Higher-order aberrations Higher-order aberrations are visual problems that require special testing for diagnosis and are not corrected with normal spectacles (eyeglasses). These aberrations include 'starbursts', 'ghosting', 'halos' and others. Some patients describe these symptoms post-operatively and associate them with the<unk>  technique including the formation of the flap and the tissue ablation. There is a correlation between pupil size and aberrations. This correlation may be the result of irregularity in the corneal tissue between the untouched part of the cornea and the reshaped part. Daytime post-LASIK vision is optimal, since the pupil size is smaller than the<unk>  flap. Others propose that higher-order aberrations are present preoperatively. They can be measured in micrometers (µm) whereas the smallest laser-beam size approved by the FDA is about 1000 times larger, at 0.65 mm. In situ keratomileusis effected at a later age increases the incidence of corneal higher-order wavefront aberrations. These factors demonstrate the importance of careful patient selection for<unk>  treatment. A subconjunctival hemorrhage is a common and minor post-LASIK complication. Dry eyes 95% of patients report dry-eye symptoms after<unk> . Although it is usually temporary, it can develop into chronic and severe dry eye syndrome. Quality of life can be severely affected by dry-eye syndrome. Underlying conditions with dry eye such as Sjögren's syndrome are considered contraindications to<unk> . Treatments include artificial tears, prescription tears, and punctal occlusion. Punctal occlusion is accomplished by placing a collagen or silicone plug in the tear duct, which normally drains fluid from the eye. Some patients complain of ongoing dry-eye symptoms despite such treatments and dry-eye symptoms may be permanent. Halos Some post-LASIK patients see halos and starbursts around bright lights at night. At night, the pupil may dilate to be larger than the flap leading to the edge of the flap or stromal changes causing visual distortion of light that does not occur during the day when the pupil is smaller. The eyes can be examined for large pupils pre-operatively and the risk of this symptom assessed. Complications due to<unk>  have been classified as those that occur due to preoperative, intraoperative, early postoperative, or late postoperative sources: According to the UK National Health Service complications occur in fewer than 5% of cases. Other complications * Flap complications – The incidence of flap complications is about 0.244%. Flap complications (such as displaced flaps or folds in the flaps that necessitate repositioning, diffuse lamellar keratitis, and epithelial ingrowth) are common in lamellar corneal surgeries but rarely lead to permanent loss of visual acuity. The incidence of these microkeratome-related complications decreases with increased physician experience. * Slipped flap – is a corneal flap that detaches from the rest of the cornea. The chances of this are greatest immediately after surgery, so patients typically are advised to go home and sleep to let the flap adhere and heal. Patients are usually given sleep goggles or eye shields to wear for several nights to prevent them from dislodging the flap in their sleep. A short operation time may decrease the chance of this complication, as there is less time for the flap to dry. * Flap interface particles – are a finding whose clinical significance is undetermined. Particles of various sizes and reflectivity are clinically visible in about 38.7% of eyes examined via slit lamp biomicroscopy and in 100% of eyes examined by confocal microscopy. * Diffuse lamellar keratitis – an inflammatory process that involves an accumulation of white blood cells at the interface between the<unk>  corneal flap and the underlying stroma. It is known colloquially as "sands of Sahara syndrome" because on slit lamp exam, the inflammatory infiltrate appears similar to waves of sand. The USAeyes organisation reports an incidence of 2.3% after<unk> . It is most commonly treated with steroid eye drops. Sometimes it is necessary for the eye surgeon to lift the flap and manually remove the accumulated cells. DLK has not been reported with photorefractive keratectomy due to the absence of flap creation. * Infection – the incidence of infection responsive to treatment has been estimated at 0.04%. * Post-LASIK corneal ectasia – a condition where the cornea starts to bulge forwards at a variable time after<unk> , causing irregular astigmatism. the condition is similar to keratoconus. * Subconjunctival hemorrhage – A report shows the incidence of subconjunctival hemorrhage has been estimated at 10.5%. * Corneal scarring – or permanent problems with cornea's shape making it impossible to wear contact lenses. * Epithelial ingrowth – estimated at 0.01%. * Traumatic flap dislocations – Cases of late traumatic flap dislocations have been reported up to thirteen years after<unk> . * Retinal detachment: estimated at 0.36 percent. * Choroidal neovascularization: estimated at 0.33 percent. * Uveitis: estimated at 0.18 percent. * For climbers – Although the cornea usually is thinner after<unk> , because of the removal of part of the stroma, refractive surgeons strive to maintain the maximum thickness to avoid structurally weakening the cornea. Decreased atmospheric pressure at higher altitudes has not been demonstrated as extremely dangerous to the eyes of<unk>  patients. However, some mountain climbers have experienced a myopic shift at extreme altitudes. * Late postoperative complications – A large body of evidence on the chances of long-term complications is not yet established and may be changing due to advances in operator experience, instruments and techniques. * Potential best vision loss may occur a year after the surgery regardless of the use of eyewear. * Eye floaters – ocular mechanical stress created by<unk>  have the potential to damage the vitreous, retina, and macula causing floaters as a result. * Ocular neuropathic pain (corneal neuralgia); rare FDA's position In October 2009, the FDA, the National Eye Institute (NEI), and the Department of Defense (DoD) launched the<unk>  Quality of Life Collaboration Project (LQOLCP) to help better understand the potential risk of severe problems that can result from<unk>  in response to widespread reports of problems experienced by patients after<unk>  laser eye surgery. This project examined patient-reported outcomes with<unk>  (PROWL). The project consisted of three phases: pilot phase, phase I, phase II (PROWL-1) and phase III (PROWL-2). The last two phases were completed in 2014. The results of the<unk>  Quality of Life Study were published in October 2014. The FDA's director of the Division of Ophthalmic Devices, said about the<unk>  study "Given the large number of patients undergoing<unk>  annually, dissatisfaction and disabling symptoms may occur in a significant number of patients". Also in 2014, FDA published an article highlighting the risks and a list of factors and conditions individuals should consider when choosing a doctor for their refractive surgery. Contraindications Not everyone is eligible to receive<unk> . Severe keratoconus or thin corneas may disqualify patients from<unk> , though other procedures may be viable options. Those with Fuchs' corneal endothelial dystrophy, corneal epithelial basement membrane dystrophy, retinal tears, autoimmune diseases, severe dry eyes, and significant blepharitis should be treated before consideration for<unk> . Women who are pregnant or nursing are generally not eligible to undergo<unk> . Large Pupils: These can cause symptoms such as glare, halos, starbursts, and ghost images (double vision) after surgery. Because the laser can only work a section of the eye, the outer ring of the eye is left uncorrected. At night or when dark, a patient's eyes dilate and thus the uncorrected outer section of the eye and the inner corrected section, create the problems.
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