**3. Terrien's marginal degeneration (TMD)**

**TMD** is a rare corneal degeneration form. The disease is characterized by a nonulcerative peripheral corneal thinning [19]. It has a slow and chronic progression, bilaterally and asymmetric. TMD etiology still remains unknown [20]. The pathology has been associated with arthritis and meibomian gland dysfunction. TDM is more frequent in middle-aged males but can occur at any age and in females [21].

TMD is a lipid keratopathy [19]. The slit-lamp biomicroscopy evaluation displays lipid depositions at the edge of the peripheral corneal thinning [21, 22] (**Figure 15**). This lipid accumulation produces yellow-white stromal opacities [22] with superficial neovascularization. Histopathological exams demonstrate intracellular and extracellular vacuoles [21] charged with lipids in the corneal stroma. There is stromal fibrillary degeneration with fatty infiltration of collagen fibers [21, 22]. This stroma degradation produces a decrease in the number of lamellas. TMD lesions have an intact corneal epithelium and an altered Bowman's layer. Electron microscopy studies show the corneal basal membrane and the Bowman layer broken and fragmented.

#### **Figure 15.**

*AS slit-lamp evaluation of a TMD patient. The image demonstrates the lipid deposition in the inferior peripheral corneal area producing yellow-white stromal opacities.*

**31**

**Figure 16.**

*Clinical Application of Optical Coherence Tomography in the Corneal Degenerations*

TMD corneal changes can produce an increase in the corneal astigmatism [21], which clinically manifests with a visual acuity decreased. Topography evaluation is

Two types of TDM have been described. The classic one, more common, generally affects older population [20]. It is usually asymptomatic, noninflammatory, and with a slowly, chronic progress. The second type affects young patients and has a more prominent inflammatory clinical course with a faster evolution [20]. This inflammatory variant is believed to initiate hypersensitivity responses [24, 25] to an immunogenic component of the basal membrane, secreted by the degenerated basal epithelial cells [21]. It can also be produced by phagocytosis of the stromal collagen by histiocyte-like cells [26]. Thinning of the peripheral cornea, corneal opacification, neovascularization, and possible positive fluorescein staining are typically

Due to the slow progression [22], TMD is generally asymptomatic. Sometimes

the diagnosis is incidental because of mild irritation symptoms. Topographic evaluation demonstrates a flattening over the corneal peripheral thinning areas and steepening of the corneal meridian perpendicular to the corneal lesion [21]. TDM slit-lamp biomicroscopy shows the yellowish-white opacities and thinning of the peripheral cornea. The pathology generally initiates at the superior or supero-nasal area. The corneal perforation rate is 15% [21]. It can debut with redness, watering, and sudden decrease of visual acuity. The corneal perforation can cause a deep impact on the vision prognosis regardless of the surgical

Corneal AS-OCT provides a high-resolution cross-sectional image in TMD patients, and its caliper can take precise and repeatable pachymetry measurements to verify the corneal thickness in the thinner areas (**Figure 16**). It is a safe, rapid, and noninvasive digital technique that depicted structural or morphologic corneal changes. It is a digital precise method to compare the size lesions between the clinical appointments [19, 22]. Medical visits are recommended every 3 months when

AS-OCT displays the corneal stromal thinning area in TMD disease. The lesions have a non-affected epithelium. In the classic TDM type, the stroma has the same reflectivity as the normal cornea [4]. In the inflammatory TDM, the progressive stromal thinning induces corneal cavity formation with intact epithelial and endothelial layers around the lesion [4, 22] (**Figures 17** and **18**). The external epithelial layer has a normal reflectivity, and the internal endothelial layer is continuous with

*(A and B) AS-OCT scan demonstrates a corneal thinning area and a hyper-reflective zone in an inflammatory* 

*TMD patient. The anterior and the posterior corneal surfaces have their curvatures altered.*

*DOI: http://dx.doi.org/10.5772/intechopen.84244*

essential for a complete pathology study [23].

signs of the TMD inflammatory type [21].

the minimal corneal thickness is 250 μm [21].

intervention.

