Ординатура / Офтальмология / Английские материалы / LASIK A Handbook for Optometrists_Hanratty_2005

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Chart 7.1 can also be used to aid the recognition of DLK to ensure appropriate management.)

Symptoms Initially, symptoms are not distinguishable from those normally experienced with dry eye. As the condition progresses, the patient becomes aware of some grittiness and photophobia, which does not ease significantly with the use of artificial tears. A worsening of the vision also occurs. In some cases, the postoperative vision can change from 6/5 to less than 6/24 in just a few days.

(a)

(b)

Figure 8.4 (a) Fluorescein fills the gutter between the edge of the stromal bed and the edge of the flap; (b) the edge defect allows fluorescein to penetrate into the stroma which is more noticeable after the surface fluorescein drained away

Signs The inflammation is located at the interface between the flap and the stromal bed (Figure 8.5a) and has a dull granular appearance hence it is also known as Sands of the Sahara. Figure 8.5b shows a mild case of DLK, where a haze can be seen under the lower half of the flap. The small and fine ‘grains’ are close together (Figure 8.5c) and can appear almost like sand ripples in more advanced cases (Figure 8.5d). In severe cases, the DLK can make the cornea appear completely opaque.

(a)

(b)

Figure 8.5 (a) Optic section of the cornea shows DLK at the interface between the flap and the stromal bed; (b) mild DLK at 48 hours – the patient was asymptomatic (continued on next page)

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(c)

(d)

Figure 8.5 (c) Grade 1 DLK with infiltration; (d) grade 1 DLK inflammatory cells create wave-like patterns (continued from previous page)

Management Where DLK is suspected, referral to the surgeon is imperative as aggressive anti-inflammatory therapy may be required. This involves the use of topical steroids, the dose and frequency of which varies according to the severity of the condition. The surgeon usually examines the eye again after 48 hours to ensure that the condition is responding as expected. The medication is then tapered off over 2 weeks. In severe cases, lifting the flap and physically removing the inflammatory cells may be required.

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had no sign of infection 4 weeks postoperatively, but at 8 weeks presented to the clinic complaining of only mild discomfort. The causative pathogen was not identified but it was probably a slow growing organism (e.g. Mycobacterium spp.)

Signs Figure 8.6b shows an early case of microbial keratitis. The corneal lesion has not yet broken the surface of the epithelium as shown by the absence of fluorescein staining. If left untreated, it could develop into an ulcer.

Management Diagnosis and treatment of postoperative infection is not within the optometrist’s role and so referral to the surgeon is necessary. Treatment usually involves aggressive antimicrobial therapy. It is also appropriate to send a swab of the infected area for analysis. Where there is no surgeon on site, referral to an emergency centre would be appropriate in urgent cases. In non-urgent cases where clinical signs are minor and the patient is asymptomatic, it is advisable to speak to the treating surgeon if possible as it may be appropriate to supply or write a signed order for an antimicrobial agent. This would be for prophylactic use, to prevent the infection from worsening until the surgeon can examine the patient.

OTHER POSTOPERATIVE COMPLICATIONS

Dry eye

Disruption to the corneal nerves by the cutting of the LASIK flap results in a disturbance in the sensory feedback controlling tear production.

Symptoms Dry eye associated with pain is the most common early postoperative complication with one study reporting it in 42 out of 683 eyes that had undergone PRK or LASIK.7 Symptoms may also worsen when the patient resumes an activity that was temporarily stopped during postoperative recovery (e.g. VDU use or outdoor sports, where tear evaporation increases).

Signs Practitioners are all too familiar with the typical signs associated with dry eye, but in some cases the desiccation can be severe enough to cause diffusion of fluorescein into the stroma (Figure 8.7a). It can also cause corneal oedema and induce myopia. There is no typical dry eye fluorescein pattern in eyes that have undergone LASIK. In severe cases, the entire corneal surface is covered in punctuate stain. In some cases, LASIK merely exaggerates a pre-disposition to dry eye and the staining indicates punctate epithelial keratopathy (Figure 8.7b). The staining can also appear as a central band reaching from 3 to 9 o’clock (Figure 8.7c).

