**2. Terminology and staging**

Nowadays, there remain many controversies regarding disease definition, diagnosis, and management of keratoconus. Keratoconus is usually a bilateral disease in which the normal contralateral eye is believed to be in the preclinical stage of keratoconus with different terms such as subclinical keratoconus, keratoconus suspect, forme fruste keratoconus [12]. Despite the advancement of the investigations for the diagnosis of keratoconus and subclinical keratoconus, there are no definitive criteria for discriminating subclinical keratoconus from normal cornea currently [13]. The detection of keratoconus and subclinical keratoconus is crucial to prevent ectasia after refractive surgery. Moreover, some treatment modalities such as corneal collagen crosslinking can prevent vision loss in keratoconus if implement in the early stage of the disease [14]. The early stage symptoms may manifest as reduced vision, fluctuation of vision, progressive myopia and astigmatism, increasing higher order aberrations [4, 15]. When the disease progresses into an advance stage, there is a severe visual loss from high myopia, irregular astigmatism and corneal scarring.

The following criteria are mandatory to diagnose keratoconus- abnormal posterior elevation, abnormal corneal thickness distribution and clinical noninflammatory corneal thinning [10]. However, there is no clinically adequate classification system for keratoconus currently. One of the most popular grading systems is Amsler-Krumeich classification system which classified severity of diseases based on the amount of myopia and astigmatism, corneal thickness or scarring and central keratometry readings [16, 17]. However, Amsler-Krumeich classification system is considered as outdated because it relies on "old" indices (corneal steepness, refractive change, the presence of scarring), and fails to address disease impact [18]. Nowadays, other alternate classification systems are growing in number such as Shabayek-Alio system which is based on corneal higher aberrations and the keratoconus severity score (KSS) which considers average corneal power and root mean square (RMS) [19, 20]. The "ABCD grading system" that incorporates anterior and posterior corneal curvature, thinnest pachymetric values based on the thinnest point and distant visual acuity may better reflects the anatomical change than some previous classification that uses pachymetric value based on apical measurement [21]. In routine clinical practice, the term "advanced keratoconus" usually apply to any case with unacceptably poor spectacle distance vision and contact lens intolerance [18].

### **3. Diagnosis**

The keratoconus diagnosis is bases on the history and clinical examination. However, the investigations are very useful to augment the clinical examination and detect the early stage of disease. Moreover, the accurate diagnosis and early

**39**

*Keratoconus Treatment Toolbox: An Update DOI: http://dx.doi.org/10.5772/intechopen.94854*

atomic force microscopy [25].

normal noise of the testing system:

1 diopter (D) within 1 year

1.Steepening of the anterior corneal surface.

2.Steepening of the posterior corneal surface.

sion. The most important parameters include: [27, 28]

periphery to the thinnest point" [10].

**4. Disease progression**

detection of keratoconus in essential in this era which laser refractive surgery has increased markedly. Failure to detect keratoconus and subclinical keratoconus can lead to ectasia after refractive surgery [22]. Corneal topography is the primary diagnostic tool for keratoconus detection. However, corneal topography is not a faultless method and therefore other diagnostic tools such as corneal pachymetry to characterize the corneal thinning and aberrometry to characterize degradation of the corneal optics should be used as complimentary techniques [22]. Corneal tomography which based on rotating Scheimpflug camera, such as Pentacam, Galilei, or Sirius systems, provide the topographic, pachymetric, and aberrometric information simultaneously as their use is adequate enough for the keratoconus detection [12, 22]. Currently, OCT technology is being used to differentiate between eye with keratoconus and normal eye because it can provide accurate pachymetric characterization, define epithelial thickness irregularity and asymmetry that present in keratoconus [7, 23]. By analyzing the biomechanical properties of the cornea that may precede the anatomical change, the Ocular Response Analyzer and Corvis systems can provide good diagnostic accuracy [22]. Analysis of the Corneal Microstructure change in keratoconic eye from confocal microscopy such as reducing corneal nerve fiber density and nerve fiber length, reducing keratocyte density, increasing corneal stromal nerve thickness, may be useful in detecting structural changes occurring before manifestation of topographic signs [22, 24]. A combination of multiple imaging modalities, including corneal topography, corneal tomography, Scheimpflug imaging, anterior segment optical coherence tomography, and in vivo confocal microscopy will enhance early keratoconus detection. Modalities during investigations but show promise include polarization-sensitive optical coherence tomography, Brillouin microscopy, and

Keratoconus progression detection is a critical issue because the treatment nomograms have been proposed based on the grading system and ectasia progression [15, 22]. Moreover, the disease progression is differed considerably among individual. The younger the patients are, the higher their risk for rapid progression [26]. Currently, there is no global consensus of ectasia progression. The Group of Panelists for the Global Delphi Panel of Keratoconus and Ectatic Diseases had defined the definition of "ectasia progression" as a consistent change overtime in at least 2 of the following parameters where the magnitude of the change is above the

3.Thinning and/or an increase in the rate of corneal thickness change from the

Various clinical studies have used different parameters to define disease progres-

1.An increase in maximum corneal refractive power (Kmax) by more than

### *Keratoconus Treatment Toolbox: An Update DOI: http://dx.doi.org/10.5772/intechopen.94854*

*Eyesight and Imaging - Advances and New Perspectives*

family history about 15 to 67 times [11].

vision and contact lens intolerance [18].

