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Phototherapeutic keratectomy: cases in practice.

Following OT's CET article on phototherapeutic keratectomy (PTK) in the February edition, the authors present three cases from practice to demonstrate the practical applications of the technique.

1 CET POINT

Introduction

In this article, three case studies from the authors' practice will be presented: epithelial basement membrane dystrophy (EBMD); band keratopathy (BK); and recurrent corneal erosion syndrome (RCES). Each condition will be discussed including a brief background, differential diagnosis and other treatment options.

Epithelial basement membrane dystrophy (EBMD)

Background

There are over 20 known corneal dystrophies that can affect one or more of the corneal layers. They all have similar traits in that they are usually inherited, symmetric between the eyes, gradually progressive and usually have no gender predominance. (1)

EBMD (also known as map dot fingerprint dystrophy or Cogan's microcystic dystrophy) is a common bilateral condition characterised by cystic and/or whirl-like opacities in the cornea (see Figure 1). It usually affects adults aged 40 years age and above.

The cited prevalence of EBMD ranges from 2-42% and up to 33% of patients with EBMD experience severe RCE during their lifetime. (2-4)

Signs

Initially, there may be few clinical signs associated with EBMD; however, a history of recurrent erosions should suggest this diagnosis, especially if they are bilateral and occur in multiple sites. With repeated episodes of epithelial breakdown and failed attempts at the development of a stable epithelial basement membrane adhesion complex, morphological changes eventually develop, leading to the classic map-dot-fingerprint epithelial and sub-epithelial findings that characterise this dystrophy. (5)

Map lines are the most common change. These can be large grey lines and are due to thickened abnormal basement membrane extending into the epithelium. Opaque dots are the next most common sign; these are due to epithelial cells being trapped in intercellular debris in the basement membrane. Fingerprint changes are less common and appear as concentric lines due to inadequate formation of hemidesmosomes by the basal epithelial cells and duplication of the epithelial basement membrane. (6,7)

Patient symptoms

Most patients with EBMD are asymptomatic. Recurrent episodes of corneal erosion are common and, less frequently, associated with visual changes.

When present in the visual axis, the epithelial and sub-epithelial irregularities initially can result in unstable refractive results or irregular astigmatism, (8) and higher order optical aberrations, which are subjectively associated with monocular diplopia and visual distortion. In severe cases, progressive reduction in acuity does occur as the corneal changes increase in density.

Patients may initially complain of dry eye symptoms such as gritty eyes, fluctuating vision and photophobia. If there is a RCE patients may complain of sudden sharp pain, redness, watering and photophobia classically upon waking up during the night or in the morning. (4)

Diagnosis

Diagnosis of EBMD is aided by taking a thorough history and undertaking a detailed slit lamp examination to identify the hallmark signs and symptoms. (9)

Pathophysiology

The pathophysiologic hallmark of EBMD is an abnormality in the formation and maintenance of the epithelial basement membrane adhesion complex of the corneal epithelium and desquamated epithelial cells. (8) They are bilateral, may change over time and can be variable in presentation from small grouped dots to widespread maps and fingerprints.

[FIGURE 1 OMITTED]

The abnormal epithelial basement membrane means that epithelial cells cannot adhere to Bowman's layer and anterior stroma properly; this can result in RCE when the epithelium repeatedly comes off, most commonly in the morning when lid forces can tear open the epithelium.

Differential diagnosis

There are two other epithelial dystrophies to consider:

* Reis-Biicklers' dystrophy is a bilateral condition affecting the central anterior cornea. Basal layers of the epithelium are affected and gradual sub-epithelial scarring develops. Patients typically present in late childhood with RCE. Over time increased scarring leads to reduced corneal sensation (7-10)

* Meesmann's corneal dystrophy is a bilateral rare superficial corneal dystrophy characterised by distinct round-to-oval punctate opacities in the central corneal epithelium with little impact on vision. Lesions develop early in life and can persist throughout life. Patients with Meesmann's corneal dystrophy often remain asymptomatic until middle age, when intermittent, mild ocular irritation, photophobia, transient blurred vision, and irregular astigmatism can develop. In severe cases, sub-epithelial scarring produces slight central corneal opacification. (7-11)

Management

Successful treatment of EBMD relies upon enhancing conditions necessary for the formation of stable epithelial basement membrane adhesion complexes throughout the cornea. This takes place preferably before vision-reducing morphological changes in the visual axis develop.