#### *Clinical Application of Optical Coherence Tomography in the Corneal Degenerations DOI: http://dx.doi.org/10.5772/intechopen.84244*

TMD corneal changes can produce an increase in the corneal astigmatism [21], which clinically manifests with a visual acuity decreased. Topography evaluation is essential for a complete pathology study [23].

Two types of TDM have been described. The classic one, more common, generally affects older population [20]. It is usually asymptomatic, noninflammatory, and with a slowly, chronic progress. The second type affects young patients and has a more prominent inflammatory clinical course with a faster evolution [20]. This inflammatory variant is believed to initiate hypersensitivity responses [24, 25] to an immunogenic component of the basal membrane, secreted by the degenerated basal epithelial cells [21]. It can also be produced by phagocytosis of the stromal collagen by histiocyte-like cells [26]. Thinning of the peripheral cornea, corneal opacification, neovascularization, and possible positive fluorescein staining are typically signs of the TMD inflammatory type [21].

Due to the slow progression [22], TMD is generally asymptomatic. Sometimes the diagnosis is incidental because of mild irritation symptoms. Topographic evaluation demonstrates a flattening over the corneal peripheral thinning areas and steepening of the corneal meridian perpendicular to the corneal lesion [21]. TDM slit-lamp biomicroscopy shows the yellowish-white opacities and thinning of the peripheral cornea. The pathology generally initiates at the superior or supero-nasal area. The corneal perforation rate is 15% [21]. It can debut with redness, watering, and sudden decrease of visual acuity. The corneal perforation can cause a deep impact on the vision prognosis regardless of the surgical intervention.

Corneal AS-OCT provides a high-resolution cross-sectional image in TMD patients, and its caliper can take precise and repeatable pachymetry measurements to verify the corneal thickness in the thinner areas (**Figure 16**). It is a safe, rapid, and noninvasive digital technique that depicted structural or morphologic corneal changes. It is a digital precise method to compare the size lesions between the clinical appointments [19, 22]. Medical visits are recommended every 3 months when the minimal corneal thickness is 250 μm [21].

AS-OCT displays the corneal stromal thinning area in TMD disease. The lesions have a non-affected epithelium. In the classic TDM type, the stroma has the same reflectivity as the normal cornea [4]. In the inflammatory TDM, the progressive stromal thinning induces corneal cavity formation with intact epithelial and endothelial layers around the lesion [4, 22] (**Figures 17** and **18**). The external epithelial layer has a normal reflectivity, and the internal endothelial layer is continuous with

#### **Figure 16.**

*(A and B) AS-OCT scan demonstrates a corneal thinning area and a hyper-reflective zone in an inflammatory TMD patient. The anterior and the posterior corneal surfaces have their curvatures altered.*

*A Practical Guide to Clinical Application of OCT in Ophthalmology*

ciation with another disease [17].

**3. Terrien's marginal degeneration (TMD)**

disease progression.

Superficial keratectomy will be the surgical first-line therapy in most cases (**Figure 13**). The results will be conditioned by the degree of involvement of the superficial cornea and the degree of affection of the Bowman's layer described in the corneal AS-OCT images (**Figure 14**). An unbroken Bowman's layer or an altered Bowman's layer could be predictive of the strength of the adhesion of the nodules to the anterior stroma [16]. The method used to remove mechanically the opacities will be "peeling the nodules," referred in the bibliography as "Salzmann nodulectomy." In

areas of excessive thinning, a careful manual dissection will be required [17].

Keratoplasty will be used in the most severe SND cases. Fortunately, as the mid stroma and Descemet membrane are intact in most SND cases, a lamellar keratoplasty (LK) will be enough to eliminate the opacities. Penetrating keratoplasty (PKP) will be rarely required in SND patients. PKP will be reserved for cases of intraoperative perforation during LK or full-thickness corneal alterations in asso-

Corneal AS-OCT images in SND patients have an excellent correlation with the histopathologic exam. AS-OCT analysis is a useful technique that sustained SND diagnosis and helped the clinicians to decide the management and follow-up of the

