Slit Lamp Biomicroscopy PDF

SLITLAMP (BIOMICROSCOPY) Source: Brien Holden Vision Institute The slit lamp examination (SLE) is used for the binocular examination of the eye from the anterior to posterior segment. More specifically, it is used for: 1. Anterior segment exam - tear film to...

SLITLAMP (BIOMICROSCOPY) Source: Brien Holden Vision Institute The slit lamp examination (SLE) is used for the binocular examination of the eye from the anterior to posterior segment. More specifically, it is used for: 1. Anterior segment exam - tear film to anterior vitreous 2. Posterior segment exam with auxiliary lenses (78D or Hruby) 3. Intraocular pressure by Goldmann tonometry 4. Anterior chamber depth assessment (irido-cornea angle) 5. Contact lens fittings and assessments 6. Gonioscopy 7. Minor surgical procedures 8. Laser delivery system INSTRUMENTATION There are many different types of biomicroscopes with variable features. All biomicroscopes, however, are composed of 2 basic parts that sit on a common pivoting base: OBSERVATION SYSTEM (MICROSCOPE) Binocular eyepieces Magnification control ILLUMINATION SYSTEM Adjustable light beam (variable height, width, angle) Filters (red-free, cobalt blue, diffuser)  METHODS OF ILLUMINATION: 1. DIFFUSE ILLUMINATION - A wide unfocused beam of light directed obliquely toward the eye PROCEDURE 30-45 degrees angle between observation & illumination systems Wide open slit beam Low to medium magnification With or without diffusing filter PURPOSE Generally used to obtain an overall view of the eye and adnexa (lids, lashes, conjunctiva, sclera, cornea, iris) 2. OPTIC SECTION - A thin slit beam (minimum possible < 0.25 mm) that optically slices the tissues examined allowing the visualization of tissue layers and depth. PROCEDURE 30-45 degree angle between observation and illumination systems Thin slit beam (as thin as possible) Medium to high magnification PURPOSE Assess the different layers and zones of the tissue examined Permits the assessment of the depth of anomalies or bodies within a tissue Generally used to evaluate the cornea & lens Used in the van herrick method to assess the depth of the anterior chamber 3. PARALLELEPIPED - A slit beam of 1-2 mm that illuminates a rectangular area of tissues - This optically sections a parallelepiped of the tissue observed providing a layered 3-dimensional view PROCEDURE 30-45 degree angle between observation and illumination systems 2-3 slit beam (slightly wider than an optic section) Medium to high magnification PURPOSE Assess the different layers and zones of the tissue examined in 3-D Assess the depth & extent of abnormalities within a tissue (abrasions, scarring, FB) Allows the simultaneous visualization of the anterior, middle & posterior areas of tissues generally used for the tear film, cornea & lens 4. CONICAL BEAM - Small spot or square of light produced by narrowing the vertical height of a parallelepiped PROCEDURE 40-50 degree angle between observation and illumination systems 2-3 mm spot or 2-3 slit beam both in height & width Initial low magnification gradually increased to high magnification Room must be completely dark & examiner must be dark-adapted Beam is focused in the anterior chamber (localize cornea & lens and focus in between) Normal anterior chamber is optically empty (dark) Compare darkness of AC zones above and below light path to zone in the light path Direct the illumination source from both the nasal and temporal sides PURPOSE Used to evaluate the clarity of the anterior chamber Assess debris in anterior chamber (usually cells & flare or blood)  5. CONICAL BEAM - Small spot or square of light produced by narrowing the vertical height of a parallelepiped PROCEDURE 40-50 degree angle between observation and illumination systems 2-3 mm spot or 2-3 slit beam both in height & width Initial low magnification gradually increased to high magnification Room must be completely dark & examiner must be dark-adapted Beam is focused in the anterior chamber (localize cornea & lens and focus in between) Normal anterior chamber is optically empty (dark) Compare darkness of AC zones above and below light path to zone in the light path Direct the illumination source from both the nasal and temporal sides PURPOSE Used to evaluate the clarity of the anterior chamber Assess debris in anterior chamber (usually cells & flare or blood) METHODS OF OBSERVATION 1. DIRECT PROCEDURE Observation and illumination systems are focused coincidentally The area under observation is thus directly illuminated by the incident light PURPOSE Method most commonly used General examination purposes