Contact Lenses after LASIK
Laser in-situ keratomileusis is the most popular type of refractive surgery. More than 16 million US patients have received LASIK for visual correction since the procedure was approved in the mid 1990s. In the vast majority of cases, the procedure results in successful resolution of the visual complaint, and the patient requires no further intervention; however in some cases LASIK surgery results in complications or suboptimal visual correction. At this point the patient faces a choice: further refractive intervention, spectacles or contact lenses. Given these options, a significant percentage of patients opt for contact lenses.
Fitting contact lenses in a post-LASIK patient is notoriously complicated due to the changes to the corneal surface during surgery. The topography of a post-LASIK cornea is vastly different from a preoperative corneal surface. In myopic corrections, the corneal surface will feature a significantly flattened central region, with a comparatively steep peripheral surface, whereas in hypermetric corrections, the central area is steepened.
Because of these changes, there are a number of challenges to fitting contact lenses in these patients. Traditional soft lenses are often not an option; rigid gas permeable (RGP) lenses, reverse geometry lenses or combination “piggyback” are usually required. Additionally, these patients require more appointments and follow-up to ensure a proper fit.
The corneal is responsible for two-thirds of the eye’s overall refractive power. The transparent, avascular corneal tissue is maintained anteriorly by a tear layer and posteriorly by the aqueous humor of the anterior chamber. Oxygen is delivered via diffusion through the tear layer anteriorly. The cornea is prolate in shape; flatter peripherally and steeper centrally, which creates an aspheric optical system.
The cornea is made up of five distinct layers. The corneal epithelium is the outer-most corneal layer and is the site of the air-tear interface. This interface helps smooth microirregularities on the epithelial surface, which would lead to refractive errors and a degraded image. Deep to the corneal epithelium is Bowman’s layer, a thin layer separating the epithelium from the stroma. The corneal stroma, which represents almost 90% of overall corneal thickness, is composed of highly organized collagen fibrils structured into lamellae, which are responsible for the tensile strength and structure of the cornea. Descemet’s layer follows, which separates the stroma from the endothelium. The deepest layer of the cornea, the corneal endothelium, is charged with maintaining corneal fluid balance; if the endothelium becomes too thin, stromal swelling occurs, which can interfere with transparency and disrupt vision.
Corneal topography is a non-invasive imaging technique that measures the contours of the cornea. It has become an invaluable tool in preoperative assessment and postoperative management of refractive surgical procedures. Further, topographical analysis of a postoperative cornea is extremely helpful in difficult contact lens fitting. The topography of a typical, unaltered cornea is prolate; with a steeper curvature centrally and a relatively flatter periphery.
Types of Contour Maps
Topographical contour maps are the product of corneal topographic imaging, and can be presented in four ways.
Axial (Sagittal) Maps
These maps are based on para-axial ray theory. They have good repeatability and are considered the most useful and easiest to verify.
Tangential maps include extreme curvature values and can better characterize irregular astigmatism, if it is present. They also reflect the apex more accurately. Compared to axial maps, they are less repeatable and will characterize flat areas flatter and steep areas steeper.
Corneal Height Maps
Corneal height maps are created based on how the height of the cornea compares to a reference sphere. They are less repeatable then both axial and tangential maps.
Refractive Power Maps
Refractive power maps convert detected curvature into a corresponding refractive reading. They are considered the least useful for contact lens fitting.
Changes to Corneal Topography After LASIK
Every kind of refractive surgery alters corneal topography. During LASIK, the stromal lamellae are permanently severed, which reduces tension in the peripheral layers of the stroma. Less tension results in peripheral expansion, which increases the curvature of the periphery. The peripheral expansion generates a radial force that pulls down on the central cornea and flattens it. The biomechanical flattening effect occurs in both myopic and hyperopic LASIK repairs,.
Changes After Myopic Repairs
The post-surgical cornea takes on an oblate topography – flatter centrally with a relatively steep periphery. As the degree of correction (and therefore amount of ablation) increases, this effect is increased; the greater the correction, the bigger the difference between flat center and steep periphery.
Changes After Hypermetropic Repairs
In hypermetropic repairs, the central cornea is heightened compared to the periphery.
Corneal Irregularities After LASIK
High order aberrations can occur after LASIK, as the result of corneal irregularities created by the laser ablation during surgery. Reported HOAs include decreased night vision, glare, halos and visual distortion.
