Clinical Optometric Procedures: Objective Refraction

Clinical Optometric Procedures: Objective Refraction

CHAPTER 1 – OBJECTIVE REFRACTION

• This chapter includes a review of:
• Retinoscopes
• Retinoscopy

INTRODUCTION

Objective refraction comprises a host of various techniques that may be employed to determine the patient’s refractive correction. It is usually performed for the determination of the starting point of a subjective refraction.

More importantly, it is a technique which the practitioner has to rely on entirely when a subjective refraction cannot be ascertained. This would be in cases of the patient malingering (i.e. feigning poor/better acuity than they actually have), uncooperative patients like children, patients who are unable to communicate subjective responses to you and in patients who are unreliable in terms of subjective responses. It is a procedure that becomes more accurate with a greater amount of practice. Both retinoscopy and autorefraction are methods of objective refraction. In many cases, autorefraction is used to replace retinoscopy, however, issues of instrument reliability, problems inherent due to the nearness of the target in the instrument, and poor cooperation on the part of patients makes retinoscopy a far more superior and more adaptable technique to perform than autorefraction.

Retinoscopy is a technique that is used to objectively determine the refractive error of a patient. It does not require the patient’s responses and therefore can be performed on children and non-verbal individuals.

There are two kinds of retinoscopes:

1. Spot retinoscopes – contain an ordinary light source which projects a “patch” or “spot” of light 2. Streak retinoscopes – contains a special source with a linear filament which produces a “line” or “streak” of light

RETINOSCOPES

The first retinoscopes used a light source placed just behind the patient’s shoulder while modern retinoscopes have the light source built into them (i.e. they are self-luminous retinoscopes). Retinoscopes allow us to shine a light into a person’s eye and look at the light reflected back from their retina. This reflected light as seen in the person’s pupil is called the retinoscopic reflex or “ret reflex”.

Advantages of Retinoscopes

Spot Retinoscopes

1. Astigmatism can be detected with spot retinoscopy by noting the shape of the ’ret reflex’. In an uncooperative patient, it may not be possible to achieve prolonged viewing if the patient’s fixation is not steady, and the examiner has to depend on occasional glimpses for assessment of the reflex. In streak retinoscopy the reflex is always a slit, regardless of the presence of astigmatism, whereas in spot retinoscopy significant astigmatism will make the reflex appear elliptical. The correct axis of the astigmatic correction is more rapidly determined than with spot retinoscopy. International Centre for Eyecare Education 2. The time it takes for the examiner to rotate the streak from one position to another, an uncooperative patient may change their fixation position to one requiring more or less accommodation. This might be interpreted as astigmatism. With the spot retinoscope, the eye with no astigmatism (or corrected astigmatism) will always return a circular reflex, even though the speed and/or direction may change.

Streak Retinoscopes

1. The end point of retinoscopy is sometimes easier to observe with streaks than with spot retinoscopes.

2. All modern streak retinoscopes have an adjustment for changing the retinoscope beam vergence from being divergent to convergent. This is not always available on spot retinoscopes.

Apart from the problems with uncooperative patients noted above, the choice of “spot” or “streak” is a matter of individual preference.

Optics of the Retinoscope

The retinoscope consists of 2 major systems that have various parts. The systems of the retinoscope are the projection system and the observation system (Fig. 1.1).

• Projection system
• This part of the sytem illuminates the retina and comprises the following parts:
• Light source, i.e. a small bulb that projects light onto the retina (RPE and choroid)
• Condensing lens which lies in the path of the light projected from the bulb to focus the light onto the mirror
• Mirror which is placed within the head of the instrument. It bends the light at right angles to the axis of the

handle so that the light is projected from the head of the instrument

• Focusing sleeve which varies the distance between the bulb and the lens so that the light projected from the
• retinoscope either diverges (plane mirror effect) or converges (concave mirror effect)
• Current source or rechargeable/replaceable battery in the retinoscope handle

Observation system

This part of the retinoscopic optical system allows the practitioner to view the retinal reflex. The light reflected off the retina passes through an aperture in the mirror and out through the sight hole at the rear of the head. The light that is reflected from the retina are acted upon by the optical components of the eye and therefore the observation of this reflected light provides the practitioner information about the optics of the patient’s eye International Centre for Eyecare Education Figure 1.1 The retinoscope

Beam Settings of the Retinoscope

The sleeve not only rotates the streak orientation but also changes the beam from divergent to convergent (Fig.