Treatment options for early symptomatic cases:

* Monitor patient if symptoms not severe and patient is coping

* Preservative-free topical lubricants can be used to treat ocular irritation. With RCE a lubricating or hyperosmotic ointment can be used at night (12)

* Topical hyperosmotic agents, sodium chloride 2% and 5% solution and ointment are used during daytime hours to minimise epithelial oedema allowing normal attachment complexes to form. (12)

In more advanced cases where substantial epithelial erosions have developed, more aggressive intervention is indicated:

* Bandage contact lens for RCE to promote epithelial healing and for pain relief (10,13,14)

* Prophylactic antibiotic drops are given at the same time to reduce the risk of microbial infection. Oral doxycycline can stabilise the epithelium and basement membrane (15-16)

* Epithelial debridement (either manual or with diamond burr polishing) or stromal puncture for RCE if resistant to topical or oral treatment (12,17,18)

* Corneal graft if chronic scarring severely reduces the vision.

Disadvantages of the treatments above are that the underlying cause of the condition is not addressed.

Phototherapeutic keratectomy (PTK)

PTK treatment for corneal dystrophies is very successful at reducing symptoms in the majority of cases. (8) PTK recurrence of dystrophy in the treated area is rare, (19-21) and if it does occur it is usually after six to nine months. (22-24) Success rates above 86. (6) % have been reported. (8,19,25)

The best visual results are in superficial corneal dystrophies because deeper dystrophies are more difficult to treat and the rate of recurrence is higher. (1)

[FIGURE 2 OMITTED]

Band keratopathy (BK)

Background

BK is a chronic corneal degeneration due to deposition of calcium salts from the tear film at the epithelium, casement membrane, Bowman's layer and anterior itroma.

Causes

The condition is age-related with patients typically over SO years old, (7) and may be associated with longstanding ocular inflammation such as chronic uveitis, phthisis bulbi and end-stage glaucoma. (26,27) Some cases have an hereditary component (primary hereditary band ceratopathy), (28) whereas others may result from metabolic conditions due to increased serum calcium and phosphate and renal failure. (26,27)

Signs

Slit lamp examination shows a white, grey band visible cross the cornea (see Figure 2). Usually the deposits start in the corneal periphery at 3 and 9 o'clock and then coalesce and extend towards the centre to form a continuous band.

There is a peripheral clear zone between the limbus and the edge of the keratopathy. Superior and inferior corneal are not usually affected.

Differential diagnosis

* Interstitial keratitis; this is an active inflammation within the stroma--corneal opacities, stromal oedema and vascularisation may be seen. The causes can be bacterial (for example, tuberculosis), viral (herpes) or parasitic (onchocerciasis). Patients present with a watery eye, ocular ache, photophobia and blurred vision. There will also be systemic symptoms associated with the underlying cause (7)

* Spheroidal degeneration; this is a bilateral condition which features yellow oily deposits at the limbus and is associated with high UV exposure and / or reflected light. The deposits may appear band shaped and are associated with pingeculae. (29)

Common symptoms

Patients will present with varying reduction to visual acuity if the deposits cross the visual axis with severity dependent on location and density of deposits. Calcium deposits may be fine or thick and flaky. If flaky, it can break off causing epithelial defects and painful symptoms.

The band can also disrupt the tear film so patients may experience dry eye symptoms. Patients may present with cosmetic concern or visual reduction as the plaque extends further across the cornea.

Management

* Tear supplements (drops or ointment) and bandage contact lenses are useful for surface irritation

* Surgery is indicated for visual improvement and / or ocular comfort (30-32)

* For the irregular flaky type of BK superficial manual debridement combined with chelating agent such as EDTA are recommended as this can restore vision by removing calcium deposits and the discomfort caused by the irregular calcium surface may resolve. However, there is a risk of corneal scarring, lengthy rehabilitation time and recurrence with manual debridement (33)

* Underlying conditions with elevated calcium or phosphate levels are treated to prevent recurrence.

PTK for BK

PTK is excellent for removing the fine BK with an appearance of ground glass. Healing is rapid with excellent visual results. PTK is not recommended for the irregular, raised, flaky-type, as calcium does not ablate at the same rate as corneal stroma. (34) Hence, there is a risk of obtaining a very irregular corneal surface after treatment.

Recurrent corneal erosion syndrome

Background

Recurrent corneal erosion syndrome (RCES) is a common clinical condition involving the corneal epithelium and epithelial basement membrane. It can be associated with anterior corneal dystrophy, or superficial corneal trauma (such as paper cuts, fingernail injury or a tree branch injury), or unrelated to corneal disease or previous trauma (idiopathic). (35) Dystrophies which can be associated with RCES are EBMD, Reis-Biicklers', lattice and granular.

