Posterior segment complications of refractive

surgery

Refractive eye surgery Is any eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling of the cornea or the lens. Successful refractive eye surgery can reduce or cure common vision disorders such as myopia, hyperopia and astigmatism, as well as degenerative disorders like keratoconus.

CORNEAL REFRACTIVE SURGERY

The most common methods today use excimer lasers to reshape the curvature of the cornea Clearly, LASIK is an anterior segment procedure, but it could have posterior segment consequences. Although rare, posterior complications following LASIK have been documented, and including retinal tears, retinal detachments, retinal hemorrhages, macular holes, and choroidal neovascular membranes

The relationship between the LASIK procedure and vitreoretinal complications is difficult to establish, since such complications occur with a higher incidence in patients with high myopia, being the majority of patients undergoing refractive surgery. There is also fact that vitreoretinal complications observed share a common pathophysiology, which is posterior vitreous detachment (PVD)

The suction and the increase in pressure induced by the suction ring used to fixate the eye while the microkeratome creates the flap could elongate the eye along the anteroposterior axis, which in turn could cause a contraction in the horizontal axis. This combination of events may push the lens anteriorly and cause vitreoretinal traction at the vitreous base and the posterior pole and facilitate PVD.

Cutting the flap with a femtosecond laser rather than a microkeratome requires lower suction but longer duration. LASIK with the femtosecond laser has been reported with rhegmatogenous RD, macular hemorrhage and. Epi-LASIK, which also requires relatively longer suction durations, has been associated with optic neuropathy.

Retinal detachments

It is interesting that retinal detachments occurred at approximately 9 months after LASIK. Therefore, corneal refractive surgery probably does not increase the rate of retinal detachment any more than if the patient had not undergone surgery.

When planning surgical treatment of RD following LASIK, certain factors should be considered. Post-LASIK patients may be dissatisfied with the myopic shift following encircling scleral buckling, and alternative techniques (such as segmental scleral buckling, PPV or pneumatic retinopexy) may be considered. If scleral buckling is performed, the vitreoretinal surgeon should understand that the patient may desire future LASIK enhancement if retinal reattachment is achieved and if good central vision returns. Conjunctival scarring and anterior placement of an encircling buckling element may prevent proper placement of a microkeratome following successful scleral buckling.

If PPV is chosen to treat RD, the surgeon should attempt to protect the corneal flap during surgery to avoid flap dislocation

Macular hemorrhage

Theoretically, when a break in Bruch’s membrane occurs, it allows the progression of the neovascularization under the retina. The increase in intraocular pressure (IOP) to levels over 60 mm Hg during suction with the microkeratome suction ring up to 4 mm posterior to the limbus may exert posterior traction. This mechanism may open the gap in Bruch’s membrane even more. In patients with high myopia and lacquer cracks, LASIK should be considered contraindicated and some other method of refractive surgery offered (i.e. phakic IOL

Macular hole

Macular hole has reported to occurs 6 m- 1y after LASIK for myopia.

LENS-BASED REFRACTIVE SURGERY

Phakic IOL: Angle supportedIris supportedPosterior chamber lens (precrystalline)Clear lens extraction with IOL implantation:MyopiaHypermetropiaAstigmatismPrespyopiaAnisometropia

Posterior segment complications of lens refractive surgery

Perforated globeSupra-choroidal haemorrhageDropped nucleusCystoid macular oedemaMacular phototoxicityMacular infarction Retinal detachmentPostoperative endophthalmitis

Perforated globeAccidental perforation of the globe is an acknowledged complication of peribulbar, retrobulbar anaesthesia. High myopia is a strong risk factor for globe perforation in peribulbar anaesthesia. Signs and symptoms of perforation include intense ocular pain, sudden loss of vision and hypotony. Interestingly, in one review, about 50% of the patients had no immediate symptoms or signs of perforation

This injury could be avoided by minimizing the number of injections, use of blunt needle, noting negative aspiration before injection, inspection of aspirate for blood or vitreous fluid and to wiggle the syringe before injecting, to ensure that the globe is not pierced by the needle (although not universally accepted). It is also recommended to discontinue the injection if corneal edema or resistance to injection occur.

Supra-choroidal haemorrhage

Risk factors: older age, taking at least one cardiovascular medication, glaucoma, elevated preoperative intraocular pressure, the lack of orbital compression after LA , PC rupture, HTN, axial myopia, retrobulber injections, coughing and valsalva.

Intra-operative SCH:Signs: Shallow AC ^ IOP Dark red reflex Iris prolapse Extrusion of introcular contents.