1.2).

• When the beam is divergent (sleeve down) add plus for a “with” motion and minus for an “against” motion.

This is also referred to as plane mirror retinoscopy ( “with” motion = same direction of reflex movement as the motion from the restinoscope’s streak/ “against” motion = opposite direction of reflex movement as the motion from the retinoscope’s streak)

• When the beam is convergent (sleeve up) add plus for an “against” movement and minus for a “with”
• movement. This is also referred to as concave mirror retinoscopy (see the below diagrams)
• Convergent and divergent beam settings

a: The divergent beam b: The convergent beam Figure 1.2 (a) Retinoscope in divergent beam position; (b) Retinoscope in convergent beam position International Centre for Eyecare Education In most cases, the practitioner will have the sleeve in the down position (divergent beam/plane mirror); however, convergent beam or concave mirror retinoscopy may be preferred when:

• The practitioner is unsure if the movement being observed is either “with” or “against”. By changing from

divergent to the convergent beam, the movement should change direction of the movement. This would make it easier to decide if there really is movement present (“with” will become “against” and “against” will become “with”).

• Convergent beam allows more light to enter the eye, making it easier to perform retinoscopy on patients with

small pupils or opacities in the media.

• Many practitioners favor the “with” movement as opposed to the “against” movement since it is easier to

perceive. This is especially the case in high ametropia where the reflex is very dull and the “against” movement is difficult to discern. Practitioners therefore slide the sleeve up to the concave or convergent position so that the dull against movement becomes a distinct slow with movement which is now easier to neutralize.

• While the practitioner should take cognizance of these changes in the direction of the movement of the “ret

reflex”, he must keep in mind that the refractive correction is the same, the refractive state of the patient is the same, it is only the direction of the ret reflex that is different.

• The retinoscopic reflex when viewed through the retinoscope appears to be located in the plane of the

patient's pupil. It is recommended that the observer must be within one meter or less from the patient’s eye in order to clearly see the fundus reflex. When the light is passed over the eye, the reflex will appear to move.

This movement helps us to assess the patient’s refractive error.

• The movement can be “with motion” (in hypermetropia), “against motion” (in myopia) or no movement

(neutral in emmetropia). This direction of movement is a guide to refractive error. If there are different movements in different meridians this indicates the condition of astigmatism where there are differences in the refractive corrections for the principle meridians.

• Rays of light from a normal (emmetropic) eye are reflected off the retina (from the retinoscope) and exit the

pupil as parallel rays. If the retinoscope is held at a distance of one meter from the patient's eye, then a +1.00 D spherical ('working lens") is required to focus the parallel light rays at a one-meter distance. This is known as making the patient’s eye conjugate with the optometrist's eye. Similarly, when working at any working distance can be compensated for with an appropriate working distance lens. For example, if refracting at a distance of 50cm, a +2.00D spherical working lens is needed.

• The aim of retinoscopy is to find the lens that would produce a neutral reflex. This neutral reflex is one that

appears stationery and fills the pupil. However, it must be noted that this reflex is at an infinite speed making it appear to be stationery. Neutrality is achieved by adding lenses to make the reflex brighter, move faster, and ultimately neutralize the movement.

• While autorefractors have become quite accurate, an experienced retinoscopist can achieve the same

degree of accuracy. Performing retinoscopy also allows the examiner to view the quality of the optical medium of the eye, picking up cases of keratoconus and providing information that the autorefractor cannot.

RETINOSCOPY

• Types of Retinoscopy

Static Retinoscopy

A technique which allows the determination of the refractive error for distance while maintaining accommodation in a fixed state. Patient fixation is maintained at a distance of 6m.

