Ординатура / Офтальмология / Английские материалы / Clinical Ophthalmology A Systematic Approach 7th Edition_Kanski, Bowling_2011

kanski 7th

Fig. 16.5 Retinal tears. (A) Complete U-shaped; (B) linear; (C) L-shaped; (D) operculated; (E) dialysis

Fig. 16.6 (A) Giant retinal tear involving the immediate post-oral retina; (B) vitreous cortex is attached to the anterior margin of the tear

(Courtesy of CL Schepens, ME Hartnett and T Hirose, from Schepens’ Retinal Detachment and Allied Diseases, Butterworth-Heinemann, 2000)

Clinical examination

Head-mounted indirect ophthalmoscopy

1Principles. Indirect ophthalmoscopy provides a stereoscopic view of the fundus. The light emitted from the instrument is transmitted to the fundus through a condensing lens held at the focal point of the eye, which provides an inverted and laterally reversed image of the fundus (Fig. 16.7A). This image is observed using a special viewing system in the ophthalmoscope. As the power of the condensing lens decreases the working distance and the magnification increase but the field of view is reduced, and vice versa.

2Condensing lenses of various powers and diameters are available for indirect ophthalmoscopy (Fig. 16.7B).

•20 D (magnifies ×3; field about 45°) is the most commonly used for general examination of the fundus.

•25 D (magnifies ×2.5; field is about 50°).

•30 D (magnifies ×2; field is 60°) has a shorter working distance and is useful when examining patients with small pupils.

•40 D (magnifies ×1.5; field is about 65°) is used mainly to examine small children.

•Panretinal 2.2 (magnifies ×3; field is about 55°).

879 / 1137

kanski 7th

3Technique

aBoth pupils are dilated with tropicamide 1% and, if necessary, phenylephrine 2.5% so that they will not constrict when exposed to a bright light during examination.

bThe patient should be in the supine position with one pillow, on a bed (Fig. 16.8), reclining chair or couch and not sitting upright in a chair.

cThe examination room is darkened.

dThe eyepieces are set at the correct interpupillary distance and the beam aligned so that it is located in the centre of the viewing frame.

eThe patient is instructed to keep both eyes open at all times.

fThe lens is taken into one hand with the flat surface facing the patient and throughout the examination is kept parallel to the patient's iris plane.

gIf necessary, the patient's eyelids are gently separated with the fingers.

hIn order to enable the patient to adapt to the light he should be asked to look up and the superior peripheral fundus should be examined first.

iThe patient is asked to move the eyes and head into optimal positions for examination. For example, when examining the extreme retinal periphery, the patient is asked to look away from the examiner.

Fig. 16.7 (A) Principles of indirect ophthalmoscopy; (B) condensing lenses

Fig. 16.8 Position of patient during indirect ophthalmoscopy

Scleral indentation

880 / 1137

kanski 7th

1Purposes. Scleral indentation should be attempted only after the art of indirect ophthalmoscopy has been mastered. Its main function is to enhance visualization of the peripheral retina anterior to the equator (Fig. 16.9); it also permits a kinetic evaluation of the retina.

2Technique.

aTo view the ora serrata at 12 o’clock, the patient is asked to look down and the scleral indenter is applied to the outside of the upper eyelid at the margin of the tarsal plate (Fig. 16.10A).

bWith the indenter in place, the patient is asked to look up; at the same time the indenter is advanced into the anterior orbit parallel with the globe (Fig. 16.10B).

cThe examiner's eyes are aligned with the condensing lens and indenter.

dGentle pressure is exerted so that a mound is created (Fig. 16.10C) and the indenter is then moved to an adjacent part of the fundus. The indenter should be kept tangential to the globe at all times, as perpendicular indentation will cause pain.

Fig. 16.9 Appearance of retinal breaks in detached retina. (A) Without scleral indentation; (B) with indentation

Fig. 16.10 Technique of scleral indentation. (A) Insertion of indenter; (B) indentation; (C) mound created by indentation

(Courtesy of NE Byer, from The Peripheral Retina in Profile, A Stereoscopic Atlas, Criterion Press, Torrance, California, 1982 – fig. C)

Goldmann three-mirror examination

1Goldmann three-mirror lens consists of four parts; the central lens and three mirrors set at different angles. Because the

881 / 1137

kanski 7th

curvature of the contact surface of the lens is steeper than that of the cornea, a viscous coupling substance with the same refractive index as the cornea is required to bridge the gap between the cornea and the goniolens. It is important to be familiar with each part of the lens as follows (Fig. 16.11):

•The central part provides a 30° upright view of the posterior pole.

•The equatorial mirror (largest and oblong-shaped) enables visualization from 30° to the equator.

•The peripheral mirror (intermediate in size and square-shaped) enables visualization between the equator and the ora serrata.

•The gonioscopy mirror (smallest and dome-shaped) may be used for visualizing the extreme retinal periphery and pars plana.

•It is therefore apparent that the smaller the mirror, the more peripheral the view obtained.