METHODS OF OBSERVATION 1. DIRECT PROCEDURE Observation and illumination systems are focused coincidentally The area under observation is thus directly illuminated by the incident light PURPOSE Method most commonly used General examination purposes 2. INDIRECT OR PROXIMAL PROCEDURE Observation and illumination systems are not focused coincidentally The incident light is on an area immediately adjacent to the object or area of interest (2 methods): o Focus slit lamp on area to be examined and look adjacent to it (Fig. 17.7)(area examined slightly adjacent to focuses area) o Focus on area to be examined and then off-set slit beam (Fig. 17.8) (better view is obtained because the area to be examined will be in clear focus) PURPOSE Provides ‘softer’ illumination of structures and fine details Useful when a bright direct light source ‘bleaches out’ the area to be seen Used to view the iris, fine vascularization, pigment spots, corneal edema, etc. Figure 17.7 Indirect Illumination Step 1 Figure 17.8 Indirect Illumination Step 2 3. RETRO-ILLUMINATION PROCEDURE Object under observation is illuminated by light reflected from a deeper structure The desired area/object is viewed directly or indirectly using light shining from behind (Fig. 17.9 and 17.10) Any structure can be used to reflect the light including the retina The angle of illumination is generally between 30-45 degree For retinal retro-illumination, however, the angle of the illumination system is between 0 degree-5 degree PURPOSE Provides ‘softer’ illumination of structures and fine details Useful when a bright direct light source ‘bleaches out’ the area to be seen Used to view the iris, fine vascularization, pigment spots, corneal edema, etc. Figure 17.9 Diagram of difference between observation Figure 17.10 Diagram of difference between observation and illumination systems in direct retro-illumination and illumination systems in indirect retro-illumination 4. SCLEROTIC SCATTER PROCEDURE A bright parallelepiped focused on the limbus causes light transmission within the cornea In a normal cornea, light is internally reflected within the cornea A bright halo around the limbus is produced A normal cornea where the internally reflected light travels freely appears clear Corneal abnormalities will cause light scatter and appear gray or white PURPOSE Especially useful to view subtle corneal changes (edema, scars, striae, foreign bodies, etc.)  6. SPECULAR REFLECTION PROCEDURE Parallelepiped beam Initial low magnification Biomicroscope is moved to place observation system on the reflected light from the cornea A bright specular reflection will be seen Gradually increase magnification At this point the angle of incidence = the angle of reflection The tear film will appear on the anterior parallelepiped surface The endothelium will appear on the posterior parallelepiped surface PURPOSE Used to observe irregularities, deposits, or excavations in a smooth surface Especially useful for corneal endothelium and tear film evaluation FILTERED ILLUMINATION PROCEDURE Use of various filters to enhance the assessment of certain structures and abnormalities e.g. cobalt blue, yellowwratten, red-free, neutral density filters Often incorporated to biomicroscope, otherwise can be added PURPOSE Cobalt blue: used with fluorescein dye to visualize corneal staining Yellow wratten: a barrier filter used with fluorescein to visualize corneal staining Red-free: makes blood vessels & rose bengal stain appear black to enhance contrast Neutral density: uniformly decrease illumination intensity VAN HERICK TECHNIQUE - used to assess anterior chamber depth PROCEDURE: Use low to medium magnification. 60 degree angle between arms of the slit lamp with the observation system perpendicular to the eye. Focus an optic section of medium to maximum height exactly at the limbus (Temporal & Nasal). To be sure, focus slit slightly on the cornea initially, and then move it outwards towards the limbus until it begins to widen (indicates that it is bridging the corneo-scleral transition area). Move back inward to the thinnest last observable optic section. Compare the depth of the anterior chamber indicated by the dark shadow (between the iris and cornea) to the thickness of the cornea (indicated by the optic section Establish the ratio between the dark shadow (DAC) and the corneal thickness (CT): Dac = Depth anterior chamber CT = Depth of the cornea Van Herick Grading System Van Herrick Grading System: Grade DAC / CT ~0 0: AC extremely narrow/closed I: < 1/4 II: 1/4 III: 1/4 to 1/2 IV: > 1/2 Source: Van Herick W, Shaffer RN, Schwartz A. Estimation of width of angle of anterior chamber. Am J Ophthalmol 1969;68:626-9.  