If ICL surgery has been recommended, it helps to ask why it may suit your eyes better than laser surgery, whether there is enough space for the lens, and how its power, size, and astigmatism axis will be determined. Even if your corneal condition makes ICL a useful option, we still need to confirm that there is enough space inside the eye, assess the surrounding tissues, and determine the prescription to be corrected before making a surgical plan.
ICL surgery places a vision-correcting lens behind the iris and in front of your natural lens, which remains in place. It works in a different part of the eye from laser surgery, which changes your prescription by removing corneal tissue. This difference also explains why the preoperative examinations are different.
When might ICL be recommended instead of LASIK or PRK?
ICL may be considered when a large amount of myopia needs correcting or when corneal thickness or shape limits laser correction. Laser surgery removes corneal tissue according to the correction required. Even in corneas of the same thickness, the amount of tissue remaining after surgery can differ with the prescription.
This is one reason to consider ICL for high myopia. If correcting your prescription would require removing a large amount of corneal tissue, preserving the cornea and correcting the eye’s refractive power with an implanted lens may offer an alternative. However, high myopia does not mean everyone needs ICL surgery. Laser surgery may remain an option if the corneal findings and amount of correction allow it.
“You have a thin cornea, so we recommend ICL” is not a complete explanation. Your actual corneal findings need to be considered alongside the prescription to be corrected. What matters is whether an appropriate amount of tissue and a suitable corneal shape can be maintained after correction, rather than simply whether the cornea is thinner than average.
Being unsuitable for laser surgery does not automatically make you suitable for ICL. We must also check whether there is enough room for the lens and whether the internal structures of your eye are suitable. The reasons laser surgery is limited and the conditions that allow ICL surgery need to be assessed separately.
Which examinations determine whether ICL surgery is suitable?
An ICL examination involves more than measuring your prescription. It assesses the space for the lens, internal eye structures, the cells that help keep the cornea clear, your natural lens, eye pressure, and retina.
| Examination findings | What they help establish for ICL surgery |
|---|---|
| Refraction, corrected visual acuity, and prescription changes | The amount of myopia and astigmatism to correct, prescription stability, and the vision that may be achievable with correction |
| Internal structures, including anterior chamber depth and angle | The space available for the lens and its relationship to surrounding tissues |
| Corneal endothelial cells | The number and shape of the cells that help maintain corneal clarity |
| Eye pressure, natural lens, and retina | Conditions that may limit surgery or require treatment or observation first |
| Corneal thickness and shape | Overall eye assessment and comparison with other vision correction options |
Before surgery, EYEREUM Eye Clinic performs corneal and endothelial examinations, imaging of the internal eye space, retinal and optic nerve assessments, and cycloplegic refraction, among other tests. Each provides different information. The actual tests and their sequence may vary with your eye condition.
Anterior chamber depth (ACD) is the distance from the inner surface of the cornea to the front of the natural lens. The anterior chamber angle relates to the peripheral drainage pathway for aqueous humor, the fluid inside the eye. We also consider crystalline lens rise (CLR), which describes how far forward the natural lens projects. At EYEREUM, we analyze these structures together using anterior segment OCT. Even when the front-to-back depth appears adequate, a narrow peripheral angle may lead to pressure problems after lens implantation. No single measurement can determine whether there is enough space.
When comparing numbers on examination reports, the measurement references must also match. An ACD measurement taken from the outer surface of the cornea differs from one taken from the inner surface by the thickness of the cornea. The FDA review documentation for EVO ICL also distinguishes these measurement references. If measurements differ between clinics, first check whether the same distance was measured.
Corneal endothelial cells regulate fluid balance to help keep the cornea transparent. A low cell count or abnormal cell shape can change the risk assessment for lens implantation. ICL may not be suitable if the internal eye space is limited or endothelial cell health is a concern even when the myopic prescription falls within the treatment range.
Retinal and optic nerve examinations serve a different purpose. ICL corrects refractive error; it does not treat retinal or optic nerve disease itself. We therefore assess both the vision that may be achievable with prescription correction and conditions that need separate treatment or observation. In high myopia, it is particularly important to assess associated problems, including retinal disease, before surgery.
How are lens power and the astigmatism axis determined?
