Recommended
More Related Content
What's hot
What's hot (20)
Similar to New microsoft power point presentation
Similar to New microsoft power point presentation (20)
Recently uploaded
Recently uploaded (20)
New microsoft power point presentation
- 1. SPECTACLE REFRACTION VS OCULAR REFRACTION By… OPTM. JAINULL ABEDIN
- 2. BEFORE WE MOVE TO THIS WE NEED TO UNDERSTAND… REFRACTION PHYSICS- The change in the direction of the ray of light, sound, heat passing obliquely from one medium into another in which its wave velocity is different. OPTHALMIC- The ability of the eye to refract light that enters it so as to form an image on the retina.
- 3. SPECTACLE REFRACTION The power of the correcting lens, specified at the same plane in order to refract light to be focused clearly on the RETINA is termed as spectacle refraction. • The power which is required to correct any refractive error of the eye such as Myopia, Hypermetropia or Astigmatism by the help of correcting lens.
- 4. MYOPIA- When a parallel rays of light coming from infinity are focused in front of the retina due to the mismatch between the axial length of the eye or refractive power of the eye is known myopia. It is corrected by… a) Gasses – Concave lenses b) Contact lens c) Surgical
- 5. 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 or the axial length of the eye is known as hypermetropia. It is corrected by.. a) Glasses – Convex lenses b) Contact lenses
- 6. ASTIGMATISM- In this type of refractive error wherein the refraction varies in two different meridian, in which distortion of image affecting at all distance. So astigmatism literally means lack of focal point. It is corrected by.. a)spectacle b) contact lens c)surgery d)laser
- 7. OCULAR REFRACTION The refraction brought about by the refractive media of the eye… • Cornea (1st principle plane of ocular refn.) • Aqueous humor • Crystalline lens • Vitreous body The refraction of light produced by the media of the normal eye and resulting in the focusing of images upon the retina Which usually takes place in emmetropic or normal eye
- 8. COMING TO THE POINT So far we have discussed in the previous slides about the refraction that takes place through two different plane… • The spectacle plane • The Ocular plane Cornea. The amount of refraction which takes place in different case of refractive errors correction can be calculated
- 9. CALCULATING THE OCULAR REFRACTION POWER IN CASE OF MYOPIA / CONCAVE LENS- • If the spectacle refraction is -20.00D • At a vertex distance of 12mm • The ocular refraction of the eye will be:- OCULAR REFRACTION (OR) = FOCAL LENGTH (FL) – VERTEX DISTANCE (VD) OR= - 5-1.2 ( FL - VD) OR= -6.2 OR= 100/-6.2 OR= -16.12 THINGS TO REMEMBER Convert VD- MM into CM by dividing 10 Convert FL by dividing total diopter by 100
- 10. IN CASE OF HYPERMETROPIA / CONVEX LENS- • If the spectacle refraction is +20.00D • At a vertex distance of 12mm • The Spectacle refraction of the eye will be:- OCULAR REFRACTION (OR) = FOCAL LENGTH (FL) + VERTEX DISTANCE (VD) OR= +5-1.2 (FL - VD) OR= +3.8 OR= 100/+3.8 OR= +26.31 THINGS TO REMEMBER Convert VD- MM into CM by dividing 10 Convert FL by dividing total diopter by 100
- 11. NOTE’S 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 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. So as we get the spectacle power we can convert it into ocular power.
- 12. THANK’S…
Editor's Notes
- CONVERT VD INTO CM BY DIVIDING 10 CONVERT FL BY DIVIDING TOTAL DIOPTER BY 100