**TMD** is a rare corneal degeneration form. The disease is characterized by a nonulcerative peripheral corneal thinning [19]. It has a slow and chronic progression, bilaterally and asymmetric. TMD etiology still remains unknown [20]. The pathology has been associated with arthritis and meibomian gland dysfunction. TDM is more frequent in middle-aged males but can occur at any age and in females [21]. TMD is a lipid keratopathy [19]. The slit-lamp biomicroscopy evaluation displays lipid depositions at the edge of the peripheral corneal thinning [21, 22] (**Figure 15**). This lipid accumulation produces yellow-white stromal opacities [22] with superficial neovascularization. Histopathological exams demonstrate intracellular and extracellular vacuoles [21] charged with lipids in the corneal stroma. There is stromal fibrillary degeneration with fatty infiltration of collagen fibers [21, 22]. This stroma degradation produces a decrease in the number of lamellas. TMD lesions have an intact corneal epithelium and an altered Bowman's layer. Electron microscopy studies show the corneal basal membrane and the Bowman layer broken and

**30**

**Figure 15.**

fragmented.

*AS slit-lamp evaluation of a TMD patient. The image demonstrates the lipid deposition in the inferior* 

*peripheral corneal area producing yellow-white stromal opacities.*

#### **Figure 17.**

*AS slit-lamp evaluation of a TMD patient. (A) The corneal periphery has a lipid deposition and an extensive thinning area. (B and C) Same TMD patient after an amniotic membrane grafting technique. The image demonstrates how the corneal disorder has been restored.*

#### **Figure 18.**

*Corneal AS-OCT of the same TMD patient of Figure 17. (A) Longitudinal scan analysis demonstrates corneal cavitation. (B, C) Transversal scan evaluation also shows the cavitation in the stromal area.*

the rest of the normal endothelial corneal tissue. The corneal thinning areas can show hyper-reflectivity, and AS-OCT evaluation is able to demonstrate corneal cavities not visible in the slit-lamp biomicroscopy [22] (**Figures 17** and **18**).

AS-OCT also evaluates the anterior and the posterior corneal curvatures. Classically, TMD is classified in five clinical stages depending on the disease progression. Recently, a new staging method has been reported [19]. The new classification is based on the anterior and posterior curvatures and the size of the thinnest area, analyzed by corneal AS-OCT. This new staging is useful to evaluate the TMD progression and to plan the surgical management, evidencing the importance of the AS-OCT images to supervise the pathology development.

Due to the slow progression of most TMD cases, the pathology can be managed conservatively in most patients. Noneffective pharmacotherapy has been demonstrated. Nonsurgical interventions include spectacle prescription, rigid gas-permeable contact lenses, scleral lenses, and prosthetic replacement of the ocular surface ecosystem (PROSE) [21]. Eye rubbing has to be avoided.

**33**

procedure in more severe cases.

**4. Band keratopathy**

**Figure 19.**

*cavitation zone.*

*Clinical Application of Optical Coherence Tomography in the Corneal Degenerations*

Surgical procedures are considered when the corneal thickness decreased 150 μm. Nevertheless, some authors prefer an expectant attitude even when the cornea reaches this cross-sectional length [27]. Surgical interventions include the tectonic grafting, whose purpose is to prevent or repair perforation areas in the absence of the donor cornea. The main techniques are conjunctival flaps, scleral autotransplantation, and amniotic membrane grafting (**Figure 19**). Keratoplasty is considered in patients who want to improve their visual acuity. LK is the first technique to consider in this TMD patient [22]. If not, PKP is another possible surgical

*AS-OCT image from the same TMD patient from Figure 18. (A) The cavitation zone following an amniotic membrane grafting replace technique. The amniotic membrane layers can be distinguished in the scan. (B–D) The image shows how the amniotic membrane has been integrated in the corneal area and has replaced the* 

Corneal collagen cross-linking has recently been reported as a good option before performing surgical procedures. It seems to stop the disease evolution,

Band keratopathy is characterized by calcium deposition in Bowman's layer, most frequently in the interpalpebral zone. The pathology is usually associated with systemic disorders, such as hypercalcemia, or ocular diseases, such as uveitis, chemical burns, intraocular silicone oil, and phthisis eyes after surgeries [28]. AS-OCT imaging is useful for the analysis and measure of the calcium depo-

sition and helpful in achieving a correct pathology management. It shows a

return the thinning area, and improve visual acuity [28].

