Refractive Surgery for Hyperopia

From EyeWiki


Background

Hyperopia is the optical term for farsightedness, a condition in which parallel light rays focus behind the retina, making near objects blurry. In severe hyperopia, even distant objects appear blurry. Hyperopia can be classified as low [≤2.00 diopters (D)], moderate (2.00-4.00 D) and high (>4.00 D).

Concept

Refractive surgery options for hyperopia are designed to increase focusing power and converge and focus the light rays on the retina instead of behind the retina. This can be done by either cornea based surgeries or lens based surgeries.

Cornea based surgeries include excimer laser techniques such as Photorefractive Keratectomy (PRK), Laser in situ keratomilieusis (LASIK) or Small incision Lenticule Extraction (SMILE). Other techniques typically for low hyperopia include conductive keratoplasty and laser thermal keratoplasty.

Lens based surgeries include placement of intraocular lenses either phakic IOLs or refractive lens exchange.

History

Farsighted individuals often experience progressive difficulty with uncorrected vision as they age.

Clinical diagnosis

The detection of hyperopia is not difficult with a complete eye exam. In younger patients, cycloplegic (anticholinergic) eye drops often help determine the extent of hyperopia.

Diagnostic procedures

Determination of pupil size, corneal thickness/shape/power as well as endothelial cell counts help determine candidacy. For intraocular procedures, it is beneficial to perform axial lenth measurements. Manifest and cycloplegic refraction are recommended to select the appropriate treatment. The shape of light reflected off the retina can be used to describe elements of aberration or blur and is the basis for custom excimer surgery.

Refractive procedures for hyperopia- Cornea based:

Conductive keratoplasty (CK):

Conductive Keratoplasty (CK) is used to correct low hyperopia with or without astigmatism, typically between +0.75D to +3.00D. The principle of CK is based on properties of collagen and its response to temperature change. Radio frequency current of 350-400kHz is delivered to the peripheral cornea using a hand held probe along a circumferential optical zone. Spots of energy are delivered to a stromal depth to 500 microns in multiples of 8. This results in heating of the collagen fibrils to 55-65°C which results in shrinkage of the collagen in the periphery. As the cornea cools, the periphery tightens and maintains its shape and this results in relative flattening of peripheral cornea and induced steepening of the central cornea.

CK is safe and effect procedure in low hyperopia, however, studies have shown that the effects are not permanent and regression is often seen in long term follow up studies.[1]

Laser thermal keratoplasty (LTK)

To help reshape the cornea and treat low hyperopia, Holmium:YAG laser burns are applied to peripheral cornea to mechanically steepen the cornea. However, long term studies show regression. LTK is considered suboptimal to CK as penetration of corneal tissue is less in LTK (65% depth) as compared to CK (80% depth).

Excimer laser based surgery

Most commonly performed refractive procedures include use of excimer laser to reshape the cornea. While myopic corrections are very successful with little regression, with modern reractive surgery, hyperopic correction is more challenging due to short axial lengths, small cornea diameter, and narrow anterior chamber. Large ablation zones are required as peripheral cornea is re-shaped and this can induce more optical aberrations. In addition, there is more risk of regression over time with hyperopic refractive surgery. It is very important to discuss these concerns with patients pre-op and set reasonable expectations.

PRK

Photorefractive Keratectomy (PRK) has been performed routinely since the 1990s for correction of myopia, hyperopia and astigmatism. It involves, removal of corneal surface epithelium and subsequent laser ablation using excimer laser. PRK results in good visual outcomes but post operative pain, time for visual recovery, risk of post op haze and infection led to transition to flap based LASIK procedure in routine cases. However, PRK is still preferred over LASIK in certain cases - Thin corneas (CCT <500 microns with residual stromal bed thickness may be less than 200 to 300 microns where LASIK may not be ideal); flat corneas (<41D), steep corneas (>48D), epithelial basement membrane disease, recurrent corneal erosions, narrow palpebral fissures or deep set orbits leading to difficult LASIK flap creation.

The technique of PRK has also evolved over the years to address specific complications of PRK. Use of therapeutic bandage contacts after the procedure and topical NSAID has helped with pain post op. use of intra-operative Mitomycin C application on stromal bed can limit the occurrence of corneal haze.

LASIK

In hyperopic LASIK procedure, the area of excimer ablation is exposed by flap creation using either a mechanical device or an infrared laser and the excimer laser pulses are applied in the midperiphery of the cornea to produce steeping in the center.

Predictability of refractive outcomes for hyperopic LASIK is less as compared to myopic LASIK and is shown to depend on the degree of hyperopia, associated astigmatism and the age of the patient at the time of the surgery. Studies sow that residual post op refractive error after hyperopic LASIK has a logarithmic association with patient age at time of surgery. Younger patients tend to be undercorrected while older have a tendency towards overcorrection.[2]

Studies comparing PRK to LASIK for hyperopia have found that both procedures are comparable in refractive outcomes.[3] [4]

SMILE

Small-incision lenticule extraction (SMILE) is a technique of refractive in which a corneal lenticule is removed to re-shape the cornea. SMILE can theoretically be done safely in a higher degree of hyperopia than traditional LASIK, however SMILE is not FDA approved for hyperopia. Since it is a new procedure, studies with long term follow up are limited. A prospective study conducted on 93 eyes undergoing SMILE for hyperopia were included and followed for 12 months post op showed that UCVA was 20/40 or better in 95% of the eyes with good topographic stability.[5] SMILE may be preferred over LASIK in patients who lay contact sports to avoid flap related complications and has reported dry eye syndrome post op.

