Temporal properties of positive and negative defocus on emmetropization.

Studying the temporal integration of visual signals is crucial to understand how time spent on different visual tasks can affect emmetropization and refractive error development. In this study we assessed the effect of interrupting positive and negative lens-imposed defocus with brief periods of unrestricted vision or darkness. A total of forty-six marmosets were treated monocularly with soft contact lenses for 4 weeks from 10 weeks of age (OD: + 5D or - 5D; OS: plano).

COVID-19: ensuring safe clinical teaching at university optometry schools.

The COVID-19 pandemic has been spreading across the globe for several months. The nature of the virus (SARS-CoV-2) with easy person-to-person transmissions and the severe clinical course observed in some people necessitated unprecedented modifications of everyday social interactions. These included the temporary suspension of considerable elements of clinical teaching at optometry schools worldwide.

Changing accommodation behaviour during multifocal soft contact lens wear using auditory biofeedback training.

Biofeedback training has been used to access autonomically-controlled body functions through visual or acoustic signals to manage conditions like anxiety and hyperactivity. Here we examined the use of auditory biofeedback to improve accommodative responses to near visual stimuli in patients wearing single vision (SV) and multifocal soft contact lenses (MFCL). MFCLs are one evidence-based treatment shown to be effective in slowing myopia progression in children.

Short Interruptions of Imposed Hyperopic Defocus Earlier in Treatment are More Effective at Preventing Myopia Development.

The purpose of this study was to evaluate the effect of interrupting negative lens wear for short periods early or late during the development of lens-induced myopia in marmosets. Sixteen marmosets were reared with a -5D contact lens on their right eye (plano on contralateral eye) for 8 weeks. Eight marmosets had lenses removed for 30 mins twice/day during the first four weeks (early interruption) and eight during the last four weeks (late interruption).

IMI - Report on Experimental Models of Emmetropization and Myopia.

The results of many studies in a variety of species have significantly advanced our understanding of the role of visual experience and the mechanisms of postnatal eye growth, and the development of myopia. This paper surveys and reviews the major contributions that experimental studies using animal models have made to our thinking about emmetropization and development of myopia. These studies established important concepts informing our knowledge of the visual regulation of eye growth and refractive development and have transformed treatment strategies for myopia.

IMI - Myopia Control Reports Overview and Introduction.

With the growing prevalence of myopia, already at epidemic levels in some countries, there is an urgent need for new management approaches. However, with the increasing number of research publications on the topic of myopia control, there is also a clear necessity for agreement and guidance on key issues, including on how myopia should be defined and how interventions, validated by well-conducted clinical trials, should be appropriately and ethically applied. The International Myopia Institute (IMI) reports the critical review and synthesis of the research evidence to date, from animal models, genetics, clinical studies, and randomized controlled trials, by more than 85 multidisciplinary experts in the field, as the basis for the recommendations contained therein.

Gene expression in response to optical defocus of opposite signs reveals bidirectional mechanism of visually guided eye growth.

Myopia (nearsightedness) is the most common eye disorder, which is rapidly becoming one of the leading causes of vision loss in several parts of the world because of a recent sharp increase in prevalence. Nearwork, which produces hyperopic optical defocus on the retina, has been implicated as one of the environmental risk factors causing myopia in humans. Experimental studies have shown that hyperopic defocus imposed by negative power lenses placed in front of the eye accelerates eye growth and causes myopia, whereas myopic defocus imposed by positive lenses slows eye growth and produces a compensatory hyperopic shift in refractive state.

Accommodation and Phoria in Children Wearing Multifocal Contact Lenses.

Purpose: To determine the effect of multifocal contact lenses on accommodation and phoria in children.

Methods: This was a prospective, non-dispensing, randomized, crossover, single-visit study. Myopic children with normal accommodation and binocularity and no history of myopia control treatment were enrolled and fitted with CooperVision Biofinity single vision (SV) and multifocal (MF, +2.

Axial eye growth and refractive error development can be modified by exposing the peripheral retina to relative myopic or hyperopic defocus.

Purpose: Bifocal contact lenses were used to impose hyperopic and myopic defocus on the peripheral retina of marmosets. Eye growth and refractive state were compared with untreated animals and those treated with single-vision or multizone contact lenses from earlier studies.

Methods: Thirty juvenile marmosets wore one of three experimental annular bifocal contact lens designs on their right eyes and a plano contact lens on the left eye as a control for 10 weeks from 70 days of age (10 marmosets/group).

Eyes in various species can shorten to compensate for myopic defocus.

Purpose: We demonstrated that eyes of young animals of various species (chick, tree shrew, marmoset, and rhesus macaque) can shorten in the axial dimension in response to myopic defocus.

Methods: Chicks wore positive or negative lenses over one eye for 3 days. Tree shrews were measured during recovery from induced myopia after 5 days of monocular deprivation for 1 to 9 days.

The effect of simultaneous negative and positive defocus on eye growth and development of refractive state in marmosets.

Purpose: We evaluated the effect of imposing negative and positive defocus simultaneously on the eye growth and refractive state of the common marmoset, a New World primate that compensates for either negative and positive defocus when they are imposed individually.

Methods: Ten marmosets were reared with multizone contact lenses of alternating powers (-5 diopters [D]/+5 D), 50:50 ratio for average pupil of 2.80 mm over the right eye (experimental) and plano over the fellow eye (control) from 10 to 12 weeks.

Foveal cone density shows a rapid postnatal maturation in the marmoset monkey.

The spatial and temporal pattern of cone packing during marmoset foveal development was explored to understand the variables involved in creating a high acuity area. Retinal ages were between fetal day (Fd) 125 and 6 years. Cone density was determined in wholemounts using a new hexagonal quantification method.

