**6. Future directions**

*Eyesight and Imaging - Advances and New Perspectives*

**Non- progressive** Spectacles Spectacles

**Progressive** Spectacles Spectacles

*Adapted from JAMA Ophthalmol. 2014 Apr 1;132(4):495–501.*

*Cataract Refract Surg. 1998 Apr;24(4):456–63. [17] Stage 1 Kmax < 48 D, thickness > 500* μ*m, absence of scarring. Stage 2 Kmax 48–53 D, thickness 400–500* μ*m, absence of scarring. Stage 3 Kmax 54–55 D, thickness 200–400* μ*m, absence of scarring. Stage 4 Kmax > 55 D, thickness < 200* μ*m, central corneal scarring.*

**Management**

ICRS ICRS

ICRS ICRS

CXL CXL CXL

*The classification of keratoconus was based on Krumeich JH et al.A. Live-epikeratophakia for keratoconus. J* 

**Stage 1 Stage 2 Stage 3 Stage 4**

CL intolerance CL intolerance

CL intolerance CL intolerance

BL transplantation BL transplantation

BL transplantation BL transplantation

DALK/PK

DALK/PK

CL CL CL CL

CL CL CL CL

**Classification\* Disease progression**

*5.2.3.3 Bowman layer transplantation*

*Management algorithm in various stages of keratoconus.*

**Table 5.**

The PK or DALK may be disrupted by complications such as suture-related problems, graft rejection, epithelial wound-healing abnormalities, corneal curvature changes due to progression of KC in the peripheral host cornea resulting in disappointing visual results [86]. In KC corneas, pathological changes include the reduction of number of keratocytes, organization of the stromal lamellae, fragmentation or absent of Bowman's layer (BL) [91] It has been suggested that the BL may be the strongest biomechanical element of the human cornea followed by the anterior third of the cornea [92]. Therefore, the BL may play a structural role in maintaining the shape/tectonic stability in KC corneas [87]. This procedure was first described in 2014, Bowman's layer graft was positioned inside the recipient corneal stroma in a sandwich technique, without corneal incision or sutures, to pull the anterior corneal surface flatter and create homogeneous corneal topography [86]. BL transplantation can be performed under local anesthesia and low dose topical steroid can stop within 1 year post-operative, minimizing the risk of glaucoma development or cataract formation [86, 87, 93]. The reported complications are low such as intraoperative microperforation of the Descemet's membrane [87, 93]. Because of the transplanted tissue is acellular, no episodes of allograft rejection have been observed [86, 87]. This procedure may postpone penetrating keratoplasty (PK) or deep anterior lamellar keratoplasty (DALK) and potentially allowed long term contact lens wear [86]. Although graft preparation and surgical technique can be challenging, assisted technologies, such as femtosecond laser and intraoperative anterior segment optical coherence tomography (OCT), may

**54**

Treatment for advanced KC has trended away from invasive procedures such as PK and even DALK toward minimally invasive procedures such as CXL, ICRS or BL transplantation. Although keratoconus is a multifactorial disease, the pathogenesis of the disease is very much affected by genetic factors and positive family history [2, 8, 97]. By identifying pathogenic genes and changing the structure of cell proteins, gene therapy may be a very promising and effective treatment modality to change the course of the disease [15].
