1. CLINICAL APPROACH TO REFRACTIVE ERRORS
Ayesha Abdullah

2. Learning objectives
By the end of this lecture the students would be able to;
Correlate optics with the various types of refractive errors & their correction with lenses
Describe the clinical presentation of refractive errors
Describe the clinical protocol for the assessment of refractive errors

3. To begin with Refraction ? Refractive errors?
Main refractive surface of the eye?
How much is the refractive power of the cornea?
40-44 diopters
Why is it so?
So its mainly corneal refractive error!
How much is the role of lens in refraction?
What is the role of accommodation in refraction?
During accommodation in a youthful eye the lens can change its refractive power from 19 D to 33 D

4. What determines the type and amount of refractive error?
Refractive power of the cornea and the lens
Length of the eye (1m.m. changes represents about 3 dioptres change in refraction)
Refractive errors of up to 5 D are considered to be biological variation
Higher degrees of refractive errors are associated with structural anomalies of the ocular structures e.g. the cornea, lens, choroid and the retina

5. What is emmetropia & ametropia?
The state of having no refractive error is emmetropia ; a balanced state of refractive power of the cornea, lens and the length of the eyeball.
Parallel rays of light are brought to a focus on the fovea
The state of the eye when parallel rays of light are not focused on the fovea is called ametropia
The state of having no refractive error is emmetropia ; a balanced state of refractive power of the cornea, lens and the length of the eyeball.
Parallel rays of light are brought to a focus on the fovea when the eye is not accommodating
The state of the eye when the refractive power of the cornea, lens and the length of the eye do not correlate and as a result the parallel rays of light are not focused on the fovea is called ametropia

6. Emmetropia
Axial length matches dioptric power of the eye & parallel rays of light are brought to a focus onto the retina

7. Ametropia
When parallel rays of light are NOT brought to a focus onto the retina
Ametropia could be :
Axial (1m.m. changes represents about 3 dioptres change in refraction. )
Curvature (1m.m. change in radius of curvature of cornea represents about 6 dioptres of change in refraction. )
Index ; due to change in the refractive index of the refractive media

8. Types of ametropia Myopia, common in young age group
Hypermetropia/ hyperopia, common in very young children & old age
Astigmatism; common in young age group but less common than myopia

9. Myopia (near-sightedness)
Parallel rays brought to a focus in front of the retina. The eye is stronger for the axial length of the eye

10. Simple myopia
Usual onset by adolescence but may begin as late as 25 years of age.
Gradually increases until the eye is fully grown.
Seldom exceeds -6 dioptres.

11. Pathological myopia
Commonly begins as physiological but rather than stabilizing when adult size of the eyeball is achieved, the eye continues to enlarge.
It is associated with pathological changes in the posterior segment that can be seen on ophthalmoscopy
It can lead to complications like retinal breaks and detachment
Can go upto over -20 diopters

12. Hyperopia/ Hypermetropia
Parallel rays brought to a focus BEHIND the retina. The eye is weaker for the axial length of the eye.
What would happen if the person accommodates?

13. Hyperopia
Manifest
Latent – to measure this the accommodation has to be knocked off through cycloplegic agents like cyclopentolate and atropine
At which age do you think the latent would become manifest?
Total

14. Hyperopia
At birth practically all eyes are hypermetropic to the extent of +2.5 to +3.0 diopters. Emmetropisation ensues as the eye grows. Emmetropia may not be reached and hypermetropia may persist. May also occur pathologically due to orbital mass, intraocular tumour, retinal oedema and RD.

15. Astigmatism
The eye has different refractive power in different meridians of the eye e.g.
Vertical rays being focused in one position (in front, behind or on the fovea) and horizontal rays focused on another
When the two meridians are at right angle to each other its called regular astigmatism otherwise its termed as irregular astigmatism

16. Astigmatism May also be classified:
Simple – One axis ametropic either myopic/hyperopic
Compound – both axes ametropic but either myopic or hypermetropic.
Mixed – each axis of opposite power.

17. Simple Myopic astigmatism

18. Mixed astigmatism

19. How do refractive errors present?
Asthenopia ,eyestrain & visual fatigue
Blurring of vision
Ocular discomfort with itching, burning of the eyes and at times increased sensitivity to light etc
Headache, rarely could be attributed to refractive errors. Headache presenting after visual work especially in those above 40 years could be because of RE, however a headache presenting early morning is extremely unlikely to be because of RE

20. In children Can present in a variety of ways
In preverbal children it can present as delayed milestones of visual development; inability to focus at visually stimulating objects, follow light or bright object
Squint
Lazy eye or eyes

21. In school going children
Lack of interest in visual tasks, class work
Generally apathic or withdrawn behaviour
Difficulty in reading or seeing the black/ white board from distance
Squint
Lazy eye

22. Signs Decreased visual acuity that improves with pinhole
The eyeball may be obviously small(hyperopia) or large (myopia)
The cornea my be conical in shape (irregular astigmatism (keratoconus)
Pupils are normal
Posterior segment may show abnormalities

24. Posterior segment signs
In pathological myopia retinal degenerations ( myopic crescent, lattice) , breaks ( holes and tears) etc
In hyperopia psedupapilloedema ( blurring of optic disc margins with hyperopia of greater than 5 D)
In high degrees of astigmatism the optic disc may appear oval

25. Normal fundus

28. Treatment of RE
Spectacles
Contact lens
Refractive surgery

30. Refractive assessment
Check VA with and without spectacles
Check with a pin hole
Pupillary examination
Ophthalmoscopy.
Cover test with and without correction
Objective refraction/retinoscopy/refraction/ autorefraction (cycloplegic in children)
Subjective refraction

31. Subjective verification Duochrome test
Subjective verification Duochrome test. Muscle balance – Maddox rod for distance. Near vision correction Maddox wing for near

32. Presbyopia
What is presbyopia?
How is it corrected?