High Myopia and Cataract Surgery

Key Points at a Glance

Highlights of this disease

• High myopia is defined as a spherical equivalent of -6.0 D or more, or an axial length of 26.5 mm or more, and is found in about 2% of the population.
• In highly myopic eyes, the risk of nuclear cataract is 3 to 5 times higher, and the risk of posterior subcapsular cataract also increases.
• Elongation of the axial length reduces the accuracy of IOL power calculation, often leading to postoperative hyperopia.
• AI-driven new-generation formulas (Kane, Hill-RBF) are significantly superior in refractive accuracy compared to conventional formulas.
• During surgery, the risk of posterior capsule rupture and zonular dialysis increases, requiring careful technique.
• The risk of postoperative retinal detachment is high, and long-term follow-up with fundus examination is essential.

1. High Myopia and Cataract Surgery

Myopia is found in about 25% of the general population. High myopia is defined as a spherical equivalent of -6.0 D or more, or an axial length of 26.5 mm or more. Approximately 2% of the population falls into this category. Pathologic myopia refers to a spherical equivalent of -8.0 D or more, or an axial length of 32.5 mm or more.

High myopia increases the risk of developing cataracts. The Singapore Malay Eye Study showed that patients with high myopia have a 3- to 5-fold increased risk of nuclear cataract and about a 30% increased risk of posterior subcapsular cataract. The association between myopia and posterior subcapsular cataract (PSC) is particularly strong, with reports indicating that the prevalence of PSC increases by about 21% per diopter increase in myopia ²⁾. On the other hand, some studies suggest that the prevalence of cortical or nuclear cataracts does not show a clear association with the degree of myopia ²⁾.

Cataract surgery in eyes with high myopia presents many challenges not seen in emmetropic eyes, such as elongated axial length, presence of posterior staphyloma, and laxity of the lens capsule. Thorough preoperative evaluation by an experienced surgeon is key to achieving good visual outcomes ³⁾.

Q Are people with high myopia more likely to develop cataracts?

A

High myopia increases the risk of nuclear cataract by 3 to 5 times and also significantly increases the risk of posterior subcapsular cataract. However, nuclear cataract is easily confused with myopic refractive changes (myopic shift due to nuclear sclerosis), and its direct association with axial length is not always clear ²⁾.

2. Main Symptoms and Clinical Findings

Subjective Symptoms

The subjective symptoms of cataracts in highly myopic eyes are as follows.

• Decreased visual acuity: As nuclear cataracts progress, myopia becomes stronger. Both distance and near vision gradually decline.
• Blurred vision (haze): In posterior subcapsular cataracts, blurred vision becomes noticeable in backlight or bright environments.
• Monocular diplopia: May occur due to irregularity of nuclear sclerosis or cortical opacities.
• Floaters: In high myopia, posterior vitreous detachment (PVD) tends to occur early, and patients frequently complain of floaters.

Clinical Findings

The characteristic cataract-related clinical findings in high myopia are as follows.

• Nuclear cataract: The most common type of cataract, presenting with nuclear sclerosis and nuclear coloration. As it progresses, the degree of myopia further increases.
• Posterior subcapsular cataract (PSC): Granular opacities are observed on the posterior surface of the lens. It is strongly associated with high myopia.
• Posterior staphyloma: Found in approximately 70% of eyes with an axial length exceeding 33.5 mm, making axial length measurement difficult.
• Early posterior vitreous detachment: In highly myopic eyes, posterior vitreous detachment tends to occur at a young age, and the vitreous cortex frequently remains on the macula.
• Myopic retinal degeneration: Approximately 62% of myopic eyes show some form of myopic or age-related retinal degeneration.

3. Causes and Risk Factors

The reasons why cataracts progress more rapidly in highly myopic eyes are multifactorial.

• Elongation of axial length: It is thought to increase oxidative stress on the lens, promoting nuclear sclerosis.
• Vitreous liquefaction: In high myopia, vitreous liquefaction progresses early. The liquefied vitreous may affect the metabolic environment of the lens.
• Synergistic effect with aging: Both aging and axial elongation are factors that reduce corrected visual acuity.

Risk factors that increase the need for cataract surgery include the following:

• Rapid change in myopia degree: Suggests progression of nuclear cataract.
• History of refractive surgery: IOL power calculation becomes more complex in eyes with prior LASIK or PRK.
• Myopic macular degeneration: An independent factor limiting postoperative visual recovery.

Prevention and daily care

• People with high myopia should undergo a dilated fundus examination at least once a year.
• If floaters suddenly increase or you see flashes of light, there may be a retinal tear, so see an ophthalmologist immediately.
• If your prescription changes frequently due to cataract progression, consult your doctor about the timing of cataract surgery.

