Ophthalmology · MU Sofia

15. Central and peripheral vision. Visual acuity. Examination methods *

Explains form sense and visual acuity as the threshold for discriminating two spatially separated targets, distinguishing minimum visible from minimum resolvable separation and recognition. It then covers distance testing with Snellen charts at 6 m, LogMAR scoring, the principles of the 6/x notation, and a step-by-step fallback from counting fingers to hand movements and light perception when letters cannot be read. Near vision testing with Jaeger charts and the N-notation is included, followed by brief notes on low vision aids such as magnifiers, telescopic glasses and closed-circuit TV.

Inside: 4 sections · 1 labelled picture · 15 flashcards · 6 min

Topic 15 of 91 in the MU Sofia syllabus for Ophthalmology (Medicine, Year 4). The free AceMed note covers it in 4 sections, about 930 words (6 min of reading), with 15 flashcards.

In this note

  1. Form sense
  2. Visual acuity .Methods of examination, principles Topic 12
  3. Low vision aids
  4. Visual acuity testing

Form sense

= ability to distinguish between shapes of object and cones mainly thus most acute in fovea and decrease very rapidly towards the periphery

Visual acuity (subtype of form sense)

=threshold of discrimination of two spatially separated targets

  • minimum visible → ability to determine whether an object is there or not
  • Resolution (ordinary visual acuity )

Minimum resolvable= minimum separation between two points distinguished as two

Ordinary visual acuity → is a function of foveal region and histologically it is 0.004mm as it is a diameter of the cones in the fovea

In test , the form sense or reading ability is tested thus it can been looked at the ability to identify the spatial characteristics of a test figure (letters= Snellen)

  • Recognition =not only discriminates between two objects but links it to a certain experience which uses cognitive functions

Visual acuity .Methods of examination, principles Topic 12

Form sense

= ability to distinguish between shapes of object and cones mainly thus most acute in fovea and decrease very rapidly towards the periphery

Visual acuity (subtype of form sense)

=threshold of discrimination of two spatially separated targets

  • minimum visible à ability to determine whether an object is there or not
  • Resolution (ordinary visual acuity )

Minimum resolvable= minimum separation between two points distinguished as two

Ordinary visual acuity à is a function of foveal region and histologically it is 0.004mm as it is a diameter of the cones in the fovea

In test , the form sense or reading ability is tested thus it can been looked at the ability to identify the spatial characteristics of a test figure (letters= Snellen)

  • Recognition =not only discriminates between two objects but links it to a certain experience which uses cognitive functions

Visual acuity (VA) measures clearness of vision. It depends on optical and neural factors, i.e., (i) the sharpness of the retinal focus within the eye, (ii) the intactness and functioning of the retina, and (iii) the sensitivity of the interpretative faculty of the brain

Examination methods

  • Must be measured one eye at a time for both distance & near type test

Distance : Snellen =traditional chart (measured at 6 m or 20 feet)

LogMARà 0 is normal 6/6 or 20/20=1. 0 log mar score

Principles of Snellenà usually letters or E for illiterate patients

  • 6/6= normal 6/5 or 6/4 even better as they can read even the low lines

Numerator =distance of patient from Snellen chart (usually 6m or 20m)

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