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Light streaks / stripes of light

"Doctor, since I had this ocular surgery, when I go outside at night I see streams and long streaks of light across the outdoor lights everywhere I look." What is that? »

This page aims at bringing some elements to better address this issue.

(In french below)

Definition of light streaks

Light streaks are a visual symptoms characterized by the perception by the eye of the a bright straight line emanating from either side of a bright light source.
Unlike circular halos or glare, the spreading of the perceived light spread is straightand always oriented in the same direction.

The mechanism behind this visual symptom is a phenomenon of diffraction of the incident light by has fine structure which is oriented, and can be single or repeated. Light streaks belong to the general group of unwanted visual phenomena called «» dysphotopsias« .

Demonstration of light streaks

Dirty deposits on the glass of windows or windshields can commonly give rise to this kind of phenomenon. It is easy to reproduce by simply leaving a fatty drag there transparent surface: smearing your finger there window but has spectacle lens suffices to cause the diffraction of light by the tiny linear deposits at the surface of the glass. Observing year incoming light source through some dirty linear deposits or scratches it has transparent surface, can clearly render characteristic light streaks, which are always perpendicular to the main axis of scratches however.

light streaks by a smartphone camera

After taking night photo by a smartphone (left), the following photographs (right) were obtained by leaving voluntarily, with the pulp of the finger, some dirt trails we the front optic glass window of a smartphone. The orientation of the bright streaks that are visible around bright light sources in the photographs, is perpendicular to the direction of the dirt spread hand on the glass surface.

Light streaks in ophthalmology

When the direction of the light streak varied with the orientation of the patient's head, the phenomenon is so-called "entoptic". It arises from one of the optical structures of the affected eye (cornea, intraocular lens or in the vast majority of casees).

In ophthalmology, the two main causes of perception of light streak are:
– The folds of the posterior capsule after cataract surgery and replacement of the opaque crystalline lens with year intraocular lens (IOL). A scratch line marked of the optic of the IOL can also cause the perception of some light streak (s).
– The macro-folds formed by the partial displacement of has LASIK flapbecause these are usually grossly parallel folds.

Case example:

Here is the drawing provided by a patient which perceived oblique light streaks around bright light sources immediately after cataract surgery of his right eye.

Ophthalmic examination at the slit lamp revealed the presence of a single posterior capsular fold marked.

depiction of light streaks

Depiction by a patient of the light streaks around vehicle lights, which were noticed immediately after uncomplicated cataract surgery. Slit lamp examination revealed the presence of a vertical capsular fold in the nasal portion of the pupil. Representation by a patient of the luminous streaks perceived around vehicle headlights at the immediate onset of acataract surgery. On slit lamp examination, a posterior capsular fold is present in the nasal portion of the pupillary area.

The orientation of this fold was consist with the perceived light phenomenon, but this assessment requires the "vertical reversal" of the apparent direction of the capsular foldto reflect the orientation of the patient's retina opposite of that fold.

capsular fold after cataract surgery has a perpendicular direction to the perceived light phenomena

The orientation of the light streak is indeed perpendicular to the fold in a landmark oriented from the retina of the subject, and not from that of the review (note the perfect orthogonality of the patient's perceived light streak and the fold as seen from the retina). The orientation of the light streaks is perpendicular to that of the fold, if you consider orientation of it as 'seen from the retina. Note perfectly perpendicular orientation between the direction of the light streak and the capsular fold seen in the retina.

The optical phenomenon involved in the genesis of luminous streaks is related to the diffraction of light by the rectilinear folds (posterior capsule, LASIK flap, scratch of the IOL's optic, etc.). The dimension (scale) of the diffracting object (i.e. the capsular fold) are of the same global scale of the wavelengths of visible light (micron scale).

flap fold diffraction

According to the Huygens principle, the fold of the capsular bag may act as a secondary source of light waves. (According to Huygens' principle every point we have wave front of light can be considered to be a secondary source of spherical wavelets). The fold causes a local disturbance to the the path of the incoming wavefront, which explains the lateral spread in the vicinity of the fold. The principle of Huygens, each of the points located in the path of a wave front light re emits waves in all directions. By summons, the wave front spreads forward. An obstacle as the crease creates a side light diffraction and explains the visual perception of luminous sprawl perpendicular to the direction of the bend.

