measure the BVP using a focimeter. This is not possible with a phoropter. Indeed, for all phoropter lens powers and their combinations, you are placing your trust in the manufacturer. In addition, the pantoscopic angle and vertex distance can be controlled more easily with a trial frame. Any changes in head position could vary these parameters in a phoropter, but do not in a trial frame as it is fitted to the patient’s head.

■Patients with low vision: Large dioptric changes in sphere and a high-powered Jackson cross-cylinder ( 0.75 or 1.00 D) are required in the subjective refraction of low vision patients to enable them to appreciate a difference in vision. These can be used very easily during a trial frame refraction. In addition, the trial frame can provide larger aperture lenses and allow unusual head and eye positions that may be necessary for low vision patients using eccentric fixation.

■Patients with binocular vision problems and children: The trial frame can stimulate less proximal accommodation than a phoropter. In addition, it is possible to perform the cover test with large aperture lenses in a trial frame, but not with a phoropter. Children can also see their parent/guardian more easily.

■Patients with hearing problems: The phoropter obscures the patient’s view of the examiner and therefore prevents communication with sign language or simple hand signals.

■Patients with large angle strabismus: Retinoscopy can be done on the line of sight with a trial frame without occluding the fellow eye, allowing for a more accurate measure of refractive error and particularly astigmatism.

4.7 STATIC RETINOSCOPY

Retinoscopy provides an objective measurement of a patient’s ametropia. Static retinoscopy provides an assessment of the distance refractive correction. Video clips showing a selection of retinoscopy reflexes and how their appearance changes during neutralisation are provided on the website .

4.7.1 Objective measurement of refractive error

An objective measurement of refractive error is the only assessment available in patients who are unable to cooperate in a subjective refraction, such

as young children. It is also heavily relied upon when subjective responses are limited (patients who do not speak the same language as you and those whose subjective responses are poor) or unreliable (malingerers). In more routine patients, it provides an objective first measure of refractive error that can be refined by subjective refraction.

4.7.3 Procedure

A concise summary of the procedure is provided in Box 4.1.

1.Prior to the retinoscopy procedure, you should attempt to estimate the refractive correction from relevant case history (section

4.7.2 Advantages and disadvantages

Retinoscopy provides a more accurate result of refractive error in a greater array of patients than autorefraction, although autorefraction (section 4.8) is a useful and reliable alternative in many ‘standard’ adult patients. Retinoscopy also provides a sensitive assessment of the ocular media (e.g. early detection of cataracts, keratoconus), can be used to determine refractive error at distance and near, identify accommodative dysfunction, and is portable and less expensive. Its major disadvantage is that it requires several years of training to become proficient at using it. When a subjective refraction is not possible, limited or unreliable, it is preferable to have more than one assessment of objective refractive correction.

There appears to be no research literature that compares the accuracy of streak or spot retinoscopes or refractions using negative or positive cylinders. The procedure will be described for streak retinoscopy, but spot retinoscopy appears an acceptable alternative. Streak retinoscopy is designed to be superior in detecting and correcting small amounts of astigmatism. As the name suggests, spot retinoscopy uses a spot of light rather than a streak. There is therefore no need to rotate the streak to determine the astigmatic meridians. In an astigmatic eye, the spot retinoscopic reflex is elliptical rather than circular, and the long and short axes of the ellipse determine the two astigmatic meridians. Otherwise the procedure is the same as for streak retinoscopy.

Positive cylinders have the advantage of making retinoscopy easier to learn, as ‘with’ movement is typically easier to see than ‘against’ movement. However, negative cylinders are preferred as they are standard in phoropters. In addition, there is the possibility of stimulating accommodation during subjective refraction when removing a plus cylinder from a trial frame to replace it with one of another power. For these reasons the procedure will be described using negative cylinders.

Box 4.1 Summary of retinoscopy procedure

1.Estimate the refractive correction from relevant case history and VA information and focimetry/ lensometry.

2.Position the phoropter or trial frame appropriately and set the PD.

3.Dial in the working distance lenses if appropriate.

4.Switch on the duochrome (bichromatic), spotlight or a similar large target.

5.Explain the test to the patient.

6.Dim the room lights.

7.Set the retinoscope mirror to the plano position and align yourself with the visual axis of the patient’s right eye.

8.Look across to the left eye and if ‘with’ movement is observed, add positive lenses until ‘against’ movement is obtained.

