Theory of Retinoscopy

DEFINITION Retinoscopy is the name given to the objective method of determining the refractive errors by using retinoscope.

Retinoscopy

procedure The fundus is illuminated by means of a mirror or by a self illuminated streak retinoscope situated classically 1 or 2/3 meter away from the subject.

Principle The illuminated area of fundus is not seen by the observer but only acts as a source. The rays emanating from the source from an illuminated area in the plane of the pupil of the subject which is called retinoscope shadow or reflex.

Objective method Examiner sits at 67 cms away from the patient ( Point of reversal is at 1.50D) The Patient is normally seated and looking towards the far end of the room. Source of light is from behind the patient. The Examiner looks through a plane mirror with central perforation, and light is reflected into the patient’s eye. The Examiner is slowly moved from side to side in different meridians, and movement of the shadow is noted.

Stages of retinoscopy Illumination stage : Light is directed into the patient’s eye to illuminate the retina . Reflex stage : A image of the illuminated retina is formed at the patient’s far point. Projection stage : The image at the far point is located by moving the illumination across the fundus and noting the behavior of the luminous reflex seen by the observer in the patient’s pupil.

Illumination Stage Plane mirror

Illumination by Streak Retinoscopy

Reflex Stages

Reflex Stages

Reflex Stages

Projection Stage Hypermetropia

Emmetropia

Myopia less than 1.50D

Myopia of 1.50D

Myopia > 1.50D

Retinoscopy Movement Speed Brilliance Width

Methods In Hypermetropia, emmetropia and myopia <1.50D = the reflex moves in the same direction.( with movement) In Myopia of 1.50D= there is no shadow In Myopia of > 1.5D= the shadow moves in the opposite direction. ( against movement) The procedure is done for each meridians separately In astigmatism, they are different. If the axes are oblique, the shadow themselves will seem to move obliquely and the mirror is then tilted accordingly.

Calculation Refraction of Patients eye = lens required to reach end point = -1.50D(Myopia) Since the Examiner is sitting at 1mt distance and if he is at 2/3rd mt, it will be -1.5D(myopic) So the refraction of the eye= -1.50D +lens

Example If the end point is with +4.0D lens: Refraction = -1.50D +4.0D lens= +2.50D Similarly with -3.50D lens: Refraction = -1.50D -3.50D = -5.0D If the end point is with +1.50D lens Refraction = -1.50 +1.50D = 0 the patient is emmetropic In case of astigmatism, each meridian is to be calculated separately

Subjective Verification of Refraction

Subjective Verification After objective test, it should always be verified subjectively by testing the visual acuity

Procedures Each eye is to be tested separately, the other eye being blocked, and then finally tested together. Appropriate lenses, as found by objective test, are inserted in the trial frame. Slight modification of the inserted lens gives a maximum visual acuity. Verification may be needed with a cross cylinder, or astigmatic fan in case of astigmatism

Duochrome Test To test if the eye has been under corrected or over corrected or is properly corrected

Astigmatic fan To know the axis and power in Astigmatism.

Jackson's Cross Cylinder To refine the axis and power of Cylinder.

Fogging Method Sometimes fogging method is necessary to induce a relaxation of accommodation especially in hypermetropia.

Example Here, the eyes are made artificially myopic by addition of convex lenses (Ex+4.0D). This is then gradually lessened by a small fraction (0.50D) until the maximum acuity is just reached. The first lens is not removed until the next is in position, to prevent from accommodation becoming active.

Procedures As a rule, the patient is given the strongest hypermetropic, or weakest myopic correction with normal visual acuity. The addition of the correction for near work (if necessary), and testing of the acuity with near- types, uniocularly and then binocularly Then the spectacles have been ordered with necessary comments (Ex) Constant wear, Near works only

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