Slit lamp biomicroscopy

Detailed explanation of slit lamp

1. SLIT LAMP BIOMICROSCOPY PRESENTER - Hira nath dahal

2. Presentation layout Introduction Optical principle Components Examination procedures Illumination types Uses

3. Introduction Slit lamp: instrument designed specifically to examine the eye and adnexa Operational components consists of a binocular microscope and a light source provides light in the form of slit to observe various ocular structures Provides stereoscopic view of external adnexa , external eye, AC, iris, lens and anterior vitreous

4. History Alvar Gullstrand( Stockholm) Nobel Prize in medicine and physiology(1911) Vogt(1919) - first to describe use of specular microscopy Mawas (1925) - biomicroscopy Various modification by Kohler, Goldmann

5. Optical principle Two systems- illumination and observation Mounted on a movable trolley about a common centre and vertical axis Foci on the same plane These two systems coupled around the same centre of rotation to ensure par-focus of microscope and slit beam Coplanar, coaxial and copivotal

6. Works on the same principle of compund microscope Objective lens(+22D) and eye piece(10-14D) Adjustable illumination system A narrow " slit " beam of very bright light produced by lamp . This beam is focused on to the eye which is then viewed under magnification with a microscope

7. Types based on illumination system Zeiss slit lamp biomicroscope - Light source at the bottom Haag streit slit lamp biomicroscope - Light source at the top

8. HAAG STREIT ZIESS

9. OPTICAL PRINCIPLE OF HAAG-STREIT TYPE Vertical illumination system

10. OPTICAL PRINCIPLE OF ZEISS TYPE Horizontal prism reflected light source

11. Parts of slit lamp Mechanical support Forehead rest Chin rest Fixation target Power supply unit Locking controls Joystick Observation system Binocular eyepieces Camera/video adapter Observation tube Magnification changer

12. Illumination system Light source-halogen, xenon, W lamps(200000-400000lux) Condenser lens system- 2 planoconvex lens, convexities in apposition Slit and other diaphragms- stenopaic slits Filters(Neutral density filter, cobalt blue , red free filter) Projection lens- small diameter Reflecting mirror/prism

13. TYPICAL SLIT LAMP ILLUMINATION SYSTEM

14. The slit within illumination system must have sharply demarcated edges and be adjustable Slit width and height must be adjustable such that any shaped patch from a slit to circle may be projected- increase illumination methods Graduated slit width- size of lesion Ability to rotate lamp housing- if a protractor scale included Must have the facility to displaced of offset sideways(decoupled)

15. THE LIGHT BEAM IS CONTROLLED BY KNOBS OR LEVERS

16. Filters Green(red free)- Increase contrast when looking for corneal and iris neovascularization Increase the visibility of rose bengal staining ND filters- Reduce beam brightness and increase comfort for the pt Polarizing filters- Reduce unwanted specular reflection and enhance visibility of subtle defects

17. Filters Cobalt blue- Fluorescein staining Keratoconus - fleischer’s ring Kodak Wratten No.12(Yellow) Barrier filter placed in front of viewing system Enhancing green staining

18. Graticule Measurement and lens fit Pupil size, HVID, etc

19. Objective system The resolution of image is governed by NA of microscope dependant upon- The diameter of objective The working distance The refractive index of medium between objective lens and eye The wavelength of light

20. Biomicroscope Objective(2 planoconvex lens=22D), eye piece(+10D), enlarged image of near object Tubes converged at 10-15° for good stereopsis A pair of prisms to re-invert the image Range of accomodation - ×6 to ×40 Czapskiscope with rotating objectives- Haag Streit , B&L, Thorpe Littman Galilean telescopic system- Zeiss , Rodenstock , American optical Zoom system- Nikon

21. Biomicroscope Variable magnification Low 7x-10x general eye Medium 20x-25x structure layer High 30x-40x details Optics of compund microscope Two types- – The Grenough type – The Galilean changer type

22. Mechanical parts

23. Procedure Position the patient Adjust the chin rest height so that the outer canthus of the patient is at the level of the mark given Forehead on the head rest. Turn the switch on – begin with minimum illumination Use the focusing rod to adjust the focus of the eyepiece Now start ur observation.

24. Order of Examination Tears Lid margins/Lashes Conjunctiva Cornea Anterior chamber Iris Lens Anterior vitreous

25. HAND HELD SLIT LAMP A portable slit lamp Used to examine the pt in supine position Fits into lightweight case Wider interpupillary dioptic range and field of view.

