Does cataract surgery improve your sleep?
The blue-light screens of our laptop and mobile devices were in the news again this week. There is concern regarding the effects of using screen technology, particularly in the evening and late at night, on the ability to sleep and the quality of sleep. What does this have to do with cataract surgery?
The impact of cataract on sleep and the impact of using blue light-rich screen technology on sleep are linked by a fundamental mechanism which evolved to control and direct our sleep-wake cycle.
An evolutionarily primitive part of the brain called the suprachiasmatic nucleus (SCN) governs our sleep-wake cycle. The sleep-wake cycle follows a circadian rhythm, and it is vital for ensuring normal healthy brain function and overall good health in general.
Shakespeare described sleep as the “balm of hurt minds, great nature’s second course, chief nourisher in life’s feast” (Macbeth – 2.2.46-51).
We all know how wonderful it feels to wake up refreshed after a good night’s sleep. The SCN governs our sleep-wake cycle with the production of a hormone called melatonin. Our SCN knows when we should be awake and knows when we should be asleep by the presence of blue light.
The light, which falls on our retinas during the day and which we use for seeing stimulates photoreceptors. These photoreceptors respond to light of different wavelengths and send messages to nerve cells called retinal ganglion cells. The retinal ganglion cells stimulate the visual processing parts of the brain so that we can create our view of the world. We are visual-dominant creatures, and over one-third of the brain is involved in processing visual information; this is much more than is devoted to processing the information from our other senses.
Research has recently identified retinal ganglion cells that are not stimulated by photoreceptors but which themselves respond to blue light. These blue light-responding retinal ganglion cells send messages directly to the SCN. It is these cells that inform our body that it is daytime and that we should be awake and, conversely, inform our body when it is night time and when we should sleep. These specialized retinal ganglion cells respond selectively to blue light.
It is likely that this is an adaptation from our evolutionary past. Life evolved in the sea and light transmission in the sea is dominated by blue light. The simplest of creatures show circadian rhythms in their physiology and behavior, and so it is likely that this ancient system for regulating the sleep-wake cycle evolved in the blue light-rich environment of the sea, and therefore responds selectively to blue light.
The problem with modern screens is that blue-light LEDs illuminate them. Nakamura et al received the Nobel prize in physics in 2014 for the invention of blue light-emitting diodes. These LED lights offer considerable advantages over incandescent lamps because of their lower energy demands and, for the lights themselves, longer life spans.
Unfortunately, the wavelength of light where the LEDs are most powerful falls precisely on the sweet spot for maximum stimulation of the SCN. This means that if we lie in bed late at night playing Candy Crush on our iPhone, or reading our iPad, we are providing a high level of stimulation to the part of our brain telling it that it feels like daylight and we should be awake. This is precisely the time of day when we should be trying to decrease stimulation of this part of the brain so that the SCN stimulates the right hormones to regulate our sleep and encourage us to fall asleep.
How does blue-light stimulation relate to the impact of cataract on an individual?
As the natural human crystalline lens turns into a cataract, the lens develops a yellow tint gradually turning brown. Therefore as the cataract develops it causes a disproportionate reduction in the transmission of blue light compared with the other light wavelengths.
This means that cataract formation results in progressive loss of normal stimulation of the SCN, contributing to the disruption of the sleep-wake cycle and circadian rhythms of the body.
As people age, other factors can disrupt sleep. The areas of the brain involved in deep-wave sleep, unfortunately, appear to deteriorate more rapidly than other parts of the brain so that older people‘s sleep is less efficient. If lack of SCN stimulation further disrupts the ability to fall asleep and to wake at the correct time, this can have a significant impact on an individual’s quality of life and health.
There are now numerous studies that show the beneficial impact of cataract surgery on improved sleep quality. The first time I paid attention to this effect was when a patient walked into my clinic for her first post-operative visit after cataract surgery and said that immediately afterward she had had her first night of uninterrupted sleep in years.
Interestingly her sleep quality had been gradually deteriorating in recent years, and it appeared that the decline in sleep quality had matched the gradual deterioration in her quality of vision due to cataract formation (her story appeared in the Daily Mail, and you can read it if you follow this link.
Staff in many optician practices and eye clinics up and down the country focus on a patient’s ability to read the visual acuity chart with spectacles. In most of the UK, this is the only metric that is used to decide whether or not a patient should have cataract surgery.
In many areas, the visual acuity is effectively a rationing tool to limit the amount of cataract surgery provided. There are undoubtedly many people in the country who are suffering from the effects of sleep deprivation due to cataract formation causing loss of the normal circadian rhythm. Not only would these people benefit from having improved vision after cataract surgery, but they would also benefit from having improved quality of sleep along with all of the attendant health benefits that come with it.
Different intra-ocular lens implants offer different levels of blue-light transmission. There are lens implants that block ultraviolet light and transmit the full blue-light spectrum. There are also yellow tinted lenses that reduce transmission of blue light. There is evidence that both lens technologies provide people with improved sleep quality after cataract surgery because both types of lens technology give hugely increased blue light transmission compared with a cataractous human lens.
There are pros and cons to each of the lens designs and we’ll come back to this issue in another blog post. As with everything we do at Custom Vision, we customize our lens choice for patients. We select lenses with different blue-light transmission characteristics for different patients depending on their eye health, eye color and lifestyle.
When it comes to blue light and sleep regulation, as with so many things in life, it isn’t all good, and it isn’t all bad. What matters is that we have the right amount of blue light at the right time of day. Too much blue light from screen technology in the evening is bad for our sleep patterns. Not enough natural blue light stimulation during the day because of cataracts is also bad for our sleep patterns.
If you are an older person with sleep difficulties and you have not yet had cataract surgery, come and see us for a consultation and we’ll assess every aspect of your eye health. You may well find that we can not only help you to see the world better, but we can help you to sleep better.
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