Management Topical lubricants are prescribed according to the severity of patient symptoms. Hypromellose or equivalent is usually the first agent to be tried for mild-to-moderate signs of dry eye and can be used as often as required.

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If the patient is not gaining adequate relief, this will be apparent by the copious amounts of lubricant they get through in the first 48 hours. For moderate- to-severe dry eye, a carbomer lubricant may improve comfort. In severe cases, a liquid paraffin-based preparation may be prescribed. Often, a battery of different lubricants is required for use at different times of the day.

In some cases, dry eye can be aggravated by preservatives in multidose containers. If the patient complains of increased discomfort or stinging immediately after insertion, it would be advisable provide a preservative free agent instead.

(a)

(b)

Figure 8.7 (a) Fluorescein can penetrate into the stroma with severe epithelial keratopathy; (b) inferior superficial keratopathy (continued on next page)

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(c)

Figure 8.7 (c) Band of punctate fluorescein between 3 and 9 o’clock (continued from previous page)

Figure 8.8 Collagen punctum plugs are inserted to give temporary relief from dry eye symptoms

Where lubricants are insufficient, temporary collagen punctum plugs can be inserted (see Figure 8.8) by either the surgeon or the optometrist (provided training has been carried out). If the symptoms are significantly reduced with the collagen plugs, silicone ones can be inserted for a semi-permanent effect. By 1 month, the dry eye symptoms ought to be reduced. By 3–6 months, symptoms are usually minimal and punctum plugs can be removed if they have not fallen out already.

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Epithelial ingrowth

Signs of epithelial ingrowth may be seen at the 1 month aftercare. The incidence of epithelial ingrowth is approximately 2% but does vary according to surgical technique, microkeratome and epithelial characteristics.9 The ingrowth tends to occur along the flap edge and is continuous with surface epithelial cells in the majority of cases.10 It is secondary to postoperative invasion by surface epithelial cells under the flap,5 although it is also possible by implantation during treatment. The risk of ingrowth is minimised by tight apposition of the flap to the stromal bed.

Figure 8.9a shows a significant area of epithelial ingrowth, but action is not necessary as it extends only 2 mm from the flap edge. Ingrowth is naturally self limiting and the majority of cases do not need action.6 Epithelial ingrowth can also appear away from the flap edge at sites where debris has been present or where epithelial cells have been introduced under the flap during treatment. Epithelial cells can also migrate from the flap edge as in Figure 8.9b which shows a more aggressive ingrowth superiorly near the flap hinge. The vision was unaffected and the patient was asymptomatic. The case was referred to the surgeon for assessment. The ingrowth was non-progressive and monitoring was the only further action required.

In some cases, the cells may become necrotic and release lytic enzymes which cause flap melt. In the example shown in Figure 8.9c, the flap edge has melted leaving a widened gutter between the flap and the untreated cornea. If signs of this are seen, it must be referred to the surgeon. Where the condition is progressive, the management is to lift the flap, scrape the ingrowth out and then irrigate before replacing the flap. The patient is subsequently monitored for possible recurrence of ingrowth. Eventually, epithelial cells will fill the gutter and the epithelium will be a smooth surface.

(a)

Figure 8.9 (a) Epithelial ingrowth – if it encroaches the visual axis or extends beyond 2 mm from the flap edge it may need to be removed (continued on next page)

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(b)

(c)

Figure 8.9 (b) Epithelial ingrowth located near the flap hinge; (c) progressive epithelial ingrowth can cause the overlying flap to melt (continued from previous page)

VISUAL COMPLICATIONS

High expectations that are not met

Spectacle wearers are often accustomed to a high level of corrected vision that is regularly checked and improved if necessary. Laser eye surgery aims to improve the unaided vision of the patient but it cannot guarantee to match the best corrected acuity achieved with spectacles.