The dysphotopsies include the undesirable visual symptomss that occur usually after cataract surgery with pose a intraocular implant.
These symptoms typically include the perception of bright or dark light croissants, on the outskirts of the Visual field, the halos or streaks or marked spicules goshawks of light sources. Functionally, the dysphotopsies reflect the existence of travel light "unexpected."as multiple light reflections by the faces or the edge of the implant, or a combination of reflection and refraction phenomena causing an asymmetrical illumination of the retinal periphery.
The dysphotopsies are the consequence of changes brought about by the cataract surgery on the anterior segment of the eyewhich mainly consist of the replacement of a natural lens of high volume and more low (the lens) by an artificial low volume but more strong index (the implant). This causes the appearance of some open spaces of refractive material, and thus opens the possibility of atypical bright routes, particularly for light rays that cover the eye with a particular angle (peripheral rays). Eyebrow limits the impact of these rays when they come from the top, but not always when they come from the side and temporal region. It stops nasal will stop from rays of peripheral sources located in nasal a two eyes, but these sources however are by definition in the temporal Visual field of the other eye.
In addition, artificial lens implant has lower curvature, and high refractive index than the lens optical surfaces, which exposes to an increased risk of unwanted light reflections, including yet for the rays emanating from side light sources. This problem is well known for the photographic objectives, which include a large number of high index lenses. Despite the care taken in their optical design and their surfacing, most of the photos are equipped with "sun shield" that reduce phenomena such as the "flare", which is related to the occurrence of spurious reflections.
The term dysphotopic is often used to designate the bright halos caused by multifocal optical: this designation is questionable, because the perception of bright circle around sources of bright lights, at night, is expected and directly related to the multifocal character of these implants.
This page is dedicated to the real dysphotopsies, which are not desirable optical properties of multifocal implants (induction of successive bright homes for different distances of useful vision), but are the result of bright routes which can be considered as parasites and 'unexpected '..
We by the of positive dysphotopic When the operated eye perceives "bright" lights, unwanted shiny areas, and dynegative sphotopsie (or 'darkness') when instead a dark area is reported, generally in the temporal portion of the Visual field.
Why the dysphotopsies are more common after cataract surgery and placement of implant intra ocular?
The dysphotopsies are related to some incident light rays, and who reach the retina after having borrowed a particular ride, as a free space between the iris and the perspective of the implant (absence of refraction by it), or reflection by the edge of this perspective.
Unlike the rays corresponding to conventional optical aberrations of low or high degree, this trip includes a significant portion of bright reflections (for example, by the circular edge of the optics of the implant), and/or less than refractions (a lateral incident Ray passes 'between the iris and the implant").
THENot operated eye is relatively immune from the occurrence of this type of light journeys because the crystalline occupies a significant within the anterior chamber volume, and 'word' completely pupillary opening. This prevents from rays of a bright light source device to penetrate the posterior without have been refracted or broadcast by the lens Chamber. The lens is equipped with a refractive index whose value is different from the kernel to the peripheral cortex (gradient), and its surfaces are curved and relatively little reflective, as evidenced by the difficulty raised by the observation of reflection images tell of Purkinje III and IV.
Conversely, the artificial lens implant has a constant and higher refractive index, and thereby its optical surfaces have a smaller turning radius. These characteristics predispose to the development of unwanted reflections with the surfaces of the implant. case of multiple reflections of rays, whose trip ends on the retina, there is a risk to perceive any ghosting or spread of sources of bright lights. These images are not seen for weaker sources, because the intensity of the incident light flux decreases at each reflection.
There was a free variable space between the edge of the iris and the front of the optics. If this space is wide, it can be crossed by some rays refracted by the temporal part of the cornea, without meeting the anterior or the edge of the optics can impress directly the photosensitive retina; in these situations, a colourful Crescent, or the dark opposite perception is possible (see below).
In this example, the patient complained of the perception of peripheral light fringes, which some had an "S" shape This aspect has been reported to the geometry of the edge of the implant (insertion of haptics). The distance between the cornea and the optics is greater than 6mm!
