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Vision problems
Vision problems & prescriptions: Questions and Answers
Short sightedness, long sightedness, astigmatism and presbyopia explained in plain language, including why each one happens, how it is measured, and which of them laser vision correction can and cannot change.
Short sightedness, long sightedness, astigmatism and presbyopia explained in plain language, including why each one happens, how it is measured, and which of them laser vision correction can and cannot change.
General educational information. It does not replace an examination, and it cannot tell you what is happening in your own eyes.
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Vision problems
Most refractive questions come down to which part of the eye is doing the mis-focusing. A cornea that is too curved, a cornea that is too flat, a cornea curved unevenly, or a lens that has stiffened with age. Those are four different problems and they do not have the same set of answers.
Presbyopia is the one worth reading up on before booking anything, because it is the reason a good result at 60 is a different conversation from a good result at 30.
Vision problems & prescriptions questions and answers
Vision problems
Short sightedness, long sightedness, astigmatism and presbyopia explained in plain language, including why each one happens, how it is measured, and which of them laser vision correction can and cannot change.
Short sightedness is a condition in which light from distant objects comes to focus in front of the retina instead of on it, which makes distance vision blurred while close vision stays relatively clear.
It usually happens because the eyeball is slightly too long for its focusing power, or because the cornea is too curved. Both cause the same thing: distance blur.
It is one of the most common reasons people need glasses at all, and uncorrected refractive error is one of the largest contributors to avoidable vision impairment worldwide.
Short sightedness is caused by the shape of the eye, meaning its length and the curvature of the cornea, and it develops from a combination of inherited tendency and environmental factors such as time spent on close work.
The contribution of environment is why the conversation about children now includes outdoor time and near-work habits, which is a change from treating short sightedness as purely genetic.
Yes, particularly in childhood and the teenage years, when the eye is still growing. Progression usually slows and then stabilises in early adulthood, though it does not stabilise at the same age for everyone.
A prescription that is still changing is one of the reasons surgery is usually deferred, because a treatment planned from a moving prescription may not match the eye a year later.
The focusing error can be corrected permanently by laser surgery in suitable eyes, in the sense that the corneal reshaping does not reverse. The eye can still change with age, so the prescription can drift later in life.
Higher short sightedness also carries a slightly higher background risk of retinal problems regardless of whether surgery is performed, which is an argument for continuing regular eye examinations rather than treating correction as the end of the story.
A small amount of regression is possible, and the cornea does not regrow the tissue that was removed. What is more common is a prescription change related to ageing rather than a return of the original error.
Yes, short sightedness is the refractive error most commonly treated with LASIK. How much can be corrected for a given eye depends on corneal thickness and shape rather than on the prescription alone.
The options for high short sightedness are laser procedures where the cornea can safely spare the tissue, and lens-based options such as an implantable lens where it cannot. Which applies to you depends on your measurements.
An important part of the assessment at high prescriptions is the retina rather than the cornea, because highly short sighted eyes are more prone to retinal problems and those should be examined regardless of what is planned at the front of the eye.
It cannot be prevented with certainty. In children, time outdoors is consistently associated with slower development of short sightedness, and treatments exist that aim to slow its progression. In adults, there is nothing established that stops a refractive error from developing.
The distinction worth keeping is between slowing and preventing. Slowing progression in a child is a recognised clinical aim with recognised methods; preventing an adult from becoming short sighted is not something any treatment here claims to do.
The eye’s length and the focusing power of its cornea are not reversed by treatment: glasses, lenses and surgery compensate for them. In children the prescription usually increases as the eye grows, and in some adults it continues to change slowly.
What this depends on
Age, and whether growth has finished
How the prescription has changed over previous years
Whether the cornea is stable or showing signs of change
High short sightedness generally means a prescription beyond the moderate range, and there is no single boundary that every clinician uses. What matters practically is that higher prescriptions ask more of the cornea, which is why they are planned from thickness and shape measurements rather than from the prescription alone.
Higher short sightedness is also associated with a greater chance of retinal problems later in life, which is a reason for regular dilated examinations rather than a reason for alarm. That monitoring question is separate from whether laser surgery is suitable.
What this depends on
The measured prescription
Corneal thickness and the shape of the cornea
Whether a lens-based option would be safer for your eye
Higher short sightedness is associated with a greater chance of retinal detachment, retinal changes and, later, glaucoma and cataract. The association is with the length of the eye rather than with wearing glasses, and it is a reason for regular dilated examinations.
