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Managing Corneal Ectasia Prior to Keratoplasty

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Managing Corneal Ectasia Prior to Keratoplasty Review Managing corneal ectasia prior to keratoplasty Expert Rev. Ophthalmol. 10(1), 33–48 (2015) Fernando The advent of refractive surgery allowed for great advances in the understanding of Faria-Correia1–6, pathophysiology, diagnosis and treatment of corneal ectatic diseases. The different Allan Luz6–8 and associations that highlight the importance of this range from the need for early diagnosis in the screening process of candidates for laser vision correction to the impact of refractive Renato 6,8–10 surgery technologies on treatment. Keratoconus is still an indication for corneal transplant, Ambrosio Jr* and it is expected that about 5–20% of the patients may require it. However, considering 1Cornea and Refractive Surgery technological advances, the current treatment options are diverse and can be customized to Department, Hospital de Braga, Braga, each case. This review overviews the fundamental knowledge related to corneal ectatic Portugal 2Instituto CUF, Porto, Portugal diseases management and its management prior to keratoplasty. Whereas this is an area of 3Oftalconde, Porto, Portugal dynamic development of scientific knowledge, we present fundamental concepts, along with 4Clı´nica Oftalmologica Dr Hora´ cio information on the most recent studies and future prospects. Correia, Braganc¸a, Portugal 5School of Health Sciences, University KEYWORDS: corneal biomechanics . corneal ectasia . corneal tomography . crosslinking . enhanced screening of Minho, Braga, Portugal . 6Rio de Janeiro Corneal Tomography intracorneal ring segments keratoconus keratoplasty post-LASIK ectasia topoguided-PRK and Biomechanics Study Group, Rio de Janeiro, Brazil 7Hospital de Olhos de Sergipe, Sergipe, Keratoconus and ectatic corneal diseases have the ability to generate such data, which must Brazil been widely studied for over 150 years [1,2]. be properly interpreted by the surgeon [4,8–11]. 8Universidade Federal de Sa˜o Paulo, However, the advent of refractive surgery has Sa˜o Paulo, Brazil 9Cornea and Refractive Surgery enabled the greatest advances in the under- Corneal ectatic diseases Department, Instituto de Olhos Renato standing of pathophysiology, diagnosis and Corneal ectasia is a condition characterized by Ambrosio, Rio de Janeiro, Brazil treatment of such diseases. Understanding biomechanical failure [12]. The cornea is under 10VisareRio, Rio de Janeiro, Brazil *Author for correspondence: ectatic diseases of the cornea is essential for constant stress as a result of the intraocular [email protected] the refractive surgeon. The different associa- pressure, as well as stress generated by the eye- tions that highlight this importance varies lids, the extraocular muscles or other external from the need of early diagnosis in the screen- trauma sources. Eye rubbing has a great impact ing process of selecting candidates for laser in corneal ‘biomechanical stress’ [13]. There is a vision correction (LVC) to the impact of new ‘structural susceptibility’ that is related to indi- technologies related to refractive surgery in the vidual genetics and is the determinant of the treatment of these diseases [3,4]. biomechanical properties of the cornea. Corneal photoablative procedures may in- Biomechanical failure leads to thinning and duce or accelerate the progression of ectasia [5,6]. tissue protrusion without an acute inflamma- Moreover, customized surface ablation may be tory process. Recent studies indicate that successfully performed in case of keratoconus, chronic inflammatory activity may be involved with both refractive and therapeutic pur- in the pathophysiology of these diseases. The poses [7]. However, the indication for elective changes are progressive and cause astigmatism refractive procedure should be well thought and irregularities (high-order aberrations), which out and conscious. may or may not be associated with myopia [12]. Knowledge about the structural, geometric Keratoconus is the most common ectatic and optical properties of the cornea is crucial. disorder, and its incidence is classically de- Advances in corneal evaluation tools are essen- scribed as one patient per 2000 inhabi- tial to identify candidates for LVC with higher tants [1,2,14]. However, some studies indicate a risk (or susceptibility) to ectatic progression. higher incidence of the disease. For example, Such information is equally important to indi- such a condition is identified in about 1–5% cate and schedule the surgery. Thus, additional of candidates for refractive surgery, which is workup should be done using technology with certainly related to a process of self-selection, informahealthcare.com 10.1586/17469899.2015.991390 Ó 2015 Informa UK Ltd ISSN 1746-9899 