Christopher C. Hull

The osteo-odonto-keratoprosthesis (OOKP).

The osteo-odonto-keratoprosthesis (OOKP), although described over 40 years ago, remains the keratoprosthesis of choice for end-stage corneal blindness not amenable to penetrating keratoplasty. It is particularly resilient to a hostile environment such as the dry keratinized eye resulting from severe Stevens-Johnson syndrome, ocular cicatricial pemphigoid, trachoma, and chemical injury. Its rigid optical cylinder gives excellent image resolution and quality. The desirable properties of the theoretical ideal keratoprosthesis is described. The indications, contraindications, and patient assessment (eye, tooth, buccal mucosa, psychology) for OOKP surgery are described. The surgical and anaesthetic techniques are described. Follow-up is life-long in order to detect and treat complications, which include oral, oculoplastic, glaucoma, vitreo-retinal complications and extrusion of the device. Resorption of the osteo-odonto-lamina is responsible for extrusion, and this is more pronounced in tooth allografts. Regular imaging with spiral-CT or electron beam tomography can help detect bone and dentine loss. The optical cylinder design is discussed. Preliminary work towards the development of a synthetic OOKP analogue is described. Finally, we describe how to set up an OOKP national referral center.

Optical coherence tomography may be used to predict visual acuity in patients with macular edema.

PURPOSE To determine whether the volume of retinal tissue passing between the inner and outer retina in macular edema could be used as an indicator of visual acuity. METHODS Diabetic and uveitic patients with cystoid macular edema (81 subjects, 129 eyes) were recruited. Best corrected logMAR visual acuity and spectral optical coherence tomography (OCT/SLO; OTI, Toronto, ONT, Canada) were performed in all patients. Coronal OCT scans obtained from a cross section of the retina between the plexiform layers were analyzed with a grid of five concentric radii (500, 1000, 1500, 2000, and 2500 μm centered on the fovea). The images were analyzed to determine the amount of retinal tissue present within each ring. A linear regression model was developed to determine the relationship between tissue integrity and logMAR visual acuity. RESULTS A linear relationship between tissue integrity and VA was demonstrated. The volume of retinal tissue between the plexiform layers in rings 1 and 2 (up to 1000 μm from the foveal center) predicted 80% of visual acuity. By contrast, central macular thickness within the central 1000 μm predicted only 14% of visual acuity. CONCLUSIONS This study showed that the cross-sectional area of retinal tissue between the plexiform layers in cystoid macular edema, as imaged by OCT, is the best indicator of visual function at baseline. Further prospective treatment trials are needed to investigate this parameter as a predictor of visual outcome after intervention.

Visual rehabilitation in end-stage inflammatory ocular surface disease with the osteo-odonto-keratoprosthesis: results from the UK

Aims: To report the long-term results of osteo-odonto-keratoprosthesis (OOKP) surgery in the visual rehabilitation of patients with corneal blindness from end-stage inflammatory ocular surface disease. Methods: A non-comparative retrospective case series of 36 consecutive patients treated at the National OOKP referral centre in Brighton, UK, between November 1996 and March 2006. Results: A total of 36 patients, with age ranging from 19 to 87 years (mean 51 (SD 19) years), were included in the analysis. The main preoperative diagnoses were Stevens–Johnson syndrome (n = 16, or 44%), severe thermal or chemical burns (n = 6, or 17%), and mucous membrane pemphigoid (n = 5, or 14%). The remainder of the cases comprised miscellaneous causes of dry eye (n = 9, or 25%), which included one each of graft versus host disease, ectodermal dysplasia, ionising radiation damage, cicatrising conjunctivitis from topical medication, trachoma, congenital trigeminal nerve hypoplasia, linear IgA disease, Sjögren syndrome and nutritional deficiency. Follow-up ranged from 6 months to 9 years (mean 3.9 (SD 2.5) years). Anatomical retention during the entirety of the follow-up period was seen in 72% of patients. The main factor resulting in anatomical failure was resorption of the OOKP lamina, which occurred in seven cases (or 19%). Predicted resorption in three cases resulted in successful planned exchange of the lamina, but two cases underwent emergency removal of the OOKP, and two cases developed endophthalmitis. Human leucocyte antigen-matched allografts suffered a higher rate of laminar resorption. Out of the entire cohort, 30 patients (or 83%) had some improvement in vision, 28 (or 78%) achieved vision of 6/60 or better, and 19 (or 53%) achieved 6/12 or better. The best-achieved vision was retained throughout the follow-up period in 61% of cases. Survival analysis suggested that the probability of retaining vision >6/60 5 years after surgery was 53 (10)%. Vision-threatening complications occurred in nine cases (or 25%) and included endophthalmitis, retinal detachment and glaucoma. De novo glaucoma occurred in six patients (or 24%) but was seen overall in 17 patients (or 47%), 10 of whom required surgical treatment. Conclusion: OOKP surgery can restore useful and lasting vision in patients suffering from end-stage ocular surface disease, for whom conventional corneal surgery is not possible. The main problems seen in this study were laminar resorption, particularly in allografts, and glaucoma.

Optical cylinder designs to increase the field of vision in the osteo-odonto-keratoprosthesis

Abstract Background: The single optical cylinders used in the osteo-odonto-keratoprosthesis (OOKP) are known to produce very small visual fields. Values of 40° are typically quoted. The purpose of this paper is to present designs for new optical cylinders that significantly increase the field of view and therefore improve the visual rehabilitation of patients having an OOKP. Methods: Computer ray-tracing techniques were used to design and analyse improved one- and two-piece optical cylinders made from polymethyl methacrylate. All designs were required to have a potential visual acuity of 6/6 before consideration was given to the visual field and optimising off-axis image quality. Aspheric surfaces were used where this significantly improved off-axis image quality. Results: Single optical cylinders, with increased posterior cylinder (intraocular) diameters, gave an increase in the theoretical visual field of 18% (from 76° to 90°) over current designs. Two-piece designs based on an inverted telephoto principle gave theoretical field angles over 120°. Aspheric surfaces were shown to improve the off-axis image quality while maintaining a potential visual acuity of at least 6/6. This may well increase the measu-red visual field by improving the retinal illuminance off-axis. Conclusions: Results demonstrate that it is possible to significantly increase the theoretical maximum visual field through OOKP optical cylinders. Such designs will improve the visual rehabilitation of patients undergoing this procedure.

