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Ophthalmic & Physiological Optics : the... May 2012We provide an account of the relationships between eye shape, retinal shape and peripheral refraction. (Review)
Review
PURPOSE
We provide an account of the relationships between eye shape, retinal shape and peripheral refraction.
RECENT FINDINGS
We discuss how eye and retinal shapes may be described as conicoids, and we describe an axis and section reference system for determining shapes. Explanations are given of how patterns of retinal expansion during the development of myopia may contribute to changing patterns of peripheral refraction, and how pre-existing retinal shape might contribute to the development of myopia. Direct and indirect techniques for determining eye and retinal shape are described, and results are discussed. There is reasonable consistency in the literature of eye length increasing at a greater rate than height and width as the degree of myopia increases, so that eyes may be described as changing from oblate/spherical shapes to prolate shapes. However, one study indicates that the retina itself, while showing the same trend, remains oblate in shape for most eyes (discounting high myopia). Eye shape and retinal shape are not the same and merely describing an eye shape as being prolate or oblate is insufficient without some understanding of the parameters contributing to this; in myopia a prolate eye shape is likely to involve both a steepening retina near the posterior pole combined with a flattening (or a reduction in steepening compared with an emmetrope) away from the pole.
SUMMARY
In the recent literature, eye and/or retinal shape have often been inferred from peripheral refraction, and, to a lesser extent, vice versa. Because both the eye's optics and the retinal shape contribute to the peripheral refraction, and there is large variation in the latter, this inference should be made cautiously. Recently retinal shape has been measured independent of optical methods using magnetic resonance imaging. For further work on retinal shape, determining the validity of cheaper alternatives to magnetic resonance techniques is required.
Topics: Biometry; Disease Progression; Eye; Humans; Models, Biological; Myopia; Refraction, Ocular; Retina
PubMed: 22486366
DOI: 10.1111/j.1475-1313.2012.00906.x -
Asia-Pacific Journal of Ophthalmology... Nov 2022The diagnosis of glaucoma depends upon indentification of characteristic damage to the optic nerve and retinal fiber layer. In many cases, however, clinicians find it...
The diagnosis of glaucoma depends upon indentification of characteristic damage to the optic nerve and retinal fiber layer. In many cases, however, clinicians find it difficult to ascertain whether glaucomatous damage is present or absent. These patients are often labeled as "glaucoma suspects," which creates a subpopulation of individuals without clear-cut disease who nonetheless must remain under surveillance. Most will never go on to develop glaucoma, yet the need for ongoing monitoring burdens clinics and health care systems. In this perspective, we illustrate possible directions and novel approaches that can be used to remedy this situation by integrating current technologies into clinical practice. In particular, we suggest that optical coherence tomography be better utilized to methodologically classify these eyes into glaucomatous and healthy categories.
Topics: Humans; Optic Disk; Nerve Fibers; Retinal Ganglion Cells; Intraocular Pressure; Ocular Hypertension; Glaucoma; Tomography, Optical Coherence
PubMed: 36278943
DOI: 10.1097/APO.0000000000000564 -
Journal of Vision Feb 2022Convolved images are often used to simulate the effect of ocular aberrations on image quality, where the retinal image is simulated by convolving the stimulus with the...
Convolved images are often used to simulate the effect of ocular aberrations on image quality, where the retinal image is simulated by convolving the stimulus with the point spread function derived from the subject's aberrations. However, some studies have shown that convolved images are perceived far more degraded than the same image blurred with optical defocus. We hypothesized that the positive interactions between the monochromatic and chromatic aberrations in the eye are lost in the convolution process. To test this hypothesis, we evaluated optical and visual quality with natural optics and with convolved images (on-bench, computer simulations, and visual acuity [VA] in subjects) using a polychromatic adaptive optics system with monochromatic (555 nm) and polychromatic light (WL) illumination. The subject's aberrations were measured using a Hartmann Shack system and were used to convolve the visual stimuli, using Fourier optics. The convolved images were seen through corrected optics. VA with convolved stimuli was lower than VA through natural aberrations, particularly in WL (by 26% in WL). Our results suggest that the systematic decrease in visual performance with visual acuity and retinal image quality by simulation with convolved stimuli appears to be primarily associated with a lack of favorable interaction between chromatic and monochromatic aberrations in the eye.
Topics: Humans; Optics and Photonics; Photic Stimulation; Retina; Vision, Ocular; Visual Acuity
PubMed: 35179553
DOI: 10.1167/jov.22.2.12 -
FASEB Journal : Official Publication of... Apr 2020The optics of the eye is the key to a functioning visual system. The exact nature of the correlation between ocular optics and eye development is not known because of...
