Ophthalmoscopy 151

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

Ophthalmoscopy 153

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 pluspowered 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 placement, 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.

154 Diagnostic Procedures in Ophthalmology

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

Ophthalmoscopy 155

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.

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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, noncystic)

•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, photocoagulation or diathermy

•Completely sheathed retinal vessels.

Outline

•Partially sheathed vessels (lattices, retinoschisis)

•Edge of buckle beneath attached retina

•Long posterior ciliary nerves and vessels (Pigmented)

•Short posterior ciliary nerves and vessels

•Chorioretinal atrophy.

Ophthalmoscopy 157

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 ophthalmoscopy. 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

158Diagnostic Procedures in Ophthalmology

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 performed 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

Fig. 10.10: Monocular indirect ophthalmoscope

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.

160Diagnostic Procedures in Ophthalmology

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 ophthalmoscopy 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 approximately 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 lens. The apparent magnification will gradually increase as the examiner moves closer to this image (i.e. closer to the patient), allowing more detailed examination. Moving closer to the image obtains a magnification of X4 to X5. As the examiner moves closer additional lenses in the ophthalmoscope are needed, to keep the image clear depending on the accommodative needs of the examiner. A viewing distance of approximately 18 cm from the patient is optimal, providing suitable magnification and a wide field of view

A disadvantage of the technique, as with conventional direct ophthalmoscopy is the lack of a true stereoscopic view, however, lateral movement and rotation of the direct ophthalmo-

scope during the examination gives good parallax clues to depth.

Penlight Ophthalmoscopy

This is a very old, basically a bedside technique that originally utilized a penlight and a high plus lens. The patient must be dilated to get as much binocularityaspossibleandlargefieldofview.The ophthalmoscope is held just below the eyes and its light directed into the patient’s eye. The patient’s eye is viewed from over the top of the ophthalmoscope while a 20 D lens is placed approximately3-4cmfromthepatient’seye.The light leaving the condensing lens must come to focuswithinthepupilallowingthefullestfieldof viewoftheretina,approximately30degrees.The imageisinvertedandlaterallyreversedandlocated betweentheophthalmoscopeandthecondensing lens.Thedegreeofstereopsisdependsonhowfully the pupil is dilated and one’s ability to converge and accommodate on the image. It gives a larger fieldofviewthanaMIOthoughlessmagnification. This is an alternative method to examine small infants.ShouldthebulbburnoutinaBIOonehas an alternative means to get a good view of the peripheral fundus? Do not put hands on the patient’s shoulder or head. Instead, use the back of the chair to steady yourself.

Direct Ophthalmoscopy

Direct ophthalmoscope (Fig. 10.12) is most commonly used instrument in ophthalmic practice. The ophthalmologist must familiarize oneself with the use of the direct ophthalmoscope in an appropriate manner.

Before being able to recognize the abnormalities in fundus, one must know what normal looks like. It is advisable to examine as many of your colleagues as possible both inside and outside clinic hours. Good observational and recording skills can be developed with practice.

Fig. 10.12: Direct ophthalmoscope

Examination Procedure

Direct ophthalmoscopy is best carried out in a dark room with fully dilated pupils. One must be familiar with the color coding of the lens wheel and the various apertures and filters. Instruct the patient to look at a distant target (the white spot light on the vision chart) and to ‘pretend’ to still see it even if obscured with your head. The patient may blink as required. Your left eye and left hand should be used to examine the patient’s left eye. The field of view of the fundus is increased when examiner goes closer to the patient’s eye. When patients with low myopes or low hyperopes are to be examined, it is better to remove their glasses. However, for myopes and hyperopes above ± 3.00 DSph and for astigmats above 2.50 DCyl, it is advisable to keep the glasses on in order to overcome problems associated with magnification, minification and distortion. The extra reflexes produced by the spectacle lenses will at first prove distracting but can be overcome with practice.

