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

36 CHAPTER 1 Clinical skills

Orbital examination

Table 1.19 An approach to examining the orbit

Consider refraction, neurological, and general systemic examintion, as indicated.

ORBITAL EXAMINATION 37

Special tests

Exophthalmometry

Using the Hertel exophthalmometer, place it level with the orbits and adjust the separation so that the foot plates rest on the lateral orbital rims at the level of the lateral canthi. Close your right eye and ask the patient to fix his/her gaze on your open (left) eye while you align the parallax markers (usually red) and read off where the patient’s right corneal apex appears on the scale. Repeat with your right eye and the patient’s left eye.

Measurements >20 mm or a difference of >2 mm between globes is suggestive of proptosis. Be aware of patient variables (racial differences, lateral orbitotomy), instrument variability (try to use the same exophthalmometer each time), and operator inconsistency.

Two-ruler test

Horizontal and vertical displacement of the globe may be demonstrated by using two clear plastic rulers. One is placed horizontally over the bridge of the nose at the level of the lateral canthi. Look for horizontal displacement by comparing the distance from the center of the nasal bridge to equivalent points on the globe (e.g., nasal limbus). Look for vertical displacement by measuring vertically (second ruler) to compare the distance from the horizontal meridian (i.e., the first ruler) to equivalent points on the globe (e.g., the inferior limbus).

38 CHAPTER 1 Clinical skills

Nasolacrimal system examination

Table 1.20 An approach to examining the nasolacrimal system

•Check for regurgitation form canaliculi on pressing sac.

Dye disappearance test

Instill a drop of fluorescein 2% into each lower fornix. Reassess at 2 min, by which time (almost) complete clearance should have occurred. Prolonged retention indicates inadequate drainage.

Probing

Under topical anesthesia, insert a straight lacrimal cannula into the lower canaliculus and guide it toward the medial wall of the lacrimal sac. Assess whether there is a

•Hard (abrupt) stop, which indicates a patent system as far as the lacrimal sac, or a

•Soft (spongy) stop, which indicates a canalicular block.

NASOLACRIMAL SYSTEM EXAMINATION 39

Irrigation

Under topical anesthesia, insert a lacrimal cannula into the lower canaliculus and place a finger against the lacrimal sac. Irrigate with saline and assess the following (see also Table 1.21):

•Flow: estimate flow (e.g., in %) conducted (i.e., down nose/back of the throat) vs. regurgitated; if regurgitated, note from which canaliculus.

•Quality of regurgitated fluid: clear or purulent.

•Lacrimal sac distension.

Jones testing

This may be considered in cases of partial obstruction to ascertain the level of block (Table 1.22).

Primary test

Instill fluorescein 2% into the lower fornix. After 5 min, assess for dye recovery with a cotton tip (can be moistened with 4% cocaine) placed at the nasolacrimal duct opening (below the inferior turbinate) or with a nasendoscope.

Secondary test

Wash out the fluorescein from the lower fornix. Under topical anesthesia, insert a lacrimal cannula into the lower canaliculus and irrigate. Assess dye recovery from the nose as before.

Table 1.21 Interpretation of probing and irrigation tests

Table 1.22 Interpretation of Jones test

40 CHAPTER 1 Clinical skills

Refraction: outline

History

Box 1.4 Essential history

•Age; profession; driver; special requirements; Department of Motor Vehicles (DMV)

•Visual symptoms

•Past ophthalmic history

•Family ophthalmic history

•Past medical history

•Drugs/allergies

•Previous eyeglasses/contact lens use

Examination

Box 1.5 Preparation

• Focimetry on current eyeglasses (p. 44) ROOM LIGHTS ON

•VA—unaided + with PH

•Cover/uncover test

•Measure interpupillary distance (IPD) (distance) lset up trial frame

Box 1.6 Retinoscopy

ROOM LIGHTS OFF

•Ask patient to look at a nonaccommodative target (e.g., green duochrome).

•Correct for working distance (e.g., if you work at 2/3 m put in +1.5D DS).

•Fog fellow eye with a high PLUS DS lens to prevent accommodation.

•Check retinoscopy reflex.

•Identify axis of astigmatism.

•Neutralize reflex in one meridian with DS lenses.

•If reflex is “with” then add PLUS, if “against,” then add MINUS.

•When point of reversal is reached in one meridian, add cylindrical lenses to neutralize in the other meridian.

•Occlude eye not being tested.

•Check VA.

•Verify sphere.

•Ask patient to look at the smallest line that he/she can see clearly.

•Verify sphere by offering ± DS (usually ± 0.25 DS to fine-tune, but may need ±0.5 DS if poor VA).

•Ask, “Is the line clearer and easier to read with lens 1 or 2?”

•Verify cylinder axis.

•Ask patient to look at a round target/easily readable “O.”

•Use cross-cylinder (0.50 D cross-cylinder cf 1.00 D if poor VA).

•Align handle with axis of trial cylinder.

•Ask, “Is the circle rounder and clearer with lens 1 or 2?”

•Rotate trial cylinder toward the preferred cross-cylinder position with respect to its sign ,i.e., a plus trial cylinder is rotated toward the plus sign of the cross-cylinder.