The optics of the eye is the key to a functioning visual system. The exact nature of the correlation between ocular optics and eye development is not known because of the paucity of knowledge about the growth of a key optical element, the eye lens. The sophisticated optics of the lens and its gradient of refractive index provide the superior optical quality that the eye needs and which, it is thought, has a major influence on the development of proper visual function. The nature of a gradient refractive index lens, however, renders accurate measurements of its development difficult to make and has been the reason why the influence of lens growth on visual function remains largely unknown. Novel imaging techniques have made it possible to investigate growth of the eye lens in the zebrafish. This study shows measurements using X-ray Talbot interferometry of three-dimensional gradient index profiles in eye lenses of zebrafish from late larval to adult stages. The zebrafish lens shows evidence of a gradient of refractive index from the earliest stages measured and its growth suggests an apparent coincidence between periods of rapid increase in refractive index in the lens nucleus and increased expression of a particular crystallin protein group.
Topics: Animals; Cornea; Lens, Crystalline; Mathematical Computing; Optics and Photonics; Refractometry; Zebrafish
PubMed: 32103543
DOI: 10.1096/fj.201902607R -
Clinical & Experimental Optometry May 2019Optical coherence tomography angiography (OCT-A) is an emerging technology that allows for the non-invasive imaging of the ocular microvasculature. Despite the wealth of... (Review)
Review
Optical coherence tomography angiography (OCT-A) is an emerging technology that allows for the non-invasive imaging of the ocular microvasculature. Despite the wealth of observations and numerous research studies illustrating the potential clinical uses of OCT-A, this technique is currently rarely used in routine clinical settings. In this review, technical and clinical aspects of OCT-A imaging are discussed, and the future clinical potential of OCT-A is considered. An understanding of the basic principles and limitations of OCT-A technology will better inform clinicians of its future potential in the diagnosis and management of ocular diseases.
Topics: Angiography; Diagnostic Techniques, Ophthalmological; Eye; Forecasting; Humans; Microvessels; Tomography, Optical Coherence
PubMed: 30537233
DOI: 10.1111/cxo.12854 -
Eye (London, England) Feb 2014To describe pathological changes in the anatomy of highly myopic (axially elongated) eyes, enucleated globes were examined by light microscopy and ocular structures were... (Review)
Review
To describe pathological changes in the anatomy of highly myopic (axially elongated) eyes, enucleated globes were examined by light microscopy and ocular structures were measured histomorphometrically. These studies revealed that highly axially myopic eyes show continuous thinning of the sclera starting at or behind the equator with a maximal thinning at the posterior pole; a profound thinning of the choroid decreasing from ∼ 250 to <10 μm in extreme axial myopia, secondary macular defects in the Bruch's membrane associated with a complete loss of retinal pigment epithelium and choriocapillaris, and retinal photoreceptors; a Bruch's membrane of normal thickness in contrast to the profound thinning of the choroid and the sclera; an up to 10-fold elongation and thinning of the peripapillary scleral flange as anterior roof of the orbital cerebrospinal fluid space, and subsequently a retrobulbar extension of the cerebrospinal fluid space; an increased distance of the peripapillary arterial circle of Zinn-Haller to the optic disc border; an elongation and thinning of the lamina cribrosa with a subsequently decreased distance between the intraocular pressure compartment and the retrobulbar orbital cerebrospinal fluid pressure compartment; an increasing exposure of the peripheral posterior lamina cribrosa surface to the cerebrospinal fluid space, no longer buffered by the solid optic nerve tissue; and the development and enlargement of parapapillary gamma zone, in contrast to a myopia-independent parapapillary beta zone. These anatomical changes may be associated with high axial myopia-related complications such as an increased susceptibility of glaucomatous optic neuropathy and myopic retinopathy.
Topics: Axial Length, Eye; Bruch Membrane; Choroid; Humans; Myopia, Degenerative; Optic Disk; Optic Nerve Diseases; Posterior Eye Segment; Retinal Diseases; Sclera
PubMed: 24113300
DOI: 10.1038/eye.2013.223 -
Eye (London, England) Feb 2017Blindness afflicts ~39 million people worldwide. Retinal ganglion cells are unable to regenerate, making this condition irreversible in many cases. Whole-eye... (Review)
Review
Blindness afflicts ~39 million people worldwide. Retinal ganglion cells are unable to regenerate, making this condition irreversible in many cases. Whole-eye transplantation (WET) provides the opportunity to replace diseased retinal ganglion cells, as well as the entire optical system and surrounding facial tissue, if necessary. Recent success in face transplantation demonstrates that this may be a promising treatment for what has been to this time an incurable condition. An animal model for WET must be established to further enhance our knowledge of nerve regeneration, immunosuppression, and technical aspects of surgery. A systematic review of the literature was performed to evaluate studies describing animal models for WET. Only articles in which the eye was completely enucleated and reimplanted were included. Study methods and results were compared. In the majority of published literature, WET can result in recovery of vision in cold-blooded vertebrates. There are a few instances in which mammalian WET models demonstrate survival of the transplanted tissue following neurovascular anastomosis and the ability to maintain brief electroretinogram activity in the new host. In this study we review in cold-blooded vertebrates and mammalian animal models for WET and discuss prospects for future research for translation to human eye transplantation.
