The Lamp of the Body

“The eye is the lamp of the body. So, if your eye is sound, your whole body will be full of light; but if your eye is not sound, your whole body will be full of darkness.” Matthew 6:22-23.

It is really easy to miss these two important verses as they occur sandwiched between some of the most profound sayings of Jesus in the New Testament. In Matthew Chapter 6, Jesus lays out an uncompromising toolkit for how we should live our lives. Shortly before the quotation, Jesus gives us the words for how to pray to the Father (Matthew 6:9-13), explains forgiveness (Matthew 6:14-15), tells us how to fast and warns us against hypocrisy (Matthew 6:16-18), and the benefits of storing up treasures in heaven alongside the pitfalls of focussing wealth on earth (Matthew 6:19-24). Following such weighty subject matter comes our opening quotation on the eye.

This quotation is not any less substantial than the other points Jesus raises. While the eye is not literally our physical eye, it serves a compelling metaphor for our spiritual well-being and ties together the theme running through these articles that our physical senses serve as gateways to our spiritual senses.

Windows of the Brain

Our eyes are highly complex structures and are second in complexity only to that of the human brain. Given that the eyes originated as outgrowths from the brain during our development in the womb, the link between both organs is not surprising. The eyes emerging in this way is literally the brain taking a peek at its surroundings. When you look at someone’s eyes, you’re looking into a direct connection with that person’s brain. A window to the brain, as it were.

Common Sense

Sight is by far the most frequently mentioned physical sense in the Bible. Sight and its associated terms such as vision, see, behold, eyes, look and blindness, are mentioned some 2,000 times, though obviously in a variety of contexts. Whenever sight is mentioned, it adds enormous depth to the meaning of the passage as it often serves as a mirror for the spiritual condition. Just after the healing of the blind man in John 9:39, Jesus said, “For judgment I have come into this world, so that the blind will see and those who see will become blind.” Jesus’ stark warning holds a mirror on the spiritual condition of the Pharisees witnessing the miracle and mockingly asking Jesus if they were blind too. As they considered themselves the educated religious elite the idea of being considered blind was insulting to them. The blindness of which Jesus spoke was to their own spiritual poverty.

Perhaps a better-known Scriptural quotation is, “Why do you see the speck that is in your brother’s eye, but do not notice the log that is in your own eye?” in Matthew 7:3 which offers an uncompromising instruction to fix ourselves before trying to fix others. There is a thematic connection between these three opening passages. In Matthew, Jesus warns that if your eye is unhealthy, your whole body is in darkness. In John 9, the Pharisees are a living example of that warning and Matthew 7:3 suggests an introspective way to improve how to see the world.

An Eye for Creation

With so many references to sight and vision in the Bible, you can’t help but come across numerous examples for yourself. As this section is about religion and science and if your dealings with biology have been limited, this might be a good opportunity to explore some amazing facts about your eyes and eyesight. As with all the other senses, and with most of the processes that occur in the body, we are usually totally unaware of significant parts of ourselves and how they function – until something goes wrong and it then becomes our focus. With eyesight, we don’t need to do anything special – just open our eyes and off we go, taking in and navigating the amazing world around us.

Spending time learning about our eyes is a worthy spiritual pursuit. Our eyes and the way we process the images we see, are not just part of God’s Creation but an awe-inspiring, part of His Creation. One that He has granted to us as a personal gift. We don’t just wander around Creation, we are ourselves a wonder of Creation.

Vision – More Than Just The Eyes

However remarkable our eyes may be, being able to see involves much more than just our eyes. In theatre terms, they are just front of house. Vision is a product of countless processes occurring in the brain. Like the other senses, vision is a construct of the brain, meaning that the actual image that falls on the retina is significantly different from the final perception of that same image within the brain.

What you actually perceive is a highly edited, reconstructed and predictive simulation. This may sound like something out of the film, The Matrix, where the characters are offered an alternative reality. But what the brain does offer is as faithful a reproduction of the world as possible given constraints that need to be made to optimise its processing power. Appreciating that what we perceive is not wholly the same as what we see helps us to discern what we should focus upon in life and try to edit out distractions.