33 Review Faria-Correia, Luz & Ambrosio Jr OD OS Figure 1. Anterior curvature sagittal map of a patient with mild keratoconus OD and forme fruste keratoconus OS. OD: Right eye; OS: Left eye. as each patient with keratoconus is more likely to seek help condition and free of acute inflammation and lipid deposits, because of their visual impairments [3,10]. It is a progressive which differentiates PMD from other diseases, such as Terri- and bilateral disease, but can be quite asymmetric. It may be en’s marginal degeneration and Mooren’s ulcer, which are not associated with systemic diseases such as Down syndrome, considered as ectatic diseases [1,2]. Keratoglobus is a condition retinitis pigmentosa, Leber congenital amaurosis, mitral valve even more rare that PMD, defined by overall thinning of the prolapse and other connective tissue diseases, such as Ehlers– cornea and severe protrusion, with a significant increase of the Danlos and Marfan syndrome. However, one of the most anterior chamber depth [1]. Therefore, the differentiation important associations is related to ocular allergic diseases, between keratoconus, PMD and keratoglobus is possible only such as atopic dermatitis and vernal keratoconjunctivitis through the pattern of thinning [2,16]. Proper classification has [1,2,14]. clinical relevance, since clinical aspects and therapeutic manage- Besides keratoconus, other disorders that are classified within ment are distinct. Ectasia progression with thinning and tissue this group of natural ectatic diseases are pellucid marginal protrusion may also occur after trauma or surgical procedures. degeneration (PMD) and keratoglobus. Such conditions are Such situations can lead to biomechanical failure of corneal rarer than keratoconus and are identified based on the pattern stroma and consequent ectasia. It is vital to recognize that ecta- of thinning [1,2]. PMD has a thinning ‘band’ in the inferior sia can occur after refractive corneal surgery performed through cornea near the limbus, which induces flattening of the vertical different techniques such as radial keratotomy, laser-assisted in meridian and astigmatism against-the-rule [1,15]. The topo- situ keratomileusis (LASIK) and photorefractive keratectomy graphical feature (anterior curvature) in some cases with infe- (PRK) [5,6,17–19]. The appropriate selection of candidates for rior keratoconus may be similar to the PMD, but refractive surgery is the key to prevent this severe complication, differentiation is possible by means of a pachymetry map [1,2]. with the essential understanding and interpretation of ancillary The term ‘pellucid’ means transparent, being an avascular tests [4,8,10]. 34 Expert Rev. Ophthalmol. 10(1), (2015) Managing corneal ectasia prior to keratoplasty Review Clinical evaluation of ectatic corneal diseases Early diagnosis of keratoconus is fundamental as it may enable the early application of therapeutic strategies that minimize the effect of the disease on the patient and society. Keratoconus is generally diagnosed or suspected during gen- eral ophthalmological examination, but ancillary exams play a major role in the diagnosis, staging and follow-up of the con- dition [1]. For example, Marc Amsler published for the first time the ‘forme fruste keratoconus’ concept, based on photo- keratoscopy imaging, in a prospective study [20]. The detec- tion of early forms of ectatic disease is also essential in the OD with mild keratoconus and screening process of candidates for LVC, in order to prevent Left eye progressive iatrogenic ectasia [3,8,10]. In the mid-1980s, Stephen D. Klyce, PhD, first developed algorithms for surface reconstruction of the acquired reflection image from Placido-based videokeratoscopy, allowing color- coded maps and quantitative data of the front surface of the cornea [21]. Corneal topography represented a true revolution in the diagnosis and management of corneal disease [22].It requires caution about the scan quality, because artifacts may affect the clinical presentation [4]. Regarding ectasia, the topo- graphic pattern of inferior steepening is the most recognized one [3,23]. However, there is a great variation in the subjective classification of topographic maps, being required to define objective criteria [9]. In general, higher corneal values to 47.5 D are suspected. Additionally, the asymmetry between B the values in the 3 mm radius in the upper and lower regions (or between the nasal and temporal regions) is suspected when greater than 1.4 D [24,25]. Such parameters are integrated in the calculation of the keratoconus percentage index, described by Rabinowitz and Rasheed [26]. In addition, several indices derived from curvature data are available in different commercial devices. Other technologies were a further improvement in corneal imaging, such as corneal tomography
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