Refractive development II: Modelling normal and myopic eye growth.

Purpose: During refractive development, eye growth is controlled by a combination of genetically pre-programmed processes and retinal feedback to minimise the refractive error. This work presents a basic differential model of how this process may take place.

Methods: The description starts from two bi-exponential descriptions of the axial power P (or dioptric distance) and total refractive power P, the difference between which corresponds with the spherical refractive error S.

Estimating the astigmatic power of the crystalline lens and eye from ocular biometry.

Purpose: To estimate the astigmatic power of the crystalline lens and the whole eye without phakometry using a set of linear equations and to provide estimates for the astigmatic powers of the crystalline lens surfaces.

Methods: Linear optics expresses astigmatic powers in the form of matrices and uses paraxial optics and a 4 × 4 ray transfer matrix to generalise Bennett's method comprehensively to include astigmatic elements. Once this is established, the method is expanded to estimate the contributions of the front and back lens surfaces.

The Effect of the Zonular Fiber Angle of Insertion on Accommodation.

With age, there is an anterior shift of the ciliary body in the eye, which alters the angle of zonular insertion in older eyes compared with younger eyes. This study aims to simulate lens accommodation with different zonular angles to consider the influence of zonular position on lens accommodative capacity. Models were constructed based on lenses aged 11, 29, and 45 years using a 2D axisymmetric structure that included a capsule, cortex, nucleus, and zonular fibers.

Generalised models of the vertebrate eye.

Purpose: To present a set of closed-form analytical equations to create a consistent eye model balance based on clinically measured input parameters in a single step. These models complement the existing iterative approaches in the literature.

Methods: Two different approaches are presented, both considering the cornea and lens as equivalent thin lenses.

Bi-exponential description for different forms of refractive development.

It was recently established that the axial power, the refractive power required by the eye for a sharp retinal image in an eye of a certain axial length, and the total refractive power of the eye may both be described by a bi-exponential function as a function of age (Rozema, 2023). Inspired by this result, this work explores whether these bi-exponential functions are able to simulate the various known courses of refractive development described in the literature, such as instant emmetropization, persistent hypermetropia, developing hypermetropia, myopia, instant homeostasis, modulated development, or emmetropizing hypermetropes. Moreover, the equations can be adjusted to match the refractive development of school-age myopia and pseudophakia up to the age of 20 years.

The influence of variations in ocular biometric and optical parameters on differences in refractive error.

Purpose: To present a paraxial method to estimate the influence of variations in ocular biometry on changes in refractive error (S) at a population level and apply this method to literature data.

Methods: Error propagation was applied to two methods of eye modelling, referred to as the simple method and the matrix method. The simple method defines S as the difference between the axial power and the whole-eye power, while the matrix method uses more accurate ray transfer matrices.

Allowable movement of wavefront-guided contact lens corrections in normal and keratoconic eyes.

Purpose: The goal was to use SyntEyes modelling to estimate the allowable alignment error of wavefront-guided rigid contact lens corrections for a range of normal and keratoconic eye aberration structures to keep objectively measured visual image quality at or above average levels of well-corrected normal eyes. Secondary purposes included determining the required radial order of correction, whether increased radial order of the corrections further constrained the allowable alignment error and how alignment constraints vary with keratoconus severity.

Methods: Building on previous work, 20 normal SyntEyes and 20 keratoconic SyntEyes were fitted with optimised wavefront-guided rigid contact lens corrections targeting between three and eight radial orders that drove visual image quality, as measured objectively by the visual Strehl ratio, to near 1 (best possible) over a 5-mm pupil for the aligned position.

The potential influence of the ligament of Wieger on the crystalline lens shape.

This research uses mathematical modelling to evaluate the influence of the ligament of Wieger on the crystalline lens shape at rest, and during accommodation. An axisymmetric model of the anterior segment, including the ligament of Wieger, was created using the finite element method. Different conditions including variations of stiffness and positions of the ligament, with and without the ligament, were tested to see how they affected lens curvature and optical power.

Mean cycloplegic refractive error in emmetropic adults - The Tehran Eye Study.

Purpose: In children under 20 years, refractive development targets a cycloplegic refractive error of +0.5 to +1.5D, while presbyopes over 40 years generally have non-cycloplegic errors of ≥ +1D.

Longitudinal changes in crystalline lens thickness and power in children aged 6-12 years old.

Objectives: To determine the three-year changes in crystalline lens power (LP) and thickness (LT) in children and their associated factors.

Methods: Schoolchildren aged 6-12 years living in Shahroud, northeast Iran were examined in 2015 and 2018. The Bennett formula was used to calculate LP.

Definitions for Keratoconus Progression and Their Impact on Clinical Practice.

Purpose: There is currently no consensus on which keratoconus need cross-linking nor on how to establish progression. This study assessed the performance of diverse progression criteria and compared them with our clinical knowledge of keratoconus evolution.

Methods: This was a retrospective, longitudinal, observational study.

Retinal shadows produced by myopia control spectacles.

Purpose: To analyse ocular coherence tomography (OCT) images of the retinal shadows caused by defocus and diffusion optics spectacles.

