Exploring Visual Sensing of the Human Eye

The Human Eye is a very power tool for visual sensing. Using a dynamic lens system to focus light, the human eye can zoom in and out of a desired object of interest.With combinations of photoreceptors, the human eye is like a high pixel resolution camera that records the light intensity per "pixel" and transmits it to the brain. With its complex anatomical design, there are a lot of properties of vision that emerges. These sensing properties can be explored and studied for practical and scientific uses.

Let us explore the different sensing properties of the Human Eye.

First, let us identify the minimum distance at which the human eye can focus. So, by using a pen placed squarely in front of a person's face, then slowly bringing it closer towards the eyes, the distance at which the pen becomes a blurry image, that is the minimum distance at which the human eye can focus. Table 1 tabulates the minimum distance at which the right eye, left eye and both eyes can focus the pen.

Table 1: The Minimum Distance at which the Eye can Focus

Based on the two people presented in table 1, even though their right eye have the same minimum focus distance, there is a significant variation in the minimum focus distance of their left eye and both eyes.

Next, let's look at the maximum angle of peripheral vision. According to this, peripheral vision is the ability to see objects and movement outside the direct line of vision. So, in order to determine the maximum angle of peripheral vision, the person of interest must first fixate his/her gaze at a point (point A), preferably on a wall, then slowly move a vertically placed pen to the left (and then later to the right) from the point of gaze on the wall. At the point (point B) where the person can no longer see the pen, measure the angle between the point B to the person and point A to the person. It is important to take note that at all times, both eyes must be open and must only fix their gaze on point A. Table 2 tabulates the result of this procedure.

Table 2: Maximum Angle of Peripheral Vision.

Based on table 2, Person A and Person T has a significant difference between the maximum angle of their lateral peripheral vision. Take note that peripheral vision includes the ability to detect movement, which is actually an important trait for drivers or for anyone doing activities which involves the use of peripheral vision.

Now, let's examine Visual Acuity. According to this, the fovea is a tiny pit located in the eye that provides the clearest vision. It is where the photoreceptors in the eye are highly concentrated. In order to find the range at which the fovea focuses the most, the person of interest is to concentrate his/her vision at a letter in a collection of texts 9 to 12 pixel font size, eye-level and with around 25 cm distance from the brigde of the nose. Letters surrounding the designated letter is initially covered. At each time interval, a letter is slowly uncovered until the person is unable to discern the letter. Table 3 tabulates the angle pertaining to visual acuity.

Table 3: Angle of Visual Acuity. Take note that these are measured in degrees. Also, this is different from peripheral vision.

Another key feature of the human eye is its Scotopic and Photopic Vision. According to Wikipedia (pardon us for the lack of more credible references), Scotopic Vision is the vision of the eye under low light condition while Photopic Vision is the vision of the eye under well-lit conditions. To examine how the human eye responds to these types of conditions, the person of interest is subjected to an experiment that involves the setup shown in Figure 1. This setup simulates scotopic and photopic visual conditions by enclosing colored strips inside the box. Light entering this box is regulated by a small hole by varying the distance of the light source. The person is then to record the color seen as the field of observation becomes brighter. The order of color seen is then tabulated in Table 4.

Table 4. Order of color sensed with increasing brightness.

In the visual acuity experiment, the collection of texts used were from a newspaper. The letters were uncovered one at a time. There may be certain anomalies in the detection of letters for sometimes the person knows the word, thus, the brain may subconsciously provide the ample letter that the word has.This relationship of the eye and the brain must be explored. There are several experiments suggesting to study this relationship using interactive text as shown here and here too. They use these texts to somehow fool the way we see things. A similar method with collection of these types of images is needed in a proposed experiment to study this eye-brain relationship.