Venkata Avadhanam

Keratoprostheses for corneal blindness: a review of contemporary devices

According to the World Health Organization, globally 4.9 million are blind due to corneal pathology. Corneal transplantation is successful and curative of the blindness for a majority of these cases. However, it is less successful in a number of diseases that produce corneal neovascularization, dry ocular surface and recurrent inflammation, or infections. A keratoprosthesis or KPro is the only alternative to restore vision when corneal graft is a doomed failure. Although a number of KPros have been proposed, only two devices, Boston type-1 KPro and osteo-odonto-KPro, have came to the fore. The former is totally synthetic and the latter is semi-biological in constitution. These two KPros have different surgical techniques and indications. Keratoprosthetic surgery is complex and should only be undertaken in specialized centers, where expertise, multidisciplinary teams, and resources are available. In this article, we briefly discuss some of the prominent historical KPros and contemporary devices.

A brief review of Boston type-1 and osteo-odonto keratoprostheses

Globally there are ≈4.9 million bilaterally corneal blind and 23 million unilaterally corneal blind. Majority of this blindness exists in the developing countries, where resources for corneal banking and transplant surgery are less than adequate. Survival of corneal grafts gradually declines over the long term. Corneal transplantation has poor prognosis in vascularised corneal beds, ocular surface disease and viral keratitis. Keratoprosthesis (KPro) remains as a final option for end-stage ocular surface disease, multiple corneal transplant failures and high-risk corneal grafts. Boston type-1 KPro and osteo-odonto-keratoprosthesis are the two devices proven useful in recent years. Choice of a keratoprosthetic device is patient specific based on the underlying diagnosis, ocular morbidity and patient suitability. KPro surgery demands a high level of clinical and surgical expertise, lifelong commitment and extensive resources. Improvements in techniques and biomaterials may in the future provide retainable KPros that do not need regular follow-up of patients, have low complications but high retention rates and may be produced at a low cost on a mass scale to be available as ‘off the shelf’ devices. Because KPros have the potential to effectively address the burden of surgically treatable corneal blindness and may also eliminate the problems of corneal transplantation, more research is required to develop KPros as substitutes for corneal transplantation even in low-risk cases. In those countries where corneal blindness is a major liability, we need a two pronged approach: one to develop eye donation, eye banking and corneal transplantation and the second to establish centres for keratoprostheses, which are affordable and technically not challenging, in a population where default on follow-up visits are high. Until the latter is achieved, KPros should be viewed as a temporary means for visual restoration and be offered in national and supraregional specialised centres only.

Mitomycin-C for mucous membrane overgrowth in OOKP eyes.

Purpose: The aim of this study was to report the use of mitomycin-C (MMC) in the treatment of mucous membrane overgrowth in eyes with osteo-odonto-keratoprosthesis (OOKP). Methods: Records of 4 cases with mucous membrane overgrowth after stage 2 OOKP surgery were reviewed. Results: All the patients had undergone a mucous membrane trimming procedure followed by MMC application. None of the patients had any episode of recurrence of the mucous membrane overgrowth after a single application of MMC in the follow-up period that ranged from 1 to 11 years. Conclusions: MMC can successfully arrest mucous membrane overgrowth in OOKP-implanted eyes including refractory cases.

Suturing techniques and postoperative management in penetrating keratoplasty in the United Kingdom

Aims To report on the suturing techniques and aspects of postoperative management in penetrating keratoplasty in the United Kingdom. Methods A postal questionnaire was sent to 137 ophthalmic consultants identified from a Royal College of Ophthalmology database as having a special interest in anterior segment surgery. The questionnaire surveyed surgeon preferences for surgical and suturing technique for penetrating keratoplasty surgery, and the postoperative care of corneal grafts. Results In all, 68% of questionnaires were completed and returned: 73% of respondents used a Flieringa ring or equivalent, 94% routinely used cardinal sutures, with 50.5% removing them at the end of the procedure. The most common suturing technique for routine penetrating keratoplasty was a single continuous suture (35%). In these cases, a 10/0 nylon suture was used by 89%. Sixty-six percent changed their technique in high-risk cases, 52% used a 3-1-1 knot, and 75% made a distinction between a reef and granny knot, with 76% using a reef. Thirty percent buried the knots within the donor material, and 29% within the host tissue. Twenty-five percent had no routine time for graft suture removal, but 41% removed them between 1 and 2 years post-surgery. After suture removal, 98% used steroids and 88% used topical antibiotics. Thirty-four percent stopped topical steroids before suture removal, with 38% stopping topical steroids more than 3 months prior to suture removal. Conclusion This survey demonstrates that there is considerable variation in suturing techniques and postoperative care for penetrating keratoplasty. These significant variations in practice need to be considered when interpreting outcomes and research.