Laser vision correction changes the cornea and not the length of the eye, so it does not remove this. Whatever your vision is like after surgery, the retina still needs the same monitoring as before.
There is a substantial inherited component, and the chances are higher when one or both parents are short sighted. Environment also matters, with sustained near work and less time outdoors associated with earlier onset in children.
What this depends on
Family history
The child’s age when the prescription was first noticed
How much time is spent outdoors versus on close work
Long sightedness is a condition in which light comes to focus behind the retina, which the eye can often compensate for at a distance by focusing harder, at the cost of effort and eventual blur.
That effort is why long sightedness often presents with tired eyes, headaches after reading and symptoms that seem out of proportion to a modest prescription.
Long sightedness is caused by the eye being shorter than its focusing power requires, or by the cornea being flatter than average. It is often present from birth and frequently runs in families.
Long sightedness can be treated with laser correction, but it is assessed more cautiously than short sightedness because treating it requires removing tissue towards the edge of the cornea and outcomes are more variable at higher prescriptions and in older eyes.
Laser correction can address long sightedness in suitable eyes, but where the condition is mild and only affects reading vision after forty, a different problem may be the real one, and it may have different solutions.
Distinguishing between long sightedness and presbyopia matters clinically, because they look similar from the inside and are treated differently. That distinction is made during an examination, not from symptoms alone.
No. Long sightedness (hyperopia) is a focusing error you are born with, where the eye’s optical power is too weak for its length. Presbyopia is the age-related stiffening of the lens that affects near focus later in life. Both blur close vision, and they are different problems with different corrections.
The reason the two get merged is that they feel similar: reading gets harder, and holding things further away helps. The reason it matters is that they respond to different treatments. Hyperopia is a refractive error a laser or lens can correct; presbyopia is a change in the lens that no laser can reverse.
Yes, and mild long sightedness is common in young children, whose eyes focus well enough to compensate for it. Most grow out of it as the eye lengthens. A young child with a high prescription may need glasses, because the effort of compensating can affect how the eyes work together.
A child who compensates well will not complain, which is why the finding usually comes from a routine examination rather than from a parent noticing something. That is one of the arguments for testing children before school rather than waiting for a symptom.
What this depends on
The size of the prescription
Whether the eyes are straight and working together
Whether vision is reduced even with the correction in place
The prescription itself usually changes little. What changes is your ability to compensate for it: the lens stiffens with age, so the same amount of long sightedness becomes harder to hide, and people often notice symptoms in their thirties or forties that were always there.
This is also why someone can be told they are long sighted at 42 after a lifetime of seeing well. The finding is not new; the compensation is.
What this depends on
Your measured prescription now versus earlier records
How much of your blur is at distance and how much at near
It can be corrected rather than cured. Glasses, contact lenses and refractive surgery all change where light focuses in the eye; the shape of the eye itself is unchanged, and it can keep changing with age. Long sightedness can also be corrected during cataract surgery, when the natural lens is replaced anyway.
What this depends on
The size of the prescription and the shape of the cornea
Whether you also have astigmatism or reading-vision loss
There is a strong inherited tendency, and the way the eye grows matters as much as eye optics: a shorter-than-average eye is long sighted. A family history does not predict an individual’s prescription, but it is a reason to have children tested rather than to wait for symptoms.
By refraction: a test that finds the lens power that gives you the clearest vision, expressed as a prescription with a plus sign for long sightedness. In younger patients the measurement is usually repeated after drops that relax the focusing muscle, because otherwise the eye hides part of the prescription.
The drops matter more in this prescription than in short sightedness. A long sighted eye compensates by focusing harder, and a refraction taken without relaxing that effort can understate the true figure, which is the figure surgery would be planned from.
What this depends on
Whether the measurement was taken with the eye relaxed
It can, because the eye is doing continuous work to compensate. The usual pattern is discomfort after sustained near tasks, such as reading or screen work, rather than a headache on waking. Blur is not always present, which is what makes this easy to attribute to something else.
What this depends on
How long the symptoms take to appear and what triggers them
Whether they improve when you stop the task
Whether the eye examination shows a prescription needing correction
Surface treatments and flap procedures can both correct hyperopia, and lenticule extraction is not a routine hyperopia treatment on the platforms in general use. The choice depends on your measurement and on what is cleared for use where you are treated.