Contact Lenses After LASIK
LASIK surgery, while often very successful, can produce a number of outcomes that require additional visual correction. These include under- and over-corrections, refractive error shifts, irregular astigmatism, central islands, corneal haze and multifocal corneas,. Patients have several options to address these issues including additional surgery, spectacles and contact lenses.
Indications for Contact Lenses
The indications for contact lenses after LASIK are residual ametropia, irregular astigmatism, anisometropia and decentered ablation zone. Bandage contact lenses are occasionally used after LASIK for corneal protection.
Types of Lenses
Therapeutic (Bandage) Lenses
Therapeutic (bandage) contact lenses (TCLs) were traditionally used after older refractive surgical procedures, like photorefractive keratectomy, to protect the cornea from inflammatory cells in the postoperative period,.
Although not commonplace, TCLs can be used in the initial 1-2 days after LASIK to protect the flap, prevent epithelial ingrowth and provide additional patient comfort,. The best lens to use in this setting is generally a silicon hydrogel disposable lens.
Soft (Hydrophilic) Contact Lenses
Traditional soft contact lenses can occasionally be used in post-LASIK patients as long as the primary postoperative complaint is anisometropia and they only require small refractive corrections. Patients with significant residual refractive errors, astigmatism or other corneal abnormalities are not good candidates for these lenses. The advantages of soft contact lenses are patient comfort and good centration. The disadvantages are poorer acuity and difficult fitting.
Small studies on contact lens fitting in post-LASIK patients reveal that between 10-25% of those requiring corrective lenses after surgery are able to achieve adequate vision correction with hydrophilic lenses. In a study of 29 eyes with irregular astigmatism induced by LASIK, 26% of patients were fit successfully with hydrophilic lenses.
There is one soft contact lens specifically designed for use in post-refractive surgery eyes, the Harrison Post Refractive Lens (Paragon Vision Sciences, Mesa, Arizona).
Toric Soft Contact Lenses
These lenses are appropriate for post-LASIk patients with minor astigmatism (> 0.75 DC). They are associated with atypical rotation when fit on oblate (vs prolate) corneas, therefore fitting may be more difficult and empiric fitting is not recommended.
Toric lenses are not recommended for higher-degree astigmatism due to instability issues, nor are they capable of correcting irregular astigmatism.
Rigid Gas Permeable Lenses
Rigid Gas Permeable lenses are considered the lens of choice when fitting patients after LASIK surgery. There are a number of qualities inherent in RGP lenses that make them the most-used lens in these patients. They are able to correct high degrees of both regular and irregular astigmatism, have high oxygen permeability and offer good visual acuity correction,. They are also fairly well tolerated by patients.
Despite this, fitting the RGP lens to a post-LASIK cornea is difficult, especially in a higher order corrections. Markedly flattened central regions can result in instability, central pooling and trapped bubbles, therefore it is important use pre- or postoperative topography of videokeratoscopy measurements when fitting patients with these lenses,,.
Reverse Geometry Lenses
These lenses are a type of RGP lens that is indicated with there is a significant difference between the flat center and the steep periphery,. These lenses have a steep secondary curve to accommodate the flattened central region.
Occasionally, a patient may be hypersensitive to RGP lenses or experience lid sensation. Soft lenses would be the ideal solution, however these lenses cannot achieve the same visual acuity that is possible with RGP lenses. In these cases, a “piggyback lens” (RGP lens fitted on top of a soft lens) can be used. Silicon hydrogels are the soft lens of choice in this combination, as their increased rigidity avoids draping of corneal abnormalities, and they have higher oxygen permeability than conventional soft lenses.
Lenses for Post-Hypermetropic Repairs and Iatrogenic Corneal Ectasia
In the post-hypermetropic patient, the central cornea is steeper than the periphery. The cornea takes a similar shape (steep centrally and flatter peripherally) in iatrogenic corneal ectasia, a rare, but serious post-LASIK complication, wherein the weakened cornea bulges out, similar to keratoconus.
Contact lenses are indicated for repairs of mild-moderate hypermetropic repairs and iatrogenic corneal ectasia. Sometimes RGP lenses can be used, but there are also a number of specifically designed multi-curve lenses that can be used in hard to fit cases. There include the Woodward design and the Rose K lens.
