objective refraction

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Objective Refraction:

Objective Refraction presented by Nilima sen optometry intern at Shekar Nethralaya

Objective refraction:

Objective refraction The examiner determines the type and degree of refractive error without active perticipation of the patient. Very essential as well as useful for determinig the type and degree of refractive error maily in young patient and patients with poor communication.

Methods:

Methods The objective refraction methods include – 1. Retinoscopy 2. Conventional refractometry 3. Autorefractometry

Retinoscopy:

Retinoscopy The determination of the refractive state of the eye by means of retinoscope. It is invented by Ophthalmologist Dr. Jack Copeland.

Retinoscopy:

Retinoscopy It is also known as ‘skiascopy’ or ‘shadow test’ . Retinoscopy is an objective method of finding out the refractive error by utilizing the technique of neutralization. A spot of the fundus of the pt’s eye is illuminated by reflecting light into the eye with a plane or concave mirror & the image of this illuminated spot formed by the pt’s eye, is observed, when the light is reflected back.

Principle of Retinoscopy:

Principle of Retinoscopy The principle of retinoscopy is to convert the observed eye into a degree of myopia that the image formed by the fundus infront of the observed eye coincides with the pupillary plane of the observer.

Pre-requirement for Retinoscopy:

Pre-requirement for Retinoscopy 1. Dark room- - Preferably 6mt long or which can be converted into 6mt by use of a plane mirror. 2. A trial set- - A standard trial box with sph. & cyl. lenses of powers (plus & minus). - Accessories:- prisms, plano lenses, opaque disc, pinhole, stenopeaic slit, maddox rods & red & green glass.

Pre-requirement for Retinoscopy contd….:

Pre-requirement for Retinoscopy contd…. 3. A trial frame- -light in weight with comfortable fitting nose rest. -fitted with four compartments for lodging sph. lens, cyl. lens, occluder & the any of the accessories. 4. Distance vision chart- -A snellen’s self illuminated vision box. 5. Near vision chart- -Jaeger chart, reduced snellen’s test types are used for testing near vision.

Pre-requirement for Retinoscopy contd….:

Pre-requirement for Retinoscopy contd…. 6. Retinoscope- -It is invented by Ophthalmologist Dr. Jack Copeland. -It is a simple device to perform the retinoscopy. -There are 3 types of retinoscope. 1. Plane mirror 2. Pristely-Smith mirror 3. Self illuminous streak retinoscope

Types of Retinoscope If one does not have autorefractor, the retinoscope is one of the most useful & essential clinical assessment tools for eye care professional.:

Types of Retinoscope If one does not have autorefractor, the retinoscope is one of the most useful & essential clinical assessment tools for eye care professional.

Use of plane mirror:

Use of plane mirror The use of plane mirror is to obtain ideal results by opening hole in the centre of mirror which should be 4mms in size. By a plane mirror, rays are slightly divergent causing less illumination & counter balanced by appearance of a circular dark patch. To overcome this difficulty, a weak concave mirror of 150cm focal length is used which converges rays of light on the cornea. It acts as a plane mirror for all practical purposes.

Situation of source of light:

Situation of source of light The shape of the illuminated area depends upon the shape of the original light source. The light is usually kept at about 25cms behind the pt & is small about 25mms in diameter. The observer sits at about 1mt distance, so distance of mirror from the light source is 1.25 metres. The rays that enter the pt’s eye are reflected rays from the mirror, so the eye of the pt will be 2.25metres from the immediate source of light.

Size of retinal image in Retinoscopy:

Size of retinal image in Retinoscopy

Use of streak Retinoscopy:

Use of streak Retinoscopy The streak retinoscopy is more popular in detecting astigmatism. When the light of retinoscope is thrown on the pupil, a band of light is seen partly in the pupillary aperture & partly outside the pupil above & below. When the retinoscope is moved horizontally, the band in the pupil may move either “with or against” the movement of retinoscope. With movement Against movement

Use of streak Retinoscopy contd…. :

Use of streak Retinoscopy contd…. With movement indicates hypermetropia or myopia of less than 1D & against movement indicates myopia. Suitable lens is placed before the eye for neutralize the band when the pupil will be filled by uniform light. Now the retinoscope is moved vertically, if still the pupil is filled by uniform light. It means there is no astigmatism.