Long sightedness is one of the reasons a clinic’s assessment matters more than its advertising. The correction reshapes the cornea to make it steeper, which places different demands on your tissue than the more common myopia treatment.
What this depends on
Your corneal thickness and shape
The size of the prescription
What the surgeon performs regularly, and what is approved locally
Astigmatism is a refractive error caused by the cornea or lens being curved more in one direction than another, so light is focused unevenly and vision is blurred or distorted rather than simply out of focus.
The usual description is that things look smeared or have ghosting at certain angles rather than being uniformly soft, and that is a recognisable difference for many people once it is explained.
Most astigmatism comes from the natural shape of the cornea, and it is often present from birth. It can also be caused or worsened by injury, surgery or a condition such as keratoconus that changes the cornea over time.
Astigmatism can be corrected with glasses, contact lenses, laser surgery or, in some cases, lens-based surgery. Which one is appropriate depends on the amount, the regularity of the cornea and whether it is stable.
Yes, astigmatism is routinely treated with LASIK, often together with short or long sightedness in the same procedure. Very large amounts, or astigmatism from an irregular surface, may need a different approach.
Small residual or regressed astigmatism is possible after any refractive procedure. It is usually measured at follow-up and may be small enough to leave alone, correctable with glasses, or worth a further treatment.
Regular astigmatism is an even curvature difference that glasses can correct. Irregular astigmatism is an unevenness that ordinary glasses cannot fully correct, and it is associated with conditions that change the corneal surface, such as keratoconus or scarring.
The distinction is clinical rather than academic: irregular astigmatism is one of the findings that changes what is possible, and specialised lenses or a different treatment plan may be the answer rather than laser surgery.
What this depends on
The topography map rather than the glasses prescription
Whether the pattern is stable between visits
Whether there is any history of trauma or previous surgery
It can change slowly, and a small amount of against-the-rule astigmatism is common as people get older. A rapid change in one eye, or a new difference between the two eyes, is worth examining rather than watching.
Uncorrected astigmatism can cause eye strain and headaches, particularly after sustained reading or screen work, because the eye works harder to find a clear image. The symptom is not specific to astigmatism, so an examination is what distinguishes it from an uncorrected prescription or dry eye.
Yes, and both do it well for regular astigmatism. Glasses need a cylinder value in the prescription; contact lenses need a toric design, which is a lens with a specific orientation that has to stay in position on the eye to work.
Toric lenses rotating slightly on the eye is a common reason someone reports their contact lens vision is good but fluctuates. It is worth mentioning to whoever fits lenses for you rather than putting up with it.
What this depends on
How much astigmatism you have and which axis it sits on
Standard LASIK corrects distance vision, and it does not restore the near focus that is lost with presbyopia. Some clinics offer specific strategies aimed at reducing reading dependence, and each involves its own trade-offs.
The strategies usually accepted include monovision, where the two eyes are deliberately treated differently, and a small planned amount of short sightedness in one eye. Both trade some distance sharpness or binocular comfort for near vision.
Whether either suits you depends on your prescription, your work and how you would feel about the compromise, which is why it is a discussion rather than a setting.
Presbyopia is the age-related loss of the ability to focus on close objects, caused by the natural lens inside the eye becoming less flexible. It affects almost everyone eventually, including people who have had laser eye surgery.
It is not a disease and not a complication of anything. It is the lens doing what lenses do with age, and it is why reading glasses become necessary in the forties for most people.
Reading glasses become necessary because the lens inside the eye can no longer change shape enough to focus on near objects. The change is gradual and usually noticed first in low light or when tired.
LASIK does not restore the lens’s ability to change focus, so it cannot undo presbyopia. It can be used in strategies that reduce reading dependence, at the cost of some distance sharpness or binocular balance.
Those strategies include monovision and a small deliberate under-correction in one eye. Both are compromises, and whether a compromise is acceptable depends on your work, your hobbies and how you drive at night.
SMILE corrects the focusing error of the cornea, and presbyopia originates in the lens, so SMILE does not restore near focus on its own. It can form part of a plan designed around reading vision, and that plan is a decision made with your surgeon.
The options for reading vision include reading glasses, varifocals, multifocal contact lenses, and surgical approaches such as monovision or lens replacement. Each trades something, and none restores youthful focusing power.