2Mirror positioning

•The mirror should be positioned opposite the area of the fundus to be examined; to examine the 12 o’clock position the mirror should be positioned at 6 o’clock.

•When viewing the vertical meridian, the image is upside down but not laterally reversed, in contrast to indirect ophthalmoscopy. Lesions located to the left of 12 o’clock in the retina will therefore also appear in the mirror on the left-hand side (Fig. 16.12).

•When viewing the horizontal meridian, the image is laterally reversed.

3Technique

aThe pupils are dilated.

b The locking screw of the slit-lamp is unlocked (Fig. 16.13A) to allow the illumination column to be tilted (Fig 16.13B).

cAnaesthetic drops are instilled.

dCoupling fluid (high viscosity methylcellulose or equivalent) is inserted into the cup of the contact lens; it should be no more than half full.

eThe patient is asked to look up; the inferior rim of the lens is inserted into the lower fornix (Fig. 16.14A) and quickly pressed against the cornea so that the coupling fluid is retained (Fig. 16.14B).

fThe illumination column should always be tilted except when viewing the 12 o’clock position in the fundus (i.e. with the mirror at 6 o’clock).

gWhen viewing horizontal meridians (i.e. 3 and 9 o’clock positions in the fundus) the column should remain central.

hWhen viewing the vertical meridians (i.e. 6 and 12 o’clock positions) the column can be positioned left or right of centre (Fig. 16.15).

iWhen viewing oblique meridians (i.e. 1.30 and 7.30 o’clock) the column is kept right of centre, and vice versa when viewing the 10.30 and 4.30 o’clock positions.

jWhen viewing different positions of the peripheral retina the axis of the beam is rotated so that it is always at right angles to the mirror.

kTo visualize the entire fundus the lens is rotated for 360° using first the equatorial mirror and then the peripheral mirrors.

lTo obtain a more peripheral view of the retina the lens is tilted to the opposite side asking the patient to move the eyes to the same side. For example, to obtain a more peripheral view of 12 o’clock (with mirrors at 6 o’clock) tilt the lens down and ask the patient to look up).

m The vitreous cavity is examined with the central lens using both a horizontal and a vertical slit beam (Fig. 16.16).

nThe posterior pole is examined.

Fig. 16.11 The Goldmann three-mirror lens

882 / 1137

kanski 7th

Fig. 16.12 (A) U-tear left of 12 o’clock and an island of lattice degeneration right of 12 o’clock; (B) the same lesions seen with the three-mirror lens positioned at 6 o’clock

Fig. 16.13 Preparation of the slit-lamp for fundus examination. (A) Unlocking the screw; (B) tilting the illumination column

883 / 1137

kanski 7th

Fig. 16.14 (A) Insertion of the three-mirror lens into the lower fornix with the patient looking up; (B) three-mirror lens in position

Fig. 16.15 The illumination column is tilted and positioned right of centre to view the oblique meridian at 1.30 and 7.30 o’clock

884 / 1137

kanski 7th

Fig. 16.16 Biomicroscopy showing posterior vitreous detachment without collapse. The posterior hyaloid face is indicated by the long arrow ‘a’ and the retina by the short arrow ‘b’

(Courtesy of CL Schepens, CL Trempe and M Takahashi, from Atlas of Vitreous Biomicroscopy, Butterworth-Heinemann, 1999)

Fundus drawing

1Technique. The image seen with indirect ophthalmoscopy is vertically inverted and laterally reversed. This phenomenon can be compensated for when viewing the fundus if the top of the chart is placed towards the patient's feet (i.e. upside down). In this way the inverted position of the chart in relation to the patient's eye corresponds to the image of the fundus obtained by the observer. For example, a U-tear at 11 o’clock in the patient's right eye will correspond to the 11 o’clock position on the chart; the same applies to the area of lattice degeneration between 1 o’clock and 2 o’clock (Fig. 16.17A).

2Colour Code (Fig. 16.17B)

a The boundaries of the RD are drawn by starting at the optic nerve and then extending to the periphery.

bDetached retina is shaded blue and flat retina red.

cThe course of retinal veins is indicated with blue. Retinal arterioles are not usually drawn unless they serve as a specific guide to an important lesion.

d Retinal breaks are drawn in red with blue outlines; the flat part of a retinal tear is also drawn in blue.

eThin retina is indicated by red hatching outlined in blue, lattice degeneration is shown as blue hatching outlined in blue, retinal pigment is black, retinal exudates yellow, and vitreous opacities green.

885 / 1137

kanski 7th

Fig. 16.17 Technique of drawing retinal lesions. (A) Position of the chart in relation to the eye; (B) colour coding for documenting retinal pathology

Finding the primary break

The primary break is the one responsible for the RD. A secondary break is not responsible for the RD because it was either present before the development of the RD or formeds after the retina detached. Finding the primary break is of paramount importance and aided by the following considerations.

1Distribution of breaks in eyes with RD is approximately as follows: 60% in the upper temporal quadrant; 15% in the upper nasal quadrant; 15% in the lower temporal quadrant; 10% in the lower nasal quadrant. The upper temporal quadrant is therefore by far the most common site for retinal break formation and should be examined in great detail if a retinal break cannot be detected initially. It should also be remembered that about 50% of eyes with RD have more than one break, and in most eyes these are located within 90° of each other.