*DOI: http://dx.doi.org/10.5772/intechopen.84244*

*Clinical Application of Optical Coherence Tomography in the Corneal Degenerations DOI: http://dx.doi.org/10.5772/intechopen.84244*

#### **Figure 19.**

*A Practical Guide to Clinical Application of OCT in Ophthalmology*

*demonstrates how the corneal disorder has been restored.*

the rest of the normal endothelial corneal tissue. The corneal thinning areas can show hyper-reflectivity, and AS-OCT evaluation is able to demonstrate corneal cavities not visible in the slit-lamp biomicroscopy [22] (**Figures 17** and **18**). AS-OCT also evaluates the anterior and the posterior corneal curvatures. Classically, TMD is classified in five clinical stages depending on the disease progression. Recently, a new staging method has been reported [19]. The new classification is based on the anterior and posterior curvatures and the size of the thinnest area, analyzed by corneal AS-OCT. This new staging is useful to evaluate the TMD progression and to plan the surgical management, evidencing the importance of the

*cavitation. (B, C) Transversal scan evaluation also shows the cavitation in the stromal area.*

*Corneal AS-OCT of the same TMD patient of Figure 17. (A) Longitudinal scan analysis demonstrates corneal* 

*AS slit-lamp evaluation of a TMD patient. (A) The corneal periphery has a lipid deposition and an extensive thinning area. (B and C) Same TMD patient after an amniotic membrane grafting technique. The image* 

Due to the slow progression of most TMD cases, the pathology can be managed conservatively in most patients. Noneffective pharmacotherapy has been demonstrated. Nonsurgical interventions include spectacle prescription, rigid gas-permeable

contact lenses, scleral lenses, and prosthetic replacement of the ocular surface

AS-OCT images to supervise the pathology development.

ecosystem (PROSE) [21]. Eye rubbing has to be avoided.

**32**

**Figure 18.**

**Figure 17.**

*AS-OCT image from the same TMD patient from Figure 18. (A) The cavitation zone following an amniotic membrane grafting replace technique. The amniotic membrane layers can be distinguished in the scan. (B–D) The image shows how the amniotic membrane has been integrated in the corneal area and has replaced the cavitation zone.*

Surgical procedures are considered when the corneal thickness decreased 150 μm. Nevertheless, some authors prefer an expectant attitude even when the cornea reaches this cross-sectional length [27]. Surgical interventions include the tectonic grafting, whose purpose is to prevent or repair perforation areas in the absence of the donor cornea. The main techniques are conjunctival flaps, scleral autotransplantation, and amniotic membrane grafting (**Figure 19**). Keratoplasty is considered in patients who want to improve their visual acuity. LK is the first technique to consider in this TMD patient [22]. If not, PKP is another possible surgical procedure in more severe cases.

Corneal collagen cross-linking has recently been reported as a good option before performing surgical procedures. It seems to stop the disease evolution, return the thinning area, and improve visual acuity [28].

#### **4. Band keratopathy**

Band keratopathy is characterized by calcium deposition in Bowman's layer, most frequently in the interpalpebral zone. The pathology is usually associated with systemic disorders, such as hypercalcemia, or ocular diseases, such as uveitis, chemical burns, intraocular silicone oil, and phthisis eyes after surgeries [28].

AS-OCT imaging is useful for the analysis and measure of the calcium deposition and helpful in achieving a correct pathology management. It shows a

#### **Figure 20.**

*(A, B) AS slit-lamp evaluation showing calcium deposition in the superficial cornea of a patient with band keratopathy.*

#### **Figure 21.**

*(A, B, C) AS-OCT evaluation from the same patient of Figure 20. There is a hyper-reflective zone in the calcium deposition areas causing shadows in the corneal stroma below the lesions.*

hyper-reflective material around Bowman's layer causing shadowing in the posterior cornea stroma [3, 29, 30] (**Figures 20** and **21**).

The calcium deposition can result in a loss of visual acuity. The aim of the surgical techniques will be to restore the corneal transparency. AS-OCT imaging can help to decide the optimal surgical technique as the scans show the depth of the lesions [28].
