- The procedure of determining & correcting refractive errors is termed as refraction.
The refraction comprises two complementary methods:
A. Objective methods:
B. Subjective methods:
- Subjective refining of refraction
- Subjective verification of refraction
- 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:
- Normal eye (Emmetropia)
- 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.
- Deduction of 1D for 1m & 1.5D when retinoscopy is performed at 2/3rd m (67 cm) distance.
- 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.
- Atropine 1% ointment is the drug of choice.
- 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:-
- Accommodation is abnormally active (eg spasm of a accommodation)
- Objective findings by retinoscopy do not agree with the patient’s subjective requirement.
- 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.
- 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.