Objective method of refraction retinoscopy It's the most valuable method of estimating the optical state of the eye , it's useful and accurate up to (0.25D) correction. Goal of retinoscopy: Is to determine the nature of the patient’s refractive error. Is to approximate the lens power that will neutralize the error and improve vision. Is to assess the refractive error in infants, small children, illiterate persons, mentally retarded, uncooperative individuals and patients with speech loss.

Types of retinoscope Classical retinosope= Reflecting retinoscopy: It consists of a separate source of light which is bright, narrow and fixed behind and above the shoulder of the patient. The observer catches a perforate mirror with a central opening not less than 4mm in diameter. This plane perforated mirror reflects the light from the source into the patient’s eye which sends the image that can be seen by observer's eye as red reflex (R.R) through the central opening. Movements of the illuminated area of the patient's retina are produced by tilting the mirror. The used mirror may be plane or concave but the plane one gives a better result.

B. Luminous retinoscope: In which both of light source and mirror are incorporated. It's standard modern instrument, easily manipulated with the advantage that the intensity and type of the beam can be readily controlled. It's portable. The most popular luminous retinosope today is the streak retinoscope as it produces more easily recognized red reflex, it also allows the axis of the meridian of astigmatism to be more readily identified separately. It contains a strong convex lens for condensation of light in the patient's eye. Even greater efficiency is obtained from the modern retinoscopy by the use of halogen bulbs and rechargeable batteries.

The retinoscope has a viewing system and illuminating system The viewing system consists of a small a aperture at the head of the retinoscope that enables the examiner to see. The illuminating system consists of light source which is a straight line filament of the bulb in streak retinoscope, plane mirror and a condensing lens between the mirror and the bulb. A movable sleeve is present that envelops the whole retinosope, the bulb may be rotated 360 and moved up down to adjust its focus.

What happens during retinoscopy The illuminating system of the retinoscope shines divergent rays of light into the patient’s eye. The illuminated area of the patient’s retina acts as an object in dark room that reflects the light to be seen on the patient’s pupil as red reflex. When the operating sleeve is in the lowest position the light rays emitted from the retinoscope are slightly divergent (nearly parallel), here the instrument acts with Plano-mirror effect, where the light rays cross and diverge, because the rays cross the reflex moves in opposite direction with the concave mirror as compared to the Plano mirror effect. The degree of divergence of light rays entering the eye from the illuminating system of the retinoscope depends on the distance between the retinoscope and the patient eye, for example if the retinoscope held at distance 67 cm from the patient eye, the rays produced are divergent therefore, a + 1.50 D lens is put in the trial frame, so that the divergent rays when entering the patients pupil are in fact parallel.

The vergence of the rays that leave the patients eye is dependent on the refractive error of the patient’s eye. The rays leave to the far point of the patient’s eye. - In emmetrope the rays leave parallel - In myope the rays leave convergent - In hypermetrope leave divergent The examiner sees these light rays against the background of the pupil and observes their motion as the retinoscope beam sweeps from side to side or from up to down. If the image formed between the eyes of patient and the observer, the red reflex moves opposite to the movement of the retinoscope (high to moderate myope). If the image formed behind the eye of the observer (low myopia) or the eye of the patient (hypermetropia) the red reflex moves with the movement of the retinoscope.

When the far point of the patient’s eye corresponds to the nodal point of the observer's eye the neutral point (end point) is reached, where no movement of red reflex is noticed. The final objective of retinoscopy is to find the lens that places the far point in the plane of the observers eye, at this point the retinoscopic reflex is said to be neutralized. That is, there is neither with nor against movement, and the patients pupil seems to be filled with light. The working distance between the eye of the examiner and the eye of the patient, and is the reciprocal of the power in diopters which should be deduced from the power of the lenses that were added during retinoscopy to reach the neutral point. - If the W.D is 2 ms we deduce 0.50D. - If the W.D is 0.5 ms we deduce 2.00D. - If the W.D is 1 m we deduce 1.00D.