SLIT LAMP BIOMICROSCOPY OVERVIEW ILLUMINATION METHOD Characteristic Diffuse Illumination Optic Section Parallelepiped Conical section Angle between SL arms 30-45degree 30-45degree 30-45degree 40-50degree Width of slit beam Maximal Minimal 1-2 mm 2-3mm Height of slit beam Maximal Maximal Maximal 2-3mm Filter None, diffuser, None None, Colored None colored Light intensity Variable Maximal Variable Maximal Magnification Low - Medium Medium-High Medium-High Medium-High METHODS OF OBSERVATION Direct Indirect Retro- Specular Dispersion Characteristic Van Herick Illumination Illumination Illumination Reflection Scleral Focus / Slit- Coincident or Coincident or Coincident Coincident Coincident Coincident lamp arm-lock not not 30-45 degree for Angle between cornea; 30-45 degree 30-45 degree 45-60degree 30-45 degree 60 degree SL arms 0-5 degree for lens-iris Optic section Optic section or Optic section Optic section Type of beam or Parallelepiped or Parallelepiped or Optic Parallelepiped Parallelepiped Parallelepiped Section Height of Slit Medium beam Variable Variable Variable Variable Variable - Maximal None, All Filter others None None None None None Intensity of light Variable Variable Variable Medium-High Maximal Medium- High Magnification Variable Variable Medium-High Medium-High Low-High Low-High Table 17.2 Observation Techniques SLIT LAMP ROUTINE ASSESSMENT: 1. Explain the purpose of the test and give proper instructions 2. Appropriately set up o Wash hands o Disinfect chin and forehead rests o Position patient properly with chin & forehead firmly against rests o Align markings on head rest with patient canthi o Dim room illumination o Prepare instrument, set up illumination o Start with the right eye 3. Assess and use efficient & logical sequence to appropriately examine all tissues of the anterior segment: Lids / lashes (superior /inferior), Tear film, Conjunctiva / sclera (temporal/nasal), Cornea, AC angle, iris, Lens, Anterior vitreous, AC clarity, Superior tarsal conjunctiva (lid eversion) 4. Record assessment and findings appropriately Biomicroscopy NS SN CC CC Figure: Example of biomicroscopy examination record  FUNDOSCOPY Source: Brien Holden Vision Institute NORMAL FUNDUS COLOR OF THE FUNDUS There is variation in the background colour of the overall fundus between individuals. The background colour of the fundus is reddish-orange due to the pigment in the retinal pigment epitheliallayer (RPE), choroid and vasculature. In individuals with sparse pigment, like in Caucasians, the choroid vasculature is more visible and the fundus therefore has a more red appearance. In individuals with dense pigment, like in Asians and African patients, the increased pigment content in the fundus gives a tessellated or tigroid appearance which are observed as dark streaks of pigment OPTIC NERVE HEAD (ONH) The ONH lies nasal to the macula or can be observed most easily when the practitioner observes the retinal when he is about 15 degrees temporally positioned relative to the eye being examined. The ONH dimensions on average: 5.5° wide and 7.5° wide. Its projection in the visual field is referred to as the blindspot, since the ONH is devoid of photoreceptors. The outer margins of the ONH are indicated as the disc margin and should be clear and defined. A lack of clarity of these margins may indicate the presence of pathological conditions. The central portion of the ONH is marked by an excavation which is referred to as the physiological optic cup. It is the point of exit of the ganglion cell fibres from the retina into the optic nerve. The intraocular pressure tends to have an impact on the morphology of the cup and the neuro-retinal rim. An assessment of the C/D ratio is the size of cup relative to disc. A. OPTIC DISC Optic disc size: The size of the optic disc (OD) is not constant among individuals Optic disc diameter: ~ 5.5° wide horizontally and ~7.5° wide vertically (Fig. 16.8). Optic disc shape: The OD is slightly vertically oval. On average, vertical diameter being about 7-10% larger than the horizontal Disc margins: The scleral rim (Fig. 16.9) is the limit of the disc and may appear as a partial or total white circle peripheralto the normally pink neuroretinal rim (NRR) Margins of the disc should be distinct Figure 16.9 Normal optic nerve head – (a) scleral rim is indicated between arrows; (b) distinct optic disc margin B. OPTIC CUP (OC) The position of the cup within the disc may be central or decentered The optic cup is the excavation of the ONH  Figure 16.12 (a) Centrally placed cup within the optic disc; (b) decentrally placed cup within the optic disc C. CUP-TO-DISC-RATIO (C/D) Physiological cupping is 0.3 Asymmetric C/D ratios that differ by 0.2 or more between the 2 eyes is usually suggestive of glaucoma orother pathology One must determine what the ratio is between the horizontal and vertical diameter of the cup to the horizontaland vertical diameter of the disc D. NEURORETINAL RIM (NRR) NEURORETINAL RIM SIZE This is the pink ring of capillary-rich tissue present on healthy optic nerve heads.  