Forward Scattering Properties of Corneal Haze

Brouwere, D. De; Ginis, Harilaos; Kymionis, George D.; Naoumidi, Irini; Pallikaris, Ioannis G.

doi:10.1097/opx.0b013e31818527b4

Cited by 11 publications

(8 citation statements)

References 15 publications

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“…Our results suggest that the subepithelial scar‐tissue layer is the primary factor contributing to the increased corneal scatter which follows surface ablations. This is in accordance with our previous finding using a less sensitive technique to measure the PSF (De Brouwere et al. , 2008).…”

Section: Discussionsupporting

confidence: 94%

“…Our results suggest that the subepithelial scar-tissue layer is the primary factor contributing to the increased corneal scatter which follows surface ablations. This is in accordance with our previous finding using a less sensitive technique to measure the PSF (De Brouwere et al, 2008). The angular distribution of scatter in hazy corneas is narrower than that of healthy corneas, suggesting that the large structures seen in the scar tissue layer contribute strongly to scatter.…”

Section: Discussionsupporting

confidence: 92%

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Narrow angle light scatter in rabbit corneas after excimer laser surface ablation

Ginis

Pentari

Brouwere

et al. 2009

Ophthalmic Physiologic Optic

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Corneal haze following excimer laser ablation is an adverse after-effect of photorefractive keratectomy (PRK) and is associated with the development of subepithelial opacities. The present work pertains to the measurement of light scattering in rabbit corneas following excimer laser treatment; to the microscopic analysis of the light-scattering corneal structures; and to the development of a mathematical model of light propagation through the post-laser treatment cornea. Photorefractive keratectomy (PRK-6D, 6 mm optical zone) followed by standard postoperative pharmaceutical treatment was performed on rabbit eyes. Animals were examined clinically on a weekly basis and sacrificed after the tenth postoperative week. Confocal microscope image sequences were acquired immediately before animal sacrifice. After the scatter measurement, the corneas were prepared for histopathological evaluation. The subepithelial structures observed using the confocal microscope correspond to refractive index (and therefore optical path difference (OPD) variation. This OPD distribution can be approximated with a fractal surface, band-pass filtered in the Fourier domain. The angular distribution of scattered light is characterised by a narrow forward peak of the order of 0.5 degrees full-width at half maximum (FWHM) in accordance with the sizes of the subepithelial structures (5-150 microm).The intensity of scattered light is correlated with the thickness of the subepithelial scar-tissue layer.

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Section: Discussionsupporting

confidence: 94%

Section: Discussionsupporting

confidence: 92%

Narrow angle light scatter in rabbit corneas after excimer laser surface ablation

Ginis

Pentari

Brouwere

et al. 2009

Ophthalmic Physiologic Optic

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“…Most of these techniques detect back-scattered light. Forward scatter has been measured using confocal microscopy ( Ginis et al., 2009 ), by making direct measurement in excised corneas ( De Brouwere et al., 2008 ) or by using stray light techniques on humans in vivo ( Van den Berg et al., 2013 , Patel et al., 2008 , Rozema et al., 2011 ) for which commercially equipment is available. In so-called Direct Compensation Stray Light measurements, a test field consisting of a dark circle split into left and right halves is surrounded by a bright ring-shaped flickering light, which serves as the glare source.…”

Section: Measurement Of Corneal Transparencymentioning

confidence: 99%

Corneal structure and transparency

Meek

Knupp

2015

Progress in Retinal and Eye Research

612

437

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The corneal stroma plays several pivotal roles within the eye. Optically, it is the main refracting lens and thus has to combine almost perfect transmission of visible light with precise shape, in order to focus incoming light. Furthermore, mechanically it has to be extremely tough to protect the inner contents of the eye. These functions are governed by its structure at all hierarchical levels. The basic principles of corneal structure and transparency have been known for some time, but in recent years X-ray scattering and other methods have revealed that the details of this structure are far more complex than previously thought and that the intricacy of the arrangement of the collagenous lamellae provides the shape and the mechanical properties of the tissue. At the molecular level, modern technologies and theoretical modelling have started to explain exactly how the collagen fibrils are arranged within the stromal lamellae and how proteoglycans maintain this ultrastructure. In this review we describe the current state of knowledge about the three-dimensional stromal architecture at the microscopic level, and about the control mechanisms at the nanoscopic level that lead to optical transparency.