9.Determine if the refractive error of the right eye is spherical or astigmatic.

10.If the reflex is dim and the movement is relatively slow, use an appropriate lens to get nearer to neutrality, and check again for astigmatism.

11.If astigmatic, determine the principal meridians.

12.Neutralise the most plus/ least minus meridian first.

13.Check the neutral point by moving forward and backward slightly from your normal working distance, and check the reflex movement.

14.Along the second meridian, add minus cylinder in a bracketing technique to achieve neutrality.

15.Repeat for the patient’s left eye.

16.Remove the working distance lenses or subtract 1.50 or 2.00 D from your final result.

17.Measure the patient’s visual acuities with the net retinoscopy result.

4.1) and visual acuity information (section

4.2) and focimetry/ lensometry (section 4.4). What is the expected refractive error given the patient’s symptoms and visual acuity

in their present spectacles? In the early years of clinical training, it may be best not to use the information from focimetry prior to retinoscopy until your retinoscopy skills have reached a competent level (during this time you should perform focimetry/ lensometry after subjective refraction to allow a comparison).

2.Set the patient’s distance PD in the phoropter or trial frame. Position the phoropter or trial frame before the patient so that the lenses will be in the patient’s spectacle plane (approximately 12 mm from the cornea) and make sure that it is level.

3.Either

a)Dial in the 1.50 DS retinoscope lens into the phoropter or place working distance lenses in the back cells of the trial frame ( 2.00 DS for a 50 cm working distance,1.50 DS for 67 cm). This technique has the advantage that all ‘with’ movements indicate hyperopia and all ‘against’ movements indicate myopia. It also provides a ‘fogging’ lens to both eyes that will relax accommodation in a low hyperope.

or

b)Do not add a working distance lens. The working distance power ( 1.50 D or2.00 D usually) must later be subtracted from your final retinoscope result. This technique has the advantage that you avoid introducing two reflection surfaces from the working distance lens, which can make retinoscopy easier in some cases.

4.Switch on the duochrome (bichromatic), spotlight or a similar target that is easy to see when blurred and does not provide a stimulus to accommodation.

5.Explain the test to the patient: ‘I’m going to shine a light in your eye and get an indication of the power of the glasses you

may need. Please look at the red and green target, and let me know if my head blocks your view. Don’t worry if the chart is blurred.’ You must ensure that your head does not block the patient’s view at any time, otherwise they are likely to accommodate to it.

6.Dim the room lights to provide a higher contrast, brighter view of the pupillary reflex, while providing enough light to allow easy viewing of the phoropter/trial case. A totally dark room may induce a dark focus response (Mohindra retinoscopy, section 4.20.7).

7.Sit or stand off to the side of the patient so that manipulation of the trial frame/ phoropter is easy. Use a comfortable working distance from the patient so that

you can change lenses in the spectacle plane easily (a comfortable arm’s length is often 67 cm or 50 cm). You should be on the patient’s right side and use your right hand and right eye to check the patient’s right eye and vice versa for the left eye.

8.Set the retinoscope mirror to the plano position (maximum divergence, with the retinoscope collar at the bottom of its range) and position the retinoscope so that you

are looking along the visual axis of the patient’s eye (their other eye is fixating the duochrome; Fig. 4.8a). If the patient is looking slightly upwards to view the duochrome, which is common if the target is above the patient’s head and viewed through a mirror, to look along their visual axis you will need to be slightly higher than the patient (Fig. 4.9).

9.Position the streak so that it is vertical. Look through the aperture of the retinoscope and direct the light at the patient’s pupil and you should see the red retinoscope reflex. Sweep the retinoscope streak across the patient’s pupil horizontally and compare the movement of the reflex in the pupil with the movement of the retinoscope. If the reflex moves in the same direction as the movement of the retinoscope streak, this is known as ‘with’ movement. If the reflex moves in the opposite direction to the

(a)

(b)

Fig. 4.8 Plan view of the position of the examiner and patient when performing retinoscopy. (a) The examiner is viewing along the visual axis of the patient’s right eye, while the patient’s left eye fixates the duochrome target. (b) The examiner views off-axis in the ‘good’ eye of a patient with strabismus. For the strabismic eye, retinoscopy could be performed along the angle of strabismus, or the good eye could be occluded and retinoscopy performed off-axis.

Fig. 4.9 Side view of the position of the patient and examiner when performing retinoscopy.

movement of the retinoscope streak, this is known as ‘against’ movement.

10.Before you begin retinoscopy on a patient younger than 60 years of age, you must try to ensure that they will not accommodate while looking at the target. If you are assessing the right eye first, look across to the left eye and if ‘with’ movement is observed, add positive lenses until ‘against’ movement is obtained. This will ensure that the left eye (which is viewing the target) is blurred by at least 1.50 D.

11.Sweep the retinoscope streak across the patient’s right pupil and compare the movement of the reflex in the pupil with the movement of the retinoscope. Mentally note the direction of movement with the streak vertical and also observe the reflex’s brightness, speed and width. Now rotate the

Fig. 4.10 Determining the two astigmatic meridians: (a) If you are ‘retting’ on axis, the reflex will move in the same direction as the retinoscopy streak. (b) If you are off-axis the reflex will move in a different direction from the direction of the retinoscopy streak. You should then rotate your streak to align with the reflex.

retinoscope streak so that it is horizontal and sweep across the pupil vertically and finally observe the reflex movement when the streak is oriented obliquely (45 and 135). For all four streak positions, mentally note the direction of the reflex movement and the relative brightness, speed and width of the reflex movements.

12.Determine if the refractive error is spherical (the observed reflex has the same direction, speed, brightness and thickness in all meridians) or astigmatic (the reflex differs in different meridians). If the reflex movement is relatively slow and any difference between the reflex speed and thickness is difficult to determine, place an appropriate spherical lens in the trial frame to get nearer to neutrality, and check again for astigmatism.

13.If astigmatic, determine the principal meridians by rotating the streak axis until the angle of the reflex movement coincides with the angle of the streak in two meridians; one perpendicular to the other (Fig. 4.10). If the principal meridians are hard to pinpoint, adjust the mirror position slightly to narrow the streak width.

14.Determine the spherical component by ‘neutralising’ (adding plus lenses to ‘with’ movement and minus lenses to ‘against’ movement until the reflex fills the entire pupil and all perceived movement stops) the most plus/least minus meridian first (the meridian with the slowest, dullest ‘with’ or fastest, brightest ‘against’ movement). The

meridian being neutralised is the meridian in which the streak is being moved. For example, to neutralise the vertical meridian, the streak is horizontal and moves vertically. If the cylinder amount is small and the most plus/least minus meridian is difficult to determine, then neutralise one meridian and then check the other. If the most plus/least minus meridian was neutralised first, then the second meridian should be showing ‘against’ motion for the plano mirror position. Use a bracketing technique to determine neutrality.

15.Check the neutral point by moving forward slightly and observing the movement of the reflex. A ‘with’ movement should be seen. If you move backward slightly from your normal working distance, an ‘against’ movement should be seen.

16.Set the minus cylinder axis parallel with the streak orientation of the least plus/most minus meridian. Move the retinoscope with the streak in this position and you should observe ‘against’ movement. Add minus cylinder in a bracketing technique to achieve neutrality. As ‘with’ movement can be easier to see than ‘against’ movement, you may wish to add minus cylinder until ‘with’ movement is just seen and then reduce the cylinder by 0.25 D. Alternatively, you may wish to neutralise the cylinder with the retinoscope in the concave mirror position (with the retinoscope collar moved to the top position), in which case you will add minus cylinder to neutralise ‘with’ movement.

17.Briefly, recheck the sphere and cylinder components for neutrality. The axis can be checked using Copeland’s ‘straddling’ technique. This involves comparing the speed of rotation and alignment of the reflex at the cylinder axis 45° with that at the cylinder axis 45°. The cylinder axis should be changed until the reflex at these two positions is the same. In spot retinoscopy, the cylinder axis can be checked and refined by sweeping the beam along the axis of the cylindrical trial lens. If the trial cylinder is oriented at the correct axis, the reflex should be in alignment with the spot of light in the trial frame. The

axis of the trial cylinder can be adjusted until this is the case. The power of the cylindrical lens should be rechecked following an adjustment of cylinder axis.

18.Repeat steps 10 to 16 on the patient’s left eye.

19.Recheck the right eye. This step may not be necessary if you have ensured that no accommodation has taken place throughout the procedure (see step 10).

20.Remove the 1.50 (or 2.00) working distance lenses (or subtract 1.50 or 2.00 D from your final result).

21.Measure the patient’s visual acuities with the net retinoscopy result.