Methods: One eye was fitted successively with the Hoya Defocus Incorporated Multiple Segments (DIMS) spectacle lens, two variations of the +3.50 D peripheral add spectacle (DEFOCUS) and the low-contrast dot lens (Diffusion Optics Multiple Segments, DOMS); each at a vertex distance of 12 mm.

New keratoconus staging system based on OCT.

Purpose: To establish a numerical spectral-domain optical coherence tomography (SD-OCT)-based keratoconus (KC) staging system and compare it with existing KC staging systems.

Setting: Eye Hospital of Wenzhou Medical University, Wenzhou, China.

Designs: Retrospective case-control study.

Combinations of Scheimpflug tomography, ocular coherence tomography and air-puff tonometry improve the detection of keratoconus.

Purpose: To determine whether combinations of devices with different measuring principles, supported by artificial intelligence (AI), can improve the diagnosis of keratoconus (KC).

Methods: Scheimpflug tomography, spectral-domain optical coherence tomography (SD-OCT), and air-puff tonometry were performed in all eyes. The most relevant machine-derived parameters to diagnose KC were determined using feature selection.

Ray tracing optimization: a new method for intraocular lens power calculation in regular and irregular corneas.

To develop a novel algorithm based on ray tracing, simulated visual performance and through-focus optimization for an accurate intraocular lens (IOL) power calculation. Custom-developed algorithms for ray tracing optimization (RTO) were used to combine the natural corneal higher-order aberrations (HOAs) with multiple sphero-cylindrical corrections in 210 higher order statistical eye models for developing keratoconus. The magnitude of defocus and astigmatism producing the maximum Visual Strehl was considered as the optimal sphero-cylindrical target for IOL power calculation.

Refractive development I: Biometric changes during emmetropisation.

Purpose: Although there are many reports on ocular growth, these data are often fragmented into separate parameters or for limited age ranges. This work intends to create an overview of normal eye growth (i.e.

Investigating the Link Between Visual Quality and Vision-Related Quality of Life in Patients With Keratoconus.

Purpose: The purpose of the study was to investigate the optical and visual determinants of vision-related quality of life (VR-QoL) in patients with keratoconus.

Methods: A cross-sectional case-control study was conducted at the Department of Ophthalmology, Antwerp University Hospital, Belgium. Patients previously diagnosed with keratoconus and healthy emmetropic or ametropic volunteers were included.

Technical notes on peripheral refraction, peripheral eye length and retinal shape determination.

Purpose: To give an overview of the misconceptions and potential artefacts associated with measuring peripheral refractive error and eye length, the use of these measures to determine the retinal shape and their links to myopia development. Several issues were identified: the relationship between peripheral refractive error and myopia development, inferring the retinal shape from peripheral refraction or eye length patterns, artefacts and accuracy when measuring peripheral eye length using an optical biometer.

Methods: A theory was developed to investigate the influence of artefacts in measuring peripheral eye length and on using peripheral eye length to make inferences about retinal shape.

Influence of Specialty Contact Lens Wear on Posterior Corneal Tomography in Keratoconus Subjects.

Objective: To evaluate the effect of specialty contact lens (CL) wear on posterior corneal tomography in keratoconus subjects.

Methods: Patients with keratoconus who were wearing specialty CL were included in this retrospective cohort study. Tomographic parameters were evaluated with Scheimpflug imaging (Pentacam HR) before lens fitting and immediately after removal of CLs worn habitually for a period of several months.

Influence of rigid lens decentration and rotation on visual image quality in normal and keratoconic eyes.

Purpose: To investigate whether the movement of a rigid sphero-cylindrical contact lens has a greater impact on the visual image quality in highly aberrated eyes than in normal eyes.

Methods: For 20 normal and 20 keratoconic SyntEyes, a previously determined best sphero-cylindrical rigid lens was permitted to shift by up to ±1 mm from the line of sight and rotate up to ±15°. Each of the 52,111 lens locations sampled was ray-traced to determine the influence on the wavefront aberration.

Influence of eye tilt on corneal densitometry.

Purpose: To investigate whether Pentacam densitometry readings are affected by corneal tilt.

Methods: In a prospective study, the right eyes of 86 healthy participants aged 42.8 ± 20.

Combining Spectral-Domain OCT and Air-Puff Tonometry Analysis to Diagnose Keratoconus.

Purpose: To investigate the diagnostic capacity of spectral-domain optical coherence tomography (SD-OCT) combined with air-puff tonometry using artificial intelligence (AI) in differentiating between normal and keratoconic eyes.

Methods: Patients who had either undergone uneventful laser vision correction with at least 3 years of stable follow-up or those who had forme fruste keratoconus (FFKC), early keratoconus (EKC), or advanced keratoconus (AKC) were included. SD-OCT and biomechanical information from air-puff tonometry was divided into training and validation sets.

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 () and a limited range of refractive errors.

Methods: The study used the previously published biometric data of participants (Age: years) with . Measurements included objective refraction, anterior and posterior corneal radii of curvatures, and internal distances.