Measuring the space for a lens is different from determining the correction needed for clear vision. Even when the internal structures are suitable for surgery, the amount of myopia and astigmatism must be established accurately to calculate the appropriate lens power.
Autorefraction measures the eye’s refractive state. Subjective refraction then checks the correction you actually need by having you look at an eye chart while lenses are changed and you compare which gives clearer vision. We consider both the instrument readings and the prescription that provides your clearest vision. These refractive findings are used in the lens power calculation to select the implanted lens. At EYEREUM, we separately assess autorefraction, checking your current glasses prescription, and visual testing to find the correction you need.
The eye’s focusing ability, or accommodation, can affect measurements of myopia and hyperopia, so cycloplegic refraction is also used. If your glasses prescription has continued to change recently, we need to consider the pattern of change as well as the current measurement. Further changes after correction could mean needing glasses again, which is why refractive stability is assessed.
For a toric ICL, which corrects astigmatism, the amount and axis of astigmatism are separate considerations. The amount indicates how much correction is needed; the axis indicates its direction. Even with the same amount of astigmatism, a different axis requires a different lens orientation. We therefore look beyond whether astigmatism is present and review its measured amount and axis alongside corrected visual acuity.
At EYEREUM, we examine the amount and axis of astigmatism and the optical characteristics of the whole eye. A toric lens must be aligned with the axis planned before surgery. Aligning the lens axis is a separate step from selecting its power. Rotation away from the planned orientation can affect astigmatism correction.
Can ICL size be decided directly from the measurements?
ICLs come in different sizes as well as powers. The examination findings are used to select a size appropriate for your eye. Two people with the same myopic prescription may need different lens sizes because their internal eye structures differ.
Information used in sizing includes anterior chamber depth, horizontal corneal width, and measurements of internal eye structures. White-to-white (WTW), the distance between the two visible corneal borders, is one indicator used in lens size selection.
These measurements are considered alongside the available lens sizes to choose a size for your eye. The recommended lens size is based on these measurements rather than the prescription alone.
The gap between the ICL and your natural lens is called the vault, or vaulting. It helps us assess whether appropriate spacing is maintained after implantation. A gap that is too small raises concern about contact with the natural lens; one that is too large can raise concerns such as narrowing of the anterior chamber angle.
Before surgery, eye measurements are used to predict the lens position and spacing. After surgery, the actual vault, eye pressure, and natural lens are checked. These preoperative and postoperative assessments have different roles. The actual vault still needs to be checked after implantation, regardless of the preoperative calculations.
If LASIK or PRK is also possible, what should you compare with ICL?
When several procedures are suitable, compare how they correct vision and how follow-up care differs. Laser surgery changes the refractive power of the cornea; ICL adds a lens inside the eye.
ICL has the advantage of not removing corneal tissue to correct the prescription, but it is an intraocular operation. Risks including cataract, increased eye pressure, and endothelial cell loss, as well as the possibility of lens adjustment or replacement must also be considered. Regular examinations remain necessary after implantation.
ICL is not automatically the better option simply because it does not remove corneal tissue. The remaining corneal thickness and structural stability after laser surgery should be considered alongside the internal structures that determine whether ICL implantation is possible.
If the reasons for a recommendation are unclear, you can ask for a fuller explanation of the results or seek another clinician’s opinion. Your existing test results and proposed lens and surgical plan can help you compare those opinions.
Frequently asked questions
If my results meet the criteria, is ICL the best choice?
Meeting the criteria means ICL can be considered. To understand why it is recommended, you also need to compare whether other procedures are possible and the expected benefits and burdens of each option.
Does having more or newer examination equipment make the ICL decision more accurate?
Different devices measure different things. Imaging the internal eye space, examining endothelial cells, and confirming the prescription and astigmatism axis cannot replace one another. More important than device names or numbers is understanding how each result contributes to decisions about suitability, lens power, and lens size.
If an ICL is removed later, does my eye return to its preoperative state?
An ICL can be removed or replaced if needed. However, lens removal also requires surgery, and it cannot be assumed that the eye will return to exactly the same condition as before the original operation.
Consider your preoperative eye condition and long-term care as well as the possibility of lens removal.