A classic experiment in Optics is to study the diffraction of light waves emitted by a monochromatic source (eg laser pointer) by a thin thread, gold hair, which have thickness of several tens of microns. When a thin wire intercepts the light laser, a diffraction phenomenon is generated. It can be displayed there screen which will feature typical bands of light (from the measurement of the angular width of the central luminous line, one can determine the thickness of the wire used for the experiment).

diffraction of laser diffraction source hair.

Typical pattern of diffraction of a laser source (red point) by a human hair. The hair is oriented Pacific. The pattern of diffraction by a hair from a red laser (pointer) source. The hair is oriented vertically.

In physiological optics, light sources perceived by the eye in everyday life are polychromatic and non-coherent; more simply, the light waves they emit are less organized (synchronous in time and space) than a laser source. Therefore, the lateral light spreading generated by the diffraction of the waves is less uniform, because the constructive and destructive interference are much less systematized.

Nevertheless, the Directorate of this light spreading corresponds to that inflicted by the diffractive structure of rectilinear geometry to the flow of incident light waves, and are mutually orthogonal.

flap and fold light streak mechanism

The fold is located on the the path of the light refracted by the cornea and the IOL The lateral diffraction band is focused onto the retina have a straight line, which is strictly perpendicular to the fold. The capsular fold is interposed on the path of light refracted by the cornea and intraocular implant. The image formed in the retinal plan is strictly perpendicular to the capsular bend light spread.

Some patients perceive thin iridescent gold colored side fringes "as a rainbow" at the edges of a central light streak emitted by intense white light source, such as a flash-lamp. This colorful spread reflects the sensitivity of the diffractive phenomenon to the wavelength of the light radiation into play, and echoes the intimate wave mechanism of the optical phenomenon involved in the appearance of the disturbing bright light streaks.

Beside careful slit lamp examination, there are no. investigationnal tool which can enable to objectivate the effect on ocular wavefront local of the light path disturbances. Shack Hartman aberrometers are not conceived to highlight and resolve local scatter and diffraction sources within the eye. However, double pass instruments (eg OQAS, HD-Analyzer) may help to tradeoff the scatter incured by marked LASIK flap flods.

The treatment of annoying bright streaks depends on the their cause: smoothing the flap folds in casee of complicated LASIK, however perform has YAG laser capsulotomy in casee of symptomatic capsular folds.

These maneuvers are generally effective and lead to the disappearance or high attenuation of these light streaks.

References:

  • Choi CJ, Melki SA. Maddox rod effect to confirm the visual significance of laser in-situ keratomileusis flap striae. J Cataract Refract Surg. 2011; 37 (10): 1748-50.
  • Holladay JT, Bishop I, Lewis JW. Diagnosis and treatment of mysterious light seen by streaks patients following extracapsular cataract extraction. J Am Intraocul Soc Implant. 1985; 11 (1): 21-3.

See Related content: Rainbow glare

In french:

"Doctor, since I had surgery to cataract surgery, when I go out at night, I see some kind of streaks, long streaks of light around the outdoor lights, everywhere I look. What is it that? »

This page live to bring answers to this type of Visual complaints.

The light streak(s) corresponds to a visual symptom characterized by the perception by the eye of a "light line", a "straight burr", a kind of "light elongation", emanating on either side of a bright light source. Light streaks are a type of undesirable visual sensation sometimes experienced after cataract surgery(dysphotopic).

In contrast to the circular halos, bright sprawl is straight is always oriented in the same direction. The mechanism behind this is a phenomenon of diffraction the incident light by a fine structure-oriented, single or repeated.

