Slit lamp examination lecture

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  • 1. DR.Prashant .P.PatelSenior resident,Aravind Eye Hospital, Tirunelveli.

2. Slit lamp Biomicroscopy It is a dynamic examination in which eye andocular adnexa are scanned anteroposteriorly andhorizontally. Slit Lamp: It is a misnomer since slit is only oneof the various other diaphragmatic openingpresent in the instrument. Slit lamp biomicroscopy:1) Term introduced by Mawas in 1925.2) Examination of living eye by means ofmicroscope and slit lamp. 3. The slit-lamp is one of the important examination tools ofophthalmologists. One of the most important advantages of slit-lamp examination is thatone can examine the eye structure in three dimensions (3D). There are three basic requirements for appreciation of depth with a slit-lamp. The first depends upon the clinician possessing a third grade of binocularvision called stereopsis. The second involves the direction of the incoming light source, and isdependent upon the fact that the light beam can be moved so it comes infrom one side or the other. The third involves the shape of the slit. 4. History Purkinje: One of the first individuals to applymicroscopy to the living eye , who studied the iriswith an adjustable microscope by illuminating thefield of view. Louis de Wecker : He made the uniocular slit-lampcombined an eyepiece, objective and adjustablecondensing lens within a tube. It was improved by Siegfried Czapski who addedbinocularity to the microscope. However, none of the units had sufficient andadjustable illumination. 5. Allvar Gullstrand: An ophthalmologist and1911 Nobel laureate introduced the illuminationsystem which had for the first time a slitdiaphragm, therefore Gullstrand is creditedwith the invention of the slit lamp. 6. Henker and Vogt improved upon Gullstrandsdevice in 1911 by creating an adjustable slit-lampby combining Czapskis microscope withGullstrands slit-lamp illumination. 7. Basic design of slit lamp The three main components of the modernslit-lamp are:1) Illumination system2)Observation system3) Mechanical system 8. Mechanical system It is mainly concerned with: Positioning of patient. Adjustment for observer and patient. Adjustment of illumination and observationssystem. It generally contains following hard ware. 9. Fixation lightHead restCanthal alignment markChin restLock for slit lamp baseJoy stickPower unit 10. Chinrest adjust-ment knobHeight adjustmentswitch 11. Mechanical coupling: Mechanical systemprovides coupling of microscope andillumination system along a common axis ofrotation that coincides their focal planes. This arrangement ensures that light falls onthe point where microscope is focused. 12. Illumination SystemIt is based on Kohler illuminationThe light source L is imaged in the objective O by the collectorsystem K. The objective in turn produces an image at S in themechanical slit located next to the collector system. The image ofthe light source at O is the exit pupil of the system.The filament is imaged on to the objective lens but themechanical slit is imaged on to the patients eye. 13. Khler illumination provides a veryhomogeneous slit image. 14. Illumination System The illumination system of most slit-lampsconsists of two different designs. The first design: the Haag-Streit typeillumination, allows de-coupling in the verticalmeridian. Such vertical de-coupling is particularly usefulwhen performing gonioscopy to minimizereflections and for indirect fundus examination togain increased peripheral views. 15. In the Zeiss type the illumination comes from below.The second design: the Zeiss type illumination system, does not allow decoupling inthe vertical meridian. 16. Illumination system control Angle Width Type1.Neutral density2.Red free3.Cobalt blue Height Intensity 17. Observation system Should have following Characteristics : Optimum stereoscopic observation. Selectable magnification. Large field of view. Large depth of field. Enough space in front of themicroscope for manipulations on theeye. 18. Observation system is composed of An objective lens: Two planoconvex lenses withtheir convexities put together. Magnifying lenses Telescope Pair of prisms: To reinvert the image. Eyepiece Converging tubes: They are converged at anangle of 10-15 degree, to provide goodstereopsis. 19. The object is located at the object side focalpoint of the magnifying lens that magnifiesthe object image projecting it virtually toinfinity. The image is than viewed with respectivemagnification through telescope. 20. Change in magnification Grenough type: Galilean changer type: Czapskiscope with rotating objective: Zoom system: 21. The Grenough type(Classical HaagStreit)Flip lever to changemagnification 22. The Galilean Magnificationchanger 23. The Galilean Magnification changer It utilises the Galilean telescopes to alter themagnification. It has two optical components: 1)Positive lens 2)Negative lens Lenses are arranged in turret arrangement. It provides large range of magnifications,typically five. 24. The Galilean Magnification changer 25. The Galilean Magnification changerKnob to changemagnification (3or 5step) 26. Czapskiscope with rotating objectives The different objectives are usually placed ona turret type of arrangement that allows themto be fairly rapidly changed duringexamination. 