The application of stereotactic navigation surgery to orbital decompression for thyroid-associated orbitopathy.

OBJECTIVES: To describe the application of stereotactic guidance, its preoperative workup, and limitations, if any, during orbital decompression surgery of the lateral orbital wall for thyroid-associated orbitopathy (TAO). METHODS: Case-controlled series of seven patients who underwent stereotactic-guided surgical navigation during external approach balanced orbital decompression with maximal debulking of the lateral wall. RESULTS: A progressive increase in debulking of the greater wing of sphenoid and exposure of dura was noted in the series. The average proptosis reduction was 9.36 mm. No complications were encountered during any of the cases, nor was there any new onset postoperative diplopia. In all cases, exposure of dura was planned and did not present as a surprise. Stereotactic setup added 10 min to preparation time. CONCLUSIONS: Stereotactic guidance improves anatomic localization and precision during orbital decompression, increasing confidence, and reducing surgical stress. The ability to accurately determine the maximal limits of decompression real time, while confirming depth of bone removal, offers the possibility of reduced risk of iatrogenic injury. Stereotactic navigation allows for improved intraoperative localization that may improve the ability to maximally decompress the lateral wall, including the zygoma, orbital roof, and trigone, and extending towards the optic nerve with exposure of dura through smaller incisions.

Medpor porous polyethylene implants in orbital blowout fracture repair.

PURPOSE: Various materials are used in orbital blowout fracture repair. We describe a series of patients with orbital blowout fractures that were repaired using porous polyethylene (Medpor) sheets. METHODS: A non-comparative interventional case series is described of 30 blowout fractures of 30 patients aged 7-60 years (median 29 years) who underwent orbital blowout fracture repair with Medpor sheets. The mean follow-up was 19.1 months (minimum 5 months). The indication for surgery in 6 cases was non-resolving diplopia. The remaining 24 cases had surgery for enophthalmos. Ten cases underwent primary or secondary hydroxyapatite orbital implantation at the same time as orbital floor blowout fracture repair. Data were collected on postoperative motility and diplopia, enophthalmos, cosmesis, complications and re-operations. RESULTS: In no case was diplopia worsened by blowout fracture repair. Where surgery was performed for the correction of enophthalmos, late surgery did not compromise the surgical results. There were no intraoperative complications. The one major complication was a case of recurrent implant infections leading to implant removal. There were 3 minor postoperative complications: 2 cases of postoperative infraorbital anaesthesia and one case of a palpable titanium screw. Re-operations were performed for pre-existent diplopia, lid laxity, socket abnormalities and mid-facial deformities. None of these arose from the blowout fracture repair. CONCLUSIONS: The study suggests that in orbital blowout fracture repair Medpor implants are safe and effective with few complications. Late surgery for enophthalmos is technically more difficult but is not associated with poorer functional or cosmetic results.

Silicone intraocular lens compression and double lens implants in diseased eyes.

PURPOSE: To assess the outcomes of double lens implants in hyperoptic eyes with associated pathology. METHOD: Double lens implants were used in 4 eyes of 4 patients each with a different ophthalmic or neuro-ophthalmic disease. Biometry was performed in the standard contact fashion and lens power formulae used included SRK/T, Holladay and Hoffer Q. RESULTS: Average spherical equivalent refraction improved from +6.875 D to +0.38 D. Absolute average prediction error was greatest for SRK/T (2.65 D) and least for Holladay (1.73 D). Refractive suprises were influenced by the underlying disease process. One patient showed central lens compression. CONCLUSION: Underlying disease can produce biometry errors. Structural ophthalmic or neurological disease is not a contraindication to the use of double lens implants. Double lens implants are useful to correct refractive error in the presence of underlying disease.

The glabellar flap dissected.

The glabellar flap is effective in the reconstruction of defects within the medial canthal region. The unique contour of the medial canthal region presents a challenge in the surgical planning of the glabellar flap, which is only briefly described in texts. We describe its step by step construction, including the indications and precautions. We also include a section on variations in design for improved closure. With careful planning, the glabellar flap provides excellent cosmetic results.

Influence of corneal shape on limbal light focusing.

PURPOSE: Light incident at the temporal cornea is focused by the peripheral anterior eye to the nasal limbus, the usual site of pterygium formation. Parameters that may contribute to observed individual variations in the degree of limbal light focusing were assessed. METHODS: Computer-assisted optical ray tracing techniques were applied to a human anterior segment model. The angle of incident light (theta, 95 degrees to 108 degrees posterior to the sagittal plane), corneal central radius of curvature (ro, 7.2 to 8.4 mm), and shape factor (p) were varied, and the effect on distal limbal intensity (I) was calculated. RESULTS: The magnitude of intensity peaks (Ipeak) is dependent on theta and ro. Steeper corneas have higher intensity peaks (Ipeak approximately 21.5X at ro = 7.2 mm, p = 0.75), and flatter corneas have lower intensity peaks (Ipeak approximately 8X at ro = 8.4 mm, p = 0.75) (cf Ipeak approximately 14X for a standard cornea, ro = 7.8 mm, p = 0.75). Anteroposterior location of intensity peaks is dependent on theta and ro. Steeper corneas have intensity peaks situated more anteriorly, whereas flatter corneas have more posteriorly placed peaks. Distal light distribution profiles demonstrate that intensity peaks are not always centrally located. At lower angles of incidence (theta = 100 degrees, ro = 7.8 mm, p = 0.75), peak intensity is located approximately 1 mm above and below the horizontal plane. The overall distribution (envelope) of light at the distal limbus is apparently independent of corneal shape. CONCLUSIONS: Differences in corneal topography can account for the clinical observation of individual variation in the degree of limbal light focusing. Whether individuals with corneas capable of developing intense limbal foci may be more predisposed to developing pterygium requires further study.