Ординатура / Офтальмология / Английские материалы / Retinal and Vitreoretinal Diseases and Surgery_Boyd, Cortez, Sabates_2010
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Optical Systems for Ocular Diagnosis and Vitreoretinal Surgery
Ultrasound B
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Purpose of the Ultrasound B
Ultrasound imaging equipment (type B), allows retina specialists to «see» the eye in great detail without the pain and risk of exploratory surgery, or the limitations and uncertainty inherent in traditional visual examination. Ultrasound is used to detect and diagnose many eye diseases (retinal detachments, vitreous hemorrhages) and injuries (intraocular foreign bodies), to measure the eye prior to corrective surgery, and directly as a treatment tool (Figure 3).
Anophthalmologistusesultrasonicimaging to help diagnose the underlying cause(s) of a patient’s symptoms, to assess the general condition of an injured eye, and to evaluate the eye prior to surgery. Situations that may call for ultrasonic imaging include:
1).Excessive tearing or visible infection. These external symptoms could indicate a serious underlying problem such as a tumor, an internal infection, the presence of a deeply
Figure 3: B-Scan Ultrasound for Detection of Vitreoretinal Diseases. The B-scan ultrasound computerized technology helps surgeons detect vitreoretinal diseases such as retinal detachments, vitreoretinal tractions, vitreous hemorrhages and luxated crystalline lenses or intraocular lenses. In this B-scan picture you may observe a large retinal detachment with traction over the central visual axis (arrow).
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lodged irritant (foreign body), or the effects of a previously unrecognized injury. When a patient presents with general symptoms, ultrasound can speed diagnosis if a serious condition is suspected.
2). Impaired vision. Fuzzy vision, poor night vision, restricted (tunnel) vision, blind spots, extreme light sensitivity, and even blindness can all stem from inner eye conditions ranging from glaucoma and cataracts, to retinitis, detached retina, tumors, or impaired blood circulation.
3). Eye trauma. The eye can be damaged by a direct impact or a puncture wound, as a result of a general head trauma, or by
intense light exposure. Even when the cause of injury is obvious, ultrasound can reveal the exact type, extent, and location of damage, from deformations and ruptures to internal bleeding, and help guide emergency care efforts.
Importance of Binocular
Indirect Ophthalmoscopy
An important era began in the late 1940’s, when Charles Schepens introduced the binocular indirect ophthalmoscope (Figures 4 A-K). It is, by far, the most valuable instrument available for evaluation of the detached retina and other pathologies of the
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Figure 4 A-B: Precise Way to Hold Condensing Lens. Figure |
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Figure 4C: Examining the Patient’s Left Eye. Examiner is observing superonasal quadrant of patient‘s left eye fundus. He stands to left of patient, and third finger of left hand controls lower lid. Right hand controls head, and thumb of right hand controls upper lid. To observe temporal half of left fundus, examiner should stand on right side of patient. Left third finger then controls upper lid, and right thumb retracts lower lid.
Figure 4D: Examining the Patient’s Right Eye. Observer is standing on left side of patient, examining superior retina, and is shown holding lens in his left hand. Thumb and index finger control lens, and third finger simultaneously retracts lower lid. Right hand is used to control patient‘s head, and thumb of this hand retracts upper lid. These hand positions permit examination of entire temporal half of right fundus. To observe nasal half, examiner should stand on right side of patient. Left third finger will now be used to hold upper lid, and right thumb now retracts lower lid. Considerable movement of examiner’s body and head will be necessary to see entire fundus.
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Figure 4E: Coordinated Movement of Observer‘s Head and Tilting of Lens. The coordinated movement of the observer’s head and the tilting of the lens is a maneuver that takes considerable practice. The head is not moved on the neck but, rather, the whole torso is moved from side to side and forward and backward while the lens is appropriately tilted. It is essential to practice this maneuver until it is completely natural and automatic.
Axis is formed by examiner’s visual axis (split by prisms in headpiece), condensing lens, patient’s pupil, and area of fundus under study. Fulcrum of this axis is patient’s pupil (Figure 4F). In order to observe another part of fundus, observer’s head must move and lens tilt in such way that new axis also has its fulcrum in pupil.
Figure 4F: Enables view of fundus through cloudy media or around partial intraocular opacities. Excellent survey technique allowing large field of view. Allows easier examination of peripheral fundus than direct ophthalmoscopy. Facilitates determination of fundus depressions and elevations. Fundus examination is faster and comparison between eyes is easier. A supplemental mirror can be attached to many binocular indirect models, permitting simultaneous visualization by examiner, student, colleague or client.