NRR assessment is necessary in ophthalmoscopic evaluation of the ONH. The NRR size is correlated with disc area. A larger disc has a tendency to have a larger NRR. NRR SHAPE NRR is usually broadest Inferiorly, followed by Superior disc margin, Nasal disc area and finally the Temporal disc region (the “ISNT rule” as termed by Werner) (Fig. 16.14) NRR pallor may be a sign of ON damage Notching of the cup or vertical elongation of the cup indicates compromise to the nerve fiber. The change in size and thickness of the NRR (review rule of ISNT) is of utmost importance in the diagnosis of early glaucomatous ONH damage, which may show up before visual field defects a Figure 16.14 Comparisons of the neuroretinal rim indicating that the ISNT rule is satisfied RETINAL VESSELS The veins are thicker, darker because they carry de-oxygenated blood. They have transparent walls. The arteries are narrower and brighter red in colour. The CRA and CRV emerge at optic disc and enter the nerve fibre layer. Both arteries and veins have a relatively smooth path. Tortuosity may be a congenital variation or indicate the presence of vascular pathology. The normal A/V ratio 2:3. In general, the caliber of the vessels should be uniform with no area of compression at the crossing of vessels The arteriolar light reflex is the ratio width of the light that is reflected off the surface of an artery to the overallwidth of the artery. The arteriolar light reflex is usually expected to be 1/3 or 1/4 MACULA It is area of the fundus that is rich in retinal cone photoreceptors The macula lies approximately 2 disc diameters (DD) temporal to the optic disc.  Its area spans 5mm in diameter. Macula is darker in pigmentation than the rest of the fundus. This is attributed by: − Increased pigmentation in the RPE layer − Xanthophyll pigment giving the macula an orange/brown hue Macula pigment is uniformly distributed. The central region of the macula is known as the fovea centralis (foveal avascular zone). It is an area that is very slightly excavated relative to the surrounding area of the macula. It gives rise to a foveal reflex when illuminated, as it is a thinner aspect of the macula. Foveal avascular zone (center portion of macula) is entirely dependent on the choriocapillaries for its nutrition and O2 supply.  Types of Retinal Pathology Arteriolar narrowing: subtle, with generalised arteriolar narrowing with typical copper or silver wire appearance. Most commonly associated with the early stages of hypertensive retinopathy. Arteriovenous nipping/nicking: areas of focal narrowing, and compression of venules at sites of arteriovenous crossing. The typical appearance involves bulging of retinal veins on either side of the area where the retinal artery is crossing. Most commonly associated with hypertensive retinopathy. Dot and blot haemorrhages: arise from bleeding capillaries in the middle layers of the retina and may look like microaneurysms if small enough. They are most commonly associated with diabetic retinopathy. Flame haemorrhages: larger haemorrhages with a flame-like appearance caused by rupture of pre-capillary arterioles or small veins in the retinal nerve fibre layer. Most commonly associated with hypertensive retinopathy, thrombocytopaenia, retinal vein occlusion and trauma. Cotton wool spots: appear as small, fluffy, whitish superficial lesions and represent infarcts of the neuro-retinal layer. They are most commonly associated with diabetic retinopathy and hypertensive retinopathy. Hard exudates: waxy yellow lesions with relatively distinct margins arranged in clumps or rings, often surrounding leaking microaneurysms. They are most commonly associated with diabetic retinopathy and hypertensive retinopathy. Neovascularisation: formation of new blood vessels that appear as a net of small curly vessels, with or without associated haemorrhages. They may be located on the optic disc or elsewhere on the retina. They are most commonly associated with advanced proliferative diabetic retinopathy. Branch retinal vein occlusion: blockage of one of the four retinal veins, each of