Topics: Animals; Blindness; Disease Models, Animal; Eye; Optic Nerve Injuries; Organ Transplantation; Retina; Tissue Survival
PubMed: 27983731
DOI: 10.1038/eye.2016.272 -
Biomedical Engineering Online Jul 2022Ocular diseases are closely related to the physiological changes in the eye sphere and its contents. Using biomechanical methods to explore the relationship between the... (Review)
Review
Ocular diseases are closely related to the physiological changes in the eye sphere and its contents. Using biomechanical methods to explore the relationship between the structure and function of ocular tissue is beneficial to reveal the pathological processes. Studying the pathogenesis of various ocular diseases will be helpful for the diagnosis and treatment of ocular diseases. We provide a critical review of recent biomechanical analysis of ocular diseases including glaucoma, high myopia, and diabetes. And try to summarize the research about the biomechanical changes in ocular tissues (e.g., optic nerve head, sclera, cornea, etc.) associated with those diseases. The methods of ocular biomechanics research in vitro in recent years are also reviewed, including the measurement of biomechanics by ophthalmic equipment, finite element modeling, and biomechanical analysis methods. And the preparation and application of microfluidic eye chips that emerged in recent years were summarized. It provides new inspiration and opportunity for the pathogenesis of eye diseases and personalized and precise treatment.
Topics: Biomechanical Phenomena; Cornea; Finite Element Analysis; Glaucoma; Humans; Intraocular Pressure; Optic Disk; Sclera
PubMed: 35870978
DOI: 10.1186/s12938-022-01019-1 -
Middle East African Journal of... 2015Potential errors and complications during examination and treatment of strabismic patients can be reduced by recognition of certain optical issues. This articles reviews... (Review)
Review
Potential errors and complications during examination and treatment of strabismic patients can be reduced by recognition of certain optical issues. This articles reviews basic as well as guiding principles of prism optics and optics of the eye to equip the reader with the necessary know-how to avoid pitfalls that are commonly encountered when using prisms to measure ocular deviations (e.g., during cover testing), and when observing the corneal light reflex to estimate ocular deviations (e.g., during Hirschberg or Krimsky testing in patients who do not allow for cover testing using prisms).
Topics: Blinking; Cornea; Eyeglasses; Humans; Lens, Crystalline; Strabismus
PubMed: 26180462
DOI: 10.4103/0974-9233.159691 -
Ophthalmic & Physiological Optics : the... May 2016Over the past 25 years, optical coherence tomography (OCT) and adaptive optics (AO) ophthalmoscopy have revolutionised our ability to non-invasively observe the living... (Review)
Review
PURPOSE
Over the past 25 years, optical coherence tomography (OCT) and adaptive optics (AO) ophthalmoscopy have revolutionised our ability to non-invasively observe the living retina. The purpose of this review is to highlight the techniques and human clinical applications of recent advances in OCT and adaptive optics scanning laser/light ophthalmoscopy (AOSLO) ophthalmic imaging.
RECENT FINDINGS
Optical coherence tomography retinal and optic nerve head (ONH) imaging technology allows high resolution in the axial direction resulting in cross-sectional visualisation of retinal and ONH lamination. Complementary AO ophthalmoscopy gives high resolution in the transverse direction resulting in en face visualisation of retinal cell mosaics. Innovative detection schemes applied to OCT and AOSLO technologies (such as spectral domain OCT, OCT angiography, confocal and non-confocal AOSLO, fluorescence, and AO-OCT) have enabled high contrast between retinal and ONH structures in three dimensions and have allowed in vivo retinal imaging to approach that of histological quality. In addition, both OCT and AOSLO have shown the capability to detect retinal reflectance changes in response to visual stimuli, paving the way for future studies to investigate objective biomarkers of visual function at the cellular level. Increasingly, these imaging techniques are being applied to clinical studies of the normal and diseased visual system.
SUMMARY
Optical coherence tomography and AOSLO technologies are capable of elucidating the structure and function of the retina and ONH noninvasively with unprecedented resolution and contrast. The techniques have proven their worth in both basic science and clinical applications and each will continue to be utilised in future studies for many years to come.
Topics: Fundus Oculi; Humans; Ophthalmoscopy; Optics and Photonics; Retina; Tomography, Optical Coherence
PubMed: 27112222
DOI: 10.1111/opo.12289