Dynamic Retinoscopy

A technique that determines the near refractive error, while not having control over accommodation. This method of Retinoscopy investigates the patient’s accommodative response. Patient fixation is less than 6m.

Mohindra Retinoscopy

A technique that determines the distance refractive error when patient fixation is more difficult to maintain. This method encourages the patient to fixate the light source.

Radical Retinoscopy

A variation of static retinoscopy that is employed especially in cases where media opacities are present and in cases of very high refractive error.

For the purposes of this module, static retinoscopy will be discussed, however, other methods of retinoscopy will be discussed in other specialist modules such as low vision.

Retinoscope Reflex Movements

The practitioner will observe the streak reflected from the rim of a trial lens held in front of a patient’s eye.

Through the trial lens and pupil a narrower band of light being reflected from the person’s retina will be observed.

• This is the ’ret reflex’ (Fig. 1.3).
• Figure 1.3 Retinoscopic reflex International Centre for Eyecare Education

Figure 1.4 View through a trial lens using a streak retinoscope When you move the retinoscope (spot or streak), the ‘ret reflex’ moves. The movements of the ret reflex may be ‘‘with’’, ‘’against’’ and neutral. This reflex is not always positioned in the principal meridians but can appear in oblique orientations as well (Fig. 1.4).

With motion

‘’With’’ motion, the ‘ret reflex’ moves in the same direction as the sweeping of the retinoscope streak. Figure 1.5 shows the streak moving across the rim of the trial lens from your left to right. If the ret reflex moves in the same direction as the streak projected from the trial lens rim, this is termed “with” motion.

• Figure 1.5 View of with motion through streak retinoscope sight hole

Against motion

In an ‘’against’’ motion, if the streak moves from left to right, the ret reflex will move from right to left (opposite direction). The ret reflex is moving in the opposite direction as the streak projects from the trial lens rim (Fig. 1.6).

• This is an “against” movement.International Centre for Eyecare Education
• Figure 1.6 View of against motion through streak retinoscope sight hole

Neutrality (no movement)

With the streak moving from left to right when the whole pupil is filled with light and there is no observable movement of the “ret reflex” as the streak sweeps across the pupil (Fig. 1.7). This is considered neutrality or end point.

• Figure 1.7 View of neutrality through streak retinoscope sight hole

Astigmatic reflex

An astigmatic reflex with present with several types of movements: (if neutralizing with minus cylinders)

• Both meridians presenting with ‘’against’’ motion. The practitioner will neutralize the meridian with faster

motion first.

• Both meridians presenting with ‘’with’’ motion. The practitioner will neutralize the meridian with slower motion

first.

• If you find it difficult identifying the difference in the speed of the movements, check both meridians with each

addition of lens, until one gets neutralised. The remaining meridian should have an ‘’against’’ movement which you will now neutralize with minus cylinders with the axis parallel to the streak.

Performing Static Retinoscopy

Set up

• Retinoscopy must be performed with the examiner and patient being at eye level. The examiner in directly in

front of the patient, with his right eye aligned with the patient’s right eye (Fig. 1.8). The examiner must ensure that while he is in front of the patient, he must not obstruct the patient’s view of the presented or projected target.

Figure 1.8 The pathway of the retinoscopes light and the examiner’s visual axis coincide

• Set the trial frame to the correct PD and make sure it fits the patient comfortably. This ensures that the

lenses fitted in the trial frame have their optical center coincident with the patient’s visual axis. The vertex distance may also be set on the trial frame to the standard employed in your country. In many cases it can range from 12 to 14mm. This measurement is especially important when taking into consideration high prescriptions where even slight adjustments of the vertex distance can produce a resultant difference in the prescription being offered to the patient. This can result in problems when patients are finally prescribed their spectacles and they are unable to view through them unlike through the trial frame.

Procedure

1. Static retinoscopy is a binocular technique in which both eyes may be fogged with the working distance lenses or the technique can be performed without the working distance lenses. However, adjustments (subtraction of plus power appropriate to working distance used) must be made to the final Rx. Each method has its inherent advantages.