Ocular wavefront aberrations in the common marmoset Callithrix jacchus: effects of age and refractive error.

The common marmoset, Callithrix jacchus, is a primate model for emmetropization studies. The refractive development of the marmoset eye depends on visual experience, so knowledge of the optical quality of the eye is valuable. We report on the wavefront aberrations of the marmoset eye, measured with a clinical Hartmann-Shack aberrometer (COAS, AMO Wavefront Sciences).

Evaluation of AAV-mediated expression of Chop2-GFP in the marmoset retina.

Purpose: Converting inner retinal neurons to photosensitive cells by expressing channelrhodopsin-2 (ChR2) offers a novel approach for treating blindness caused by retinal degenerative diseases. In the present study, the recombinant adeno-associated virus serotype 2 (rAAV2)-mediated expression and function of a fusion construct of channelopsin-2 (Chop2) and green fluorescent protein (GFP) (Chop2-GFP) were evaluated in the inner retinal neurons in the common marmoset Callithrix jacchus.

Methods: rAAV2 vectors carrying ubiquitous promoters were injected into the vitreous chamber.

Imposed anisometropia, accommodation, and regulation of refractive state.

Purpose: To determine the effects of imposed anisometropic retinal defocus on accommodation, ocular growth, and refractive state changes in marmosets.

Methods: Marmosets were raised with extended-wear soft contact lenses for an average duration of 10 weeks beginning at an average age of 76 d. Experimental animals wore either a positive or negative power contact lens over one eye and a plano lens or no lens over the other.

Expression of synaptic and phototransduction markers during photoreceptor development in the marmoset monkey Callithrix jacchus.

Marmoset photoreceptor development was studied to determine the expression sequence for synaptic, opsin, and phototransduction proteins. All markers appear first in cones within the incipient foveal center or in rods at the foveal edge. Recoverin appears in cones across 70% of the retina at fetal day (Fd) 88, indicating that it is expressed shortly after photoreceptors are generated.

Microarray analysis of choroid/RPE gene expression in marmoset eyes undergoing changes in ocular growth and refraction.

Purpose: Visually guided ocular growth is facilitated by scleral extracellular matrix remodeling at the posterior pole of the eye. Coincident with scleral remodeling, significant changes in choroidal morphology, blood flow, and protein synthesis have been shown to occur in eyes undergoing ocular growth changes. The current study is designed to identify gene expression changes that may occur in the choroid/retinal pigment epithelium (RPE) of marmoset eyes during their compensation for hyperopic defocus as compared to eyes compensating for myopic defocus.

Accommodation and induced myopia in marmosets.

Accommodation may indirectly influence visually guided eye growth by affecting the retinal defocus signal used to guide growth. Specifically, increased lags of accommodation associated with low stimulus-response (S-R) function slopes will impose increased hyperopic blur on the retina and may induce axial elongation and myopia. The purpose of this study was (1) to measure accommodation in awake, free viewing marmosets and (2) compare accommodation behavior in marmosets before and after inducing different amounts of myopia with binocular spectacle lenses.

Development of the neural retina and its vasculature in the marmoset Callithrix jacchus.

The morphological sequence of retinal development in the New World marmoset monkey Callithrix jacchus is similar to previous reports in Macaca and humans. The incipient fovea is present at fetal day (Fd) 100 as the only part of the retina that contains five distinct layers, including a single layer of cone photoreceptors. A foveal pit begins to form at Fd 135 in the center of the foveal avascular zone which is surrounded by a ring of blood vessels (BV) and astrocytes.

Change in the synthesis rates of ocular retinoic acid and scleral glycosaminoglycan during experimentally altered eye growth in marmosets.

Purpose: The purpose of this study was to examine the possibility that all-trans-retinoic acid (RA) in the eye is a signal related to changes in scleral extracellular matrix in a primate model of postnatal eye growth.

Methods: Juvenile marmosets (Callithrix jacchus) were divided into two experimental groups based on their response to monocular deprivation with diffusers: group 1, treated eyes becoming longer than fellow control eyes (n = 8), and group 2, treated eyes becoming shorter than control eyes (n = 7). Eyes were enucleated, dissected, and assayed for changes in the rates of scleral glycosaminoglycan (GAG) synthesis and ocular RA synthesis.

Characteristics of accommodative behavior during sustained reading in emmetropes and myopes.

Accommodation has long been suspected to be involved in the development of myopia because near work, particularly reading, is known to be a risk factor. In this study, we measured several dynamic characteristics of accommodative behavior during extended periods of reading under close-to-natural conditions in 20 young emmetropic and stable myopic subjects. Accommodative responses, errors, and variability (including power spectrum analysis) were analyzed and related to accommodative demand and subject refractive error.

The response to visual form deprivation differs with age in marmosets.

Purpose: To characterize the effects of visual form deprivation by diffuser in marmoset monkey eyes across a range of ages.

Methods: Twenty-four common marmosets were grouped by onset of deprivation (group 1: 0-39 days, n = 6; group 2: 40-99 days, n = 10; and group 3: 100-200 days, n = 8). Monocular form deprivation was induced with a white translucent diffuser worn for 28 to 88 days (mean durations: group 1, 32 days; group 2, 56 days; and group 3, 51 days).

Temporal integration characteristics of the axial and choroidal responses to myopic defocus induced by prior form deprivation versus positive spectacle lens wear in chickens.

Purpose: In chicks, the temporal response characteristics to form deprivation and to spectacle lens wear (myopic and hyperopic defocus) show essential differences, suggesting that the emmetropization system "weights" the visual signals differently. To further explore how the eye integrates opposing visual signals, we examined the responses to myopic defocus induced by prior form deprivation vs. that induced by positive spectacle lenses, in both cases alternating with form deprivation.