26. Illumination types: Diffuse Direct Wide beam, optic, parallelopiped , conical Specular Tangential Indirect Proximal Retro Sclerotic scatter

27. Diffuse illumination light is spread evenly over the entire observed surface most often used in slit lamp photography 45 degree angle and fully open slit If no ND filter(diffuser), decrease intensity least amount of magnification (6X or 10X). The cobalt blue and red-free filters also act as diffusers, but white light is generally used

28. Observe: eyelids, lashes, conjunctiva, sclera, pattern of redness, iris, pupil, gross pathology, and media opacities CL fit

29. Direct illumination Observation and illumination system focus at the same point Vary angle of illumination Variable magnification Variable width and height of light Types: Broad beam Optic section Parallelopiped conical

30. Broad beam illumination To examine large area

31. Optic section Narrow focused light(<0.25mm wide) Indicate depths Localize: Nerve fibre , blood vessels, infiltrates, Cataract Anterior chamber angle

32. Optic section Used to evaluate the structural layers of the cornea and lens Good judgement of the depth of corneal foreign body or position of cataract

33. Parallelopiped Broader view, illuminated block of cornea Angle between two systems 40 - 50 deg. Slit width: 1 to 2 mm Provides a layered view of the cornea and the lens Higher magnification than the wide beam to evaluate both the depth and extent of corneal abrasion, scar of FB

34. Observe corneal stroma , epithelial breakdown, lens surface and endothelium Punctate keratitis , corneal nerve fibres in stroma , water clefts

35. Conical illumination Produced by reducing the height of a parallelopiped Square spot of light, darkened room Used to examine AC cells and flares

36. Indirect (proximal)illumination Observation and illumination system are not focused at the same point Vary angle of illumination Slit beam is off set Low to high magnification Beam is focused on an area adjacent to the area to be observed

37. Iris pathology, iris sphinters , epithelial vesicles and erosions

38. Retro illumination Object of regard is illuminated by reflected light Vary angle of illumination Moderately wide beam Slit beam is off set Medium to high magnification Reflected light from iris or fundus

39. Types Direct Prism or mirror is used so that light reflected from lens or iris is directly aligned with area under observation Pathology is seen against light background Indirect Prism is offset so that area under observation is between focal light beam and light reflected from iris/lens Pathology is seen against dark background Marginal Prism is offset so that light reflected from lens/iris at pupil margin is aligned with area under observation

40. Vascularization , epithelial edema, microcysts , vacuoles, dystrophies, lens opacities and CL deposits

41. Sclerotic scatter A tall, wide beam is directed onto the limbal area, light undergoes TIR and comes out from the limbus of next side The illuminator should be slightly offset for this technique and directed from a moderate angle. 10X magnification, with the microscope directed straight ahead. Normal portion of cornea looks dark and any opacities on the path of light show grey reflex.

42. Central corneal epithelial edema, corneal abrasions, corneal nebula and macula, FB in cornea

43. Specular reflection Produced by separating the microscope and slit beam by equal angles from the normal to the cornea Separation of 50 deg produces the best specular reflection The area of high reflection --- zone of specular reflection Small zone of reflection is seen at one time , so we should instruct the patient to change gaze so that large area can be examined. High magnification is required.(40 times) Endothelial cells can be counted and pathology in them can be viewed.

44. Endothelial cell layer, tear film debris, tear film lipid layer thickness

45. Tangential illumination Angle between the slit and microscope 70 – 80 deg Used to see iris freckles and tumors, general integrity of cornea and iris

46. Oscillatory illumination Quick to and fro movement Minutes objects in AC

47. Clinical Uses Diagnostic Anterior segment Evaluation Goldmann Applanation Tonometry TBUT test Staining ( Fluorescein , Rose Bengal etc.) Visiometry Gonioscopy FFA and Clinical Photography

48. Therapeutic Epilation Foreign Body Removal Contact Lens (fitting and post-wear evaluation) Corneal epithelial debridement (herpetic keratitis ) Insertion of punctal plugs

49. References Schmidt A.F.T.Slit Lamp Microscopy Bhatt S S . Basics of slit lamp microscopy IACLE contact lens modules Grosvenor T. Primary Care Optometry Clinical procedures in optometry