Femtosecond laser technology has recently enabled femtosecond-assisted penetrating keratoplasty (FAKP). The femtosecond laser is a type of laser that can produce pulses of light of extremely short duration. The application of femtosecond laser in surgery results in no thermal effect or shock wave, so that this laser is unlikely to cause tissue injuries outside the irradiation area of the laser beam. The femtosecond laser is ablative and utilized to perform incision with varying size and shape of the cuts of the corneal tissue. The laser can be used to accurately cut a more complex shape of both the donor tissue and the host tissue, such as a top hat, mushroom, Christmas tree, or zigzag configurations using software products, such as the IntraLase (AMO, Inc, Santa Ana, CA, USA), which is otherwise known as IntraLase-enabled keratoplasty (IEK). These arrangements provide better fixation of the corneal graft. The graft interfaces are readily visible on OCT, but residual host corneal tissue can reflect light and create “noise” that degrades anatomic detail on Pentacam-Scheimpflug imaging (Fig. 2.2).

A rare but potentially vision-threatening complication of a retrobulbar or peribulbar block performed prior to corneal transplant surgery is intraorbital hemorrhage. Expanding proptosis, pain, ophthalmoplegia, and decreased vision are the immediate signs of a retrobulbar hemorrhage. An orbit CT without contrast can be obtained to confirm and localize the hemorrhage, which appears as hyperattenuating collections in the acute setting (Fig. 2.3). An emergent lateral canthotomy and inferior cantholysis may be required to decompress the orbit and prevent an ischemic optic neuropathy or a central retinal artery occlusion.

One of the most dreaded complications of penetrating keratoplasty is expulsive suprachoroidal hemorrhage. This occurs due to spontaneous bleeding of a choroidal blood vessel after decompression of the globe and has an incidence of approximately 0.5–1.1 % of corneal transplantation cases. After phacoemulsification and foldable IOL implantation, UBM typically reveals shifting of the iris posteriorly, and deepening of the anterior chamber by 850 micrometers on average. Risk factors for suprachoroidal hemorrhage include older age, a history of glaucoma or myopia, hypertension, diabetes mellitus, generalized atherosclerosis, and Valsalva maneuver in the context of an open eye, such as sudden coughing during the surgery. Preventative measures include proper positioning of the patient, adequate anesthesia, best possible control of blood pressure, and reducing the intraocular pressure prior to surgery with medication, such as intravenous mannitol. Postoperatively, a noncontrast CT of the orbit can be obtained to demonstrate the extent of the hemorrhage, which can project beyond the margins of the globe through the corneal incision (Fig. 2.4). Otherwise, B-scan ultrasound is the imaging modality of choice for assessing the status of the retina and evaluating the potential for visual restoration.

Other early postoperative complications of penetrating keratoplasty include wound leakage and hypotony, persistent epithelial defect, infection, elevated intraocular pressure, and primary graft failure, that is, failure of the donor graft to achieve optical clarity. The most devastating complication is endophthalmitis (Fig. 2.5), and its incidence after penetrating keratoplasty ranges from 0.2 to 2.0 %. The source of infection is usually the patient’s periocular flora or a contaminated donor tissue. Risk factors for the development of endophthalmitis include concomitant vitrectomy, aphakia, history of previous surgery or inflammation, and corticosteroid use. Endophthalmitis is a clinical diagnosis and a view to the retina is usually precluded by the presence of intense vitritis. Thus, although B-scan ultrasound is not diagnostic of endophthalmitis, it can show the status of the retina and choroid prior to any surgical intervention. Orbital signs and symptoms (painful proptosis, ophthalmoplegia) suggest spread of the infection to the orbit and panophthalmitis. In such cases, orbital CT or MRI is indicated to assess the extent of orbital involvement and rule out the presence of an abscess. Treatment depends on the severity of the infection but generally includes removal of the graft, repeat penetrating keratoplasty, intravitreal injections of antibiotics, and, sometimes, pars plana vitrectomy. The main differential diagnosis for infectious endophthalmitis is toxic anterior segment syndrome. Toxic anterior segment syndrome is a sterile postoperative inflammatory reaction caused by a noninfectious substance that enters the anterior segment. The process typically begins 12–48 h after anterior segment surgery, is Gram stain and culture negative, and often responds to steroid treatment.

Corneal melt (keratolysis) consists of a breakdown of the cornea with expansion of the anterior chamber, which can occur as a complication of corneal transplant surgery. Inflammation at the limbus appears to be a causative factor for postoperative corneal melting. Damage to the limbal stem cells predisposes to invasion of conjunctival epithelium onto the corneal surface, which in turn leads to an irregular and unstable epithelium, with corneal ulceration. Since the cornea forms the anterior wall of the eye, loss of structural integrity leads to enlargement of the anterior chamber. This produces a characteristic appearance on CT, in which the distended anterior chamber is filled with material of a similar attenuation to the vitreous chamber (Fig. 2.6). In addition, there may be accompanying inflammatory or infectious changes that are apparent on imaging. Corneal melt can be treated using a full-thickness corneal button denuded of endothelium in conjunction with temporary tarsorrhaphy and systemic steroids.

Corneal transplant donors are routinely screened for the presence of various infectious diseases, such as HIV and hepatitis B and C. Nevertheless, there have been rare instances of prion transmission from corneal transplantation, resulting in Creutzfeldt–Jakob disease. Patients typically present with a rapidly progressive dementia. Brain MRI, particularly diffusion-weighted imaging, can be very helpful in the diagnosis of Creutzfeldt–Jakob disease, in which diffusion abnormalities involving the cortex and deep gray matter nuclei can be observed (Fig. 2.7).