4. Diagnosis and Examination Methods

Importance of Preoperative Evaluation

In patients with high myopia, the probability of having a history of refractive surgery or retinal disease is about 10 times higher than in emmetropic eyes. A detailed ophthalmic history is extremely important.

Axial Length Measurement

Accurate measurement of axial length is the most important preoperative examination for cataract surgery in highly myopic eyes.

• Optical biometry (e.g., IOLMaster): If the patient can fixate, it can estimate the refractive axial length from the corneal vertex to the fovea with high precision. However, reports indicate that in eyes with axial length exceeding 27.0 mm or those using minus power IOLs, the IOL power may be underestimated.
• Ultrasound A-scan (contact or immersion method): Measures the anatomical axial length from the corneal vertex to the posterior pole. The presence of posterior staphyloma can overestimate axial length, leading to postoperative hyperopia.

Corneal Endothelial Cell Density Examination

It is desirable to have a preoperative count of 2,000 cells/mm² or more. If the count is 1,500 cells/mm² or less, consideration must be given to the choice of surgical method.

Fundus examination

Detailed fundus examination under mydriasis confirms the presence of retinal tears, lattice degeneration, and posterior staphyloma. The presence of myopic macular degeneration is a predictor of postoperative visual acuity.

Q Is preoperative evaluation by a vitreoretinal specialist necessary?

A

Some surgeons request evaluation by a vitreoretinal specialist before cataract surgery in high myopia patients, but this practice is not universal. At a minimum, a detailed preoperative fundus examination under mydriasis is essential.

5. Standard treatment

Selection of IOL power calculation formula

In highly myopic eyes, the accuracy of conventional IOL power calculation formulas decreases. In particular, third-generation formulas have insufficient accuracy in estimating the effective lens position (ELP), which can cause postoperative hyperopic shift ¹⁾.

The characteristics of the main formulas are shown below.

Formula	Characteristics	Accuracy for long axial length
SRK/T	Third-generation, widely used	Tendency toward hyperopia
Barrett Universal II	Multivariate theoretical formula	High accuracy
Kane / Hill-RBF	AI-driven	Highest accuracy

Suzuki et al. (2025) compared four formulas in 80 eyes with axial length ≥30.0 mm ¹⁾. The MAE of Kane and Hill-RBF were 0.51 D and 0.52 D, respectively, significantly lower than SRK/T (P < 0.05). The MAE of Barrett Universal II was 0.66 D, with no significant difference from SRK/T. The proportion of refractive errors exceeding ±1.0 D was 7.5% for Kane and Hill-RBF, and 42.5% for SRK/T. In the subgroup with axial length ≥32.0 mm, Kane achieved the lowest MAE of 0.44 D.

In long eyes (≥26.0 mm), SRK/T, Holladay 1, and Holladay 2 formulas were previously considered accurate, but recent evidence shows that newer formulas such as Olsen, EVO, Kane, Hill-RBF, and Barrett Universal II are accurate for all axial lengths ³⁾. In long eyes with anterior chamber depth ≥3.5 mm, the Haigis formula is also accurate ³⁾. Applying Wang-Koch (W-K) axial length correction to third-generation formulas is also useful ³⁾.

IOL Selection

In high myopia, note the following points:

• IOL implantation is the principle: IOL implantation is recommended over leaving the eye aphakic. The IOL acts as a barrier against vitreous movement and retinal traction.
• Acrylic lens recommended: Considering the possibility of future vitreous surgery, acrylic lenses are preferred over silicone lenses.
• Setting the target refraction: Since minus-power IOLs have a high rate of postoperative hyperopia, some surgeons set the target refraction to around -2.0 D (myopic shift).

Cataract surgery after refractive surgery

In eyes with a history of LASIK or PRK, accurate assessment of corneal refractive power becomes difficult, further reducing the accuracy of IOL power calculation ³⁾. This tends to cause postoperative hyperopia. It is recommended to use multiple formulas, such as the Barrett True K formula and the ASCRS online calculator, to determine the power. Regardless of whether preoperative LASIK data is available, 80–90% of cases are expected to be within ±1 D, but it is important to explain to the patient that 10–20% may have a power deviation of ±1 D or more.

Surgical technique considerations

In highly myopic eyes, the anterior chamber is deep and the lens capsule is relaxed and large, so the following techniques are recommended.

• Properly pressurize the anterior chamber with ophthalmic viscosurgical devices during continuous curvilinear capsulorhexis (CCC).
• Minimize leakage from the incision and anterior chamber collapse.
• Lower the height of the irrigation bottle and increase the flow rate. Prevents the anterior chamber from becoming excessively deep.
• When LIDRS (Lens-Iris Diaphragm Retropulsion Syndrome) occurs: Lift the pupillary margin with a spatula or sinskey hook to allow fluid to flow past the pupil.

