Retinoscopy

RETINOSCOPY


REFRACTION

  • The procedure of determining & correcting refractive errors is termed as refraction.

The refraction comprises two complementary methods:

A. Objective methods:

  1. Retinoscopy
  2. Refractometry 
  3. Keratometry

B. Subjective methods:

  1. Subjective refining of refraction 
  2. Subjective verification of refraction

RETINOSCOPY

  • Also c/d skiascopy or shadow test.
  • An objective method of finding out the error of refraction by the method of neutralization.
  • With the help of a retinoscope, light is thrown onto the patients eye.
  • Through a hole in the retinoscope’s mirror the examiner observes of red reflex, which also moes when the retinoscope is moved.
  • Depending upon the movement of the red reflex when a plane mirror retinoscope is used at a distance of 1 meter, the results are interpreted as:

i) No movement of red reflex→ Myopia of 1D.

ii) Red reflex moves along with retinoscope→ It indicates any of the following:

  1. Normal eye (Emmetropia)
  2. Hypermetropia, or myopia less than 1D

iii) Red reflex moves against to the retinoscope → Myopia more than 1D.

Rough estimate of refractive error after retinoscopy

  • Made by taking into account the retinoscopy findings & following deductions.
  1. Deduction of 1D for 1m & 1.5D when retinoscopy is performed at 2/3rd m (67 cm) distance.
  2. Deduction for cycloplegic (1D for atropine, 0.5D for homatropine, 0.75D for cyclopentolate)
  • For e.g, when retinoscopy finding is 5D with the procedure performed at 1m distance using atropine as cycloplegic then appropriate refractive error (RE) will be:
  •    RE=5D-1D (for distance)-1D (for cycloplegics)= 3D

Cycloplegics in refraction (cycloplegics in Retinoscopy)

  • Cycloplegics are drugs which cause paralysis of ciliary muscles (accommodation) and dilatation of pupil.
  • Use of cycloplegics is useful in refraction & there are certain situations where they are indicated.
  1. Atropine 1% ointment is the drug of choice.
  2. 15-20 years:
  • Homatropine (2% drop), Cyclopentolate (1% drop), Tropicamide (5%, 10% drop) are used.
  • Atropine must be used if the patient has a convergent squint or has high hypermetropia.
  • There is no need for cycloplegia as a routine in adults (20-40 years).

Cycloplegics are indicated in following situations:-

  1. Accommodation is abnormally active (eg spasm of a accommodation)
  2. Objective findings by retinoscopy do not agree with the patient’s subjective requirement.
  3. If the pupil is small.
  • If the patient is above 40 years, cycloplegia is rarely necessary.
  • Only mydriatic (10% phenylephrine) may be needed when the pupil is narrow or media is slightly hazy.

Exam Important

  • Retinoscopy is used for Detecting errors of refraction.
  • Shadow test is used in Retinoscopy.
  • Objective assessment of the refractive state of the eye is termed Retinoscopy.
  • No movement of red reflex  in retinoscopy → Myopia of 1D.
  • Red reflex moves against to the retinoscope → Myopia more than 1D.
  • The end point of streak retinoscopy is Streak disappears and the pupil appears completely light or dark.
  • Cycloplegics are Homatropine , Cyclopentolate , Tropicamide are used.
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