What is Slit-Lamp? what is the Use Of Slit-lamp?

Introduction

  • The slit lamp is indispensable for the detailed examination of virtually all tissues of the eye and some of its adnexa.
  • It is routinely used for examination of the anterior segment, which includes the anterior vitreous and those structures that are anterior to it.
  • The lamp facilitates an examination of the anterior segment and posterior segment of the human eye which includes the eyelid, sclera, conjunctiva, iris, the natural crystalline lens, and cornea.
  • In addition to the physical (visual)examination, Tonometry, linear measurement of tissues or lesions, and ophthalmic photography. contact lens fitting Etc.
  • The binocular slit-lamp examination provides a stereoscopic magnified view of the eye structures in detail, enabling anatomical diagnoses to be made for a variety of eye conditions. A second, hand-held lens is used to examine the retina.

History

  • The concept come in 1850 by Hermann von Helmholtz
  • In 1911 the credit goes to Allvar Gullstrand.
  • In 1919 lamp and magnification is introduced by Vogt Henker
  • In 1926, the slit lamp instrument was redesigned.
  • In 1927 the stereo cameras has been introduced
  • In 1930, Rudolf Theil further developed the slit lamp, encouraged by Hans Goldmann.
  • In 1938 vertical and horizontal movement and joystick was introduced
  •  In 1976 the halogen bulb was introduced.
  • In 1996 the last major development

Types 

There are two different types of slit lamps based on the location of their illumination system:
Zeiss type
  • In the Zeiss type slit lamp, the illumination is located below the microscope(Integrated illumination type).
  • This type of slit lamp is named after the manufacturing company Carl Zeiss.
Haag Streit type
  • In the Haag Streit type slit lamp, the illumination is located above the microscope(Tower illumination type).
  • This type of slit lamp is named after the manufacturing company Haag Streit.

Slit-lamp is composed of three basic systems:

  • Observation system (Microscope)
  • Illumination system (Slit-lamp)
  • A mechanical system (Engineering support)

OBSERVATION SYSTEM (MICROSCOPE):-

  • It works on the same principle as a compound microscope. Which is composed of two optical elements, an objective, and an eyepiece.
  • The objective lens (+22 D) is towards the patient, whose eye forms the object. The eyepiece is +10 to +14 D and is towards the examiner.
  • The objective lens consists of two planoconvex lenses with their convexities facing each other.
  • The illuminating system can be adjusted to vary the width, height, and angle of incidence of the light beam.
  • Slit lamps provide a range of magnification from 6X to 40X.

ILLUMINATION SYSTEM:-

  1. Light source
  2. Slit and other diaphragms
  3. Filters
  4. Projection lens

Light source,

  • Originally, a Nernst lamp was used as a light source which was followed by a Nitra lamp, arc lamp, mercury vapor lamp, and finally halogen lamps.
  • It provides illumination of 2X 10^5 to 4X 10^5 lux.
  • The illuminating system can be adjusted to vary the width, height, and angle of incidence of the light beam.
  • Slit lamps provide a range of magnification from 6X to 40X.

Slit and other diaphragms,

  • The height and width of the slit can be varied using two knobs.
  • There are some stenopaeic slits 2.0 and 0.5mm to provide a conical beam of light.

Filters
Different filters can be inserted into the illumination beam,

  • Cobalt Blue
  • Red free
  • Neutral density
  • Heat absorbing
  • Grey
  • Yellow filter
  • Diffuse

Projection lens
Forms an image of the slit at the eye. This has two advantages:

  • It keeps the aberrations of the lens down, better quality image.
  • It increases the depth of focus of the slit, better optical section of the eye.

MECHANICAL SUPPORT SYSTEM

  • Joystick arrangement
  • Up and down movement arrangement
  • Patient support arrangement
  • Fixation target

Principles of Slit-Lamp Illumination

The slit lamp is capable of illuminating the tissues of the eye in several different ways, any or all of which can be useful, depending on the clinical situation. The beginning ophthalmology resident should strive early to master all of these techniques of illumination, to be able to use the slit lamp to its full advantage.

Types of Illumination

The slit lamp exam is dynamic; the observer uses multiple types of illumination simultaneously.

  • The three main categories of illumination are DIFFUSE, DIRECT, AND INDIRECT.
  • Diffuse illumination provides an even light over the entire ocular surface.
  • With direct illumination techniques, the light is shone directly onto the area or structure of interest.
  • With indirect illumination methods, the object of interest is illuminated by light that is reflected off of another structure.

Methods of Illumination

There are s basic methods of illumination using the slit-lamp:-

Diffuse Illumination

Direct Illumination

  • Parallelopiped
  • Optical section
  • Pinpoint (conical)
  • Tangential
  • Specular Reflection

Indirect Illumination

  • Retro Illumination
  • Sclerotic scatter
  • Transillumination
  • Proximal Illumination

SLIT-LAMP BIOMICROSCOPY ROUTINE

While performing slit-lamp biomicroscopy, the following routine may be adopted:-

  • The slit lamp should be set up in a room that is free of dust.
  • Excessive heat or humidity, as well as exposure to direct sunlight, should also be avoided.
  • The patient should be positioned comfortably in front of the slit-lamp with his/her chin resting on the chin rest and forehead as opposed to the headrest.
  • If the table is too low, or too high, the patient will be uncomfortable.
  • Beginning the actual examination you should adjust the eyepieces of the slit lamp oculars.
  • If you wear glasses or remove glasses, the oculars must be set to compensate for your refractive error.
  • The examination should be carried out in the semidark room so that the examiner’s eyes are partially dark-adapted to ensure sensitivity to low intensities of light.
  • Diffuse illumination is used for a short time as necessary.
  • Medications like ointments and anesthetic eye drops produce corneal surface disturbances which can be mistaken for pathology.
  • Low magnification should be first used to locate the pathology and higher magnification should be used to examine it.
  • You will also need to set the pupillary distance (PD) of the oculars.
  • If your slit lamp has a fixation light, have the patient look at that.If you do not have a fixation device, you can ask the patient to look straight ahead at your ear or over your shoulder at a large letter or other targets at the end of the room.
  • It is a good idea to begin the examination at 6X or 10X magnification. You can move to 16X or more when you examine the cornea and internal structures and when you see some abnormality that warrants closer inspection.

During the test, the doctor will examine all areas of your eye, including the:

  • Eyelids
  • Iris
  • Lens
  • Sclera
  • Cornea
  • Retina
  • Optic Nerve
  • Cataracts, Which Is An Opacity Or Cloudiness Of The Lens
  • Macular Degeneration And Eye Disease That Destroys The Central Vision
  • Optic Nerve, Such As Glaucoma
  • Bleeding In The Eye
  • Foreign Body In The Eye
  • Conjunctivitis
  • Corneal Injury Such As Corneal Ulcer Or Corneal Swelling
  • Diabetic Retinopathy
  • Fuchs’ Dystrophy
  • Keratoconus (Fleischer Ring)
  • Retinal Detachment
  • Retinal Vessel Occlusion
  • Retinitis Pigmentosa
  • Sjögren’s Syndrome
  • Toxoplasmosis
  • Uveitis

Many other investigative techniques utilize the slit lamp:

  • Gonioscopy
  • Hruby-lens
  • Fundus examinations
  • Tonometry
  • Van Herick’s technique
  • Pachymetry
  • Tearscopeâ
  • Photography using 35 mm, video, or digital systems
  • Aesthiometry