Eyes Versus Cameras

Our eyes are often likened to how cameras operate and the analogy is correct up to a point. While a traditional camera captures a faithful image of a scene, the same can’t be said of the human eye. Our eyes don’t operate as passive windows on objects. If we saw the world through a successive number of rapid snapshots, the brain’s processing power would soon be overwhelmed. The brain takes a different approach which still gives us a staggeringly wonderful image of our surroundings. To explain how this occurs, let’s first look at the issues the brain needs to deal with.

Picture Imperfect

One similarity between the eye and a camera is how the lens in each distorts the image. This distortion is governed by fundamental laws of physics (optics) where light passing through a glass lens, in the case of a camera, or an organic lens, in the case of the eye, bends or refracts light. When we look at something, the eye’s lens inverts the image that lands on the retina at the back of the eye. The image is upside down, back to front, flat (2D) and blurry at the edges. Given that we have two eyes that see slightly different parts of the visual field, the brain has a mammoth undertaking to reconcile all these distortions to produce the perfectly orientated picture we eventually see. What makes this even more incredible is that it does this in a tenth of a second. We need vision to spot dangers and seize opportunities so seeing in real-time is essential. Any lag might lead to our demise.

The brain is so clever and the eyes are hard-wired to the brain through the optic nerves. The optic nerve attaches to the back of each eyeball and at this point of connection, the retina has no photoreceptors so can’t detect light. This results in a blind-spot or two blind-spots for both eyes. You’d think there should be two dark patches in our vision – and there are but we don’t perceive them.

The blind-spot has a diameter of around 2mm and though this might seem very small and insignificant, it represents a surprisingly large gap in our field of view. I remember having a digital television display that had lost a couple of its pixels and though this represented a tiny percentage of the whole screen, it was sufficient to be highly irritating, and I couldn’t help my eyes being drawn to the blanked-out area. However, what we perceive in the brain is a right-way-up, correctly orientated, 3-dimensional, crystal-clear image without any dark missing spots.

Filling In The Blanks

The brain “fills-in” the dark patches which should be formed by the blind-spots. Knowing how this is done should make you even more appreciative of the inner workings of the brain. The technical term for this process is perceptual completion.

The brain acts as a generative AI system whose processes are similar to those found in the latest photo-editing software. Because we have two eyes which are 6cm apart for adults, the two blind-spots in our visual field do not overlap. The brain samples the missing segment from the corresponding part of the other eye. Essentially, the right eye sees what the left eye is missing and vice versa. It applies this information to cover up the missing areas from the opposite eye and creates a complete picture.

If you have a questioning mind, you are probably thinking, well, what happens if you close one eye. The visual information from the closed eye won’t be available to compensate the open eye. You might even be trying this now. The image you perceive from having just one eye open also appears to be complete. Here, the brain fills-in the missing area based on cues and clues surrounding the dark spot. Filling-in sounds a bit like a child colouring-in a picture book but it’s not as simple as this analogy. The brain doesn’t just replace the dark-spot with a simple colouring-in. Instead, the brain uses highly skilled guesswork. It actively colour-and-texture matches, connects patterns and lines so you will never know that in reality there is nothing there. The moment you shift your gaze the whole process starts anew without any perceivable delay. Imagine, this occurs every moment you’re using your vision.

The Power of Prediction

Predicting what’s missing and including it seamlessly require less processing power than producing a pixel-by-pixel faithful representation of the image. The brain has admittedly a tremendous amount of processing ability but while it’s processing visual images, it’s also interpreting all our other senses as well as controlling our movements and countless other physiological processes required to keep the body alive. For us, we are sublimely unaware of what goes on and think we are seeing a faithful and high-definition rendering of our surroundings.