LASIK is preferred to SMILE for hyperopic astigmatism and mixed astigmatism and in cases of high wavefront aberrations and topographic irregularities where topo-guided LASIK treatment can be performed.

Intracorneal inlays

Corneal inlays are thin segments of biocompatible synthetic material that are inserted into the corneal stroma either under corneal flaps or into intra-stromal pockets created by femto-second laser. They work by increasing the anterior corneal curvature, providing a single diffractive optic or using small aperture pin hole optics. These inlays are approved for use in low hyperopia or presbyopia. The major problem with such inlays is the wound-healing response following their insertion and can incite corneal haze, scarring and melting. However their use is considered reversible and they can generally be removed easily. Another issue is that as presbyopia progresses, the refractive benefit from the inlay may be lost necessitating a removal or exchange. There are a few different corneal inlays available in the United States.[6]

Recently it has been suggested that implantation of allogenic corneal tissue may be an option for the treatment of hyperopia. Allogenic tissue has the advantage of being biocompatible and the corneal tissue can be customized and precisely shaped to meet the refractive needs of individual patients.

Refractive procedures for hyperopia- Lens based:

Phakic Intraocular Lens

Phakic Intraocular Lens surgery involves placement of an artificial lens inside the eye without disturbing the eye's natural lens. The phakic intraocular lens (pIOLs) is then either affixed in front of the iris (e.g. Verisyse) or placed behind it (e.g. Visian ICL), depending on the model used. The procedure is performed one eye at a time and may be done sequentially on the same day. Sutures are used to close the Verisyse incision but are not routinely required for the Visian ICL procedure. Studies show good visual outcomes after phakic IOL implantation for hyperopia. [7][8]

Phakic IOLs are approved for use in hyperopia given good candidate selection is performed. Toric pIOL designs enable spherocylindrical correction. Anterior chamber depth and endothelial cell count must be evaluated pre operatively.

Main complications of angle supported IOLs are endothelial cell loss. Iris fixated pIOLs cause chronic inflammation, UGH syndrome, endothelial loss and pupillary block. Posterior chamber pIOLs can cause anterior subcapsular cataract formation, pigment dispersion, and pupillary block. [9]

Refractive Lens Exchange

Refractive Lens Exchange surgery is simply cataract surgery with intraocular lens placement prior to the formation of a cataract. This option corrects the refractive error as well as eliminates the formation of cataract in the future. After a thorough exam and explanation of the possible risks, cataract surgery is performed. Studies show that outcomes for bilateral refractive lens exchange in hyperopic patients without presbyopia with trifocal intraocular lenses were similar to outcomes for patients undergoing refractive lens exchange for hyperopia with presbyopia.[10]

A study found similar visual outcomes after artisan phakic IOL implantation versus refractive lens exchange for young patients for high hyperopia but phakic IOL is preferable due to preservation of accommodation.[11]

Surgical follow up

Hyperopic refractive surgery does require follow up with a qualified doctor. One possible follow up schedule could be: the day after surgery, one week after surgery, and one month after surgery. Annual checks are advisable after most intraocular surgery.

Complications

Excimer surgery risks include: glare, halo, dry eye, decreased best corrected vision, infection over time, and inflammation/scar.

Intraocular Surgery risks include: pupillary block and cataract (specifically for phakic intraocular lenses), endothelial cell loss, glare, halo, decreased best corrected vision, infection, and inflammation.

References

  1. https://eyewiki.aao.org/Conductive_Keratoplasty
  2. Biscevic A, Bohac M, Ahmedbegovic-Pjano M, etal. The relationship between patient age and residual refractive error after uneventful laser in situ keratomileusis for moderate-to-high hyperopia. Eur J Ophthalmol 2021;31(4):1725-1732.
  3. El-Agha MS, Johnston EW, Bowman RW, etal. Excimer laser treatment of spherical hyperopia: PRK or LASIK? Trans Am Ophthalmol Soc 2000;98:59-66
  4. Settas G, Settas C, Minos E, etal. Photorefractive keratectomy (PRK) versus laser assisted in situ keratomileusis (LASIK) for hyperopia correction. Coch Database Syst Rev. 2012 Jun 13;2012(6):CD007112.
  5. Pradhan K, Reinstein D, Carp G, etal. Small Incision Lenticule Extraction (SMILE) for Hyperopia: 12-Month Refractive and Visual Outcomes. J Refract Surg 2019;35:442-450
  6. https://www.ophthalmologytimes.com/view/intracorneal-inlays-correction-presbyopia-and-low-hyperopia
  7. Koivula A, Zetterström C. Phakic intraocular lens for the correction of hyperopia. J Cataract Refract Surg. 2009;35(2):248-55
  8. Pesando PM, Ghiringhello MP, Di Meglio G, Fanton G. Posterior chamber phakic intraocular lens (ICL) for hyperopia: ten-year follow-up. J Cataract Refract Surg. 2007;33(9):1579-84.
  9. Jonker SMR, Berendschot TTJM, Saelens IEY, etal. Phakic intraocular lenses: An overview. Indian J Ophthalmol. 2020 Dec; 68(12): 2779–2796.
  10. Djodeyre MR, Ortega-Usobiaga J, Beltran J. Bilateral Refractive Lens Exchange With Trifocal Intraocular Lens for Hyperopia in Patients Younger Than 40 Years: A Case-Control StudyJ Refract Surg. 2021;37(8):524-531.
  11. Pop M, Payette, Y. Refractive lens exchange versus iris-claw Artisan phakic intraocular lens for hyperopia. J Refract Surg 2004;20:20-4
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