BASIC CONCEPTS Flashcards
EMMETROPIA
the image of an object at infinity is formed on the retina when accommodation is fully relaxed
ACCOMMODATION
adjustment of dioptric power of the eye brought about by a change in the shape of the crystalline lens + allows the eye to focus at many distances from very fair to very near
AMETROPIA
state where refractive error is present e.g. image of an object at infinity is not formed on the retina when accommodation is fully relaxed
FAR POINT
a point in space conjugate with the retina when accommodation is fully relaxed
emmetropia - far point is at infinity
SPHERICAL AMETROPIA
myopia + hypermetropia are types of spherical ametropia
correctable with spherical lens
ASTIGMATISM
image of a point object is not a single point but rather two focal lines, which are generally mutually perpendicular
astigmatism is correctable using a cylindrical lens of a combination of spherical + cylindrical
OBJECTIVE REFRACTION
practitioner measures the refractive error without any response from the patient
SUBJECTIVE REFRACTION
patient has to make responses based on instructions from the practitioner
RETINOSCOPY
objective method of determining the refractive error of the eye
useful when measuring refractive error in children + those with language/ learning difficulties
may highlight hypermetropia in those with very active accommodation or allow early detection of cataract
TYPES OF RETINOSCOPE
STREAK + SPOT
STREAK RETINOSCOPY
a streak of light is directed through the pupil of the eye + the practitioner observed the patch of light reflected from the retina
patch known as the reflex
HOW TO NEUTRALISE AGAINST MOVEMENTS
introduce a minus lens of an appropriate power in front of eye
against movements always indicate MYOPIA
WITH MOVEMENTS INDICATE WHAT?
HYPERMETROPIA