• Performing the technique with working distance lenses

The advantage of using this method is that “with” movements indicates hyperopia and “against” movements indicates myopia. In addition, the fogging lenses are able to fully relax the patient’s accommodation, especially in cases of low hyperopia.

• Performing the technique without working distance lenses

The advantage of this technique is that it frees up trial lens spaces in the trial frame. It also prevents additional reflection surfaces from the working distance lenses and the correcting lenses. International Centre for Eyecare Education 2. The room illumination should be dim, otherwise it will be difficult to observe the “ret reflex”. If the room is too dim, it will be difficult for the practitioner to see what he/she is doing. The patient’s pupil will be larger and therefore the examiner would be faced with more aberrations as a result of the larger pupil diameter.

3. Check that the retinoscopic beam is divergent by moving the sleeve to its lowest position. That is, closest to the battery handle.

• Start with the streak of the retinoscope orientated vertically. Observe the position of the reflex within the

eye. In cases where the principle meridians lie at 90 and 180 degree, this vertical streak will coincide with one of the principal meridians. The streak is then orientated horizontally to observe the reflex in this meridian (Fig. 1.9a). However, in cases where they don’t coincide (Fig. 1.9b), then the practitioner must rotate the streak on the retinoscope so it is in line with the “ret reflex” (Fig. 1.9c).

Figure 1.9 Aligning the beam of the retinoscopic light source with that of the ret reflex

• If you are doing retinoscopy on the person’s right eye, you need to place the retinoscope over your right

eye. Your right eye should be in line with the person’s right eye. Hold the retinoscope in your right hand.

• Ask the patient to look at a fixation target like a spot of light or a 6/60 target at least 3 metres away.

This helps to relax accommodation and keep the eyes steady.

• To get an accurate measurement of refractive error you need to keep the retinoscope very close to the

patient’s line of sight (visual axis).

• Ask the patient to inform you if your head gets in the way of the target. Encourage him to look at the

distance target and keep reminding him to keep looking at the distance target and not at the ret light.

Also ensure that the patient keeps both eyes open.

• For retinoscopy on the person’s left eye, move to the left side of the person and use the retinoscope in

your left hand with your left eye (examiner’s right eye for patient’s right eye, examiner’s left eye for patient’s left eye). Remember to keep close to the patient’s visual axis How to calculate the working distance lens:

The working distance lens is determined by the dioptric equivalent of the working distance (FW). For example, if the practitioner used a working distance of 50cm (FW), then the appropriate working distance lens is given FW=1/fw  FW=1/0.5m  FW= +2.00DS.

One must make note that there are set lenses when working with phoropters. For example, most phoropters have a working distance lens of +1.50DS, indicating that the practitioner needs to perform their retinoscopy at a working distance of 67cm. International Centre for Eyecare Education 4. Scoping/sweeping to observe the ret reflex

• Sweeping the Horizontal Axis:
• Use the sleeve to turn the streak to a vertical direction (90).
• Move the streak/retinoscope from right to left to sweep the horizontal axis.
• The sweeping motion is a smooth movement that may be repeated several times while you watch the
• “ret reflex”
• Sweeping the Vertical Axis:
• Use the sleeve to turn the streak to a horizontal orientation (180°)
• Move the streak up and down to sweep the vertical axis
• The sweeping motion is a smooth movement that may be repeated several times while you watch the
• “ret reflex”
• 5. Neutralizing the ret reflex
• The reflex seen is neutralized by using lenses
• Add plus to neutralise a “with” movement
• Add minus to neutralise an “against” movement
• If you add too much plus, the movement will change to “against”. This means you have passed

neutrality and you need to remove some of the plus to return to the neutral point

• If you add too much minus the movement will change to “with”. This means you have passed neutrality
• and you need to remove some of the minus to return to the neutral point

Factors Affecting the Retinoscopic Reflex 1. Ametropia: the type and magnitude of the ametropia can be determined by the speed and brightness of the observed reflex.