Intraoperative Complications and Their Frequency

The estimated incidence of intraoperative complications in high myopia is as follows.

• Posterior capsule rupture: 2.3–9.3% for axial length > 27.0 mm
• Zonular rupture: 1.7% for axial length > 30.0 mm
• Anterior capsule tear: 1.1% for axial length > 30.0 mm

It has been reported that the risk of intraoperative complications increases by 1.22 times for every 1.0 mm increase in axial length.

Precautions and side effects in treatment

• If an IOL intended for capsular bag fixation is placed in the ciliary sulcus due to intraoperative capsular rupture, the power should be reduced by 1 D compared to the bag power in eyes with standard axial length. In long eyes with low-power IOLs, the correction should be smaller.
• In highly myopic eyes with a large ciliary sulcus, there is a high risk of IOL displacement and instability when fixed in the ciliary sulcus.
• Minus power IOLs tend to have larger postoperative refractive errors.
• Retrobulbar and peribulbar anesthesia carry a risk of globe perforation in long axial length eyes; topical anesthesia or sub-Tenon’s anesthesia is safer.

Q What happens if only one eye undergoes surgery?

A

If only one eye undergoes surgery, a significant anisometropia (refractive difference) occurs between the operated and unoperated eyes. This can interfere with daily life, so it is important to perform surgery on the other eye at an appropriate time to shorten the period of anisometropia.

6. Pathophysiology and Detailed Mechanism

In highly myopic eyes, the anteroposterior diameter (axial length) of the globe is significantly longer than normal. This elongation leads to the following structural changes, increasing the difficulty of cataract surgery.

Posterior Staphyloma and Axial Length Measurement

Posterior staphyloma is present in approximately 70% of eyes with an axial length exceeding 33.5 mm. Almost all cases of pathologic myopia have some degree of posterior staphyloma. Staphyloma is a localized expansion of the sclera, choroid, and retinal pigment epithelium, which can cause overestimation of axial length on ultrasound measurement. Additionally, macular staphyloma can cause poor fixation, reducing the accuracy of optical measurements.

Difficulty in IOL Power Calculation

In long eyes, anterior segment parameters do not change proportionally to axial length ¹⁾. This makes ELP estimation difficult with regression-based models. Inaccurate ELP estimation is the main cause of IOL power prediction error. The conventional SRK/T formula shows significantly reduced accuracy for axial lengths of 28.0 mm or more, often resulting in postoperative hyperopia ¹⁾.

The Barrett Universal II formula is based on a theoretical eye model and improves ELP estimation by using multiple biometric parameters including lens thickness and corneal diameter ¹⁾. However, it is not AI-based. AI-driven formulas such as Kane and Hill-RBF use machine learning algorithms to learn the nonlinear relationship between axial length and anterior segment parameters, achieving more accurate IOL power prediction ¹⁾.

Effects on the Vitreous and Retina

In highly myopic eyes, posterior vitreous detachment tends to occur early, and the vitreous cortex frequently remains attached to the macula. Inserting an IOL during cataract surgery acts as a physical barrier against anterior movement of the vitreous and retinal traction, contributing to a reduced risk of retinal detachment.

---

7. Latest Research and Future Perspectives (Investigational Reports)

For Patients: Please Read Carefully

The following content is currently under investigation or in clinical trials and is not standard treatment available at general hospitals. It is reference information for professionals regarding future medical developments.

Development of AI-Driven IOL Calculation Formulas

Suzuki et al. (2025) reported that in 80 eyes with extreme axial myopia (axial length ≥30.0 mm), the Kane and Hill-RBF formulas had significantly lower MAE compared to the SRK/T formula (0.51 D and 0.52 D vs. SRK/T, respectively), and the rate of refractive error exceeding ±1.0 D was only 7.5% versus 42.5% for SRK/T¹⁾. In the subgroup with axial length ≥32.0 mm, the Kane formula showed the best performance with an MAE of 0.44 D and MedAE of 0.40 D.

Further improvement in the accuracy of IOL calculation formulas using AI technology is expected ¹⁾. With the accumulation of data and optimization of learning algorithms, stable refractive outcomes may be achieved even in eyes with extremely long axial lengths.

---

8. References

1. Suzuki Y, Kamoi K, Uramoto K, Ohno-Matsui K. Artificial intelligence driven intraocular lens power calculation in extreme axial myopia. Sci Rep. 2025;15:20899.
2. Bullimore MA, Ritchey ER, Shah S, et al. The risks and benefits of myopia control. Ophthalmology. 2021;128(11):1561-1579.
3. ESCRS. Clinical practice guidelines for cataract surgery. European Society of Cataract and Refractive Surgeons. 2024.