Comparison of 640-Slice Multidetector Computed Tomography Versus 32-Slice MDCT for Imaging of the Osteo-odonto-keratoprosthesis Lamina.

Purpose: To investigate the efficacy of 640-slice multidetector computed tomography (MDCT) for detecting osteo-odonto laminar resorption in the osteo-odonto-keratoprosthesis (OOKP) compared with the current standard 32-slice MDCT. Methods: Explanted OOKP laminae and bone–dentine fragments were scanned using 640-slice MDCT (Aquilion ONE; Toshiba) and 32-slice MDCT (LightSpeed Pro32; GE Healthcare). Pertinent comparisons including image quality, radiation dose, and scanning parameters were made. Results: Benefits of 640-slice MDCT over 32-slice MDCT were shown. Key comparisons of 640-slice MDCT versus 32-slice MDCT included the following: percentage difference and correlation coefficient between radiological and anatomical measurements, 1.35% versus 3.67% and 0.9961 versus 0.9882, respectively; dose–length product, 63.50 versus 70.26; rotation time, 0.175 seconds versus 1.000 seconds; and detector coverage width, 16 cm versus 2 cm. Conclusions: Resorption of the osteo-odonto lamina after OOKP surgery can result in potentially sight-threatening complications, hence it warrants regular monitoring and timely intervention. MDCT remains the gold standard for radiological assessment of laminar resorption, which facilitates detection of subtle laminar changes earlier than the onset of clinical signs, thus indicating when preemptive measures can be taken. The 640-slice MDCT exhibits several advantages over traditional 32-slice MDCT. However, such benefits may not offset cost implications, except in rare cases, such as in young patients who might undergo years of radiation exposure.

Keratoprostheses: are we there yet?

Since the dawn of the 18th century, efforts to develop an ideal keratoprosthesis (KPro) have not yielded the dream KPro yet, but the journey to such an invention has given us a few notable devices and valuable experience with a number of biomaterials. The invention of a KPro started with a piece of silver-rimmed glass proposed by Pellier de Quengsy.1 We now have the latest iteration of Boston Type 1 KPro with a porous titanium back plate.2 Although the Pintucci KPro (Dacron mesh skirt and PMMA optic) and the AlphaCor (hydrogel matrix) were in clinical use for a good length of time, they failed to retain over the long term.1 We learnt that bio-integration is essential for the skirt and bio-inertness for the optic. Polymethyl methacrylate (PMMA) has largely solved the search for a stable and durable optic though the search for an ideal skirt material is still ethereal. As we speak, the Boston type-1 KPro and the osteo-odonto-keratoprosthesis (OOKP) have emerged as the most sustainable devices. The Boston KPro …

Managing laminar resorption in osteo-odonto-keratoprosthesis.

OOTH IN AN EYE, RATHER AN OLD ART IN THE ERA OF newscience,knownasosteo-odonto-keratoprosthesis (OOKP), is astoundingly the most durable keratoprosthesis (KPro) to date. The original inception of using tooth as a KPro skirt material was by Strampelli in the 1960s. A single rooted tooth was transverse-sectioned and itspulpcavityenlargedtoreceiveapolymethylmethacrylate (PMMA) optical cylinder. Later, the tooth-acrylic complex was implanted into the eye. 1 Falcinelli modified this technique and pioneered the present-day OOKP technique known as ‘‘modified OOKP’’ (MOOKP). Modifications included fashioning of the lamina through the sagittal section of the tooth root, use of buccal mucosa as opposed to labial mucosa, preservation of periosteum, joining of 2 small laminae to create 1 of adequate size, cryoextraction of lens, vitrectomy, a larger biconvex optical cylinder, and a posterior draining tube. 2 Undoubtedly moving from transverse to sagittal sectioning of the tooth and other modifications have improved the success of this surgery. Yet, resorption of the lamina remains a concern. In this issue, Iyer and associates reported MOOKP surgical outcomeon85eyes using toothautografts. 3 Ofthese,44 patients suffered from Stevens-Johnson syndrome (SJS) and 37 sustained chemical injuries. The rate of laminar resorption noted in this study was 23% and was first detected at an average of 37 months in the former group and at 43 months in the latter. In our study the cumulative probability of retaining an OOKP lamina was 81% over 5 years. 4 Iyer and associates 3 made an interesting observation that laminae positioned having the thin portions facing superiorly had developed resorption on that side first. Contrarily, Stoiber and associates had implanted laminas with the thin side facing inferiorly and found resorption developing inferiorly first. 5 This emphasizes that thinner portions and thin laminae are at risk of resorption. The recommended minimum thickness for OOKP lamina is 3 mm. 6 Iyer and asso