Using the Retinoscope:

Using the Retinoscope Hold the retinoscope in one hand so that you can view the patient's eye through the peephole of the scope.Depending upon the model,your thumb or index finger of the same hand is used to hold the sleeve in the sleeve-up position and to rotate the sleeve, which rotates the streak.

The basic streak reflexes:

The basic streak reflexes If the streak move across the pupil, there are 3 basic types of reflexes will be seen. 1. With motion 2. Against motion 3. Neutral reflex

The basic streak reflexes contd….:

The basic streak reflexes contd…. 1. With motion- if the streak moves across the pupil, the reflex moves across the pupil in the same direction. 2. Against motion- if the streak moves across the pupil, the reflex moves in the opposite direction. 3. Neutral reflex- if the streak touches the pupil, the pupil fill with red reflex & remains constant as the streak over across the pupil.

Streak reflex width & streak speed:

Streak reflex width & streak speed The width of the streak reflex & the apparent speed of the streak reflex moves across the pupil, it indicates that how for are from neutrality. A very wide, slow moving streak reflex with motion indicates long way from neutrality. When add plus sph power, the streak tends to narrow & speed in its apparent motion. Continue adding plus sph power & approach neutrality, the streak widens again & speeds more. At neutrality the streak reflex widens more to completely fill the pupil.

Distance for Retinoscopy:

Distance for Retinoscopy Retinoscopy is carried out preferably from a distance of 1mt. Mostly retinoscopy is preferred at about an arms length (2/3mt distances) away from the pt, which is regarded as a working distances. Lesser the distance used for retinoscopy the greater are the errors in objective assessment of the refractive error.

Neutral point:

Neutral point The neutral point is the point at which the reflected rays from the illuminated spot on the fundus after refraction by the observed eye fill the pupillary plane of the observer’s eye.

Behavior of light rays with movement of plane mirror:

Behavior of light rays with movement of plane mirror When a plane mirror is used to reflect the light, the ISL moves against the movement of mirror. Eg:- If mirror is moved upwards the ISL (S1) moves downwards & vice versa.

Behavior of light rays in emmetropia:

Behavior of light rays in emmetropia The light rays emerging out of the pt’s eye from the illuminated spot on the fundus are parallel to each other & reach the observer’s eye as such. The observer project the image of F1 to f1 & spot F2 to f2, when the spot F1 moves to F2, the image f1 also moves upwards to f2 in the same direction of movement of plane mirror

Behavior of light rays in hypermetropia:

Behavior of light rays in hypermetropia The light rays emerging out of the pt’s eye from the illuminated spot on the fundus are divergent & reach the observer’s eye. The observer project the image of F1 to f1 & spot F2 to f2. when the spot F1 moves to F2, the image f1 also moves upwards to f2 in the same direction of movement of plane mirror

Behavior of light rays in myopia of less than 1D:

Behavior of light rays in myopia of less than 1D The light rays emerging out of the pt’s eye from the illuminated spot on the fundus are convergent & meet at f1 & f2 behind the observer sitting at 1mt from the pt. Since these rays are intercepted by observer so projects to f3 & f4. When the spot F1 moves f2 (upward) the image f3 also moves upward to f4 in the same movement of the plane mirror.

Behaviour of light rays in myopia of 1D:

Behaviour of light rays in myopia of 1D The light rays emerging out of the pt’s eye from the illuminated spot on the fundus are convergent & meet at the level of pupillary plane of the observer. When the illuminated spot F1 moves to F2 (upwards) the image moves to f1 & f2. So there is no movement of the shadow with the movement of the retinoscopy mirror.

Behaviour of light rays in myopia of more than 1D:

Behaviour of light rays in myopia of more than 1D The light rays emerging out of the pt’s eye from the illuminated spot on the fundus are convergent & meet at f1 & f2 in the space between the pt. & observer. When the spot F1 moves to F2 (upwards) the image f1 moves to f2 (downwards)opposite to the movement of the plane mirror.

Character of the moving retinal reflex:

Character of the moving retinal reflex 1. Speed & prilliance- - In low degree of refractive error the shadow (red reflex) seen in the pupillary area is faint & moves rapidly with the movement of the mirror. - In high degrees of refractive error, it is very dark & moves slowly.

