Objective refraction

Objective Refraction

Objective Refraction

Retinoscopy Mohammed AlJafen

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Principle of retinoscopy analysis of the light reflex created in the pupil by light reflected back from the retina for the purpose of objectively determining the refractive error

This reflected light starts with a light shining off a plane mirror of the retinoscope and then passing through the pupil to eventually shine on the retina

The light reflected back off the retina is viewed in the pupil by the examiner peeking means *the examiner sees * through a small aperture in the center of the retinoscope mirror.

Some modern retinoscopes produce a spot rather than a streak. These spot retinoscopes are more difficult to use.

The term objective refraction is used when the refractive error of an eye is determined without input by the patient .

Retinoscopy is a form of objective in which the judgment of a human operator is required to determine the refractive error.

Retinscope is done with help of instrument called RETINOSCOPY.

refractive error can be estimated objectively by a process called photorefraction.

Photorefraction is especially usueful when patient cooperation cannot be well maintained

Photorefraction is a photograph or videograph of the pupils is interpreted currently by a trained operator or clinician But there are now attempts to automated the interpretations of photographic and videographic refractors 3

Mildolt and Oleary (1978) concluded that the vitreoretinal reflex contributes significantly to the fundus reflexes of young patients when visible light is used in retinoscopy .

Common used synonyms of retinoscpy are Skiascopy and skiametry and other synonyms occasionally seen in literature are umbrascopy pupilloscpy retinoskiascopy

A restinoscpy is a small , handheld device that emits visible white light towards the pupil of the eye being analyzed and allows the operator to view the red reflex of light reflected back through the pupil from the ocular fundus .

When the R is on the eye

Right eye: the normal red reflex. Left eye: the absence of a red reflex is abnormal and could indicate a serious condition

Retinoscpic can be performed on who ?

Techniques of retinoscopy : Static retinoscopyNeeds for the acc to be relaxed Patient is asked to fixate at distance(6m) target

Dynamic retinoscopyNo needs to make the acc relaxedPatient is asked to fixate at 30 or 50 cm target

Spot Retinoscopy

Instrumentation ( structure) of RHead which has - Light bulb- Peephole- Mirror

Neck

Sleeve for rotating either down or up

Handle (electrical supply )

Static streak retinoscopy The technique of retinoscopy is used to objectively determine the refractive status of the eye relative to the point of fixation .

Retinoscopy is usually the first technique performed in the ocular examination that determines the patients refractive status , and it is immediately followed by the subjective refraction .

The retinoscopic findings , therefore , usually serve as the starting point for the subjective refraction and are independent confirmation of the subjective results .

The objective of static R is to find the position of the paraxial far point ]punctum remotum (PR)[ of the eye , an optical theory initially advocated by landolt in 1878.

The spot R reflects a beam of light from a circular source whereas the streak retinoscpe emits a beam from a line source .

Between these two forms of retinoscpes , the streak R is more useful clinically because it can be more readily applied to the determination of astigmatic corrections by assessment of the axis of cylinder and refractive powers in the two primary amertopic meridians.

The use of streak retinoscpy has generally replaced the use of spot R in ophthalmic practice .

Basically the retinoscopist views through the aperture of the R at a distance of 40 to 10 cm from the patients eye and shines the beam of the retinoscope into the pupil of patient's eye while the patient fixates a distant target.

The attributes of the pupillary reflex that signify the relative position of the far point are : WITH motion :compared with movement of the incident divergent rectangular beam ,indicates a far point location behind the retinoscope aperture (between the operator and infinity)

AGAINST MOTION of the streak indicates a far point location between the retinoscope aperture and the patients eye (moderately to highly myopic eyes)

IF the retinoscopic reflex is at NEUTRALITY, showing neither with nor against motion , the far point is located at the aperture of retinoscope

Hyperopic patients

Light focuses behind the retina

Streak movement in same direction as the retinoscope light (with motion )

Add plus lenses in this case to get neutralized ( to bring the focus point at the retina )

Myopic patients Light focuses at the point before the retina

Streak movement is in opposite of the retinoscope light (against movement )

Add Minus (-) lens to move the focus point on the retina

Emmetropic patients No motion of the reflex observed in the pupil

Known as ( neutral motion)

Scissors reflex When two band appear which move towards and away from each other like blades of scissors

Most of time occurs in only one meridian

Usually seen in kertoconus and irregular astigmatism cases

Normal cornea Vs keratoconus

Procedure of R

Procedure Patient sits at distance of 60 or 50 cm from the examiner

Patient is asked to fix his eyes at specific target to relax his accommodation

Now scope the R on patients eye and observe the light comes out of his eye .

Then determine if the motion is against , with or no motion

Make sure that you scope both meridians vertically and horizontally

If the motion in V and H is same then put + or Sphere lenses

If the motion in V and H is NOT same then put + or Cylindrical in case of astigmatism

Repeat the procedure on left eye with same steps

Working distance ( WD)Is the distance between the R and the patients eye

It can be calculated by this formula : D= 1/FWhich F is = the power of the lens .

E.g. F= 1.50D so the working distance is 0.66mm 1.50 /66cm (arms length ) so = 0.66 X 100=66 cm

The length of an averages persons arm is 66 cm

The power of the lens that focuses at best parallel light rays at 66 cm is +1.50 D

Here if u divide 1/1.5 u will get 0.66 but in Meter unit so multiply by 100 to get it in cm so u will get 66 cm 29

Neutralization In case of myopia Add lenses and then put + lenses till it get neutralizes

In case of hyperopia Add + lens till it get neutralizes

Recording R degrees. Also record the monocular visual acuity with the retinoscopy result. For example:RE: 2.00 DS/-0.50 105 6/4.5LE: 2.25 DS 6/4.52OD: 2.00/1.00 105 20/203OS: 1.75/0.75 70 20/25

References Primary care of optometry , page 183

Clinical procedure in primary eye care

Clinical refraction ,Chapter 18

Tom root ( youtube ) link : https://www.youtube.com/watch?v=ezOoPKZwNDk