Trails of dirt on vehicle windows or windscreens that can commonly give rise to this kind of phenomenon that is easy to reproduce: for example, by leaving a greasy trail on a transparent surface, for example by passing your finger over a window, or a glass of a window. By then observing a light source through the soiled or scratched surface, one can clearly perceive the characteristic light spread, which is always oriented perpendicular to the main axis of the scratches.

(see illustration above). After taking a night picture of reference by (own) view of a smartphone (left), the following photographs (right) were obtained by leaving voluntarily, with the pulp of a finger, an oily streak on optics before the smartphone. The orientation of the light streaks, which are clearly visible around the sources of bright light on stereotypes, is every time perpendicular to the main direction of sprawl in dirty drag on the surface of the optics.

When the direction of the light stripe varies with the orientation of the patient's head, the phenomenon is called "entoptic". It emanates directly from one of the optical structures of the eye concerned (the cornea or Crystalline lensartificial implant), and not from an element external to it.

In ophthalmology, the two main causes of perception of luminous streaks are:

  • Thefolds of the posterior capsule after surgery the cataract and an artificial lens implant. One stripe marked optics of the implant may also cause the perception of a bright streak (s).
  • Themacroplis formed by partial displacement of a flap of LASIK, because these folds are usually oriented in a parallel way.

Here is the drawing provided by a patient having received immediate after cataract surgery, oblique light streaks around the sources of bright light from his daily environment. Slit lamp examination revealed the presence of a fairly pronounced posterior capsular fold.

The orientation of the latter is in line with that of the perceived phenomenon,... provided that "the to invert vertically "the direction of the capsular fold to be placed in the same orientation as the retina of the patient to this. The orientation of the light streak is indeed perpendicular to the folds, in a coordinate system oriented from the retina of the subject, and not that of the examiner.

The optical phenomenon put in game for the genesis of the light streaks is related to the diffraction of light by the rectilinear folds (posterior capsule, flap of LASIK, stripe of an implant, etc.). The dimensions of the object diffractant (here the capsular fold) are neighbours of the wavelengths of visible light (microns).

(see above illustration) A classic experiment in experimental optics consists in studying the diffraction of light waves emitted by a monochromatic source (e. g. a laser pointer) by a wire, or a hair whose thickness is a few tens of microns. When the yarn intercepts laser light, a diffraction phenomenon is generated and can be visualized on a screen by a characteristic image that complements a main light line perpendicular to the yarn axis, accompanied by more peripheral lines separated by dark intervals. From the measurement of the angular width of the central light line, it is possible to determine the thickness of the wire used for the experiment.

In physiological optics, the light sources perceived by the eye in everyday life are polychromatic and non-coherent; more simply, the light waves they emit are less synchronous or organized in time and space than those of a laser source.

As a result, lateral light spread caused by the diffraction of these waves is less regular, because constructive and destructive interference are much less systematized. However, this bright sprawl management fits that inflicts on the incidental light waves flow diffractive rectilinear geometry structure. Some patients also see of thin side fringes iridescent or colored like a Rainbow at the edges of the Central bright streak emitted by an intense source of white light, as a flash lamp. This colorful sprawl reflects the sensitivity of the diffractive phenomenon throughout the wave of light radiation in game, and illustrates the intimately wave mechanism of the optical phenomenon involved in the appearance of the light streaks.

Objective investigations are limited to objectively study the effect of the folds on the ocular Wavefront. The Shack Hartman type aberrometres are not designed to highlight the effects produced by anomalies located within the eye structures such as folds (flap, or capsule). However, systems with double-pass (OQAS, HD-study) may be useful for quantifying the light diffusion induced pronounced folds of flap.

The treatment of annoying light streaks depends on the cause of the streaks: it is necessary only the flap in case of complicated LASIK, or make a YAG laser capsulotomy in case of symptomatic capsular folds. These maneuvers are generally effective and lead to the disappearance or the strong attenuation of these streaks.

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