Clinical refraction...2024 Ayan Das learn

Refraction

1. REFRACTION
Ayan Das
2
nd
Year, George College of
Management and Science

2. Introduction
In Ophthalmology and Optometry, Refraction (also known as
Refractometry) is a clinical test in which a Trial Frame or
Phoropter is used to determine the eye’s refractive error and
the best corrective lenses to be prescribed. A series of test
lenses in graded optical powers are presented to determine
which provide the sharpest, clearest vision

3. Prequisties
➢Dark room
➢Trial set
➢Trial Frame
➢Distance Vision chart
➢Near vison chart
➢Retinoscope

4. Retinoscope
➢An accurate objective measurement of the refractive state of
the eye can be made using the Retinoscope.
➢The technique is called Retinoscopy
➢Others names are-Pupilloscopy, Shadowscopy, Skioscopy,
Scotoscopy

5. Type of Retinoscope
Mainly two types. In clinical Practice Streak Retinoscope is
preferred by practitioners.
➢Reflecting(Mirror)
1.Plane mirror
2.Priestly Smith’s mirror
➢Self Illuminated
1.Spot retinoscope
2.Streak retinoscope

6. A
B
C
Fig: A-Streak Retinoscope, B-Mirror retinoscope, C-Spot retinoscope

7. Optical Principle of Retinoscope
➢Retinoscope works on Focault’s principle.
➢Retinoscopy is based on the fact that when a light is reflected
from a mirror into the eye, the direction in which the light will
travel across the pupil will depend upon the refractive status of
the eye.

8. Procedure of Retinoscopy
➢Ask the patient to fixate on target
➢Patient’s RE is examined with the examiner’s RE with the
retinoscope in right hand.
➢Working distance is about 67 cm
➢Examiner's both eye should be open
➢Examiner observes a red reflex in the pupillary area of the patient’s
eye
➢Retinoscope ismoved in both Horizontal or Vertical meridians

9. Inferences of Retinoscope
With Need more Plus
Against Need more Minus
Dim Far from Neutralization
Bright Close to Neutralization
Narrow Far from Neutralization
Wide Close to Neutralization
Slow Far from Neutralization
Fast Close to Neutralization
Movement
Brightness
Width
Speed

10. Neutralization of Red Reflex
➢Myopia : Add –ve lenses
➢Hypermetropia : Add +ve lenses

11. Problems of Retinoscopy
➢Poor or invisible red reflex
➢Changing retinoscopy findings
➢Spherical aberrations
➢Scissoring shadows
Fig:-Scissoring shadows

12. Ccommon visual Abnormalities
➢Myopia
➢Hypermetropia
➢Astigmatism
➢presbyopia

13. Myopia
➢Myopia, also called Nearsightedness or Shortsightedness is a
refractive defect of the eye in which light produces image focus
in front of the retina with accommodation at rest.
➢Those with myopia typically can see nearby objects but distant
objects appear blurred.
➢Concave or minus power lenses are prescribed to treat myopia.

15. Hypermetropia
➢Hypermetropia also known as Hyperopia or colloquially as
Farsightedness or Longsightedness, is a defect of the vision
caused by an imperfection in the eye (often when the eyeball is
too short or when the lens cannot become round enough),
causing inability to focus on near objects.
➢Light rays are focused behind the retina.
➢Convex or plus power lenses are prescribed.

17. Astigmatism
➢A condition of refraction wherein a point focus of light cannot
be formed upon the retina. Light rays enter the eye (with
accommodation at rest) do not come to a single point focus but
form focal lines.
➢Irregular curvature of anterior surface of cornea and lens cause
astigmatism.
➢Cylindrical lenses are prescribed.

19. Presbyopia
➢Presbyopia is the eye’s diminished ability to focus that occurs
with age.
➢It is not a disease as such, but a condition that affects everyone
at a certain age.
➢The first symptoms are usually noticed between the ages of 40-
50, through in fact the ability to focus declines throughout life.

21. Visual Acuity
➢It is a number that indicates the sharpness or clarity of vision.
➢A visual acuity measurement of 20/70 means—A person with
20/70 vision who is 20 feet from an eye chart sees what a
person with unimpaired (or 20/20) vision can see from 70 feet
away.
➢6/60 means–can read 60 size Optotype in the Snellen chart
from 6 meters)

22. Fig:-Snellen chart

23. Visual Acuity testing
➢Ensure proper lighting and distance from the chart of the patient.
➢Cover one eye at a time.
➢Read the smallest line possible.
➢If he/she can not see the letters then stand in front of him/her and
ask to count fingers and the visual acuity is recorded as “Finger
Counting (FC)”. If he/she can not even count fingers then hand in
different directions is moved in front of him/her and the acuity is
recorded as “Hand Movement(HM)”.

25. Near visual acuity
➢It is a measurement of howwell one can see close objects.
➢It is measured using a small handheld chart or Snellen’s near vision
chart that has paragraphs of text that is smallest at the top and
largest at the bottom.
➢These are of a standard size and “Normal” near vision is known as
N6, with “N” referring to near and the “6” referring to the size of the
letters.
➢Bright light is used during this test.

26. Fig:-Near Vision chart