CLASIFICACIÓN DE EMPRESA
6.4 Herramientas electrónicas
Lens Field of view Image mag. Laser spot Working distance
Super Quad 160® 160°/165° .5x 2.0x contact
Equator Plus® 114°/137° .44x 2.27x contact
Quad Pediatric 100°/120° .55x 1.82x contact
QuadrAspheric® 120°/144° .51x 1.97x contact
PDT Laser 115°/137° .67x 1.5x contact
Trans Equator® 110°/132° .7x 1.44x contact
Area Centralis® 70°/84° 1.06x .94x contact
Super Macula® 2.2 60°/78° 1.49x .67x contact
mag: magnification
scopy. Indirect ophthalmoscopy is carried out in a dark room with fully dilated pupils.
The equipments required for slit-lamp indirect ophthalmoscopy includes slit-lamp and condensing lens. The condensing lens may be either noncontact or contact lens.
Noncontact lenses: They are plus powered with
two convex aspheric surfaces. The +60D version has the greatest magnification and is best used for the disk and macula. The +78D version is a commonly used diagnostic lens and the +90D is good for small pupils. They are available in clear or blue-free, ‘yellow retina protector glass’. They are comfortable to the patient and minimize the risk of phototoxic retinal damage due to prolonged exposure to the focused beam.
Contact lenses: Goldman, Mainster, SuperQuad,
Equator Plus, Area centralis, Super Macula lenses are often used. Field of view and image magnifi- cation obtained by these lenses are listed in Table 10.1.
Method of Examination
For examination, minimal slit-lamp intensity can be used in a dark room. Always focus the oculars to accommodate any examiner refractive error, then set the pupillary distance, remove all filters
and keep the magnification to the lowest setting, usually X6-X10. The illumination of the slit-lamp should be adjusted for an intermediate slit height and a 2 mm width, and then placed in the straight ahead position between the oculars (zero degrees or co-axial). Before examination, ensure that the condensing lens surfaces are clean. Hold the lens vertically between the thumb and index finger of the left hand to examine the patient’s right eye and vice versa.
Examination Procedure
Instruct the patient to fixate straight ahead, to stare wide and to blink normally. Center the beam in the patient’s pupil and focus on the cornea. Now the lens is placed in front of the patient’s eye, directly in front of the cornea so the back surface just clears the lashes. Examiner’s fingers may be placed on either the brow bar or the patient’s forehead. Using the joystick, focus on the fundus image by slowly moving away from the cornea, keeping the beam centered in the pupil. Once the retinal image is focused, the magnification may be increased. Scan across the entire lens keeping it steady. In order to view the peripheral retina, ask the patient to change fixation into the nine cardinal positions of gaze. The lens is realigned and refocused the slit-lamp as necessary. To reduce interfering reflections, tilt the lens or move the illumination arm upto 10 degrees on either side, once the fundus has been focused. For fine tuning of the fundus view, lateral and longitudinal adjustments of the lens may be made to optimize the field of view. When viewing finer fundus details, intensity and magnification of slit-lamp should be increased. Head Mounted Binocular Indirect Ophthalmoscopy
Binocular indirect ophthalmoscopy (BIO) is a technique used to evaluate the entire ocular
Fig. 10.5: Optics of binocular indirect ophthalmoscopy
fundus. It provides for stereoscopic, wide-angled, high-resolution views of the entire fundus and overlying vitreous. Its optical principles and illumination options allow for visualization of the fundus regardless of high ametropia or hazy ocular media.
Light beams directed into the patient’s eye produce reflected observation beams from the retina. These beams are focused to a viewable, aerial image following placement of a high plus- powered condensing lens at its focal distance in front of the patient’s eye. The resultant image is real, inverted, magnified, laterally reversed, and located between the examiner and the condensing lens. The observer views this image through the oculars of the head-borne indirect ophthalmoscope.
An indirect ophthalmoscope (Fig. 10.6) consists of a head band for comfortable place- ment, light source with variable illumination and an adjustable mirrored surface in the main housing and knobs to align the low plus powered eyepieces (+2.00 to +2.50 D) with the examiner’s interpupillary distance. A 20 D condensing lens (Fig. 10.7A), a pair of scleral depressors (Fig.
Figs 10.7A to C: A 20 D condensing lens, B A pair of scleral depressors and C Fundus drawing sheet
Fig. 10.6: Indirect ophthalmoscope
10.7B) and fundus drawing sheet (Fig. 10.7C) are needed for a proper indirect ophthalmoscopy and documentation.
Examination Procedure
Proper placement and adjustment of the binocular indirect ophthalmoscope (BIO) is an important step in the examination. Place the loose BIO onto the head and position the bottom of the front headband one index finger width above the eyebrows. Tighten the crown strap until this headband position begins to stabilize then
position the back head strap on or below the occipital notch and tighten until secured. Now the knobs that control the instruments main housing (oculars and light tower) should be loosened and fixate straight ahead and level in vertical position the oculars and aligned tangential to or slightly angled downward from the ocular surface; this should maximize observer’s visual field and minimize horizontal diplopia. Horizontally align each ocular by closing one eye and fixating a centrally positioned thumb of an outstretched hand. Turn on the light source and fixate straight ahead on a wall at 40 to 50 cm looking at the projected light source. Use the mirror knob to vertically place the light source at the upper one-half to one-third of the field.
The headset is adjusted and the voltage set to mid-range (occasionally the sneeze reflex may start from the periphery first). The choice of condensing lens depends upon the need for a panoramic view or detail; a 30 D provides panoramic view while fundus details can be obtained with 14 D. Stereopsis is important and depends on the choice of lens. A full stereopsis is obtained with 14 D, three-quarter with 20 D and one-half stereopsis with 30 D. A 30 D lens can be used to get a view of fundus in patients with small pupil. The condensing lens should be held between the tip of the flexed index finger and the ball of the extended thumb of the non-
dominant hand and the scleral depressor with the dominant hand. The extended third finger acts as the pivot. The more convex surface should be toward the observer and the white-ringed edge closest to the patient so as to avoid bothersome light reflexes. These reflexes can be made to move in opposite direction from each other by slightly tilting the lens. Condensing lenses have their surfaces coated to reduce such reflexes. The lens must be smudge free.
The patient should have atleast some idea of what to expect in the examination. Although the patient may be examined in either sitting or supine position, it is best to recline the patient on a couch with the face directed towards the ceiling to avoid stooping. The couch or table should be just high enough to reach the examiner’s hips. The examiner stands opposite to the clock hour position to be examined. The patient is instructed to keep both the eyes open and fixate towards his outstretched hand which points to the meridian of interest.
From a working distance of 18 to 20 inches, direct the light beam into the pupil, producing a complete red pupillary reflex. Pull backward on the lens, maintaining the central position of the pupil reflex, until the entire lens fills with the fundus image. Fine adjustments are made in the lens tilt and vertex distance to produce a distortion-free full lens view. The patient must be repeatedly urged to open the fellow eye. Good cycloplegia is the most important single factor in getting co-operation in this regard. The eye with inadequate cycloplegia is very photophobic. All the vital elements involved in the visualization of the fundus, namely observer’s macula, the eyepiece of the ophthalmoscope, center of the condensing lens, patient’s pupil and the object observed in the fundus must be kept on an axis to maintain the fundal view. In order to develop and achieve a continuous sweeping picture of the fundus, a major retinal blood vessel
must be picked out from the posterior pole and followed as anteriorly as possible by the observer’s movements alone. This vessel should be then followed back to the optic disk. This maneuver needs constant practice to master it.
The problem of orientation in the fundus may be solved by learning to accurately draw the image exactly as we see in the condensing lens. The drawing chart may be placed inverted over the patient’s chest. Positioning 180 degrees away from the area of interest, the observer must think in terms of anterior in the fundus or posterior in the fundus (or central and peripheral). Draw the image seen in the lens on that part of the fundus chart that is closest to the observer.
Since 30% of the retina lies anterior to the equator, failure to study this region will result in overlooking serious pathology in many cases. Scleral depression not only allows for an easy and complete view of the ora serrata and the pars plana but also allows a better evaluation of the retinal topography making lesions such as horseshoe tears or vitreo-retinal traction more visible. It is of particular value in differentiating a retinal hemorrhage from a retinal break, in recognizing a raised from a depressed lesion and in detecting whether a foreign body lies on or anterior to the retina. The absence of an overhanging orbital margin superonasally makes initial attempts at scleral depression easier. The depressor is applied to the superior lid, without pressure, at the tarsal margin. The patient looks up and the depressor slides posteriorly parallel to the surface of the globe, as the lid retracts. The depressor is gently pressed against the globe at the equatorial region and a grayish mound is seen to come up in view from the inferior part of the fundus. In viewing the ora, it is sometimes necessary to tilt the condensing lens somewhat forward, into a plane more nearly parallel to the iris. It must be remembered that scleral depression is a dynamic technique.