2Configuration of SRF is of relevance because SRF spreads in a gravitational fashion, and its shape is governed by anatomical limits (ora serrata and optic nerve) and by the location of the primary retinal break. If the primary break is located superiorly, the SRF first spreads inferiorly on the same side as the break and then spreads superiorly on the opposite side of the fundus. The likely location of the primary retinal break can therefore be predicted by studying the shape of the RD.

aA shallow inferior RD in which the SRF is slightly higher on the temporal side points to a primary break located inferiorly on that side (Fig. 16.18A).

b A primary break located at 6 o’clock will cause an inferior RD with equal fluid levels (Fig. 16.18B).

cIn a bullous inferior RD the primary break usually lies above the horizontal meridian (Fig. 16.18C).

dIf the primary break is located in the upper nasal quadrant the SRF will revolve around the optic disc and then rise on the temporal side until it is level with the primary break (Fig. 16.18D).

eA subtotal RD with a superior wedge of attached retina points to a primary break located in the periphery nearest its highest border (Fig. 16.18E).

fWhen the SRF crosses the vertical midline above, the primary break is near to 12 o’clock, the lower edge of the RD corresponding to the side of the break (Fig. 16.18F).

The above points are important because they aid in prevention of the treatment of a secondary break whilst overlooking the primary break. It is therefore essential to ensure that the shape of the RD corresponds to the location of a presumed primary retinal break.

3History. Although the location of light flashes is of no value in predicting the site of the primary break, the quadrant in which a visual field defect first appears may be of considerable value. For example, if a field defect started in the upper nasal quadrant the primary break is probably located in the lower temporal quadrant.

886 / 1137

kanski 7th

Fig. 16.18 Distribution of subretinal fluid in relation to the location of the primary retinal break (see text)

Ultrasonography

B-scan ultrasonography (US) is very useful in the diagnosis of RD in eyes with opaque media, particularly severe vitreous haemorrhage that precludes visualization of the fundus (see Figs 17.1C and D).

Principles

1Definitions. Ultrasound is defined as sound that is beyond the range of human hearing. Ultrasonography uses high frequency sound waves to produce echoes as they strike interfaces between acoustically distinct structures.

2The transducer consists of a piezoelectric crystal which, when stimulated with an electric current, vibrates at such a frequency as to emit ultrasonic waves. If the crystal is hit by ultrasonic waves it produces an electric current. Ultrasonic waves reflected by tissues return through the probe, are absorbed by the crystal which produces a proportional electric current which is sent to the receiver. The signal is then processed and displayed as an echo on the screen. Amplification displays differences in the strengths of reflected echoes. Electric current is passed through the crystal and then switches off in a rapid cycle in order that ultrasound may be emitted and then absorbed.

3Probes may be vector or linear. In a vector probe one main source of ultrasound oscillates back and forth to produce a sweep of ultrasound. In a linear probe multiple sources of ultrasound are aligned in a grid to cover a specific area. The amount of reflected sound is portrayed as a dot of light. The more sound reflected, the brighter the dot. B-scan two-dimensional ultrasonography provides topographic information concerning the size, shape and quality of a lesion as well as its relationship to other structures. Three-dimensional imaging is also available. Uses include: measurement of tumour volume and to enhance localization of a radioactive plaque over a tumour.

Technique

Each probe has a marker for orientation that correlates with a point on the display screen, usually the left.

aAnaesthetic drops are instilled and the patient placed in the supine position.

bThe examiner should sit behind the patient's head and hold the probe with the dominant hand.

c Methylcellulose or an ophthalmic gel is placed on the tip of the probe to act as a coupling agent. d Vertical scanning is performed with the marker on the probe orientated superiorly (Fig. 16.19A). e Horizontal scanning is performed with the marker pointing towards the nose (Fig. 16.19B).

fThe eye is then examined with the patient looking straight ahead, up, down, left and right. For each position a vertical and horizontal scan can be performed.

gThe examiner then moves the probe in the opposite direction to the movement of the eye. For example when examining the right eye the patient looks to the left and probe is moved to the patient's right, the nasal fundus anterior to the equator is scanned and vice versa. Dynamic scanning is performed by moving the eye but not the probe.

887 / 1137

kanski 7th

Fig. 16.19 Technique of ultrasound scanning of the globe. (A) Vertical scanning with the marker pointing towards the brow; (B) horizontal scanning with the marker pointing towards the nose

Gain adjusts the amplification of the echo signal, similar to volume control of a radio. Higher gain increases the sensitivity of the instrument in displaying weak echoes such as vitreous opacities. Lower gain only allows display of strong echoes such as the retina and sclera, though improves resolution because it narrows the beam.

Copyright © 2011 Elsevier Inc.All rights reserved. Read our Terms and Conditions of Use and our PrivacyPolicy.

If you find this useful please saythanks in your way: dramroo

888 / 1137