Do scleral flap dimensions influence reliability of intraocular pressure control in experimental trabeculectomy?

AIM: To compare the effect on intraocular pressure (IOP) of large vs small scleral flap size during trabeculectomy using adjustable sutures. METHODS: Trabeculectomy operations were performed on nine donor human eyes connected to a constant flow infusion with real-time IOP monitoring. Large scleral flaps (4 x 4 mm, 16 mm(2), n=12) or small scleral flaps (3 x 2 mm, 6 mm(2), n=9) were constructed over 0.76 mm(2) sclerostomies. For each procedure, equilibrium IOP was measured following tight closure with two four-throw adjustable 10-0 nylon sutures. RESULTS: Five scleral flaps were thin or poorly constructed; four of these were in the initial seven procedures, implying learning effect. These had a mean absolute IOP of 7.6 mmHg (range 2.7-12.4 mmHg) and mean relative IOP of 28.3% of baseline (range 10-45.8%) after closure. In the remaining 16 good quality procedures, mean IOP was 1.3 mmHg (range 0-3.4 mmHg) after sclerostomy, confirming minimal outflow resistance before closure. Following flap closure mean IOP was 20 mmHg (SD 4.4, range 15.5-29.3 mmHg) for large (n=8), and 18.7 mmHg (SD 3.6, 15.9-25.8 mmHg) for small (n=8) flaps (unpaired t-test, P=0.26). Mean IOP (% baseline) was 71.6% (SD 8.4, range 60.6-86.6%) and 66% (SD=12.7, 46.8-86.6%) for large and small flap groups, respectively (unpaired t-test, P=0.2). CONCLUSIONS: Well-constructed scleral flaps of both sizes were able to support an average IOP at least two-thirds of baseline, and both had similar absolute IOP levels. Errors in flap construction resulted in loss of IOP control. Smaller flap size does not appear to compromise control of early postoperative IOP using adjustable sutures.

In vivo fibreoptic confocal imaging (FOCI) of the human ocular surface.

Recent developments in the miniaturization of confocal imaging technology have resulted in the development of a hand-held confocal microscope probe. There are many structures of interest in the human eye that are within reach of a fluorescence-mode confocal microscope; this study assessed the feasibility of in vivo human ocular imaging. Safety analysis was undertaken to ensure that the laser light applied to the ocular surface structures constituted no threat to patient safety. A fibreoptic confocal imaging (FOCI) probe using an illumination wavelength of 488 nm was applied to the ocular surface of four volunteers after topical administration of sodium fluorescein. Stabilization of the probe on the ocular surface was difficult, but movement artefacts could be minimized to a satisfactory level in most subjects by a variety of procedures. High-quality images of conjunctival epithelial and goblet cells, lamina propria structures, accessory lacrimal glands, lacrimal ducts and superficial sclera were obtained. Lateral resolution was 1-1.5 microm and axial resolution was approximately 30 microm; individual erythrocytes could be seen in conjunctival vessels. The rete ridges and intervening epithelial components, including the probable location of corneal limbal stem cells, could be viewed, although it was not possible to distinguish cell subgroups. The study showed that fluorescence-mode imaging of the ocular surface is a viable and promising tool for assessment of diseases and processes involving superficial ocular structures. Refinement of equipment and techniques, particularly probe stabilization, is necessary to realize fully the potential of FOCI for ocular use.

A comparative study of proxymetacaine-fluorescein and lignocaine-fluorescein use during applanation tonometry.

AIMS: To evaluate the relative merits of proxymetacaine-fluorescein (PROX-FLU) and lignocaine-fluorescein (LIG-FLU) when used to perform applanation tonometry. METHODS: This prospective, masked, double blind study assessed several aspects of the tonometry process-the duration of the stinging sensation and degree of discomfort, the extent of reflex lacrimation induced, the need for subsequent tear film manipulation to ensure an accurate tonometry reading, and total time to complete tonometry-for each preparation. RESULTS: PROX-FLU caused significantly less discomfort and reflex lacrimation than LIG-FLU and accurate tonometry was more rapidly completed when it was used. PROX-FLU was preferred by 98% of the study patients. CONCLUSION: PROX-FLU is a well tolerated and useful alternative to the more widely used LIG-FLU mixture.

Misalignment of flexible iris hook retractors for small pupil cataract surgery: effects on pupil circumference.

A graphical method was used to assess the effect on pupil shape and circumference of various flexible iris hook malpositions. Results confirmed that all hook malpositions necessitate increased pupil stretching to create space to perform a capsulorhexis of a given diameter. This method also confirmed that the addition of a fifth hook to create a pentagonal pupil reduces pupil stretching by 17%. A simple method of marking the limbus before hook insertion to ensure equidistant hook separation and thus minimize pupil stretching is suggested.