Preparation for Cataract Surgery in RGP Contact Lens Wearers
Key Points at a Glance
Section titled “Key Points at a Glance”1. Preparation for Cataract Surgery in RGP Contact Lens Wearers
Section titled “1. Preparation for Cataract Surgery in RGP Contact Lens Wearers”Contact lens materials began with rigid plastic using polymethyl methacrylate (PMMA), followed by the development of rigid gas permeable (RGP) lenses. While RGP lenses improved flexibility and oxygen permeability, initially only PMMA lenses were thought to cause corneal shape changes. However, subsequent research revealed that multiple types of contact lenses, including RGP and soft contact lenses (SCL), can cause corneal warpage, affecting the overall curvature of the cornea.
Corneal warpage was defined by Wilson et al. as “central irregular corneal astigmatism, loss of radial symmetry, and reversal of the normal pattern of gradual flattening from the center to the periphery.” Because these changes affect corneal measurements used for IOL power calculation before cataract surgery, special preoperative preparation is necessary for RGP contact lens wearers.
Long-term wear of RGP lenses can alter corneal shape (corneal warpage), leading to errors in corneal curvature measurements used for IOL power calculation. Therefore, if measurements are not taken after discontinuing lens wear and waiting for corneal shape to stabilize, there is a risk of unexpected refractive errors after surgery.
2. Main Symptoms and Clinical Findings
Section titled “2. Main Symptoms and Clinical Findings”Subjective Symptoms
Section titled “Subjective Symptoms”Corneal warpage itself often does not cause significant subjective symptoms. However, the following symptoms may occur.
- Visual fluctuation/visual instability: Vision may fluctuate immediately after lens removal.
- Decreased vision due to irregular astigmatism: Irregular astigmatism that is difficult to correct with glasses may be perceived.
- Decreased vision during contact lens wear: Fitting may become unstable due to changes in corneal shape.
Clinical Findings
Section titled “Clinical Findings”Corneal topography is the most important examination.
- Central irregular astigmatism: The color-coded map of corneal curvature shows an irregular pattern.
- Loss of radial symmetry: The normal concentric pattern is disrupted.
- Reversal of the central-to-peripheral flattening pattern: Normally, the cornea flattens gradually from the center to the periphery, but in warpage this pattern is reversed.
- Focal thickening of the corneal epithelium: With anterior focal protrusion, the epithelium thickens focally, unlike in keratoconus where it thins focally.
The clinical findings of corneal warpage are similar to those of keratoconus (KCN), with overlapping topographic changes such as irregular astigmatism with inferior steepening and scissoring reflex on retinoscopy. The differentiation between the two is detailed in the Diagnosis and Examination Methods section.
3. Causes and Risk Factors
Section titled “3. Causes and Risk Factors”The main causes and risk factors of corneal warpage in RGP wearers are shown below.
- Long-term RGP contact lens wear: The lens applies mechanical pressure to the cornea, altering its shape. The longer the wear period, the more severe the warpage and the longer the recovery time.
- PMMA hard contact lens wear: Low oxygen permeability, combined with metabolic changes, induces corneal shape changes.
- Poor lens centration: Lenses that stabilize superiorly tend to produce a color-coded map pattern similar to keratoconus.
- Long-term wear of soft contact lenses (SCLs): Although less severe than with hard contact lenses, SCLs can also cause corneal warpage. Continuous-wear SCLs tend to take longer to recover than daily-wear SCLs.
4. Diagnosis and Examination Methods
Section titled “4. Diagnosis and Examination Methods”Diagnosis of Corneal Warpage
Section titled “Diagnosis of Corneal Warpage”The diagnosis of corneal warpage is based on corneal topography analysis after discontinuation of contact lens wear.
The following findings are useful for differentiating corneal warpage from keratoconus.
| Finding | Corneal warpage | Keratoconus |
|---|---|---|
| Epithelial thickness | Focal thickening | Focal thinning |
| Corneal thickness | No significant change | Stromal thinning present |
| Reversibility | Reversible (improves with lens discontinuation) | Irreversible |
| Warpage index | Positive | Negative |
Warpage Index is a measure that combines anterior focal protrusion and localized epithelial thickening. A positive result indicates corneal warpage.