Management: Prophylactic: Avoid sudden hypotony Preplaced sutures Immediate: Wound closure Formation of AC by BSS Lowering BP Sedation Remove speculum and bridle sutures Posterior sclerotomy Subseqent: Steroid U/S Surgery

Post-operative SCHPresentations: Sudden pain Loss of vision Shallow AC ^IOPManagement:Wound intact: medical to control IOPWound not intact: surgical closureWhen to drain: Persistant flat AC Kissing choroidale Uncontrolled IOP for one week Persistant Choroidal detachment

Dropped nucleus

Management: Vitrectomy

Cystoid macular oedema

CME is the result of accumulation of fluid in the central macula in the outer plexiform layer with the formation of cystoid spaces. The term “cystoid macular edema” (CME) applies when there is evidence by biomicroscopy, fluorescein angiography (FA), and/or optical coherence tomography (OCT) of fluid accumulation into multiple cyst-like spaces within the macula.

Potentially toxic substances including PGs normaly contained in the anterior segment may diffuse posteriorly to the maculaRisk factors:Surgical approachDiabetic and HTN PatientsIris incaceration in the woundA ruptured posterior capsuleRetained lens fragment

Prophylaxis: NSAIDS Substantial subgroups of patients with refractory macular oedema show interest in other treatment modalities, including pars plana vitrectomy, medical therapy with protein kinase C inhibitors , intravitreal injection of corticosteroids or a sustained release intravitreal corticosteroid implant

Macular phototoxicity

Operating microscope light induced foveal damage is a well recognised occurrence following ocular surgery PM is the result of a photochemical and thermal lesion of the retina due to ultraviolet radiation from the operating microscope, characterized by affecting the outermost retinal layers. It is related to the intensity, exposure time and wavelength of the light source, with blue and UV light (wavelength below 300-350 nm) being the most damaging for the eye

At the clinical level, it is characterized by a yellowish lesion at the foveal level, a window defect in FA and a central or para-central scotoma which diminishes with time. The initial yellowish lesions are subsequently replaced by a dotting of the RPE or even a lamellar hole.

These patients may notice a pericentral scotoma, metamorphopsia or slight/moderate vision loss between one and four hours after exposure. The scotoma may diminish after a few months and the patient usually recovers part of the lost eyesight.

Precautions against phototoxic lesions:

The use of ultraviolet filters on the microscope, air in the AC to defocus the light from the retina. Minimizing the time and power of coaxial illumination from the microscopeKeeping the patient's body temperature low to reduce the temperature within the eye, irrigation solutions may be cooled relative to room temperature. Lowering the inspired oxygen concentration for the patient during the procedure as it has been shown that an increase in inspired oxygen markedly enhances retinal phototoxicity. Stop photosensitising treatment particularly for underlying potential photosensitising systemic conditions before surgery and taking appropriate surgical precautions (Manzouri et al., 2002).

Postoperative endophthalmitis

Postoperative acute endophthalmitis is a devastating complication after intraocular surgery and can be seen as increased pain, redness, lid edema, anterior chamber reaction, corneal haze, vitreous haze, frank exudates in the vitreous or absent red reflex. This condition needs to be treated as an emergency with maximum medical therapy and may sometimes require vitrectomy

Risk factors :Increased operative time, low experienced surgeon.Posterior capsule rupture/vitreous loss.Retained lens fragments.Inadequate sterilization of the operative field.Contamination of surgical instruments.Inadequate wounds eg, leaky

Once infection occurs, damage to ocular tissues is believed to occur due to direct effects of bacterial replication as well as initiation of a fulminant cascade of inflammatory mediators. Endotoxins and other bacterial products appear to cause direct cellular injury while eliciting cytokines that attract neutrophils, which enhance the inflammatory effect. Thus, recent efforts in controlling the damaging effects of endophthalmitis in experimental models have focused on identifying not only appropriate antibiotics for control of the infectious agent but also on anti-inflammatory agents that might disrupt the immunologic events that occur after infection

Macular infarction

With accidental entry of aminoglycosides after subconj Injection from the site of the wound so better avoided.

Retinal detachment

Risk factors:Lattice degenerationHigh myopiaRupture posterior capsuleVitreous loss

Final recommendations for refractive surgeons to consider before performing

surgery in myopic patients

•Inform the patient that retinal detachments can occur. If after refractive surgery he presents symptoms suggesting retinal traction, break, or detachment, explain the symptoms and see the patient as soon as possible.•When performing refractive lens exchange, use an IOL with a low rate of PCO.•Carefully examine the periphery of the fundus to detect any breaks or lattice degeneration that may require follow-up or laser treatment.

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