**2. Terminology and staging**

surgery center [7]. Keratoconus is more common in men than women, although both gender are affected [5]. The onset of symptoms usually presents during adolescent and may progress until the 30s. Keratoconus is associated with eye rubbing such as in allergic conjunctivitis, floppy eyelid syndrome, obstructive sleep apnea, Down's syndrome and Leber congenital amaurosis [1, 8–10]. Genetic predisposition accounts for an increased risk of keratoconus in patient that has a positive

Nowadays, there remain many controversies regarding disease definition, diagnosis, and management of keratoconus. Keratoconus is usually a bilateral disease in which the normal contralateral eye is believed to be in the preclinical stage of keratoconus with different terms such as subclinical keratoconus, keratoconus suspect, forme fruste keratoconus [12]. Despite the advancement of the investigations for the diagnosis of keratoconus and subclinical keratoconus, there are no definitive criteria for discriminating subclinical keratoconus from normal cornea currently [13]. The detection of keratoconus and subclinical keratoconus is crucial to prevent ectasia after refractive surgery. Moreover, some treatment modalities such as corneal collagen crosslinking can prevent vision loss in keratoconus if implement in the early stage of the disease [14]. The early stage symptoms may manifest as reduced vision, fluctuation of vision, progressive myopia and astigmatism, increasing higher order aberrations [4, 15]. When the disease progresses into an advance stage, there is a severe visual loss from high myopia, irregular astigmatism and corneal

The following criteria are mandatory to diagnose keratoconus- abnormal posterior elevation, abnormal corneal thickness distribution and clinical noninflammatory corneal thinning [10]. However, there is no clinically adequate classification system for keratoconus currently. One of the most popular grading systems is Amsler-Krumeich classification system which classified severity of diseases based on the amount of myopia and astigmatism, corneal thickness or scarring and central keratometry readings [16, 17]. However, Amsler-Krumeich classification system is considered as outdated because it relies on "old" indices (corneal steepness, refractive change, the presence of scarring), and fails to address disease impact [18]. Nowadays, other alternate classification systems are growing in number such as Shabayek-Alio system which is based on corneal higher aberrations and the keratoconus severity score (KSS) which considers average corneal power and root mean square (RMS) [19, 20]. The "ABCD grading system" that incorporates anterior and posterior corneal curvature, thinnest pachymetric values based on the thinnest point and distant visual acuity may better reflects the anatomical change than some previous classification that uses pachymetric value based on apical measurement [21]. In routine clinical practice, the term "advanced keratoconus" usually apply to any case with unacceptably poor spectacle distance

The keratoconus diagnosis is bases on the history and clinical examination. However, the investigations are very useful to augment the clinical examination and detect the early stage of disease. Moreover, the accurate diagnosis and early

**38**

**3. Diagnosis**

scarring.

detection of keratoconus in essential in this era which laser refractive surgery has increased markedly. Failure to detect keratoconus and subclinical keratoconus can lead to ectasia after refractive surgery [22]. Corneal topography is the primary diagnostic tool for keratoconus detection. However, corneal topography is not a faultless method and therefore other diagnostic tools such as corneal pachymetry to characterize the corneal thinning and aberrometry to characterize degradation of the corneal optics should be used as complimentary techniques [22]. Corneal tomography which based on rotating Scheimpflug camera, such as Pentacam, Galilei, or Sirius systems, provide the topographic, pachymetric, and aberrometric information simultaneously as their use is adequate enough for the keratoconus detection [12, 22]. Currently, OCT technology is being used to differentiate between eye with keratoconus and normal eye because it can provide accurate pachymetric characterization, define epithelial thickness irregularity and asymmetry that present in keratoconus [7, 23]. By analyzing the biomechanical properties of the cornea that may precede the anatomical change, the Ocular Response Analyzer and Corvis systems can provide good diagnostic accuracy [22]. Analysis of the Corneal Microstructure change in keratoconic eye from confocal microscopy such as reducing corneal nerve fiber density and nerve fiber length, reducing keratocyte density, increasing corneal stromal nerve thickness, may be useful in detecting structural changes occurring before manifestation of topographic signs [22, 24]. A combination of multiple imaging modalities, including corneal topography, corneal tomography, Scheimpflug imaging, anterior segment optical coherence tomography, and in vivo confocal microscopy will enhance early keratoconus detection. Modalities during investigations but show promise include polarization-sensitive optical coherence tomography, Brillouin microscopy, and atomic force microscopy [25].