Fundus Drawing: Color Code (Peter Morse)
Color Code Red Solid
• Retinal arterioles • Neovascularization
• Vascular abnormalities or anomalies • Vortex vein
• Attached retina
• Hemorrhages (Pre-intra-and sub-retinal) • Open interior portion of retinal break (Tears,
holes)
• Normal foveola (Drawn as red dot).
Cross lines
• Open portion of giant tears or large dialysis • Inner portion of chorioretinal atrophy • Open portion of retinal holes in inner layer
of retinoschisis
• Inner portion of the areas of retina.
Color Code Blue Solid
• Detached retina (Fig. 10.8) • Retinal veins
• Outlines of retinal breaks (Tears, holes) • Outline of ora serrata (Dentate processes, ora
bays)
• Meridional, radial, fixed star-shaped and circumferential folds
• Vitreoretinal traction tufts
• Retinal granular tags and tufts (Cystic, non- cystic)
• Outline of flat neovascularization
• Outline of lattice degeneration (Inner chevrons or Xs)
• Outline of thin areas of retina
• Intra-retinal cysts (with overlying curvilinear stripes to show configuration).
Cross lines
• Inner layer of retinoschisis
• White with or without pressure
• Detached pars plana epithelium anterior to separation of ora
• Outer surface of retina seen in rolled edge of retinal tears, inverted flap of giant retinal tear.
Stippled or circles
• Cystoid degeneration.
Interruped lines
• Outline of change in area or folds of detached retina because of shifting fluid.
Color Code Green Solid
• Opacities in the media (Cornea, anterior chamber, lens, vitreous)
• Vitreous hemorrhage • Vitreous membranes • Hyaloid ring
• Intraocular foreign bodies • Retinal opercula
• Cotton wool patches • Ora serrata pearls
• Outline of elevated neovascularization.
Stippled or dotted
• Asteroid hyalosis
• Frosting or snowflakes on cystoid, retinoschisis, and lattice degeneration.
Color Code Brown Solid
• Uveal tissues • Pars plana cysts
• Ciliary processes (Pars plicata) • Striae ciliaris
• Pigment beneath detached retina • Subretinal fibrosis demarcation lines • Choroidal nevi
• Malignant choroidal melanomas • Metastatic and other choroidal tumors • Choroidal detachment.
Outline
• Chorioretinal atrophy beneath detached retina
• Posterior staphyloma
• Edge of buckle beneath detached retina.
Color Code Yellow Solid
• Intraretinal edema
• Intraretinal or subretinal hard yellow exudates
• Deposits in retinal pigment epithelium • Detached macula in some retinal separations • Retinal edema as a result of photocoagulation,
cryothreapy or diathermy
• Long and short posterior ciliary nerves • Retinoblastoma.
Stippled or dotted
• Drusen
Color Code Black Solid
• Pigment within the detached retina (lattice, flap of horse-shoe tear, paravascular pigmentation)
• Pigment in choroid or pigmented epithelial hyperpigmentation in areas of attached retina • Pigmented demarcation lines at the attached margin of detached retina or within detached retina
• Hyperpigmentation as a result of previous treatment with cryothreapy, photocoagula- tion or diathermy
• Completely sheathed retinal vessels.
Outline
• Partially sheathed vessels (lattices, retino- schisis)
• Edge of buckle beneath attached retina • Long posterior ciliary nerves and vessels
(Pigmented)
• Short posterior ciliary nerves and vessels • Chorioretinal atrophy.
Fig. 10.8: Showing a long-standing, partial, rhegmatogenous
retinal detachment with demarcation lines and intraretinal macrocyst. A horse-shoe tear, lattice degeneration and a retinal dialysis are also seen. An improperly placed scleral buckle effect is made out. Pars plana is detached nasally. Retinoschisis with inner layer hole is seen in inferotemporal periphery. Pars plana cysts are seen inferiorly
Indirect Ophthalmoscopy in Operating Room
Many problems may be encountered whilst operating and performing an indirect ophthalmo- scopy. The fundus to be examined is usually a difficult one, with a retinal detachment and/ or PVR. The cornea may become edematous or abraded during the course of surgery. Particular care must be taken in patients having undergone LASIK surgery to prevent dislocation of corneal flap. The fundus picture may change with each step in surgery. The advantages of indirect ophthalmoscopy in the operation room stem from its safe working distance from the sterile operating field, in accurate localization of all retinal breaks and other fundus landmarks by scleral depression. It helps in obtaining a fine
needle aspiration biopsy and treatment of choroidal or retinal tumors.