Character of the moving retinal reflex contd….:

Character of the moving retinal reflex contd…. 2. Width of reflex- -In high degrees of refractive error, it is narrow. -In low degree, it is wide. -At the neutralization point, the entire pupil is filled with light. 3. In the +nce of astigmatism- -When the axis does not correspond with the movement of the mirror, the shadow appears to swirl around.

Observation of movement of red reflex:

Observation of movement of red reflex No movement of red reflex indicates myopia of 1D. When red reflex moves along with the movement of the retinoscope, it indicates emmetropia or hypermetropia or myopia of less than 1D. A movement of red reflex against the movement of the retinoscope, indicates myopia of more than 1D.

Observation of movement of red reflex contd….:

Observation of movement of red reflex contd…. with movement neutralization Against movement

Cylinder Retinoscopy:

Cylinder Retinoscopy Most people have some degree of astigmatism. A difference in the appearances of the reflexes observed in the two principal meridians is noticed, As the reflexes are neutralized with the streak rotated to keep it aligned with the reflex.

Finding the cylinder axis:

Finding the cylinder axis In the presence of astigmatism, one axis is neutralized with the appropriate sph. lens & the second axis still shows the movement of reflex in the direction of axis of astigmatism.

Finding the cylinder axis contd…. :

Finding the cylinder axis contd…. When the streak is not parallel with the reflex in the pupil. The oblique axis can be determined by rotating the streak until the break disappears. The correcting cyl. should be placed at this axis.

End point of Retinoscopy:

End point of Retinoscopy The end point of retinoscopy means neutralization of red reflex in any meridian with the movement of the mirror. It can be verified by- 1. Overcorrection by 0.25D should cause reversal of the movement. 2. By slight forward movement should observe ‘with movement’ & by slight backward movement observe ‘against movement’ .

Use of cycloplegia:

Use of cycloplegia Retinoscopy may be done undercycloplegic or mydriatic drugs or without any drug. Cycloplegics are the drugs which cause paralysis of accommodation & dilate the pupil. These are used for retinoscopy, when the examiner suspects that accommodation is abnormally active & will hinder the exact retinoscopy. When with cycloplegic retinoscopy is performed, it is called ‘wet retinoscopy’ & without cycloplegic ‘dry retinoscopy’ .

Problems in Retinoscopy :

Problems in Retinoscopy Red reflex may not be visible because of small pupil, hazy media & high degree of refractive error. This difficulty is overcome by mydriasis. Scissoring shadow occurs either in healthy cornea but with unusual difference in curvature in the centre & the corneal opacities which produce the same effect

Problems in Retinoscopy contd….:

Problems in Retinoscopy contd…. Spherical aberrations lead to variation of refraction in the centre & periphery of pupil. It may be seen in normal eyes but more marked in lenticular sclerosis. Conflicting shadows moving in various directions in different parts of the pupillary area with irregular astigmatism. Triangular shadow may be observed in patients with conical cornea.

Static & Dynamic Retinoscopy:

Static & Dynamic Retinoscopy Static retinoscopy- Retinoscopy with the pt’s accommodation relaxed, done while the pt. fixates on a target at a distance of 6mt. Dynamic retinoscopy- Retinoscopy with the pt’s accommodation in play, usually done while a pt’s accommodation on letters, words or pictures at a distance of 40 or 50cm.

Sources of error in Retinoscopy:

Sources of error in Retinoscopy Incorrect working distance. Scoping off the pt’s visual axis Failure of the pt. to fixate the distance target Failure to obtain reversal Failure to locate the principle meridians Failure to recognize scissors motion.

Automated Refarction:

Automated Refarction The “Refractometry” is an alternative method of finding out the refractive error. The instrument which is used for this technique is named as “Refractometer”.

Optical Principle:

Optical Principle Most of the autorefractometer are essentially based on two folowing principle- 1. THE SHEINER PRINCIPLE :- The refractive error of the eye can be determined by using double pinhole apertures before the pupil.

PowerPoint Presentation:

2. THE OPTOMETER PRINCIPLE :- Optometer is an instrument to measure the limit of disinct vision.The optical principle on which this instrument is based is termed as “optometer principle”.The principle permits continuous variation of power in refracting instrument.

PowerPoint Presentation:

Thank You

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