Ординатура / Офтальмология / Английские материалы / Oxford American Handbook of Ophthalmology_Tsai, Denniston, Murray_2011

16 CHAPTER 1 Clinical skills

Figure 1.9 Slit lamp with key features identified.

18 CHAPTER 1 Clinical skills

Additional techniques for anterior segment examination

Illumination techniques

Although direct illumination is most commonly used, additional pathology may be revealed by using the following techniques:

•Scleral scatter: Unlock the light source so that the slit beam can be displaced laterally to fall on the limbus while the microscope remains focused on the central cornea. Total internal reflection results in a generalized glow around the limbus and the highlighting of subtle opacities within the cornea, e.g., early edema, deposits, etc.

•Retroillumination: Direct the light source at a relatively posterior reflecting surface (e.g., iris or retina) and focus on the structure of interest (e.g., cornea, or iris and lens). View undilated for iris transillumination defects; view dilated for lens opacities.

•Specular reflection: Focus on the area of interest and change the angle of illumination to highlight discontinuities in an otherwise smooth reflecting surface, e.g., examining the endothelium for guttata.

Tear film breakup time (BUT)

Place a drop of fluorescein into the lower fornix. Ask patient to blink once and then not to blink (or hold lids open if necessary). Observe with blue light the time taken until the tear film breaks up. A result <10 sec is abnormal.

Seidel’s test

Place a drop of 2% fluorescein over the area of concern and observe with the cobalt blue light. The test is positive if there is a luminous green flow of aqueous. This results from local dilution of the stain by aqueous leaking from a surgical wound, penetrating injury or filtering bleb.

Schirmer’s test

Whatman test paper is folded 5 mm from the end and inserted in the temporal fornix of both lower lids. After 5 min, the strips are removed and the length wetted is measured. This result is an indication of basic and reflex tearing. It is normal if >10 mm, borderline at 5–10 mm, and abnormal if <5 mm. Repeating the test after the addition of a topical anesthetic gives an indication of basic secretion alone.

Applanation tonometry

Place a combination of local anesthetic and fluorescein into the lower fornix. Rotate the tonometer dial and record the pressure at which the inner aspect of the two luminous green circles just touch. Usually, the white line on the prism is aligned with the horizontal merdian; however, in high astigmatism, the red line should be aligned with the minor axis. This is also affected by corneal thickness (p. 68).

Tonometer checks and calibration

Goldmann tonometers may be checked by using the metal bar and control weight supplied. With the weight exactly midway along the bar (central stop), the tonometer should read 0 mmHg. The next two stops correspond to 20 and 60 mmHg, respectively. Significant deviation from this indicates a need for formal recalibration by the manufacturer.

20 CHAPTER 1 Clinical skills

Gonioscopy

Use an indirect (Goldmann, Zeiss) or direct (Koeppe) goniolens to assess the iridocorneal angle, including the iris insertion, the iris curvature, and the angle approach. If the angle is closed, indent (with a Zeiss lens) to see if it can be opened (“appositional closure”) or zippered shut (“synechial closure”). Describe according to the Shaffer (Table 1.7) or Spaeth (Table 1.8) grading system, recording which classification is being used (e.g., “4 = wide open” if using Shaffer) (see Fig. 1.10).

Shaffer classification

Table 1.7 Shaffer classification

Spaeth classification

Categorize according to iris insertion, angular approach, and iris curvature (e.g., D40R)

Table 1.8 Spaeth classification

POSTERIOR SEGMENT EXAMINATION (1) 23

Contact lenses provide the highest clarity and may be useful in assessing detail (e.g., area centralis for macular pathology) or where the view is poor (e.g., media opacities). The retinal view using these lenses is inverted. Three-mirror contact lenses (e.g., Goldmann) facilitate examination of the periphery; the views are mirror image rather than fully inverted.

Method

Ideally, the patient’s eyes are dilated; the fundal view obtained without dilation is usually limited in both extent and stereopsis. Adjust the slit lamp so that it is coaxial and focused on the center of the cornea. Interpose the lens 1 cm in front of the eye and draw the slit lamp back until a clear fundal view is obtained.

To view the peripheral retina, ask the patient to look in the direction of the area you wish to examine (i.e., down to view inferior retina). Troublesome reflections can be reduced by moving the illumination beam slightly off axis.

Indirect ophthalmoscope and scleral indentor

The indirect ophthalmoscope (assisted by scleral indentation) is the instrument of choice for examination of the peripheral fundus.

Optical features

The choice of lens depends on the need for greater magnification (e.g., 3-fold with 20D lens but smaller field of view) vs. wider field of view (e.g., larger field of view with 28D lens but only 2-fold magnification). The retinal view is inverted.

Method

Ensure the patient is well dilated, positioned flat, and looking straight up at the ceiling. Have lens, indenter, and retinal chart/paper (for recording findings) available. Align eyepieces and illumination by viewing your outstretched thumb. Ensure that the headband is sufficiently tight that the ophthalmoscope will remain secure as you move around. Illumination brightness is adjusted according to quality of view and patient comfort.

View from above, with the ophthalmoscope directed downward toward the pupil and with the lens held directly in the line of illumination. Resting this hand lightly against the patient’s face helps steady the lens at an appropriate focal distance for a clear fundal view. To view the peripheral retina, change the angulation by asking the patient to look in the direction of the area to be examined (i.e., down to view inferior retina) while angling your head and lens in the opposite direction.

Scleral indentation

To view, for example, the inferior ora, ask the patient to look straight up and place the indenter on the outside of the lower lid, resting tangentially against the area to be indented. Then ask the patient to look straight down, moving the indenter with the globe. Observe the area of interest while gently exerting pressure over it. Continue for 360°. Warn the patient that the procedure may be uncomfortable.

24 CHAPTER 1 Clinical skills

Posterior segment examination (2)

Instruments used in posterior segment examination (cont.)

Direct ophthalmoscope

For those who see patients in a non-ophthalmic setting, this may be the only option available for fundal examination. Ophthalmologists may also choose to use it where access to a slit lamp or indirect ophthalmoscopy is not possible (e.g., on intensive care unit patients).

•Optical features: There is high magnification (15x) but only a small field of view. The retinal view is not inverted.

•Method: Optimize your view with adequate dilation, dimmed room, and a fully charged ophthalmoscope. The field of view should be maximized by coming very near to the eye. Optimal view of the optic disc is achieved by approaching from 15° to 20° temporally while on the same horizontal level as the patient.

Additional examination techniques for posterior segment examination

Amsler grid

This is viewed at 1 foot. Ask the patient to fixate one eye at a time on the central dot and comment on whether any of the small squares are missing or distorted. There are seven charts, of which chart 1 is suitable for most patients (Table 1.10). It consists of a 20 x 20 grid of 5 mm squares each representing 1° of central field (if viewed at 1 foot).

Watzke–Allen test

While using the slit lamp and handheld lens to view the macula, project a thin strip of light across the fovea. Ask the patient whether the line he/ she sees is broken, narrowed, or complete. A clear gap (Watzke–Allen positive) suggests a full-thickness macular defect or hole.

Goldmann 3-mirror lens

This contact lens is used with the slit lamp to examine the central and peripheral fundus. This is a mirror image rather than a rotated image of the peripheral fundus (cf. standard indirect ophthalmoscopy). It comprises four parts: central (view central 30°), equatorial mirror (largest; views 30° to equator), peripheral mirror (intermediate; views equator to ora), and gonioscopic mirror (smallest; views ora serrata, pars plana and angle).

Retinal charts

One standardized representation of vitreoretinal pathology uses the code presented in Table 1.11.

Table 1.11 Retinal chart key