Editing Slit lamp (section)

== Illuminations ==
Various methods of slitlamp illumination are required to obtain full advantage of slit-lamp biomicroscope. There are mainly six type of illuminating options:{{citation needed|date=June 2022}}
# Diffuse illumination,
# Direct focal illumination,
# Specular reflection,
# Transillumination or retroillumination,
# Indirect lateral illumination or Indirect proximal illumination and
# Sclerotic scatter.
Oscillatory Illumination is sometimes considered an illumination technique.<ref>Practical Ophthalmology A MANUAL FOR BEGINNING RESIDENTS, Fourth Edition, page 218-228.</ref>
Observation with an optical section or direct focal illumination is the most frequently applied method of examination with the slit lamp. With this method, the axes of illuminating and viewing path intersect in the area of the anterior eye media to be examined, for example, the individual corneal layers.<ref>"Eye Examination with the Slit Lamp", Zeiss, p. 14</ref>

=== Diffuse illumination ===
[[File:Diffuse Illumination.jpg|thumb|100px|Diffuse Illumination of anterior segment]]
If media, especially that of the cornea, are opaque, optical section images are often impossible depending on severity. In these cases, diffuse illumination may be used to advantage. For this, the slit is opened very wide and a diffuse, attenuated survey illumination is produced by inserting a ground glass screen or diffuser in the illuminating path.<ref>"Eye Examination with the Slit Lamp", Zeiss, p. 16</ref> "Wide beam" illumination is the only type that has the light source set wide open. Its main purpose is to illuminate as much of the eye and its [[Accessory visual structures|adnexa]] at once for general observation.<ref name="Indiana">{{cite web|last=Indiana University School of Optometry|title=Slit Lamp Illumination Types|url=http://www.opt.indiana.edu/riley/HomePage/newslitlamp/1_part_one_slitlamp.html|publisher=Indiana University, Indiana: 2007|access-date=6 February 2011|archive-date=18 June 2002|archive-url=https://archive.today/20020618063614/http://www.opt.indiana.edu/riley/HomePage/newslitlamp/1_part_one_slitlamp.html|url-status=dead}}</ref>

=== Direct focal illumination ===
[[File:Focal illumination.jpg|thumb|100px|Lesions are seen in superficial layers of cornea by direct focal illumination]]
Observation with an optical section or direct focal illumination is the most frequently applied method. It is achieved by directing a full-height, hairline to medium width, medium-bright beam obliquely into the eye and focusing it on the cornea so that a quadrilateral block of light illuminates the transparent medias of eye. Viewing arm and illuminating arm are kept parfocal. This type of illumination is useful for depth localization. Direct focal illumination is used for grading cells and flare in anterior chamber by shortening height of beam to 2–1&nbsp;mm.<ref>Practical Ophthalmology A MANUAL FOR BEGINNING RESIDENTS, Fourth Edition, page 220-221.</ref>

=== Specular reflection ===
Specular reflection, or reflected illumination is just like patches of reflection seen on sunlit lake water surface. To achieve specular reflection, the examiner directs a medium to narrow beam of light (it must be thicker than an optical section) toward the eye from the temporal side. The angle of illumination should be wide (50°-60°) relative to the examiners axis of observation
(which should be slightly nasal to the patients visual axis). A bright zone of specular reflection will be evident on the temporal, midperipheral corneal epithelium. It is used to see endothelial outline of cornea.<ref>Practical Ophthalmology A MANUAL FOR BEGINNING RESIDENTS, Fourth Edition, page 221-222.</ref>

=== Transillumination or retroillumination ===
[[File:Retro-illumination.jpg|thumb|100px|Retro-illumination of anterior subcapsular cataract]]
In certain cases, illumination by optical section does not yield sufficient information or is impossible. This is the case, for example, when larger, extensive zones or spaces of the ocular media are opaque. Then the scattered light that is not very bright normally is absorbed. A similar situation arises when areas behind the crystalline lens are to be observed. In this case the observation beam must pass a number of interfaces that may reflect and attenuate the light.<ref name="Zeiss p. 17"/>

=== Indirect illumination ===
[[File:Indirect lateral illumination.jpg|thumb|100px|Indirect lateral illumination of corneal ulcer]]
With this method, light enters the eye through a narrow to medium slit (2 to 4&nbsp;mm) to one side of the area to be examined. The axes of illuminating and viewing path do not intersect at the point of image focus, to achieve this; the illuminating [[Prism (optics)|prism]] is decentered by rotating it about its vertical axis off the normal position. In this way, reflected, indirect light illuminates the area of the anterior chamber or cornea to be examined. The observed corneal area then lies between the incident light section through the cornea and the irradiated area of the iris. Observation is thus against a comparatively dark background.<ref name="Zeiss p. 17">"Eye Examination with the Slit Lamp", Zeiss, p. 17</ref>

=== Sclerotic scatter or scattering sclero-corneal illumination ===
[[File:Sclerotic Scatter.jpg|thumb|100px|Sclerotic scatter illumination showing KP on cornea]]
With this type of illumination, a wide light beam is directed onto the limbal region of the cornea at an extremely low angle of incidence and with a laterally de-centered illuminating prism. Adjustment must allow the light beam to transmit through the corneal parenchymal layers according to the principle of total reflection allowing the interface with the cornea to be brightly illuminated. The magnification should be selected so that the entire cornea can be seen at a glance.<ref>"Eye Examination with the Slit Lamp", Zeiss, p. 18</ref>