Ophthalmoscopy 161

Using a large diameter aperture, examine the external features of the eye including pupils. With a +1 or +2 D lens in the ophthalmoscope, view the pupils at a distance of 40 to 66 cms from the patient. Look for media opacities. To find the location of the opacity, note movement of the opacity with relation to the movement of the ophthalmoscope, using the pupillary plane as a reference point. If the opacity moves in the same direction as the ophthalmoscope, the opacity is located behind the iris. If the opacity moves in the opposite direction to the ophthalmoscope, the opacity is located in front of the iris.

Using the ophthalmoscope as a light source, which is held tangential to the iris one looks for any shadow that appears on the nasal side. If the nasal irido-corneal angle has no shadow, it denotes a wide-open angle. However, as this shadow increases in width relative to the overall cornea size, the angle seems narrow.

Dial up +10 DSph lens in the lens wheel and observe the eye from a distance of 10 cm. Study the red reflex to detect any media opacity. The position of opacity can be inferred from its parallax with respect to the pupil. When the patient looks up and the opacity appears to move in the same direction within the red-reflex then it is located anterior to the pupil plane (i.e. in the cornea or in the anterior chamber). Opacity that remains stationary lies in the plane of the pupil but when it moves in the opposite direction to that of the patient’s gaze it lies posterior to the pupil plane (i.e. the posterior lens or vitreous). It may be easier to move yourself slightly from side to side rather than ask the patient to move his eye to achieve the same effect. During ophthalmoscopy it is advisable to keep both eyes open and suppress the image from the other eye. It may take some practice to accomplish this.

It is better to move closer to the patient and gradually reduce the power of the lens in the wheel and focus on the crystalline lens, the vitreous and finally the fundus. The power of

162Diagnostic Procedures in Ophthalmology

lens necessary to focus on the fundus will depend on patient’s and observer’s uncompensated refractive error and accommodation. Once a blood vessel on the fundus is located, move along it and locate the point at which it branches. Then move your field of view in the direction in which the apex of the branch is pointing till you reach the optic disk.

If one controls his accommodation it allows for an estimation of the patient’s refractive error by focusing the optic disk. Retinal blood vessels should be examined in each quadrant after locating the disk. Artery to vein ratio (A/V), arteriolar light reflex (ALR), branching of vessels to all four quadrants and crossing phenomenon must be assessed.

Once again focus the disk and move nasally to view the macula. In this position you may obscure the fixation target, cause the pupil to constrict, dazzle the patient and notice some troublesome corneal reflections. These factors make the macula a difficult area to visualize. It may be useful to use a smaller aperture beam. The patient should not be asked to look into the light when viewing the macula through an undilated pupil. The patient will accommodate and this together with the bright light from the ophthalmoscope will make the pupil even smaller reducing the ability to view the whole macular area.

Finally ask the patient to look in the eight cardinal directions to view the peripheral fundus. You will need to adjust the lens in the wheel slightly as the periphery is closer to you than the optic disk requiring more focusing power (plus lens). The red-free filter makes small macroaneurysms and small hemorrhages standout more clearly. It can also be helpful in estimating the C/D ratio. It is also used to differentiate between retinal nevus and choroidal nevus. The retinal blood supply and its retinal pigment epithelium (RPE) act like a red filter.

Therefore, a nevus that lies behind the retina and located in the choroid will not be seen when viewed with the red-free filter. On the other hand a nevus located on or in the retina will still be seen with the red-free filter in place. A cobaltblue filter is useful in detection of nerve fibers drop out.

The direct ophthalmoscope gives a magnificationofapproximatelyX15andafieldofviewof 6.5 to 10 degrees. The formula M= 60 D/4 holds well for up to + or –10 Ds of refractive error.

Hruby Lens Direct Ophthalmoscopy

The use of the slit-lamp biomicroscope allows a stereoscopic view of the retina. The auxiliary lenses provide high magnification with excellent resolution. The Hruby lens (-55 D) produces an upright virtual image that is not laterally reversed.