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“…However the angular distribution of the scattering and the optical PSF can vary from subject to subject, we can say that scattered light has a much wider angular distribution on the retina than the light distribution from the optical PSF. Whereas the optical PSF of an aberrated eye will seldom exceed a with of 10min of arc, scattered light is usually assessed over angles wider than 30 minutes of arc [3].…”

Section: Angular Distributionmentioning

confidence: 99%

“…Whereas backscattered light on the cornea does not affect the retinal image quality, most light scattered on the cornea is narrowly forward directed, giving rise to reduction of the image quality. Therefore, a profound study on the forward light scattering properties in the eye is needed [3]. The aim of this thesis is to quantify the amount of light scattering addressed to the morphologic changes after refractive laser treatments and its affect on the retinal image quality.…”

Section: Introductionmentioning

confidence: 99%

Corneal light scattering following excimer laser surgery

Brouwere¹

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Introduction Increased corneal scattering is assumed to be a considerable side-effectof refractive surgery due to the postoperative healing response after photoablativesurface treatments. Clinically, corneal scattering is associated with haze development.Corneal haze is subjectively evaluated method based on the observation of the lightbackscattered on the cornea as seen under a slit lamp. However, corneal light scatteringaffects the retinal image quality only by its forward scattering component. The scopeof this thesis is to evaluate the the effect of corneal light scattering on the retinal imagequality, specifically in relation to the morphological changes in the cornea followingexcimer laser surgery.Methods Initially, the optical mechanisms of the image formation on the retina arediscussed. Following, the optical parameters of the corneal morphology are characterizedto form a theoretical model describing the forward light scattering in the cornea.Simulation of this theoretical model is done by a physical model of light scatteringon microspheres. This model is evaluated both by psychophysical and optical measurements.Further, we compared the use of two psychophysical and three opticalmethods to evaluate both the amount of light scattered in the cornea and the angulardistribution of the scattered light.Results Based on histological data of stained corneal samples and in vivo confocalmicroscopy, the morphologic corneal changes addressed to the wound healing responseare induced by the activation of keratocytes, inhibiting a newly formed unorganizedcollagen layer, a scar tissue called the foam layer. The theoretical models developed in this thesis reveal the presence of scattering particles that cause a local distortion of theincoming wavefront. The point spread function of this scattered wavefront is stronglyforward distributed with a full width at the half maximum of approximately 20 minutesof arc. After refractive treatments, the light scattering increases until 1 month aftertreatment, reducing to a long term moderate level of increased light scattering after6 months. Moreover, we derived that where, in a healthy cornea approximately 20percent of the incoming light is scattered, this value increases up to 70 percent forcorneas with marked haze. Furthermore, psychophysical data suggest that the amountof light scattered over angles from 5 to 10 degrees increases in a similar extend asobserved in the ageing eye.Conclusion The wound healing response of the cornea on photorefractive ablationtreatments result in an increase of corneal scattering. The light distribution of thisscattered light is narrowly forward peaked. Correlation of the foam layer with amountof forward light scattering suggests that the increased corneal scattering followingrefractive surgery mainly originates on this foam layer. Therefore, a correct postoperativecare of the cornea following excimer laser surgery is detrimental for an optimalretinal image quality. The effect of light scattering in the eye results on a lowering ofthe contrast sensitivity and an increased disability glare around light sources in nightvision.

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Forward Scattering Properties of Corneal Haze

Abstract: Corneal light scatter associated with the increased amount of haze after excimer laser ablation has a narrowly forward distribution that can be attributed to the subepithelial structures observed in treated corneas.

Cited by 11 publications

References 15 publications

Narrow angle light scatter in rabbit corneas after excimer laser surface ablation

Narrow angle light scatter in rabbit corneas after excimer laser surface ablation

Corneal structure and transparency

Corneal light scattering following excimer laser surgery

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