This document discusses spectacle refraction and how it relates to correcting refractive errors like myopia, hyperopia, and astigmatism. It defines spectacle refraction as the power of the lens needed to correct refractive errors at the spectacle plane. Myopia occurs when light focuses in front of the retina, and is corrected using concave lenses. Hyperopia is when light focuses behind the retina, corrected with convex lenses. Astigmatism is an irregular refraction that can be corrected using lenses, contacts, surgery, or lasers. The document also discusses how to calculate spectacle refraction from ocular refraction using vertex distance.

1. Presented by
Kabita Baruah
Arundhati Hatikakoty
BSc optometry 2nd year
RCO, Jorhat

2. SPECTACLE REFRACTION
 The power of the correcting lens, specified at the spectacle
plane is termed as spectacle refraction i.e. the power
which is required to correct any refractive error of the eye
such as myopia, hyperopia or astigmatism at the level of
spectacle plane is known as spectacle refraction.

3. MYOPIA
 When a parallel light of rays coming from infinity are
focused in front of the retina due to the mismatch between
the axial length of the eye and refractive power of the eye
is known myopia.
 It is also known as nearsightedness.

5. CORRECTION OF MYOPIA
 Myopia is corrected by
a)glasses – Concave lenses
b) contact lens
c) Surgical

6. MYOPIA CORRECTION BY
CONCAVE LENSES

7. HYPEROPIA
 When a parallel rays of light coming from infinity are
focused behind the retina due to the abnormality between
the refractive power of the eye and the axial length of the
eye is known as hyperopia.
 It is also known as farsightedness or hypermetropia.

9. CORRECTION OF HYPEROPIA
 Hyperopia is corrected by
a)glasses – Convex lenses
b) contact lenses

11. ASTIGMATISM
 It is a type of refractive error wherein the refraction varies
in different meridia
 So astigmatism literally means lack of focal point.

12. CORRECTION OF ASTIGMATISM
1) REGULAR ASTIGMATISM- Corrected by- a)spectacle
b) contact lens c)surgery
d)laser
2) IRREGULAR ASTIGMATISM- Corrected by contact
lens

14. OCULAR REFRACTION
 Ocular refraction is the refraction of light produced by the
media of the normal eye and resulting in the focusing of
images upon the retina
 It usually takes place in emmetropic or normal eye

15.  So far we have dicussed in the previous slides about the
refraction taking place through the spectacle plane and the
first principal plane of the eye i.e. cornea
 The amount of refraction which takes place in different
case of refractive errors correction can be calculated

16. VD

17. Eg: If the ocular refraction is -20.00D and the vertex distance is
13.00mm.than the spectacle refraction will be-
Given
ocular refraction = -20.00D
Focal length = -5 cm
vertex distance = 13 mm
= 1.30 cm
Focal length for Spectacle Refraction= -5-1.3 = -6.3 cm
SR=1/0.063
= -15.87 D

18. SR =1/0.037
= +27.02 D

19.  Eg : If the spectacle refraction is -25.00D at a vertex
distance of 13mm then the ocular refraction of the eye
will be
Given,
SR= -25.00D
VD=13mm= 1.3cm
Focal length=100/-25=-4.00cm
OR= -4.00-1.3
=-5.30cm
=1/0.053
=18.86D

20.  Eg : If the spectacle refraction is +25.00D at
a vertex distance of 13mm then the ocular
refraction of the eye will be-
Given,
SR= +25.00 D
VD=13mm=1.3cm
Focal length=100/+25
=+4.00cm
OR=+4.00-1.3
=2.70cm
=1/0.027
=37.03D

21. SPECIAL POINTS
When a contact lens is placed on the cornea,the difference
between ocular refraction and contact lens refraction is
very small because the distance between the corneal apex
and the first principal plane of the eye is only slightly
more than 1mm
The objective of a clinical refraction is to determine the
power of the correcting lens in the spectacle
plane.spectacle refraction is therefore of greater interest to
clinicians than is ocular refraction

22. Reference:
 Clinical optics
 http://www.google.co.in/spectacle+refraction.com