Examinations for IOL Power Calculation
Section titled “Examinations for IOL Power Calculation”Accurate IOL power calculation before cataract surgery requires the following evaluations.
- Corneal topography: Evaluates the curvature distribution of the anterior corneal surface in detail. Topography and tomography after contact lens cessation are essential for evaluating corneal ectasia 1).
- Corneal tomography (Scheimpflug imaging, etc.): Comprehensively evaluates the anterior and posterior corneal surfaces, corneal thickness, and elevation maps. It is useful for assessing irregular astigmatism and is also used to determine the indication for toric IOLs 2).
- Anterior segment OCT: Enables corneal thickness mapping and epithelial thickness mapping. In keratoconus, epithelial thickness shows a donut-shaped pattern1).
- Subjective refraction test: Confirm refractive stability after discontinuing contact lens wear.
- Corneal curvature measurement (keratometry): A basic parameter for IOL power calculation.
Contact Lens Discontinuation Period and Refractive Stability Guidelines
Section titled “Contact Lens Discontinuation Period and Refractive Stability Guidelines”To ensure accurate IOL power calculation for cataract surgery, measurements must be taken when corneal shape and refractive values are stable. The following summarizes key research findings.
The table below summarizes research on the time to refractive stability in rigid gas permeable (RGP) contact lens wearers (definition of refractive stability: subjective refraction change ≤0.5 D, corneal curvature change ≤0.5 D, normalization of corneal topography pattern).
| Study | Time to Stability | Notes |
|---|---|---|
| Wang et al. | Mean 8.8±6.8 weeks (range 1–20 weeks) | Large individual variation |
| Tsai et al. | Most by 6 weeks, 78% by 9 weeks | Longer wear time prolongs stabilization |
| Budak et al. | Approximately 5 weeks | SCL: approximately 2 weeks |
| Pannu et al. | Approximately 6 weeks | Until disappearance of topographic or refractive changes |
For soft contact lens wearers, refractive values usually stabilize after 2–3 weeks of discontinuation, but corneal shape (topography, corneal curvature) may require 4–6 weeks to stabilize.
General recommended approach:
- Hard contact lens (RGP) wearers: At least 4 weeks, with a guideline of 1 month of discontinuation for every 10 years of wear.
- Soft contact lens wearers: At least 2 weeks of discontinuation is usually sufficient.
- In both cases, individual variation is large, and it is essential to confirm stabilization of corneal shape and refractive values through actual measurements.
For RGP contact lens wearers, a cessation period of at least 4 weeks is recommended; for long-term wearers, a cessation of 1 month per 10 years of wear is advised. After cessation, multiple corneal topography measurements and refraction tests should be performed, and surgery should be scheduled only after values have stabilized. For SCL wearers, 2 weeks is usually sufficient, but continuous-wear SCLs may require a longer period.
Epithelial thickness mapping is useful: in corneal warpage, localized epithelial thickening is seen at the anterior protrusion site, whereas in keratoconus, localized epithelial thinning is observed. Additionally, corneal warpage shows no significant change in corneal thickness and is a reversible condition that improves after contact lens cessation, which are important distinguishing features.
5. Standard Treatment
Section titled “5. Standard Treatment”The standard approach for cataract surgery preparation in RGP contact lens wearers is described.
Discontinuation of Contact Lens Wear and Repeated Evaluation
Section titled “Discontinuation of Contact Lens Wear and Repeated Evaluation”The most important step is to discontinue contact lens wear and wait for the corneal shape to recover.
- Discontinuation period: At least 4 weeks for RGP lens wearers; for long-term wearers, approximately 1 month per 10 years of wear.
- Confirmation of stability: After discontinuing contact lenses, perform corneal topography and subjective refraction multiple times (at least twice) at intervals to confirm that values have stabilized.
- Target setting after cataract surgery: If the patient wishes to become independent from contact lenses, particularly careful confirmation is needed due to large individual differences.
IOL Power Calculation
Section titled “IOL Power Calculation”After confirming corneal shape stability, perform IOL power calculation.
- Corneal curvature measurement: Keratometry values are used for IOL power calculation in cataract surgery, and the astigmatism power and axis are utilized for toric IOL power selection.