•Verify cylinder power.

•Repeat the procedure but with the handle at 45° to axis of trial cylinder. This will in effect offer ± 0.25 D cyl (if using the 0.50 cross cylinder).

•Add 0.25 DS for every 0.5 DC lost.

•Refine best sphere.

•Plus 1 blur test (should reduce VA by 2 lines).

•Duochrome test (monocular and binocular; aim for no preference/slight red preference).

•Measure and record back vertex distance (BVD) if >5 DS.

•Check near requirement—at usual reading/working distance.

Box 1.8 Muscle balance, accommodation, and convergence

•Maddox rod (distance muscle balance): place in front of right eye in horizontal then vertical orientation; neutralize with prisms until patient reports that the red line passes through white spot.

•Maddox wing (near muscle balance): ask patient where arrows point.

•RAF rule (perform 3 times for each test).

•Accommodation amplitude: distance at where text blurs.

•Near point of convergence: distance where line becomes double.

42 CHAPTER 1 Clinical skills

Refraction: practical hints

Hints on retinoscopy

Positioning yourself

Aim to be as close to the patient’s visual axis without obscuring his/her fixation target. If your head gets in the way, they are likely to look at it and start accommodating.

Plus or minus cylinders

Be consistent: either work with plus or with minus cylindrical lenses.

•If using plus cylindrical lenses, you will wish to correct the most minus meridian first. This is identified by the following:

•If both reflexes are against, then it is the slower reflex.

•If one is with and one against, then it is the against reflex.

•If both reflexes are with, then it is the faster reflex.

•If using minus cylindrical lenses, you will wish to correct the most plus meridian first. This is identified similarly:

•If both reflexes are against, then it is the faster reflex.

•If one is with and one against, then it is the with reflex.

•If both reflexes are with, then it is the slower reflex.

Poor reflex

•Consider media opacity: optimize illumination, check that they are not accommodating on your head.

•Consider high refractive error: use large steps, e.g., ±5 DS, ±10 DS.

•Consider keratoconus if there is swirling reflex or oil-drop sign.

Hints on subjective refraction

Avoiding too much minus

When verifying and refining sphere, check that the patient finds it clearer and easier to read and not just smaller and blacker from the minification effect.

Higher refractive errors

•Put higher power lenses at back of trial frame.

•Measure and document back vertex distance, especially if >5.0 DS.

Prescribing reading add

Estimate requirement on the basis of age and lens status. However, this should be tailored to the individual and their needs (Table 1.23).

Table 1.23 Estimated near corrections

REFRACTION: PRACTICAL HINTS 43

Role of muscle balance tests

•These tests depend on binocular vision and are dissociative. They are therefore particularly useful for detecting and quantifying phorias (latent strabismus).

•If the patient has a manifest strabismus but no diplopia, then there is no point in doing the muscle balance tests.

•Do not prescribe prisms unless the patient is symptomatic, and first consider whether further investigation (including orthoptic referral) is necessary.

Causes of spectacle intolerance

The following may lead to asthenopia (refractive discomfort or eyestrain):

•Significant change in axis or size of cylinder.

•Change of lens form.

•Overcorrection, especially of myopes, who will end up permanently accommodating.

•Excessive near correction resulting in an uncomfortably near and narrow reading distance.

•Unsuitable bifocal or progressive lenses—consider occupation, requirements, and general needs of the patient.

44 CHAPTER 1 Clinical skills

Focimetry

The focimeter or lensometer measures the axis and power of eyeglasses and contact lenses. The instrument can also be used to find the optical center, and the power and base direction of any prism in unknown lenses.

Manual focimetry

The vertex power of the lens is measured by taking the inverse of the focal length of the unknown lens. Green light is used to eliminate chromatic aberration.

Components

•Moveable illumination target.

•Viewing telescope.

•Fixed collimating lens (renders light parallel).

Method

•Ensure the eyepiece is focused and target seen sharply focused.

•Insert unknown lens (spectacles mounted with the back surface of the lens against the rest to measure back vertex power).

For simple spherical lenses

Dial (this moves the target backward or forward) until the graticules are sharp and read off the power.

For cylindrical power

The target is rotated, as well as dialed until one set of lines is sharp. The reading is noted. The target is then dialed again until the other lines are sharp. The difference in these two readings is the cylindrical power. The axis of the cylinder is then read from the dialing wheel.

Bifocal addition

Turn the eyeglasses around to measure the front vertex power. The difference between the front vertex power of the distance and near portions is the bifocal add.

Automated focimetry

In principle, four parallel beams of light pass through the unknown lens and strike a photosensitive surface. The deflection of the beams from their original path is measured and used to compute the lens power (Fig. 1.12).

There is a support frame for the spectacles; changing the lever on the unit above the support frame will automatically read either the right or the left lens as required.

FOCIMETRY 45

Position 1: the graticules are sharp at an angle of 150° and a power of +1.0D

Position 2: the graticules are sharp at an angle of 60° and a power of +4.0D

Result: the lens prescription is therefore +1.0/+3.0 × 060.

Figure 1.12 View through the focimeter.