which drains about a quarter of the retina. Typical signs include flame haemorrhages, dot and blot haemorrhages, cotton wool spots, hard exudates, retinal oedema, and dilated tortuous veins. Drusen: yellow-white flecks scattered around the macular region representing remnants of dead retinal pigment epithelium. Most commonly caused by age-related macular degeneration. Types of Retinal Pathology Types of Retinal Pathology  DIRECT OPHTHALMOSCOPY Source: Brien Holden Vision Institute PURPOSE OF THE DIRECT OPHTHALMOSCOPY Direct ophthalmoscopy provides a view of the posterior pole region of the fundus, which includes the optic nerve and its vascular arcades and the macula. Ophthalmoscope was introduced by Hermann Von Helmholtz ADVANTAGES Easier to conduct than other methods of posterior segment evaluation Performed upright on patients allowing for more comfort Can be performed on large or small pupils Provides a relatively higher level of magnification ~15X Allows the assessment of media Portable/Handheld Upright image DISADVANTAGES Lack of stereoscopic view of the posterior segment Close working distance Provides a small field of view Produces distortion with off-axis views of the eye Limited views of media opacities are present PARTS OF THE DIRECT OPHTHALMOSCOPE Rheostat to control illumination Variable aperture sizes small to large - varying diameters (pupil size adjustment) Lens power indicator (plus and minus)  Auxiliary controls: o Red-free filter is used to differentiate retinal and choroidal lesions, Hemorrhages, pigment, subtle optic nerve head drusen and nerve fiber layer defects o Fixation cross is used to assess fixation and in some cases grade position and size of defects. o Slit beam is used to detect elevated lesions on the fundus and macula holes o Cobalt blue filter is used together with fluorescein on the cornea to assess corneal scar and abrasionas well as pupil size in the dark. OPTICS OF THE DIRECT OPHTHALMOSCOPE Figure 16.5 Optics of the ophthalmoscope 1. Illuminating system Figure 16.6 Optics of the illuminating system of the direct ophthalmoscope  The illumination system comprises: A tungsten bulb, condenser system, projection lens and reflector Bulb is centered and produces a filament image on the reflector Reflectors can be either mirrors, metallic plates, prisms A range of aperture stops and filters are present between the condensing and projection lens The illumination system also Includes a series of different size apertures A series of filters are also part of the illumination system, namely the red free filter which increases the contrast between vessels and retinal background, differentiates retinal and choroidal lesions, differentiates hemorrhages and pigment (Fig. 16.6) 2. Observation System: Figure 16.7 Optics of the observation system of the direct ophthalmoscope The observation system comprises: A sight-hole/peephole and focusing system A focusing system made of a rack of lenses Sight-hole positions the viewing axis to one side of illumination axis and so displaces the corneal reflex A bright corneal reflex can be eliminated by using a polarizing filter, however, it causes a loss of light (Fig. 16.7) PROCEDURE FOR CONDUCTING DIRECT OPHTHALMOSCOPY 1. The practitioner must grasp the ophthalmoscope such that his/her fingers are placed on the lens wheel, which allows the practitioner to adjust lens power in either the plus or minus direction. The right hand is used to hold the instrument when performing the technique on the right eye and by theleft hand when performing on the left eye. Practitioners who have physical or visual limitations may not beable to adapt to this method of instrument handling. 2. The observation aperture of the ophthalmoscope must be directly before the practitioner’s eye, thereby requiring the practitioner to move his/her head, arm and ophthalmoscope as one unit. 3. Fixation and its maintenance is essential to performing a problem-free ophthalmoscopic examination ona patient. The patient must be directed to view in the primary or straight ahead position since the optic nerve head of the posterior pole is the structure that is observed first. One may provide a large fixation target on a VA chart to assist in this process or in the case of paediatric evaluation, an interesting visually stimulating distance target. 4. The technique is best performed in dimly lit room to ensure that the pupil size is maximal in size to encourage a larger field of view upon examination. 5. It is essential to provide the patient with adequate instructions. This would include the purpose of the test the bright light and that you are likely to come very closer to their eye or face. In this way, the patient is ready for you to invade their internal space. 