These lenses are a type of RGP lens considered “the lens of last resort” in patients who have failed other lenses. Scleral lenses are wide enough to be almost entirely supported by the sclera, which allows the lens to overcome corneal surface abnormalities for a relatively easy fit. This makes them a good option for larger corneral abnormalities found in moderate to severe post-refractive ectasia.
Approach to Fitting
Patients requiring contact lenses for vision correction after LASIK can be fitted for lenses 8-12 weeks after surgery, once refraction and topography have stabilized.
Fitting contact lenses in post-refractive patients is more difficult than in nonsurgical eyes. Yeung et al found that post-LASIK patients required significantly more diagnostic lenses to establish an initial order, a higher number of trial lenses ordered to complete the fitting, and almost double the amount of office visits while fitting lenses.
Selected lenses should have a moderate-to-high oxygen transmissibility to ensure the cornea has adequate oxygen supply.
A general guideline for selecting an initial fit-trial lens was outlined by Steele & Davidson in their review of contact lenses after LASIK.
- If the patient can achieve good vision correction with a spectacle prescription, soft contact lenses can be tried first, with preference for spherical, aspheric and toric designs.
- If the patient had a significant amount of tissue ablated the best choice for initial lens fit is a RGP lens based on either pre- or postoperative topography information.
- If a large amount of tissue has been ablated, large diameter RGP lenses or reverse geometry lenses may be the better option.
- Patients who received hypermetric LASIK or whose postoperative course if complicated by iatrogenic corneal ectasia should be fit with lenses designed for keratoconus.
- Scleral lenses can be considered as a last resort.
RGP Lens Fitting
Most studies recommend starting with RGP lenses. Initial diagnostic lens selection should be selected based on pre- or postoperative topography. If this is not available, empirically selected lenses can be used. Between 70-80% of patients who require contact lenses for visual correction after LASIK end up receiving a specialty contact lens, which is almost always a RGP lens type. Trial lens fitting is recommended.
According to Steele & Davidson, the lens should be present in the mid-periphery along the horizontal meridian approximately 3.0-4.0 mm from the center of the cornea. The back optic zone radii (BOZR) should be 0.1 mm steeper than the mean keratometry reading and 9.2-10 mm in diameter. Fit can be assessed with fluorescein. Good movement (between 0.5-1.5 mm), adequate pupil coverage and good tear exchange should be insured.
If fitting a reverse geometry lens, fit should have slight central clearance, good centration and a mid-peripheral alignment.
Soft Lens Fitting
Soft (hydrophilic) lenses are a good choice for patients with pure anisometropic errors who only need small refractive corrections, or patients who cannot tolerate RGP lenses.
When fitting soft lenses on a post-LASIK patient, the first lens choice should have a BOZR that is 0.3 mm flatter than the flattest keratometry reading. The lens should have adequate centration and movement on blinking (0.5-1.5 mm) and an absence of central bubbles. There is variability in rigidity among soft contact lens brands, so failure with one type of lens does not necessarily mean failure with all hydrophilic lenses.
Combination Lens Fitting
The best approach is to fit the hydrogel soft contact lens with a low plus back vertex power and then measure keratometry with the lens in place. The BOZR should be between 7.80 – 8.00 mm. The RGP lens should center well over the soft lens.
Complications of Contact Lenses After LASIK
Complications of wearing contact lenses after LASIK are very rare, but not unheard of. Bandage lenses are associated with corneal edema, infection and increased risk for corneal striae. Lenses that do not allow adequate oxygen diffusion can compromise the integrity of the corneal stroma.
There is one reported case in the literature of late onset inflammation in a post-LASIK patient linked to cosmetic lenses. The patient was treated with high dose steroids and symptoms ultimately resolved without any significant visual compromise.
Summary and Recommendations
Contact lenses after LASIK are occasionally necessary when LASIK results in residual ametropia, irregular astigmatism, anisometropia and decentered ablation zones. Corneal topographical changes after surgery can make contact lens fitting challenging and labor intensive, thus a systematic approach should be used when fitting lenses in these patients. There are a number of different lenses available for use in these patients, but most practitioners recommend initiating fitting with a rigid gas permeable lens. In most cases, with appropriate fitting techniques, post-LASIK patients who need further vision correction should be able to successfully wear contact lenses.
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