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Figure 4G: Drawing of Fundus - Relationship of Fundus Chart to Patient‘s Eye. Chart is used, inverted, for a precise drawing of the retina. The 12 o’clock position on chart corresponds to the 6 o’clock position of patient’s eye. Likewise, the 6 o’clock position on chart corresponds to 12 o’clock position on patient’s eye. When the fundus is viewed through the condensing lens (20 dp), the inverted image seen through the lens will exactly correspond to the orientation of chart. The information in lens image can be directly drawn on inverted chart.
Figure 4H: Fundus Image Inverted. The fundus image in the condensing lens is completely inverted; that is, the image is upside down and also backwards as regards right and left. Left eye is being examined (inset). In drawing this image, it should be copied just as seen on inverted drawing chart, thus preserving normal relationships. If you look up and temporal in the patient’s eye, since the image is inverted, do you see the lower nasal part of the fundus? The answer is NO. You always see the areas which you are looking at. However, whatever field you see in the condensing lens will be inverted.
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Figure 4I: Scleral Depression. Showing depressor being applied to patient’s eye, with patient looking down. When patient looks up and depressor is introduced, examiner will be in position to see superonasal periphery.
Figure 4J: Performing Scleral Depression Through the Lids. Figure a, shows the approximately six positions of depressor on lids, sufficient to provide view of entire periphery with exception of 9 and 3 o’clock positions. Figure b, shows how, in most patients, it is possible to drag upper lid down enough to visualize nasal horizontal meridian. Figure c, shows how it is usually possible to drag upper lid down enough to examine temporal horizontal meridian.
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Figure 4K: Lateral View of Indirect Ophthalmoscopy. This side view shows a right eye observation of the retina. A proper pupil dilatation will help the surgeon through thecompletepreoperative evaluation of the retina including periphery. Since retinal detachments may present with different characteristics as peripheral degenerations and tears even in different quadrants, is imperative to observe every detail along the four quadrants of the retina.
retina and vitreous. The current high rate of reattachment is due not only to improvements in surgical technique but also to improved methods of ocular examination. Additional important information is obtained with the Goldmann three-mirror lens.
Lasers for Early Detection of Retinal Disease
Early detection and treatment of retinal disease can dramatically improve patients’ prognosis. The advent of new laser technology is helping ophthalmologists to identify and chart structural change in this lightsensitive membrane from the earliest stages. Conventional or direct ophthalmoscopy gives good two-dimensional images of the retina, revealing changes to the surface of the membrane that may indicate various disorders.
In cases of diabetic retinopathy, for example, blood vessels begin to leak, and the retina thickens—sometimes before the patient notices any visual impairment or other symptoms.
However, this conventional method of examining the retina does not enable the clinician to quantify the structural changes identified. The challenge of recent years has been to find ways to view the retina stereoscopically and to measure the pathology seen so that the diagnosis and monitoring of disease, and response to treatment, may become much more accurate.3
The advent of technologies such as the scanning laser ophthalmoscope promises a much deeper understanding of retinal pathology and more accurate assessment of effective treatment options.
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Scanning Laser
Ophthalmoscope (SLO)
The scanning laser ophthalmoscope gener- atesasuccessionofthree-dimensionalcomputer images of the retina, enabling the operator to create a topographic map of the membrane and its contours.
The Scanning Laser Ophthalmoscope (SLO) was invented by Webb, Pomeranzeff, and Hughes in 1979. It used a very narrow moving beam of light which could bypass most ocular media opacities (i.e. corneal scars, cataracts, vitreous hemorrhage) to reach the surface of the retina and record its surface detail. A live video image of the retina was displayed on a computer monitor and test results were digitally recorded. Several diagnostic tests were possible with this machine.4,5
Conventional fundus imaging using a fundus camera produces color fundus pictures. The scanning laser ophthalmoscope (SLO) has the advantages of lower levels of light exposure, improved contrast, and direct digital imaging. The background fundus and retinal vasculature have similar appearances with the two imaging modalities. Internal limiting membrane reflections are prominent with the SLO. Identification of new vessels in the diabetic fundus is easier with the SLO than with color fundus photographs. A color SLO offers all the advantages of the present monochromaticimagingsystemwiththeadded advantage of true color representation of the fundus
SLO microperimetry might be effective for quantitative assessment of retinal sensitivity in retinal scars and for detecting fixation points and determining their stability.
Scanning laser ophthalmoscopy is a retinal imaging technique that is based on the standard scanning laser microscope. The important difference is that in scanning laser ophthalmoscopy, the optics of the eye serve as the objective lens. Scanning laser ophthalmoscopes and microscopes, when equipped with a confocal aperture, offer fundamentally better performance than conventional imaging instruments. The confocal SLO generates high contrast images and can do optical slicing through weakly scattering media, making it ideal for imaging the multilayered retina.
Wide Angle Fundus Observation System for Vitreoretinal Surgery
Fundus visualization during entire vitreoretinal surgery is a must especially while operating complicated cases.
Proper visualisation of posterior pole and periphery helps surgeon to perform difficult steps with safety and efficacy and also avoid unwanted complications.