6. When beginning the examination, the practitioner begins with approximately +10.00DS lens and positions himself/herself at about 10cm from the patient (equivalent to the focus of the +10.00DS lens). This lens power facilitates a view of the anterior media structures. One would be able to observe the red-reflex whichis the reflection off the fundus. Any media disturbance would usually obstruct the view of this red-reflex. As you focus towards posterior structures, i.e. from aqueous to lens to retina, decrease the power of the focusing lens. 7. Media opacities are assessed using the principle of motion of parallax plus nodal point as reference. a. If the opacity lies in the anterior capsule, then the opacity appears to move in the same direction as the movement of the eye b. If the opacity lies in the posterior capsule, then the opacity appears to move in the opposite direction as the movement of the eye c. If the opacity lies posterior to the lens, in the vitreous gel, usually floaters, they will appear to move as the patient moves his/her eye and then float back to the original position. 8. As the practitioner completes the examination of the media, he/she will be moving closer to the patient. However, the practitioner should not get closer than the extent of the eyelashes. 9. Adjustments in the prescription used to view the eye may need to be calculated  as per formula in orderfor the practitioner to be able to see the patient’s retina clearly. The power of the correcting lens must be the algebraic sum of the ametropias of the practitioner and the patient minus the dioptric amount of their accommodation. F correcting lens = (Examiner’s Ametropia + Patient’s Ametropia) – accommodation For example: (-2.00 + 5.00) – 1.00 = +2.00DS 10. When the practitioner is ready to view the fundus and more specifically the optic nerve head (ONH), he/she may move to a position that is slightly temporal to a central view. At this point, the patient is observing along the visual axis. In some cases, it may be difficult for the practitioner to be able to obtain an immediate view of the ONH even in this position. If so, the practitioner must find a bifurcation of the vessel forms a “V” shape, which will give the practitioner a guideline as to which direction to move in order to find the ONH. 11. Once the practitioner reaches the ONH, there are several features that the practitioner would have to take note of in order to determine the health status of the retina. These features include: 12. The practitioner is required to examine all four quadrants. Either the practitioner will move towards the different quadrants or the patient looks in different directions of gaze. 13. Any abnormalities/lesions should be noted in terms of size, position from the disc in clock position. 14. The macula is examined by asking the patient to look into the light source of the ophthalmoscope, or the practitioner should move their view in a temporal direction to reach the macula. The practitioner must note the colour, any abnormalities, presence of a foveal reflex, steadiness of the position of foveal reflex with fixation and uniformity of the colouration of macula.  BINOCULAR INDIRECT OPHTHALMOSCOPY (BIO) Source: BrienHolden Vision Institute The binocular indirect ophthalmoscope (BIO) is a head borne device (headset or spectacles) that contains an illumination system and viewing oculars. A condensing lens is used to converge the light from the retina to form a real, aerial, inverted and reversed image in front of the lens that is viewed through the oculars. The BIO is the single most useful instrument for examining the entire ocular fundus with a panoramic and stereoscopic view. Advantages and Disadvantages of Binocular Indirect Ophthalmoscopy Advantages Disadvantages Stereoscopic view Inverted and inversed image Wide range of view Low magnification Wide panoramic field of view Dilation required High resolution Difficult to master High contrast May be difficult to perform for examiners with back problems Excellent depth of focus Independent of refractive error Variety of lens options Allows quick comparison between the eyes Relatively easy view through disrupted media Possibility of scleral depression Relatively short exam time  Comparison Between Direct, Monocular Indirect and Binocular Indirect Ophthalmoscopy Ophthalmoscopy Direct Monocular Indirect Binocular Indirect Stereoscopic view None None Excellent Field of view 5° (2 DD) 12° 40° (8 DD) with a 20D Peripheral