Lens replacement is the only option that addresses presbyopia and a developing cataract at the same time, which is why it comes up more often after the mid-fifties.
Monovision means deliberately correcting one eye for distance and the other for near, so the brain combines them. It reduces dependence on reading glasses at the cost of some depth perception and sharpness.
Many people adapt to it well and some do not, and the way to find out before committing is usually a trial with contact lenses. That trial is worth asking about, because it is cheap and it answers the question directly.
Age alone does not rule out laser eye surgery after forty. What changes is that presbyopia is arriving, so the discussion includes near vision and the trade-offs involved rather than distance vision alone.
It usually begins to be noticeable around the early forties and continues to change, slowly, for decades. The timing varies considerably between people, and it is affected by your existing prescription: short sighted people often notice it differently from those who have never worn glasses.
The reason there is no single age is that presbyopia measures the flexibility of the lens, and that changes gradually rather than on a birthday. What most people notice first is not blur but a need for more light, or holding print further away than they used to.
What this depends on
Your age and how fast the change is progressing
Your distance prescription
How much of the day you spend reading or on screens
The lens inside the eye becomes less able to change shape, so it cannot increase its focusing power for near objects. The muscle that changes it still works; the lens itself becomes thicker and stiffer with age.
That distinction explains the treatment options. Because the problem is in the lens rather than in the cornea, laser surgery on the cornea cannot restore the lens’s flexibility: the available approaches work by giving you a compromise instead, such as focusing one eye for distance and the other for near.
What this depends on
Age
Whether the lens has also started to cloud
Whether you have another refractive error alongside it
No. The change in the lens is not reversible by laser treatment, drops or exercise. What can be done is to compensate for it: reading glasses, varifocals, contact lenses designed for it, monovision, or lens replacement that substitutes an implant for the stiffened lens.
What this depends on
How much of the day you need clear near vision
Whether you would accept a compromise at distance
Whether there is any cataract, which changes the options
They are intraocular lenses designed to give useful vision at more than one distance, used when the natural lens is replaced: during cataract surgery, or as a refractive lens exchange in an eye without cataract. The categories are multifocal, extended depth of focus and accommodating designs.
They are a real option and not a free one. Every design that adds near vision takes something from distance or from the quality of night vision, and the trade-offs differ between designs. This is a decision worth making alongside the surgeon planning your measurements rather than from a brochure.
What this depends on
Whether cataract is present or the lens is still clear
How much night driving matters to you
Your tolerance for halos and for glasses in some situations
Yes, monovision can be created with laser vision correction: one eye is corrected for distance and the other is left or corrected for near. It is a deliberate compromise, and the usual advice is to try it with contact lenses first so you find out whether your brain tolerates it before anything permanent is done.
What this depends on
Whether you have tried monovision in contact lenses and liked it
How much night driving and detailed distance vision you need
Your dominant eye, which determines which way round it is set
It is possible, and it is a conversation rather than a yes-or-no. Correction can be planned so that your distance vision improves without making your reading worse, or deliberately set up as monovision. What surgery cannot do is give a 50-year-old the reading vision they had at 25.
The risk worth naming is the mismatch between expectation and arithmetic. Someone who is mildly short sighted and takes their glasses off to read may find that perfect distance vision removes the reading ability they had been relying on. A good assessment asks what you do without your glasses before answering.
What this depends on
Your age and the state of your reading vision
Whether you currently take your glasses off to read
What you would rather give up: distance sharpness or reading comfort
Blurred vision most often comes from an uncorrected or changed refractive error, a dry eye surface, or a problem with the lens, retina or optic nerve. Which one it is cannot be established from the symptom alone.
Two features are genuinely useful when you describe it to a clinician: whether it came on suddenly or gradually, and whether it is present in one eye or both. Those two answers change the urgency and the likely list considerably.
Vision is commonly worse in low light because the pupil widens, which allows more peripheral light through and makes any refractive error more noticeable. Night blur can also relate to dryness, cataract or an irregular corneal surface.
Halos and glare around bright lights at night can come from corneal irregularities, cataract, dryness, an uncorrected astigmatism, or the healing phase after refractive surgery. They are a symptom, not a diagnosis.
In the context of laser surgery, night vision symptoms are one of the most commonly reported side effects early on, and they frequently reduce over months. Persistent or worsening symptoms should be assessed.
