Cataract Surgery: How Does The Brain Assimilate Visual Changes?

Although cataracts are considered the leading cause of blindness worldwide, there is a simple surgical intervention that eliminates the problem and restores vision in affected people. However, this cataract surgery contains a number of complexities that are interesting to know.

Ocular cataract is a very common visual problem. According to several studies, more than 60% of the world population will develop some type of cataract after the age of 75 years. Therefore, cataracts are perceived as a threat over the years.

In addition, the symptoms of this eye pathology are part of popular knowledge: people who suffer from cataracts experience a progressive impairment of their vision functionality, which can become disabling.

What is a cataract?

What is understood clinically by ocular cataract is nothing more than lens opacification. The lens is a transparent lens inherent in the eye that is located behind the iris and pupil and allows vision to focus.

When cataracts appear, this lens becomes progressively cloudy due to the accumulation of epithelial cells that change color for pathological reasons.

These cells proliferate and prevent the normal passage of light through the lens, as, due to their translucent characteristics and brown hue, they represent a physical barrier to this passage. It’s as if the world is seen through a blurry windshield. In this way, vision is affected.

There is another clinical picture: secondary cataract. It is a pathological eye condition very similar to the previous one. It appears after surgical removal of the cataract and is due to remnants of this darkened epithelium that remained latent and began to proliferate again, opacifying the structures of the eye again.

The resulting symptomatology is similar to that caused by the primary cataract, but the eye damage is milder and less extensive. Thus, for its correction, the removal of this tissue layer by laser is enough. It is a quick, painless and risk-free procedure.

As a result of cataract formation, progressively — and more or less quickly depending on the type of cataract in question — the affected person will experience the following visual discomforts:

• Decrease in visual acuity ;
• Photophobia and glare;
• Alteration of chromatic perception — colors lose intensity and mix;
• Change in the perception of the surrounding space.

Furthermore, as an additional confounding factor, while the cataract is in the process of extension, the different degrees of pupil dilation or contraction can mask or exacerbate the symptoms.

Thus, if the pupil is too dilated, much of the light entering the eye will “avoid” cataracts and vision will be closer to normal. Now, if it’s too contracted — in low-light environments — the light will meet the cataract along the way and vision will be impoverished.

Causes of ocular cataracts

Of all the causes, the most widely accepted is the body’s normal aging process. In this sense, developing cataracts would be a logical consequence of reaching advanced ages, although it is true that only susceptible people will develop it.

In many cases, the cause is genetic and the problem is called a congenital cataract. Therefore, there is a small percentage of babies who are born with this deficit. For our peace of mind, surgical correction is indicated at this age and the results are usually good.

In addition to the above, leaving aside those conditions of unknown or undetermined origin (idiopathic cataract), three other causes are postulated as a possible origin of this oculopathy:

• A high degree of myopia — which influences ocular morphology;

• Eye injuries;
• Long-term pharmacological treatments based on steroids, especially corticosteroids — such as chronic cortisone ingestion in rheumatism or anti-allergy medications in people with allergies.

Whatever the cause of this problem, the result has such an impact on the daily performance of the person who suffers from cataracts, it usually brings with it a whole constellation of psychological annoyances, among which anxiety and depression stand out.

What is cataract surgery?

Considered a simple and safe surgical intervention, and given its outpatient nature, we are facing a type of surgery that should not frighten us. Hundreds of these surgeries are performed daily all over the world and the success rate is very high.

In short, the intervention consists of the physical removal of the cataract through an instrument inserted in the anterior part of the eyeball.

Since the tissue to be removed is adjacent to healthy eye tissue—and specifically the lens—it is necessary to remove the lens completely or partially. In this way, the eye is aphakic or without its own focusing capacity. We must remember that it was the lens, our natural lens, that allowed this focus and therefore the accommodation of vision.

To overcome this structural deficiency, an intraocular lens (IOL) is implanted in the space formerly occupied by the lens, allowing the focus of images with characteristics that complement the characteristics of the contralateral eye’s IOL.

