This power point guides an Optometrist students to have a clue on how to take an adult visual acuity during a daily clinical routine

1. VISUAL ACUITY TEST
CLINICAL OPTOMETRY
KILIMANJARO COHAS
UNIT OF OPTOMETRY
NTA 5
MWAKYOMA BSc. OPTOMETRY

2. OBJECTIVES
• At the end of this session a student should be able to:
i. Define visual acuity
ii. Describe types of visual acuity
iii. Describe different forms of visual acuity chart
iv. To assess visual acuity

3. Introduction (1)
• Vision is the process of organism to perceive an information from the
physical stimuli adopted by the photoreceptors at the retina
• The ability to resolve fine details of physical stimuli perceived by
human visual system is known as visual acuity
• Physical stimuli are those structures which are intermediated from
the optotypes constructed on a visual acuity charts
• An ability of eye to resolve the smallest line letters or symbol is taken
as a person’s visual acuity

4. Introduction (2)
• Different organism have different visual system accordingly to their
structures and environment as follows descriptions:
a) Earth worm (Lumbricus) requires only light sensitivity where by is
light sensitive cell are located in their skin epithelial cells
b) Insect with compound eye, mades with variable lenses where by
each lens focus on one photoreceptor making them to have a
limited vision
c) Vertebrate has one lens with a light control aperture

5. Definition of terms (2)
• Light perception is a light with a threshold value for vision
• Discrimination is an ability of visual system to distinguish an object
from its back-ground
• Recognition an ability to identify letters and words on a reading
material
• Resolution is an ability to see details of the optotype

6. Definition of terms (3)
• Localization is a realization of a position of an object where it is
situated on a side of other object
• Higher task a condition of visual system to stimulates other responses
such as motor response on handling something

7. Brain storming
What are clinical
visual aspects
assessment?

8. Clinical visual aspects (1)
• There are two visual clinical aspects which are:
i. Form vision (recognition)
ii. resolution

9. Clinical visual aspects (2)
• Recognition is a phenomenon of identify the shape of a target e.g.
letter, number, symbol. Acuity measured is recorded as the minimum
size which permit identification
• Resolution is an ability to discriminate two or more spatial separated
targets. A stimulus is often a black and white striped lines, recorded
as minimum separable discrimination

10. Types of visual acuity
• Detection ( minimum size which permits visibility
• Resolution
• recognition

11. Types of visual acuity test
1. Preferential test
2. Detection test
3. Naming

12. Preferential looking test
• Torch
• OKNOVIS
• Candy and beads
• Cardiff
• Teller

13. Detection
• Landlot’s C
• Tumbling E

14. Naming
• Sheridan
• Snellen letter test
• Logmar letter test
• Mar letter test

15. Visual acuity testing
• Visual acuity is tested with regard to a distance where a chart is
placed as the following places;
i. Distance
ii. Near

16. Distance visual acuity taking(1)
• It is measured at 3 to 6 metres for 4 years and above clients
• Involves naming, matching and detection
• Includes the following charts
i. Snellen chart
ii. Sheridan chart
iii. Key picture
iv. LogMAR chart

17. Distance visual acuity taking(2)
• Procedures
oRequirements
i. Illumination like out door envirement
ii. Target : snellen chart
iii. Distance 3 – 6 metre regarding to company
iv. Instructions “ read small line of letters you can”

18. Distance visual acuity taking(3)
• Steps
i. Cover the patient’s left eye with occlude and ask the patient to
keep both eyes wide open
ii. Ask a patient to read the letter of small line loudly
iii. Record
iv. If the patient did not reach 6/9 line introduce a pinhole and give
out instructions
v. Allow a patient o read letters loudly and record

19. Distance visual acuity taking(4)
vi. Occlude right eye and do the above procedures sequentially
vii. Take a both eye visual acuity when both are necked
viii. Take a visual acuity with habitual prescription by following the
above procedures

20. Near acuity taking
• Procedures
oRequirements
i. Illumination like out door envirement
ii. Target : near chart
iii. Distance 33 cm
iv. Instructions “ read small line of letters you can”
v. Record for each eye and both eyes

21. Take home note
• Visual acuity of a patient is a pilot for any ophthalmic clinician

22. Evaluation
• What is visual acuity
• Describe types of visual acuity

23. References
• Buckingham. T. (1993) Visual problem in child hood. London :
Butterworth Heinemann
• Lymo V.V. Clinical manual of refraction. Visual acuity
• Wright K. W, Stribe Y. N. J. Pediatric ophthalmology for primary eye
care. 4th edition: Ocular examination and vision screening. United
state of America. America Ophthalmology Association
• Jain. S. Simplifying strabismus. Examining a patient with strabismus.
Switzerland. Springer