For a sub-group of eleven non-presbyopic subjects (6 refractive and 5 strabismic amblyopes, mean age 29±10years) total higher order aberrations were also measured during accommodation (2.5D stimuli). Amblyopic eyes were significantly shorter and more hyperopic compared to non-amblyopic eyes and the interocular difference in axial length correlated with both the magnitude of anisometropia and amblyopia (both p <0.01). Significant differences in higher order aberrations were observed between fellow eyes, which varied with the type of amblyopia. Refractive amblyopes displayed higher levels of 4th order corneal aberrations C(4,0)(spherical aberration), C(4,2)(secondary astigmatism 90°) and C(4,−2)(secondary astigmatism along 45°) in the amblyopic eye compared to the non-amblyopic eye. Strabismic amblyopes exhibited significantly higher levels of C(3,3)(trefoil) in the amblyopic eye for both corneal and total higher order aberrations. During accommodation, the amblyopic eye displayed a significantly greater lag of accommodation compared to the non-amblyopic eye, while the changes in higher order aberrations were similar in magnitude between fellow eyes. Asymmetric visual experience during development appears to be associated with asymmetries in higher order aberrations, in some cases proportional to the magnitude of anisometropia and dependent upon the amblyogenic factor. [Copyright &y& Elsevier]