view Blurry / impossible Limited Excellent Maximal view Equator (~60°) 70% of fundus Beyond ora serrata Depth of focus Weak Fair Good Magnification 15 x 5x (fixed) 3x (20D); 2x (30D) Working distance Very close (often 15-20 cm Arm’s length uncomfortable for thepatient) Image Virtual / erect Real / inversed Real / inversed- inverted Dilation Not necessary Not necessary Recommended Ease of procedure Easy +/- easy Difficult Illumination and Observation System Light is projected from the headset and focused through a hand-held lens onto the fundus plane. The light is of variable intensity, spot diameter and color. A red-free filter is incorporated in most BIOs to enhance the observation of the nerve fiber layer and to facilitate the differentiation of some findings. Pigmented lesions underneath the retinal pigment epithelium (e.g., a nevus) will be indiscernible with the red-free filter. This filter also enhances the observation of hemorrhages and blood vessels. A cobalt blue filter, incorporated for the purpose of performing fluorescein angiography, can be also be used to enhance the detection of buried ONH drusen through induced fluorescence. The observation system is composed of sets of mirrors and prisms that optically reduce the examiner’s pupillary distance to fit it within the patient’s pupil along with the illumination beam. Condensing Lenses The condensing lenses have 3 functions: − they direct the light source into the eye − generate the aerial image of the fundus − generate image the examiner’s pupils within the patient’s pupil. The lenses usually have double aspheric anti- reflective surfaces which permit clear imaging over the entire lens. One side is typically made steeper to reduce reflections and distortions from the illuminating beam. The flattest side, often indicated by a sliver ring, should face the patient during the procedure. The lenses are available clear or yellow. The yellow filter minimizes the patient’s discomfort and reduces phototoxic short wavelengths, but the yellow may slightly alters the color of fundus findings.A detachable yellow filter is an available option. The lenses are of various powers ranging from +15 D to +40D. Power adapters are available for the 20D lens(50mm) to increase field of view. The +20 D lens is used in most clinical situations. The magnification and field of view vary with dioptric power of the lens. For a lens of the same diameter:  lens dioptric power  magnification  field of view The lens-eye focal distance is also variable with the lens power:  Power  Lens-eye distance PROCEDURE *The pupil is dilated to allow optimum view (a non dilated view is possible) 1. Adjustment of the ophthalmoscope 2. Adjust headband crown 3. Adjust the pupillary distance 4. Check illumination intensity. Usually start with lower illumination and slowly increase illumination as needed and as tolerated by the patient. Check for a proper elevation/position. Check can be done by extending arm or by looking at a wall. 5. Apply filter if desired 6. Positioning the patient - Patient should be in a supine position. If reclining is not possible, BIO is performed with the patient in a seated position 7. Patient should be looking directly up, initially (primary position) 8. Examiner should initially stand to the side of the patient, leaning over the patient 9. Keep handheld lens approximately 2 inches away from patient's eye, moving it closer or farther away to focus and refine the view 10. Examiner swivels his view around to view different parts of the retina, by tilting the head and walking around the patient 11. The doctor instructs the patient to look at various extremes of their vision 12. The macula is examined at the last, as the light is bright and patient cooperation for BIO may reduce drastically if macula is examined at the initiation of BIO RECORDING/DRAWING LESIONS Since the view obtained with BIO is inverted and reversed, documenting observed findings can be difficult at first. You can reverse and invert the image in your mind before documenting it but it is a difficult method for many. Alternatively, one can ease the drawing of lesions using the following method. Invert the fundus diagram with the 12:00 position towards the feet of the patient. The lesion is then drawn as seen in the opposite quadrant of where itis perceived (Fig. 3.23). ST  Manila Central University College of Optometry Clinical Optometry Practice 1 Name: Sabio, Ace Cedric S. Date: December 7, 2021 Section: OP3-2 Professor: Dr. Rachel Balan-Magararu NORMAL FUNDUS OPTIC CUP/PHYSIOLOGIC CUP RETINAL ARTERY OPTIC DISC MACULA FOVEA RETINAL VEIN Page 1 of 1