Aetiology

Approximately half of the cases of RCES are due to traumatic corneal abrasion. (4) Mechanical trauma to the corneal surface causes inflammation, which disrupts extracellular adhesion in the corneal epithelium. One third of cases are due to epithelium basement disorders. (4) In EBMD, morphological changes to the basement membrane matrix mean that the anterior epithelium does not adhere to the epithelial basement membrane and underlying stroma. The epithelial layer is, therefore, loose and when damaged can tear or shift out of position. Dry eye can cause adhesions between the palpebral conjunctiva and corneal epithelium.

Hence, upon opening the eyelids in the morning the epithelium can be damaged or shifted resulting in recurrence of symptoms. Rosacea can cause meibomian gland dysfunction (MGD) and dry eye, which again can contribute to RCES. (4)

Symptoms

Symptoms can vary from mild foreign body sensation to severe pain. Repeated breakdown of the epithelium can cause sudden sharp pain, photophobia, watering, and reduced vision. The symptoms usually occur during the night or early morning. The pattern and intensity of symptoms can vary with patients.

Signs and diagnosis

Sometimes the corneal erosions can resolve rapidly so by the time the patient sees the clinician there are no obvious signs. However, an epithelial defect (see Figure 3), loose epithelium, epithelial microcysts and map lines/ fingerprints can be present in many cases.

A history of previous trauma to the eye, recurrent episodes of pain on waking, family history of RCES and epithelial microcysts make diagnosis straightforward. In subtle cases, diagnosis may be more difficult. Detailed slit lamp examination should be performed before and after fluorescein instillation. Retro illumination of the cornea with a dilated pupil can show subtle signs of EBMD.

Management

There are many treatment options for RCES all with varying degrees of success. Management should be tailored to the individual patient, symptoms, and cause.

Medical management is the initial treatment choice for active erosions and to prevent future erosions. Frequent application of preservative-free artificial tears combined with a lubricating ointment at night prevents the eyelid adhering to the corneal epithelium overnight. Topical antibiotics can prevent microbial keratitis. The antibiotic drops can be combined with a soft silicone hydrogel bandage contact lens for large erosions. (9,13,14) Hypertonic solutions and ointments, such as 5% sodium chloride, can reduce comeal oedema and improve epithelial attachments. For patients with MGD and rosacea, combining mild topical corticosteroid drops, oral doxycycline and topical lubricants has been shown to be effective in treating RCES. (15,16)

[FIGURE 3 OMITTED]

Although aggressive medical management can be successful, nearly half of patients will experience recurrence of symptoms and signs, (4,36) raising the prospect that surgical intervention will be required.

Epithelial debridement, where loose abnormal epithelium is removed mechanically, is then followed by superficial keratectomy (with a diamond burr) or alcohol delamination. This is performed for lesions within the visual axis. Adhesions between the epithelium and Bowman's layer are improved following treatment. (12)

Anterior stromal micropuncture (ASP) should be reserved for lesions outside the visual axis due to scar formation, glare and blurred vision. ASP attempts to induce scar tissue between the epithelium and anterior stroma thus improving epithelial adherence. (37,38)

PTK for RCES

PTK combined with PRK allows the RCES and refractive error to be treated in one procedure. PTK allows new adhesion complexes to form between the epithelium and stroma thus making stronger attachments and reducing RCES. Areas affecting the visual axis can be treated with good visual rehabilitation. Once the corneal surface has been ablated, re-epithelialisation can occur. Shallower ablations result in less corneal haze. (39)

Adding excimer laser to manual epithelial debridement improves success rate to 74-100%.41342

A recent review found PTK to be the most effective treatment modality for RCES. (40-42)

Conclusion

There are many management options for superficial corneal pathologies ranging from simple medical treatments to surgical options. PTK is one option which is accurate, safe, minimally invasive and effective as demonstrated by the three case studies in this article.

It can reduce clinical symptoms, improve vision and delay or even avoid the need for corneal graft in certain cases. Success rates can be high and recurrence rates low for certain conditions. Proper patient selection and pre-operative counselling will ensure minimal side effects and complications. PTK can also be combined with PRK to correct ametropia. If medical management is not successful in resolving symptoms or the condition, patients should be referred onwards to the hospital eye service.

Case study

A 56-year-old man presented with bilateral map dot fingerprint corneal dystrophy to a greater extent in the right eye.