27. Zoom System Zoom system allows continuously variousdegree of magnification. E.g, Nikon photo slit lamp &Zeiss-75 Sl 28. Magnification can also be changedby changing the eyepiece power 29. Clinical Procedure Before using the slit-lamp, it is important toensure that the instrument is correctly set up. The eyepieces should be focused for the observerfor his/her own refractive error. Often a little more minus correction is requiredthan the observers actual refractive error due toaccommodation and proximal convergence. The Pupillary distance (pd) is adjusted for theobserver (perhaps the pd should be slightly lessthan that usually measured to account forproximal convergence). 30. Check that the observation and illuminationsystems are coupled, and the slit-beam is ofeven illumination and has sharply demarcatededge (otherwise irregularity of the beam maybe falsely interpreted as irregularity oftissues). The slit-lamp examination is conducted in asemi dark room. 31. Patient is seated in front of slit-lamp on anadjustable stool and his/her head is steadied byplacing chin on chin-rest and his forehead restson the bar of head-rest. Adjust the chin-rest so that the patients eyes areapproximately level with the black marker onthe side of the head rest. Focus the slit-beam on the eye by moving thejoystick either towards or away from the patient. 32. The examination should be commenced using theX10 eyepieces and the lower powered objectiveto locate the pathology and higher magnificationshould then be used to examine it. Use the lowest voltage setting on thetransformer. Select the longest slit-length by means of theappropriate lever. The angulation between the observation arm andthe illumination arm is adjusted. 33. Examination methods Types of Illumination. Slit lamp Provides three basic types of Illuminations. 1)Focal Illumination:Achieved by narrowing the slit horizontally orvertically, provides isolation of the specific areas of eye/cornea for observation. 2) Oblique illumination: It is essential for detecting andexamining findings in different layers of the cornea. 3)The Optical Section: The narrow slit beam slicesthrough the eye revealing the internal details of thetissue at all layers. 34. Types of Illumination Dffuse Illumination:Terminology :It is the type encountered in everyday life.For example light from sun or a light bulb thatdiffusely illuminate ones surroundings.Principle :It is a Initial survey examination of the face,eyelids and ocular surface.If one directly proceeds with the magnifiedexamination one is likely to miss skin disorders( suchas acne rosacea), eyelid lesions ( such as molluscumcontagiosum, small chalasion, mild ptosis).Technique: It can be done with torch light , 35. Diffuse illumination with slit lamp1)Swing the microscope aside or keep it at 30-40 of angle.2)Opening the slit beam to full height and width.3)Dialing in the neutral density filter. Beam is only 8-14 mm diameter andtherefore must be moved over the eyelids andocular surface. It can reveal location and general pattern ofeyelid, conjunctival, corneal lesions. 36. Sclerotic Scatter Terminology :In this technique for illuminating cornea, theslit beam is directed at the scleral limbus and illuminationis transmitted into cornea by total internal reflection. Opacities within the cornea scatter the light back to theobserver. Principle: Opaque sclera scatters the light at the point ofillumination, some of the light is directed in to cornealstroma, where it travels through the entire cornea byrepeatedly reflecting from its anterior and posteriorsurfaces. The light emerges around circumference of the cornea,where it encounters the opaque sclera and create aglowing halo. 37. Should be used early in the examinationbecause,1) The patient acclimates to bright light of theslit lamp before it is directed in to the pupil.2) It accurately reveals the presence andpattern of corneal opacities.3) It helps to identify faint opacities that aredifficult to see in direct illumination. 38. Technique: SLIT BEAM : Moderate width, Directed at the3- or 9-oclock scleral limbus MICROSCOPE: Independently focused ontothe cornea. 39. Direct focal slit illumination Terminology : Projection , of a narrow slit beam at anangle, to the corneal surface, producing an optical sectionthat slices through the cornea and eye. Principle: A direct narrow slit beam optically cuts throughthe cornea , providing a cross sectional view that revealsits contour and its internal structure. It forms two parallel curved surface, one that followsanterior corneal surface and one that posterior cornealsurface. Two surfa