This information is for educational purposes and does not replace an examination by a qualified eye-care professional.
Vision problemsBlur, night vision & strain
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Some sudden eye symptoms need urgent assessment
This answer explains what the symptom commonly indicates. If it has come on suddenly, or is
accompanied by pain or loss of vision, seek urgent care rather than waiting for an appointment.
Floaters are small opacities in the gel inside the eye that cast shadows on the retina. Many people have some, and longstanding floaters that are not changing are usually not an emergency.
A sudden increase in floaters, floaters with flashes, or a shadow or curtain across part of the vision is different and needs urgent assessment rather than a routine appointment. That combination can indicate a retinal problem.
Blur in one eye suggests something specific to that eye, such as a refractive difference, a surface problem, or an issue with the lens, retina or optic nerve on that side. It is worth an examination rather than a wait.
One useful habit is to test your eyes separately from time to time, because blur that is limited to one eye is easy to miss when both eyes are open.
This information is for educational purposes and does not replace an examination by a qualified eye-care professional.
Vision problemsBlur, night vision & strain
Was this answer helpful?
Thank you. We use this to decide what to improve.
Some sudden eye symptoms need urgent assessment
This answer explains what the symptom commonly indicates. If it has come on suddenly, or is
accompanied by pain or loss of vision, seek urgent care rather than waiting for an appointment.
A sudden change in vision needs urgent assessment rather than an appointment in a few weeks. It can be caused by something on the retina, a vascular event or an acute problem in the eye, and the timing matters for treatment.
Eye strain usually comes from sustained effort at a close task, often with an uncorrected or changed prescription, an unstable tear film, or prolonged focus without breaks. It is uncomfortable rather than damaging.
The common pattern is that the eyes feel heavy and the vision goes soft after long screen or reading sessions, and it improves with rest. Persistent strain despite breaks is worth an eye examination, because the cause is sometimes a prescription that no longer fits.
This information is for educational purposes and does not replace an examination by a qualified eye-care professional.
Vision problemsBlur, night vision & strain
Was this answer helpful?
Thank you. We use this to decide what to improve.
Some sudden eye symptoms need urgent assessment
This answer explains what the symptom commonly indicates. If it has come on suddenly, or is
accompanied by pain or loss of vision, seek urgent care rather than waiting for an appointment.
Double vision has two broad causes: a problem in one eye, or a failure of the two eyes to align. Both need assessment, and sudden double vision needs it urgently rather than routinely.
A simple test a clinician may ask you about is whether the double image disappears when you close one eye. It does not diagnose anything, but it points the assessment in a direction.
Blur on waking is often a tear film problem, because the eye produces less tear overnight and the surface takes a few blinks to stabilise. It can also relate to a contact lens worn overnight, which is a reason to avoid that wherever possible.
A refractive error is a mismatch between the focusing power of the eye and its length, so light does not come to a focus on the retina. Short sightedness, long sightedness and astigmatism are the three common forms, and each is described by a prescription.
Refractive error is not a disease and does not damage the eye by itself. The reason clinicians still examine the whole eye before treating it is that the same blur can sit on top of a condition that does need treatment.
What this depends on
The prescription and how stable it has been
The health of the cornea, lens and retina
Whether the blur is explained entirely by the prescription
Short sightedness blurs distance because focus falls in front of the retina, long sightedness blurs near focus for most of the day because it falls behind, and astigmatism blurs in a direction because the cornea is curved unevenly. More than one can be present at once.
There is no schedule that applies to everyone. Prescriptions often change through childhood and adolescence, settle in early adulthood, and then change again with reading vision in the forties and with cataract later. What matters is the pattern in your own records.
That pattern is also what a surgical assessment is asking about. A prescription that has been the same for a couple of years is a different proposition from one that moved last year in either direction.
What this depends on
Your age
How the prescription has changed across previous tests
Whether any change is explained by another condition
These answers describe what is generally true. They are not a diagnosis and they cannot say
whether a treatment is suitable for you, because suitability depends on measurements taken during
an examination. Only a qualified ophthalmologist who has examined you can decide.
A continuously updated clinical reference chapter covering SMILE indications, technique, outcomes and complications, written for clinicians.
Used for How the lenticule is created and removed; Indications and contraindications; Complication categories; Corneal biomechanics compared with flap-based surgery.