His refraction following recent bilateral phacoemulsification was:
R 6/[12.sup.-2]     +0.50/-5.00 x 5    6/[9.5.sup.+2]

Add +2.25 N6

L6/30               -1.50/-1.00 x 165  6/4.8


Add +2.25 N4

Pre-treatment keratometry (using a Pentacam) readings were:

R 7.93mm (42.50D) @ 5.5, 7.34mm (46.00D) @ 95.5

L 7.65mm (44.10D) @ 171,7.35mm (45.90) @ 81

The dystrophy was inducing astigmatism and affecting best corrected VA of the right eye. PTK treatment was performed with an initial 20pm tissue removal and after slit lamp examination a further 10pm were removed. At the one-week follow-up, the bandage contact lens was removed and the patient was already aware of clearer vision with a posttreatment refraction of:
R 6/15+    -3.00/-1.00 x 25   6/9.5+


At the three month post-treatment review, the patient was extremely happy with his vision and the refraction was:
R 6/19     -2.00/-1.25 x 10    6/7.5

Add +1.00 N5


Keratometry readings:

7.64mm (44.20D) @ 14, 7.33mm (46.00D) @ 104

Slit lamp examination revealed no evidence of the dystrophy, the astigmatism markedly reduced and best corrected VA improved.

Case study

An elderly female patient was referred by her optometrist for reduced vision in the right eye due toBK.

Refraction was:
R 6/28   -1.50/-3.00 x 85   6/12

Add +2.50 N5

L 6/18   +1.00/-3.00 x 85   6/6+

Add +2.50 N5


Pre-treatment keratometry (using a Pentacam) readings were:

R 8.27mm ( 40.80D) @ 90.8, 7.82mm (43.10D) @ 0.8

LE 8.12mm ( 41.60D) @ 80.3, 7.64mm (44.20D) @ 170.3

PTK treatment was performed to the right eye. At one week, it was reported that the quality of vision was much better and there was no misting. A refraction was not performed but unaided VA was 6/15.

At one month the refraction was:
R 6/24   -1.75/-1.25 x 10   6/7.5

Add +2.50 N5


Keratometry readings:

R 7.97mm (42.40D) @31.9, 7.88 (42.80D)

Slit lamp examination revealed a very good result as the calcium deposition had been removed and the astigmatism reduced by the treatment. This improved the unaided VA and best corrected VA.

Case study

This patient was stabbed in the right eye by a tree branch 12 months prior and had since suffered with RCE. Despite using regular lubricating eye drops, the patient experienced one episode of RCE per month which lasted two to three days. A nightly eye ointment was also used but there was still frequent discomfort on waking.

The refraction was:
R 6/7.5   +0.50/-0.25 x 90  6/6

Add +1.25 N5


Keratometry readings:

R 7.57mm (44.60D) @ 170, 7.42mm (45.50D) @ 80

One week after PTK treatment, VA was 6/9 and the cornea was healing well. At three months follow-up, the patient was extremely happy as the symptoms had resolved with stable refraction and VA.

Slit lamp examination revealed a clear non-staining cornea. The patient now uses occasional Viscotears before bed.

Prashant Shah is an optometrist with postgraduate diplomas in ophthalmology and in clinical optometry. He works in routine practice and within a laser clinic environment.

Victoria Rowe is an experienced optometrist who has worked for LaserVision since 2012. She also works in a paediatric clinic as well as being a community optometrist.

Acknowledgements

The authors would like to thank consultant ophthalmologists Rakesh Jayaswal and Mike Tappin for their help and support with this article. The authors and publishers acknowledge The University of Iowa and www.eyerounds.org for permission to reproduce the figures.

Exam questions

Under the enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk. Please complete online by midnight on 10 June 2016.

You will be unable to submit exams after this date. CET points will be uploaded to the GOC within 10 working days. You will then need to log into your CET portfolio by clicking on 'MyGOC' on the GOC website (www.optical.org) to confirm your points.

References

Visit www.optometry.co.uk, and click on the 'Related CET article' title to view the article and accompanying 'references' in full.

Learning objectives

Optometrists

* Be able to explain to patients about options for managing corneal pathology (Group 1.2.4)

* Understand when it is appropriate to refer patients with corneal abnormalities for specialist opinion (Group 2.10.2)

* Understand alternative approaches for managing corneal abnormalities (Group 6.1.11)

Therapeutic optometrists

* Understand alternative approaches for managing corneal abnormalities and the likely outcome for the patient (Group 1.1.2)

* Be able to explain to patients about options for managing corneal pathology appropriate to their level of understanding (Group 3.1.4)

Dispensing opticians

* Be able to explain to patients about options for managing corneal pathology (Group 1.2.4)

* Understand alternative approaches for managing corneal abnormalities (Group 8.1.3)
Optometrists                COMMUNICATION   STANDARDS         OCULAR
                            OF PRACTICE     DISEASE

Therapeutic optometrists    KNOWLEDGE       SHARE DECISION

Dispensing opticians        COMMUNICATION   OCULAR DISEASE
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Author:Shah, Prashant; Rowe, Victoria
Publication:Optometry Today
Geographic Code:4EUUK
Date:May 1, 2016
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