Examination Procedure

Patient co-operation can be enhanced by attention to his comfort and with the use of a fixation device. Once the illuminated slit is imaged in the patient’s pupil, the Hruby lens is introduced in front of the patient’s eye as close as possible without contacting the cornea or lashes.

This mode of direct ophthalmoscopy can provide a very high level of magnification, even greater than that of the monocular hand held direct ophthalmoscope. The actual level of magnification depends on that available through the slit-lamp. Stereopsis is provided to a greater degree than all other examination techniques.

The main disadvantage of this technique is the field of view. It is smaller than all other examination methods with the exception of direct monocular ophthalmoscopy (less than two disk diameters for an emmetropic patient). More dilation is required than in other binocular

techniques. The quality of the image is easily degraded by media opacities; however, increasing the slit-lamp illumination can reduce this problem. As the magnification is so high, small movements of the observer, lens, or patient have an immediately noticeable effect on image quality.

Wide-Angle Viewing System

Retcam

The Retcam (Fig. 10.13) has a 3 CCD chip video camera. It is lightweight, easy to position and has a long cable for easy patient access. It has five changeable lenses: 130°, 120°, 80°, 30° and Potrait. It has a large LCD display with 20 seconds of real time video per clip and a frame- by-frame or real time video review. It has a lighted control panel, a dual DVD-RAM for easy backup, multi-image data recall and display, side by side image comparison, high resolution 24 bit color image, instant-digital image capture and

Fig. 10.13: Retcam viewing system

Ophthalmoscopy 163

Fig. 10.14: Wide-angle fundus photograph (Retcam) of a premature infant showing retinopathy of prematurity with a demarcation ridge clearly made out

Fig. 10.15: Fundus photograph (Retcam) of a premature infant showing retinopathy of prematurity with laser photocoagulation marks. Preretinal hemorrhage is seen beyond the superotemporal vascular arcade

is US FDA approved. It provides a 130° view for easy screening for retinopathy of prematurity (Figs 10.14 and 10.15), integrated image and patient management capabilities, comprehensive photodocumentation, fluorescein angiography and built-in software for reporting, storage and archiving.

Panoret

Panoret (Fig. 10.16) is a high resolution, wideangle retinal camera based on an innovative

164 Diagnostic Procedures in Ophthalmology

Fig. 10.16: Panoret

transscleral illumination concept using a fiber optic bundle, where no pupillary dilatation is necessary. Coverage angles are 50° and 100° with interchangeable front lens assembly. It is computer assisted in auto-light, auto-brightness and contrast control along with auto-disk storage.

Fundus illumination may, however, be limited in heavily pigmented eyes. DVD recording is possible. DICOM 3.0 connectivity is available for telemedicine.

Bibliography

1.Yanoff M, Duker JS, Augsburger JJ, et al (Eds). Ophthalmology (2nd edn). St. Louis, Mosby, 2004.

2.Benson WE, Regillo CD: Retinal detachment— Diagnosis and Management (3rd edn). Lippincott-Raven, Philadelphia, 1998;75-99.

3.Regillo CD. Brown GC, Flynn Jr HW. Vitreoretinal Disease—The Essentials. Thieme, New York, 1999;41-49.

4.Schepens CL, Hartnett ME, Hirose T: Schepens’ Retinal Detachment and Allied Diseases (2nd edn). Butterworth-Heinemann, Boston, 2000;99129.

5.Rosenthal ML, Fradin S: The technique of binocular indirect ophthalmoscopy. Highlights of Ophthalmology 1967; 9:179-257.

6.Michels RG, Rice TA, Wilkinson CP. Retinal Detachment (2nd edn). Mosby, St. Louis, 1997; 347-70.

7.Havener WH, Gloekner S. Atlas of Diagnostic techniques and Treatment of Retinal Detachment. Mosby, St. Louis, 1997;1-51.