4.7.4 Adaptations to the standard technique

Monocular examiners

If you have normal visual acuity in one eye only, you may find the method of retinoscopy suggested by Barrett useful:

1.A small, bright, featureless fixation target is fixed to the retinoscope, near to the mirror. Ask the patient to observe this target.

2.Conduct retinoscopy on both eyes, using your ‘good’ eye to examine both eyes of the patient.

3.Once both eyes have been neutralised, recheck the endpoint of one eye using your good eye with the patient fixating a distance target. For example, if you have a ‘good’ right eye, then assess the patient’s right eye using your good eye.

4.Any difference in spherical component in the eye that has been rechecked should be applied to the fellow eye. Note that the difference in cylindrical component should be negligible.

Dim reflex

If the reflex is very dim or hard to interpret, the patient either has media opacities, small pupils or

high ametropia. If the patient is a high myope, moving increasingly closer to the patient’s eye will move the retinoscope closer to the patient’s far point and the reflex will become increasingly brighter and faster. Alternatively, you could just add a medium to large powered positive or negative lens and repeat retinoscopy at the normal distance.

Media opacities and/or small pupils

With patients with media opacities and/ or small pupils, you will see a dim reflex as a reduced amount of light reaches the retina and even less returns to your retinoscope. In some retinoscopes you can alter the sight hole size. For small pupils and patients with media opacities you should make sure you are using the large aperture sight hole to see as much light as possible. To retain as much light as you can, use as small a number of lenses as possible as you will lose 8% of the reflex for each lens used due to reflections. Do not use a working distance lens (see step 3 in section 4.7.3) and refract each meridian using a sphere only and convert to a sphere–cylin- der combination for the subjective refraction. You may also be able to obtain a brighter reflex by performing retinoscopy at a reduced working distance of, say, 25 or 33 cm (sometimes called ‘radical retinoscopy’). You will have to subtract a larger value from your retinoscopy result to compensate for the reduced working distance (4.00 or 3.00 D respectively for the two distances mentioned above). Remember that there is a greater chance of error when using a close working distance. For example, if you work at 62 cm rather than a correct 67 cm when using a 1.50 DS working distance lens, the error is 0.10 D. The same 5 cm error when assuming a working distance lens of 4.00 D (25 cm) is 1.00 D.

‘Scissors’ reflex

This reflex moves like the action of a pair of scissors, moving simultaneously in opposite directions from the centre of the pupil, and accurate neutralisation can be very difficult. The reflex can be due to optical aberrations, particularly coma in a normal eye or due to abnormalities in the media such as keratoconus or corneal scarring. Use lens steps larger than 0.25 DS and try to bracket the neutral point. Increasing the room light level can help as it reduces the patient’s pupil size and cuts down the peripheral aberrations.

Large pupils

Spherical aberration can provide a more against movement in the periphery of the lens compared to the centre. You must concentrate on the central reflex and ignore the remainder. Once again, increasing the room light level can help as it reduces the patient’s pupil size and cuts down the peripheral aberrations.

Patients with strabismus

Retinoscopy is ideally performed along the patient’s visual axis. In a patient with strabismus, this can be difficult, particularly when using a phoropter. Retinoscopy on the ‘good’ eye must be performed slightly off-axis (Fig. 4.8b). For the strabismic eye, it can be easier to change the fixation point for the ‘good’ eye, so that retinoscopy along the visual axis of the strabismic eye is easier. Alternatively, occlude the ‘good’ eye and perform retinoscopy slightly offaxis (Fig. 4.8b).

Accommodative fluctuations

During accommodative fluctuations, the pupil will be seen to vary in size and the reflex movement and brightness will rapidly change. This can be seen with young children who change fixation (typically to look at the retinoscope light or their parent/ guardian) and the patient needs to be reminded to keep looking at the duochrome. If these changes do not appear related to changes in fixation, then accommodative fluctuations that could be due to latent hyperopia or pseudomyopia should be suspected and a cycloplegic refraction (section 4.20) and assessments of accommodation (sections 5.17 to 5.19) should be performed.

4.7.5 Recording

Record the spherocylindrical correction that neutralised the patient’s refractive error after removing your working distance lenses. Do not use a degree sign as ° can look like a 0 and make an axis of 15° look like 150 degrees. Use ‘x’ rather than the word ‘axis’. Record the spherical and cylindrical power to the nearest 0.25 D, and the cylinder axis to the nearest 2.5 degrees. The axis should be between 2.5 degrees and 180 degrees. Use 180 rather than 0