For this purpose non-contact wide angle observation systems like BIOM and EIBOS are ideal.6
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The wide angle viewing system currently include:
-The BIOM noncontact system with a field of view of 70°, 90° or 110°.
-The EIBOS noncontact system with a field of view of 100° for 90 – diopter and 125° for 60 – diopter.
-The VOLK reinverting operating lens system (ROLS); can be used to visualize up to vitreous base and ora serrata.
Wide angle viewing systems can be used in cases of retained lens mater and removal of displaced intraocular lens as surgery at the posterior pole as well as proper inspection of the periphery of the fundus is possible using the same viewing system. In cases of diabetic patients, panretinal photocoagulation, dissection of tightly adherent membranes and gas fluid exchange are all facilitated. While working in one area, remote traction with impending development of tears or haemorrhage can be visualised in phakic, aphakic and pseudophakic patients. Surgical procedures like dissection of anterior proliferative vitreoretinopathy, gas fluid exchanges and silicone oil installation both a gas – silicone oil exchange as well as perfluorocarbon liquid silicone exchange can be performed with the same viewing system maintaining proper focus of the desired area.
Surgery for retinopathy of prematurity is best performed using the noncontact systems,
because of the decreased scleral rigidity of the infant eye and the small size of the cornea with a steep corneal curvature.7
Optical Coherent Tomography (OCT)
With the optical coherence tomography (OCT), the patterns generated by the reflection of laser beams are used to build a cross-sectional image of the retina. OCT is an excellent tool for detecting submacular abnormalities, monitoring macular holes, and guiding laser treatment.8
With OCT, the macula is scanned and 600 scan points are achieved. The scan points are displayed as a retinal thickness map. This technique has allowed investigators to determine that the normal central retinal thickness is 150 mm.
In patients with an epiretinal membrane andmacularedema,forexample,OCTprovides a unique, cross-sectional view of the retina that is not available with other techniques.
Conclusion
Such modern technologies offer great potential benefits to both patients and clinicians. They dramatically increase the scope for early detection and treatment of several vitreoretinal diseases.
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References
1.Boyd S. Fundus Examination Techniques.In: Retinal and Vitreoretinal Surgery. Highlights of Ophthalmology. 2002;5-16.
2.Li HK. Telemedicine and Ophthalmology. Survey of Ophthalmology 1999; 44(1):61-72
3.Boyd BF. World Atlas Series of Ophthalmic Surgery.1997;Vol. III,198-199.
4.Marcus DM, Brooks SE, Ulrich LD, Bassi FH, Laird M, Johnson M and Newman C. Telemedicine Diagnosis of Eye Disorders by Direct Ophthalmoscopy: A Pilot Study. Ophthalmology 1998; 105(10), 1907-1914.
5.J. Liang, D. R. Williams, and D. Miller, “Supernormal vision and high-resolution retinal imaging through adaptive optics,” J. Opt. Soc. Am. A 14, 2884-2892 (1997).
6.Natarajan S, Patel N, Mehta H, Dongargaonkar S. Advances in vitreoretinal surgery. Journal of the Bombay Ophthalmologists’ Association; Vol. 14 No. 1, 2005.
7.Initial experience using the transconjunctival sutureless vitrectomy system for vitreoretinal surgery: Fujii GY, De Juan E Jr, Humayun MS, Chang TS, Pieramici DJ Barnes A, Kent D. Ophthalmology. 2002 Oct; 109(10): 181420.
8.BoydS,ConcepciònA.EvolutionofOpticalCoherence Tomography. In: Optical Coherence TomographyAtlas and Text. Highlights of Ophthalmology. 2009; 147-150.
Suggested Readings
Boyd, BF. Retinal detachment surgery. World Atlas Series of Ophthalmic Surgery, Vol. III. 1997.
Elsner, AK, lalkh, AH, and Weiter 1l. New devices in retinal imaging and functional evaluation, in Practical Atlas of Retinal Disease and Therapy, W. Freeman (ed), Raven, NewYork, 1993, 19-35.
Fine BS, Yanoff M. Ocular histology: a text and atlas. 2d ed. Hagerstown, Md: Harper & Row, 1979:6-61.
Gutman FA. Evaluation of a patient with central retinal vein occlusion. Ophthalmology 1983;90(5):481-3.
Hartnett ME, Elsner AK. Characteristics of exudative age-related macular degeneration determined in vivo with confocal and indirect infrared imaging. Ophthalmology 103:58-71, 1996.
LeGrand’s Full Theoretical Eye (from Wyszecki & Stiles, 1982, pg 99)
Roorda, A., Campbell, M.C.W. & Cui, C. (1997) Optimal entrance beam location improves high resolution retinal imaging in the CSLO. Investigative Ophthalmology and Visual Science Supplem. 38, 1012