2. Patient’s pupil size: affects the amount of light entering and leaving the pupil. With more light entering the pupil, the reflex will appear brighter; however, in cases of very large pupil sizes, aberrations are encountered.

3. Working distance: shorter working distances leave less of a margin of error, however, appropriate adjustments must be made to the findings in the trial frame to compensate for the reduced working distances.

4. Illumination source: one that is too bright may make the pupil smaller and hence prevent enough light entering or leaving the pupil, however, a dull light source can also be problematic.

5. Nearness to neutrality: the rapid speed of the reflex as it approaches neutrality makes it difficult for the practitioner to perceive the direction of movement of the reflex.

6. Aberrations of the eye: will affect the quality of the ret reflex.

7. Obliquity of observation: viewing off-axis will induce an error of parallax that will affect the end result and produce inaccuracies.

8. Regularity of optical components: media opacities and pathological conditions affecting the media will have a tendency to degrade the light entering or leaving the eye.International Centre for Eyecare Education 9. Poor optics of the retinoscope: will produce poor reflexes.

• Common errors

1. Performing retinoscopy off-axis.

2. Performing retinoscopy at an incorrect working distance affects the working distance lens used.

3. Blocking the patient’s view of the distance chart which results in accommodation being stimulated.

4. Confusing the retinoscope sleeve positions. Using concave mirror retinoscopy instead of plane mirror retinoscopy and not making the necessary adjustment.

5. Holding lenses away from the spectacle plane.

6. Not concentrating on the movement in the centre of the pupil in patients with large pupils.

• Clinical Pearl: USING MOVEMENT TO CHECK NEUTRALITY
• When you think you have neutrality, you can check by:
• When you move forward, the ret reflex will become “with”
• When you move backward, the ret reflex will become “against”. International Centre for Eyecare Education
• Recording findings
• If using a working distance lens:

The refractive correction is recorded in spherocylindrical format after removing the working distance lenses.

e.g. OD: -1.00 / – 2.00 x 90 OS: -1.00 / -1.75 x 95 Do not use the DS for dioptres of spherical power, DC for dioptres of cylindrical power or the degree sign when recording the prescription in this form. Also use the symbol “x” for the word axis. If the axis is 0º, then it is recorded preferably as an axis of 180. These are one and the same.

• If not using a working distance lens:

The refractive correction is recorded in spherocylindrical format after adjusting the final prescription in the trial frame by the appropriate working distance correction.

e.g. If a working distance of 50cm was used and the final prescription in the trial frame was as follows:

OD: -1.00 / – 2.00 x 90 OS: -1.00 / -1.75 x 95 One would need to subtract a correction of 2.00DS from this spherical aspect of the final result. The final prescription would thus be recorded as:

OD: -3.00 / – 2.00 x 90 OS: -3.00 / -1.75 x 95 Similarly, if a final prescription of OD: +5.00 / – 2.00 x 90 OS: +3.00 / -1.75 x 95 was found, the final Rx, with assuming 50cm working distance, would be recorded as: OD: +3.00 / – 2.00 x 90 OS: +1.00 / -1.75 x 95.

• Interpretation of the final results
• The following classification of refractive error is commonly used:
• Simple myopia: minus sphere lens only.
• Simple hyperopia: plus sphere lens only.
• Simple myopic astigmatism: plano sphere with minus cylinder.
• Simple hyperopic astigmatism: plus sphere of same power as minus cylinder.
• Compound myopic astigmatism: minus sphere with minus cylinder.
• Compound hyperopic astigmatism: plus sphere with minus cylinder of less magnitude than the sphere.
• Mixed astigmatism: plus sphere with minus cylinder of greater magnitude than the sphere.

Other scenarios

• Latent hyperopes have a tendency to display more sphere on retinoscopy than on dry subjective refraction.

Patients with media opacities may display dim/dull reflexes which can make retinoscopy difficult to perform.

In these cases one may need to perform radical retinoscopy, with a reduced working distance or off-axis position. International Centre for Eyecare Education

SECTION B – VISUAL FUNCTION ASSESSMENT