Indirect ophthalmoscopy is a valuable tool in the examination of children and uncooperative adults: Since the field of view is much larger with an indirect ophthalmoscope, fundus examination is possible even in moving eye. A quick comparison with the other eye is also possible. Children would generally react more favorably to the more impersonal distance of indirect examination. It is also useful equipment in examining the anterior segment for rubeosis and tumor seedings in children with advanced retinoblastoma.
Fundus angioscopy, and transillumination with the help of a probe (Fig. 10.9) can be per- formed using indirect ophthalmoscopy; which helps in differentiating various types of fundus mass lesions. Nystagmus, aniridia, albinotic fundus, partial vitreous hemorrhage, fundus coloboma, microphthalmos and persistent hyperplastic primary vitreous can be diagnosed with the help of indirect ophthalmoscope.
Fig. 10.9: Transillumination probe Monocular Indirect Ophthalmoscopy Monocular indirect ophthalmoscopy combines the advantages of increased field of view (indirect ophthalmoscopy) with erect real imaging (direct
ophthalmoscopy). By collecting and redirecting peripheral fundus-reflected illumination rays, which cannot be accomplished with the direct ophthalmoscope. The indirect ophthalmoscope (Fig. 10.10) extends the observer’s field of view approximately four to five times. An internal lens system then reinverts the initially inverted image to a real erect one (Fig. 10.11), which is then magnified. This image is focusable using the focusing lever/eyepiece lever. It gives a field of view of approximately 30 degrees, yet it is important that the patient looks in 6 to 8 different directions to see as much of the fundus as possible. The optical system of the monocular indirect ophthalmoscope (MIO) has a lens which erects the image and allows seeing things as they actually appear anatomically. It also gives a greater working distance from the patient of 5 to 6 inches. The MIO has a yellow filter that allows one to see deeper details of the retina at about the level of the choroid. The cost of the MIO is nearly equal to that of a good binocular indirect ophthalmoscope and of course it does not allow a stereoscopic view of the retina.
Examination Procedure
To examine the right eye, remove the patient’s spectacle correction, stand to the patient’s right side, and ask him to fixate straight ahead and level with the left eye. The observer should wear his refractive correction. The iris diaphragm lever is pushed fully to the left to maximally increase the aperture size. Center the red dot on the filter dial to open the aperture for normal viewing. The observer's head should be against the forehead rest and align the eye through the instrument with the patient’s right eye. Then position several inches in front of the patient and focus through the pupil onto the fundus using the thumb and focusing lever. Adjust the focus and iris diaphragm to produce a clear maximally illuminated fundus view. Continue to approach the patient until the observer’s knuckle lightly touches the patient’s cheek, as the working distance decreases, fundus magnification increases. Angle the light slightly nasally to illuminate and visualize the optic disk.
Modified Monocular Indirect Ophthalmoscopy
A thorough fundus examination is important and required in all young patients with strabis- mus or amblyopia in order to rule out organic causes of amblyopia prior to the initiation of treatment. The patient co-operation obtained with head mounted binocular indirect ophthalmo- scope (using a 20 D lens), and slit-lamp biomicroscope (using a 90 D) is usually difficult or impossible on younger children. Also the magnification of the fundus may be inadequate to allow accurate evaluation of posterior pole details. The direct ophthalmoscope is often the best available instrument for detailed retinal examination in young patients.
However, children often become frightened as the examiner approaches closely, as is necessary with the direct ophthalmoscope and co-operation is lost. Additionally children often fix the ophthalmoscope light and track it as the examiner moves it, allowing examination of the Fig. 10.11: Optics of monocular indirect ophthalmoscopy
macula but not of the disk. The field of view is small and the magnification is more than is usually necessary. This will prevent the examiner from seeing the large area of fundus. To avoid these difficulties the direct ophthalmoscope can be used in conjunction with a 20 D condensing lens. This combination provides a moderately magnified and wider angle view of the posterior pole. This avoids the close proximity between the patient and examiner required when using a direct ophthalmoscope alone. This technique is called modified monocular indirect ophthalmo-
scopy and has been noted for its ability to provide
a good view of the retina through a small pupil. Examination Procedure
To begin the examination a red reflex is visualized through the direct ophthalmoscope held approxi- mately 18 cm from the patient’s eye. A 20 D lens is then placed 3 to 5 cm in front of the patient’s eye in the path of the ophthalmoscope light beam, the examiner then needs to move slightly toward or away from the patient until a clear image of the retina is observed.
An inverted, aerial image of the retina is produced, located between the observer and the