Most of the dysphotopsies positive arc (arc light or a potion of peripheral circle) are rare and transient (they fade then disappear in a few weeks to a few months).
They are usually present when the ambient light is low and a peripheral light source is located in the nasal or temporal vision field. This type of dysphotopic tends to fade with the constriction of the pupil. The mechanism of these dysphotopsies is undesirable reflections at the level of the edge of the implant. When the capsular bag loses its transparency (mechanism of the) secondary cataract), these phenomena tend to be reduced.
Other phenomena, such as halos, or streaks around light sources have been linked to the existence of positive dysphotopsies. The origin of these was attached to multiple light reflection problems between the surfaces of the implant, or the presence of capsular folds.
They are characterized by the perception of a Dark Crescentalways located in the temporal portion of the field of vision the eye reached. They give the impression that there is a kind of Blinder and mouth or limited peripheral vision.
This feeling of shade is related to a the unequal distribution of the light intensity emitted by sources of light devices and located in the temporal part of the Visual field. Rays from these sources are refracted by external temporal area of the cornea, and directed to the nasal retina (which is responsible for the perception of the temporal Visual field). In some configurations, especially when the space between the iris and the implant is pronounced, some rays, the more inclined, are not refracted by the implant and "impress" the very peripheral retina, while a bit less oblique rays are refracted by the edge of the implant further back. Between these two bundles of rays may appear a portion of no or little illuminated retina, and that any "illumination" is originally from the perception of a dark Crescent outside the field of vision.
A similar phenomenon may be caused by the refraction of light rays by the edge square of some models of implants. Dispersion asymmetric of rays, usually accentuated in case constrictions, pupillary can be led to a feeling of perimeter shadow whose location is a little less peripheral than that which is related to the absence of refraction by the implant. In some case, the patient describes the perception of bright and dark fringes with fine radiaires streaks. These streaks could be linked to the presence of the fibers of the zonule on this peripheral light path.
One interesting article published by J Holladay in 2012 explicit of these phenomena of "Visual darkness. These are favored by "edges square" geometry for implants of artificial crystalline lens, and by a small pupillary diameter (in wide pupillary diameter case, illumination retinal device increased "levels" the differences between highly areas and low light).
Designing as well as the risk of dysphotopic may be more When the distance between the implant and the edge of the iris is pronounced, as in the following situation (dysphotopic with an implant at four anchor Bunnylens / Hanita):
Support for the dysphotopsies
Most of the parasitic Visual phenomena after cataract surgery disappear within a few weeks. Indeed, the gradual clouding of the capsular bag causes increased light coverage (which will reduce the presence of a refraction or abnormal reflections of light devices), and reduce the feeling of peripheral darkness.
The visual cortex also probably plays a favourable role to reduce the importance of the subjective perception over time.
When the undesirable visual phenomena persist, it is important to understand its source. Change of implant is a potentially effective solution, but source of potential complications. It is a delicate gesture for intraocular structures like the posterior corneal surface (endothelium), and the capsular bag need to maintain integrity.
Of surgical techniques to insert an implant ('piggy-back') in front of artificial lens implant (in the hope to "plug" the path of light rays through a direct path of the peripheral cornea to the retina through the sulcus) have been proposed. It seems better to wait for the occurrence of a turbidity of the peripheral capsular bag, which usually occurs within a few months.
The prescription of eye drops for contract (positive dysphotopic) or dilate (dysphotopic negative) pupillary disc is a noninvasive method that sometimes reduces the intensity of the dysphotospies.
Before any preventive treatment of the dysphotopsies. It is based on the rather horizontal positioning of implants (the haptic of these are a natural barrier for the peripheral rays that come from the sides), the choice of implants with a geometric design features rounded edges...
Despite these precautions, the risk of dysphotopic is never tied after driving perfectly same surgery. Fortunately, in most of the case, the unwanted Visual phenomena fade and disappear over time.