Change in Visual Acuity with Eccentricity
Humans have a large vison field so it is important to not only test the central vison but also at the peripherals of the retina. This is because individuals tend to not notice vison loss at the peripherals compared to central vision as when an individual views an object they move their eyes and fixate on that object by using their central vison and not their peripheral. Visual acuity is highest at the fovea and lowest at the peripheral which ensures high visual acuity at fixation. A way to measure peripheral vision is the Humphrey perimetry test which assesses the vision field. Any reduction in peripheral vision can indicate the development of disease such as glaucoma or detect any blind spots, scotomas …show more content…
The aim of the experiment was to investigate the change in visual acuity across the nasal retina to an eccentricity of 45 degrees.
Method
Firstly, the subject was sat down and the Visual acuity was measured using the log mar chart, the decimal V was calculated. A display board was positioned in front of the subject at a distance of one metre ensuring the subject’s eyes were parallel to the board and the Maltese cross was positioned on the extreme left end. This is to ensure the cross was projected on to the nasal retina when the right eye was tested. The left eye was occluded using the occluder in the trial frame. The subject was instructed to fixate on the Maltese cross whilst the examiner held a black pen tip along the board and moved it away from the Maltese cross at a steady speed. The subject was instructed to identify when they can no longer observe the black pen tip and when the black …show more content…
This shows that Visual acuity changes depending on the location in the retina and could be influenced by factors which include: the receptive field size, distribution of photoreceptors and illumination. For an individual to view an object, they fixate and place the image of the object on the most sensitive part of the retina, fovea centralis to produce detailed vision. As shown in Figure 2, the fovea has a high number of cone receptors which produce high visual acuity and allows the individual to identify colour and light. A high visual acuity is due “to the 1:1 connection of a cone cell to bipolar cell to a single ganglion cell producing a small receptive field which produces high visual acuity at fixation [4]”. At the peripheral, there is a high rod density which produces low visual acuity and is due to retinal convergence of rods to a single bipolar cell, producing a larger receptive field which reduces visual acuity. Illumination affects visual acuity as rod cells are activated in dim light thereby producing low vision as there is a lack of luminance so lack of detail. Whereas, cones operate under high luminance which enables the identification of detail producing high visual
Humans have a large vison field so it is important to not only test the central vison but also at the peripherals of the retina. This is because individuals tend to not notice vison loss at the peripherals compared to central vision as when an individual views an object they move their eyes and fixate on that object by using their central vison and not their peripheral. Visual acuity is highest at the fovea and lowest at the peripheral which ensures high visual acuity at fixation. A way to measure peripheral vision is the Humphrey perimetry test which assesses the vision field. Any reduction in peripheral vision can indicate the development of disease such as glaucoma or detect any blind spots, scotomas …show more content…
The aim of the experiment was to investigate the change in visual acuity across the nasal retina to an eccentricity of 45 degrees.
Method
Firstly, the subject was sat down and the Visual acuity was measured using the log mar chart, the decimal V was calculated. A display board was positioned in front of the subject at a distance of one metre ensuring the subject’s eyes were parallel to the board and the Maltese cross was positioned on the extreme left end. This is to ensure the cross was projected on to the nasal retina when the right eye was tested. The left eye was occluded using the occluder in the trial frame. The subject was instructed to fixate on the Maltese cross whilst the examiner held a black pen tip along the board and moved it away from the Maltese cross at a steady speed. The subject was instructed to identify when they can no longer observe the black pen tip and when the black …show more content…
This shows that Visual acuity changes depending on the location in the retina and could be influenced by factors which include: the receptive field size, distribution of photoreceptors and illumination. For an individual to view an object, they fixate and place the image of the object on the most sensitive part of the retina, fovea centralis to produce detailed vision. As shown in Figure 2, the fovea has a high number of cone receptors which produce high visual acuity and allows the individual to identify colour and light. A high visual acuity is due “to the 1:1 connection of a cone cell to bipolar cell to a single ganglion cell producing a small receptive field which produces high visual acuity at fixation [4]”. At the peripheral, there is a high rod density which produces low visual acuity and is due to retinal convergence of rods to a single bipolar cell, producing a larger receptive field which reduces visual acuity. Illumination affects visual acuity as rod cells are activated in dim light thereby producing low vision as there is a lack of luminance so lack of detail. Whereas, cones operate under high luminance which enables the identification of detail producing high visual