- Use of corneal tomography: When irregular astigmatism is suspected, evaluation by topography or tomography is useful and contributes to improving the accuracy of IOL power calculation2).
Management of patients with keratoconus
Section titled “Management of patients with keratoconus”Special considerations are necessary when performing cataract surgery in patients with keratoconus.
- Assessment of progression risk: If there is a risk of progression, consider corneal cross-linking (CXL) or insertion of intracorneal ring segments (ICRS) before cataract surgery3). This stabilizes the preoperative corneal shape, enabling more accurate biometry and IOL power calculation.
- Evaluation of astigmatism: In astigmatism assessment, comprehensive evaluation of anterior, posterior, and total corneal astigmatism improves the accuracy of IOL power calculation3).
- Special considerations for IOL power calculation: In keratoconus patients, biometric measurements tend to overestimate corneal refractive power, leading to a high risk of postoperative hyperopic shift. For cases with maximum corneal refractive power (K value) ≤55 D, it is recommended to set a slight myopic target using the measured K value3).
6. Pathophysiology and Detailed Mechanisms
Section titled “6. Pathophysiology and Detailed Mechanisms”Mechanisms of Corneal Warpage
Section titled “Mechanisms of Corneal Warpage”PMMA hard contact lenses have low oxygen permeability, and both mechanical compression and metabolic disturbance contribute to shape changes. RGP contact lenses have improved oxygen permeability but can still cause corneal shape changes due to mechanical pressure.
The following mechanisms are considered for corneal warpage:
- Mechanical compression: The mechanical pressure exerted by the lens on the cornea causes elastic deformation of the cornea.
- Restricted tear exchange: Poor fit of hard contact lenses impedes tear exchange, altering corneal metabolism.
- Epithelial cell redistribution: Lens pressure alters the distribution of epithelial cells, causing localized epithelial thickening and thinning.
Differences in pathology between corneal warpage and keratoconus
Section titled “Differences in pathology between corneal warpage and keratoconus”In keratoconus, thinning of the corneal stroma progresses irreversibly, whereas corneal warpage is a reversible change. This difference is reflected in the following characteristics.
- Keratoconus: Elevation maps of the anterior and posterior cornea show island-like anterior protrusion, and corneal thickness maps show thinning that is decentered from the center. Wavefront aberration analysis shows a marked increase in higher-order aberrations (especially vertical coma).
- Corneal warpage: It does not involve stromal thinning and is primarily an epithelial-level change. It shows reversibility, with shape recovery after discontinuation of contact lens wear.
7. Latest research and future perspectives (reports at the research stage)
Section titled “7. Latest research and future perspectives (reports at the research stage)”Development of more precise methods for determining refractive stability
Section titled “Development of more precise methods for determining refractive stability”Currently, indicators are being developed to objectively evaluate refractive stability after discontinuation of contact lens wear.
In serial measurements with Pentacam at 2-week intervals, the disappearance of inferior corneal steepening (tangential inferior curvature) may serve as an indicator of refractive stability. Subjective refraction may stabilize within 2 weeks, while corneal curvature, topography, and corneal thickness may require 4 to 6 weeks to stabilize (refractive change <0.5 D, corneal curvature change <0.5 D, topographic change within central 3 mm <0.5 D, corneal thickness change <8 μm).
Improvement of IOL calculation accuracy before and after corneal cross-linking
Section titled “Improvement of IOL calculation accuracy before and after corneal cross-linking”In cataract patients with keratoconus, improvements in IOL calculation accuracy after cross-linking and corneal ring insertion are being investigated. Stabilizing corneal shape preoperatively is thought to enable more accurate biometry and IOL calculation 3). In the future, artificial intelligence (AI)-based IOL power calculation is also expected to improve accuracy.
8. References
Section titled “8. References”- American Academy of Ophthalmology Preferred Practice Pattern Committee. Corneal Ectasia Preferred Practice Pattern. Ophthalmology. 2024.
- Preferred Practice Pattern Committee. Cataract in the Adult Eye Preferred Practice Pattern. Ophthalmology. 2022;129:1-126.
- ESCRS Cataract Guidelines Committee. ESCRS Guidelines for Cataract Surgery. European Society of Cataract and Refractive Surgeons; 2023.