Eye Movement

The retina is the photosensitive part of eye that converts light energy into electrical nerve impulses that carry information about the image to the brain. Only one tiny part of the retina is able to see in high definition. This highly sensitive part is called the fovea and though it is packed with a high density of photoreceptors it captures less than 1% of the visual field. To give you an idea of how much that is, hold your arm straight out in front of you and look at your thumbnail. This is the area of your vision that your eyes can see in high definition. Although the fovea is very small in area, about 50% of the brain’s visual processing power is put towards interpreting its signals. It’s the only part of the retina that the brain processes in its entirety.

To compensate for this restricted high-resolution vision, the brain gets the eyes to move so the fovea jumps around the visual field rapidly sampling visual information. Around each eye are three pairs of muscles. These extraocular muscles pull the eyeball this way and that way to sample the visual field.  The actions of these muscles on each eye are highly co-ordinated so both eyes are directed in concert ensuring 3-D vision at all times. Rather than scanning the whole visual field, the brain takes the samples and again fills in the gaps, so what we perceive is perfect, precision vision. You can notice these jumpy or jerky movements when looking at someone’s eyes. These movements are called saccades and they are particularly noticeable if you closely watch the eyes of someone reading text from a book. If you haven’t noticed these movements before, look out for them on others as they occur all the time and are totally involuntary.

Saccadic eye movements reveal another feature of the brain. The brain finds it challenging to cope with fuzzy or blurry vision. If someone has a visual problem where one eye is slightly out of alignment, unless corrected, the brain ignores visual information from that eye and concentrates its processing on the other eye. The misaligned eye is “blind” to the brain. In normal vision, we perform saccadic eye movement to allow the eye to be still momentarily, fixate on the image clearly before it rapidly moves to another position. Vision obviously continues between one point of focus and another so we should be seeing a series of blurry images even when we’re still. In fact, we do see endless numbers of jerky out of focus movements, but they are edited out and do not reach consciousness because the brain suppresses them providing what appears to be steady vision.

Meaning in God’s Creation

Just as we are intended to find meaning when exploring the mysteries of God’s Creation, so we can obtain profound meaning from how the body works as both were made by the same Creator. When praying or meditating, we might find inspiration looking at a sunset or flowers or walking in a forest. We don’t always realise that the things that raise our spirits can only be appreciated by the highly complex, God-given processes of the human body, in this case vision.

How the brain constructs a “true’ image from raw data from the eyes speaks to me about my own faith formation. It takes only a tenth of a second from light striking the retina to an image being constructed by the brain. Perceiving an image formed in the brain is only at the start of the entire process. You need to recognise the object or image by calling on memory centres in the brain. The image is compared with previous memories of that or a similar object. The image might hold some personal significance, so emotion centres of the brain are also at play. The object you’re focusing on might be moving so predictive processing allows you to follow the movement. If you need to interact with the object in some way, such as a ball being thrown to you, you need to initiate and control bodily movement, balance and stance to catch the ball.

Likewise, we have a framework made up of our beliefs, our preconceptions and biases, current understandings, expectations and life experiences, all of which contribute to our spirituality. Just as our brain must make sense of numerous sensory inputs some of which are conflicting and ambiguous, so our spirituality struggles with interpreting multiple life events. Replying solely on our physical senses and what we perceive is not enough and we have to dig deeper. This is beautifully summarised by Paul in 2 Corinthians 5:7, “For we walk by faith, not by sight.” And again, “So we fix our eyes not on what is seen, but on what is unseen. For what is seen is temporary, but what is unseen is eternal.” (2 Corinthians 4:18).

Our physical sight and our spiritual vision are sacred gifts from God, “Ears that hear and eyes that see – the Lord has made them both” says Proverbs 20:12. Like all gifts, they need to be unpacked, explored, used, enjoyed and shared for everyone’s benefit. Being gifts from God they carry moral responsibility and stewardship both in how they work and how to use them. Using these gifts well, can flood your life and soul with light as indicated in the opening quotation, “if your eyes are healthy, your whole body will be full of light” (Matthew 6:22-23).

So, the next time you see a sunrise or an amazing landscape, remember that the wonders of God don’t just appear in front of your eyes but behind your eyes as well.

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