This is because cataracts are almost always a bilateral condition, that is, they occur in both eyes at the same time to, together, create focused light projections at the level of the retina, which will then give rise to visual representation, at the level of the brain.

However, as we well know, in many occasions the artificial can hardly replace the natural. For this reason, IOLs, being artificial lenses that also remain fixed and lack the ability of the lens to change its shape to focus and defocus, profoundly alter the functioning of the visual system at various levels.

The person in charge of building a final perceptual image, which is nothing more than the brain, must readjust to this new way of receiving the light that will be transformed into images. For this reason, it can take up to a month for people who undergo this surgery to complete this readaptation. Meanwhile, your vision is less accurate and more uncomfortable than before.

It is thanks to brain plasticity, the ability of our neural systems to reorganize, adapt and recover lost functionalities, that this re-adaptation process successfully ends and the person enjoys a good visual capacity again.

Below, we list a number of components of the visual process that can be altered after cataract surgery. These are changes the brain will learn to correct in order to achieve an effective visual system.

Changes the Brain Must Integrate After Cataract Surgery

Permanent focus and focus time replacement

As IOLs only focus and cannot vary the degree of focus, from the moment you open your eyes, you can see in a focused way at any distance, near or far – no need to strain your eyes, no need to wait a few milliseconds until your eyes move from one focus to another.

This situation causes sensory strangeness at first, but over time this distortion becomes normalized.

Need more light to see properly

While the person suffering from cataract tends to avoid brightly lit spaces, as their pupil dilates and causes visual discomfort, after surgery, that is, after IOL implantation, the brighter the environment, the better focus and vision the person will have.

This is mainly because the artificial lens does not cover the full diameter of the pupil when it is very dilated; if it is, some of the light will penetrate the eye from the outside of the IOL, causing double or blurred vision and halos of light.

Need for physical guidance

Since IOLs focus fixedly and constantly, we won’t rely on the lens’s adaptive ability to adjust our vision to objects that are at a concrete distance and position relative to us. We will ourselves be responsible for moving and changing the angles of vision to find the points of greatest visual acuity for a given object.

residual presbyopia

Generally, IOLs are more specialized in focusing on medium and long distances, and are less efficient for short ones. So it’s not unusual to need close glasses after cataract surgery.

Visual changes under physical exertion

IOLs have a lower degree of fixation within the eye than the lens does in its natural state.

Therefore, marked variations in the level of intraocular tension — the pressure that liquid substances exert inside the eye — that occur as a result of physical effort, will produce slight transient lens shifts, which will cause distortions of the perceived image.

Tendency to eye irritation

The ocular or conjunctival epithelium, after having been ruptured by surgical intervention, develops microscopic scars that will increase the eye’s degree of sensitivity to environmental irritants, such as smoke, dust, etc.

different visual convergence

A complete final image is formed by merging two images of the same object, one from each eye.

Because IOLs are positioned slightly differently than the original lenses, the exact spot on the retina that projects the light is also different.

In this way, the two images that must merge to form a final image will come from different places, and the brain will relearn how to perform this merge efficiently.

Distortion of the visual plane and object sizes

IOLs implanted after cataract surgery generally produce a flatter visual field perception, causing objects to be initially perceived as less rounded.

Furthermore, they tend to diminish the image on which the focus occurs, so that objects in the world appear to be smaller than before. The brain will need to get used to this to prevent the visual discomfort from being permanent.

Presence of visual artifacts

By artifact, in medicine, it is understood the presence of any element that should not be present in a certain place in a natural way. In the field of ophthalmology, a visual artifact would be an element that appears in the context of the functioning of the visual system and would have no reason to appear.

Specifically, IOL users may, under certain circumstances, notice some components of the lens itself or even lens movement.

This is uncomfortable and disconcerting, and sometimes it detracts from attention because it is so striking and flashy. Again, getting used to the new visual situation, thanks to neuroplasticity, will make it all less problematic.

If you have already had cataracts, are suffering from it or even if there is a possibility of developing it at some point in your life, these are some important points that, in addition to being interesting, are very useful to explain some of the results of the surgery, mainly for personal preparation before surgical intervention.