Surface wettability and hydrophilicity of soft contact lens materials, before and after wear

Surface wettability and hydrophilicity of pHEMA soft contact lenses were investigated utilising adherent liquid/laser method (ALLM) and adherent liquid/balance method (ALBM). The measurements were carried out before and after periods of 15 min to 2 h contact lens wear. Following the lens removal, the wetting angle of the contact lens of the left eyes and hydrophilicity (maximum force) of the contact lens of the right eyes of the five subjects were immediately measured, respectively, without cleaning (one value for pre-lens wear and eight values for post-lens wear). The wettability of soft contact lenses significantly increased after 15 min of wearing and stabilised at a maximum level after 30 min in vivo. Contact lens hydrophilicity was found to decrease as the lens was worn. The reduction continued for up to 1.5 h of wearing, for male cases, and for the female cases, the reduction continued until the end of the experiment.

Image quality in polypseudophakia for extremely short eyes

AIM To evaluate the image quality produced by polypseudophakia used for strongly hypermetropic and nanophthalmic eyes. METHODS Primary aberration theory and ray tracing analysis were used to calculate the optimum lens shapes and power distribution between the two intraocular lenses for two example eyes: one a strongly hypermetropic eye, the other a nanophthalmic eye. Spherical aberration and oblique astigmatism were considered. Modulation transfer function (MTF) curves were computed using commercial optical design software (Sigma 2100, Kidger Optics Ltd) to assess axial image quality, and the sagittal and tangential image surfaces were computed to study image quality across the field. RESULTS A significant improvement in the axial MTF was found for the eyes with double implants. However, results indicate that this may be realised as a better contrast sensitivity in the low to mid spatial frequency range rather than as a better Snellen acuity. The optimum lens shapes for minimum spherical aberration (best axial image quality) were approximately convex-plano for both lenses with the convex surface facing the cornea. Conversely, the optimum lens shapes for zero oblique astigmatism were strongly meniscus with the anterior surface concave. Correction of oblique astigmatism was only achieved with a loss in axial performance. CONCLUSIONS Optimum estimated visual acuity exceeds 6/5 in both the hypermetropic and the nanophthalmic eyes studied (pupil size of 4 mm) with polypseudophakic correction. These results can be attained using convex-plano or biconvex lenses with the most convex surface facing the cornea. If the posterior surface of the posterior intraocular lens is convex, as is commonly used to help prevent migration of lens epithelial cells causing posterior capsular opacification (PCO), then it is still possible to achieve 6/4.5 in the hypermetropic eye and 6/5.3 in the nanophthalmic eye provided the anterior intraocular lens has an approximately convex-plano shape with the convex surface anterior. It was therefore concluded that consideration of optical image quality does not demand that additional intraocular lens shapes need to be manufactured for polypseudophakic correction of extremely short eyes and that implanting the posterior intraocular lens in the conventional orientation to help prevent PCO does not necessarily limit estimated visual acuity.

Primary polypseudophakia for cataract surgery in hypermetropic eyes: refractive results and long term stability of the implants within the capsular bag

AIM To determine the long term visual and refractive results, and stability and complications of primary polypseudophakia using poly(methylmethacrylate) (PMMA) intraocular lenses (IOLs) for cataract surgery in hypermetropic eyes. METHODS Prospective study of 15 short or hypermetropic eyes undergoing phacoemulsification with primary polypseudophakia with two PMMA IOLs implanted within the capsular bag. RESULTS The spherical equivalent was reduced from a mean +4.87 (SD 3.00) dioptres (D) to −0.12 (1.40 D), and the deviation from the intended refraction was +0.005 (1.30) D, 23.6 (12.36) months post-implantation. The deviation from intended refraction was not statistically significant (p = 0.989; paired t test). Postoperative best corrected visual acuity (BCVA) was 6/12 or better in all eyes without macular or optic nerve co-morbidity. Interlenticular opacification (ILO) in the form of peripheral Elschnig pearls was seen in four (26.67%) eyes. A new type of ILO in the form of usually pigmented deposits in the central interface developed in five (33.33%) eyes and resulted in the appearance of Newtons rings in three. None of the eyes with ILO had any loss of BCVA or hyperopic shift. Six (40%) eyes were within 1 D from the intended refraction and 14 (93.33%) within 2 D. There was no statistically significant difference in the accuracy of the two intraocular lens calculation formulas used (SRK II and SRK/T). CONCLUSION Peripheral Elschnig pearl-type ILO can occur as a late complication of primary in the bag implantation of two PMMA IOLs. A new type of ILO is described. Both types of ILO have not to date resulted in deterioration of visual acuity in our cohort. Use of appropriate biometry techniques and IOL calculation formulas may yield more accurate refractive results.

Stringy AdS3 from the Worldsheet

A bstractWe investigate the behaviour of the bosonic string on AdS3 with H-flux at stringy scales, looking in particular for a ‘tensionless’ limit in which there are massless higher spin gauge fields. We do this by revisiting the physical spectrum of the sl2,ℝk

Superstrings on AdS 3 at k = 1

\mathfrak{s}\mathfrak{l}{\left(2,\ \mathbb{R}\right)}_k