Transcript OPTO 4101: Refraction1- lab L01: Taking history

OPTO 4101: Refraction1
Difficulties in retinoscopy
Mohammed A.M Aljarousha
Department of Optometry
Faculty of Allied Health Sciences
Islamic University-Gaza
What is the difficulties in retinoscopy???
Difficulties in retinoscopy
1.
2.
Some refractions are easy while others are extremely difficult.
Retinoscopy is an art which requires painstaking practice and can not be
learned in one day.
3. It’s essentially practical and can not be learned from text books but only
under careful supervision.
A- Difficulties due to inadequacy of technique:The subjective refraction will reveal uncorrection of (V.A) and unacceptance
of the lenses by the patient. Such state of affairs commonly results from the
mistakes of an inexperienced (unpractised), refractionist.
It’s important to keep a suitable working distance and to ensure that
retinoscopic examination is performed close to the visual axis in order to
refract the macula.
In this respect not only the horizontal orientation to be noted but also the
vertical one. Failure to observe this fact may falsely introduce a cylindrical
element during retinoscopy.
B. Difficulties due to absence of relaxation of accommodation of the examined eye:If the accommodation is not being kept inactive during retinoscopy, the retinoscopic
results are changing during the examination.
So the accommodation must be inactive during retinoscopy, this is obtained by using
two tricks:
Fogging of retinoscopy by inserting a high convex lens + 10 Ds in the trial frame in
front of the examined eye and asking the patient to look away at infinity, then
replacement of the lenses in the trial frame as retinoscopy proceeds is always done
so that neither examined eye is exposed to light without a lens before, and new lens
is inserted then the replaced lens is removed.
To get the patient to close then to open his eyes, inspecting his eye by retinoscopy
just he opens his eyes.
If the above two tricks fail to relax the accommodation especially in young persons
and children cyclopelgia (paralysis of the ciliary muscle) is used.
What is the advantages & disadvantages of
cycloplegia???
1.
2.
Paralysis of accommodation to make easy retinoscopy.
Pupil dilatation (mydriasis) leads to good visualization of red reflex.
3. Macular refraction is more accurate
Disadvantage (side effects) of cycloplegia
1. Dilated pupil alters the optical properties of the optical system of the eye,
the resulting observations are due to refraction of the lens (as the rays pass
in periphery and the central area of the lens) lead to some % of errors due
to different refractions.
2. During cycloplegia there is paralysis of the parasympathetic nerve supply to
the lens capsule with loss of it's ability to change the shape of the lens matter
leading to loss of accommodation till the tone is replaced.
3. Pupil dilatation may result in acute angle closure glaucoma (ACG) in some
persons who have a narrow angle of anterior chamber especially in those 40
years old or more , this complication must be taken in consideration before
instillation of the mydriatic drops especially patient having high degree of
hypermetropia.
What is the Special difficulties in retinoscopy???
Special difficulties in retinoscopy
I. Fainting of red reflex:
Causes
a) Opaque ocular media:
1. In corneal leucoma
2. Blood in AC (hyphema)
3. Lens opacities (immature cataract)
4. Vitreous bleeding (mild vitreous haemorrhage)
5. Retinal detachment
b) Very high refractive error:
Like high myopia or hypermetropia
Corneal leucoma
Hyphema
Vitreous haemorrhage
Retinal detachment
Special difficulties in retinoscopy
II. Variation of red reflex in different parts of the dilated pupil:
• The central part being different from the periphery
• The variation is accentuated by the dilation of the pupil (mydriasis)
• This is due to spherical aberrations tends to cause an increase in the
brightness of the center or the periphery of the pupil, depending on whether
the aberrations are negative (in HM) or positive (in Myopia).
Negative aberration (the periphery is faint and the center is shiny)
Positive aberration (the periphery is shiny and the center is faint).
Spherical aberration
Special difficulties in retinoscopy
III. Sissor Shadow:
• When a mixed aberrations (negative and positive) occurs so that one ½ the
reflex differs from the other half in its refractivity, 2 band reflexes appear
which move toward and away from each other like the blades of scissor.
• The optics of the phenomenon wherein one of the aperture is relatively
myopic and the other hypermetropic (mixed and irregular astigmatism).
Sissor shadow presents in:
1. Corneal scars
2. Irregular astigmatism like in keratoconus (irregular myopic astigmatism)
may give the similar shadow.
Corneal scar
Keratoconus
Special difficulties in retinoscopy
IV. In squinting children
V. General anesthesia may be necessary in uncooperative children.
VI. In immature cataract very confused reflexes are often obtained: