Optimising biometry for best outcomes in cataract surgery.

Biometry has become one of the most important steps in modern cataract surgery and, according to the Royal College of Ophthalmologists Cataract Surgery Guidelines, what matters most is achieving excellent results. This paper is aimed at the NHS cataract surgeon and intends to be a critical review of the recent literature on biometry for cataract surgery, summarising the evidence for current best practice standards and available practical strategies for improving outcomes for patients. With modern optical biometry for the majority of patients, informed formula choice and intraocular lens (IOL) constant optimisation outcomes of more than 90% within ± 1 D and more than 60% within ± 0.5 D of target are achievable. There are a number of strategies available to surgeons wishing to exceed these outcomes, the most promising of which are the use of strict-tolerance IOLs and second eye prediction refinement.

Diagnostic cellular yield is superior with full pars plana vitrectomy compared with core vitreous biopsy.

PURPOSE: Vitreous biopsy for the cytological assessment of suspected intraocular lymphoma and vitritis of uncertain aetiology is a standard investigation. The types of specimens generated and the diagnostic rate are variable within and between centres. There are many reasons for this but one observation that has not been considered previously is the differential distribution of cells in the vitreous gel. To test this possibility, five consecutive patients with suspected vitreous involvement by lymphoma or vitritis of uncertain aetiology underwent a core vitreous biopsy immediately before a planned full pars plana vitrectomy (PPV) and the cellularity of the two sampling techniques compared. METHODS: A prospective study of five consecutive patients requiring vitreous sampling to secure a firm diagnosis. For each of five patients, the core vitreous biopsy specimen was received in a universal tube and the PPV specimen was received in a vitreous cassette. Fluid (0.25 ml) was removed from both specimens, centrifuged and haematoxylin and eosin (H&E) stained slides prepared per sampling method. The slides were examined with a light microscope, the most cellular field selected and the number of cells per mm(2) counted and compared between sampling techniques. RESULTS: PPV specimen's, revealed a cellularity range that was 7.4 to 78 × (average 31 ×) greater than a core vitreous biopsy. In the two cases of a final diagnosis of intraocular lymphoma, the vitreous core biopsy was non-diagnostic. Furthermore, the PPV specimen generated additional cellular material for numerous ancillary investigations to permit a secure diagnosis. CONCLUSIONS: The results of this differential vitreous sampling study has strengthened our anecdotal slit lamp clinical observations that inflammatory cells and lymphoma cells are concentrated more in the cortical vitreous. Therefore, vitreous cells have less chance to be sampled if a single core vitreous biopsy is performed. Indeed, the two cases of confirmed lymphoma generated a non-diagnostic core vitreous biopsy. In our centre, this study has lead to PPV being performed as a gold standard on all patients with suspected intraocular lymphoma or vitritis of uncertain aetiology.

Predictive clinical features and outcomes of vitrectomy for proliferative diabetic retinopathy.

OBJECTIVE: To study the preoperative characteristics, complications and outcomes of vitrectomy for proliferative diabetic retinopathy and to identify any factors that may predict visual outcome. METHODS: Prospective study of 174 consecutive vitrectomies in 148 patients, with a minimum follow-up of 4 months. RESULTS: 41 (27.7%) patients had a vision of <6/60 in their better eye at presentation. Posterior retinal breaks occurred in 47 (27.0%) eyes. Postoperative complications included vitreous cavity haemorrhage in 37 (22.0%) eyes, retinal detachment in five eyes (3.0%), and rubeotic glaucoma in five eyes (3.0%). 124 (74.7%) eyes improved by at least 0.3 LogMAR units, and 15 (9.0%) worsened by at least 0.3 LogMAR units. 119 (71.7%) eyes had a visual acuity of 6/60 or better, and 27 (16.3%) were counting fingers or worse. Only 16 (11.1%) patients had a vision of <6/60 in both eyes at latest follow-up. Preoperative vision in both the operated eye and the contralateral eye, macular detachment, and long-acting intraocular tamponade were independent predictors of poor postoperative vision, but this model accounted for only a small proportion of the observed variation in outcomes. CONCLUSIONS: Major complications are rare after vitrectomy for proliferative diabetic retinopathy, and >70% of eyes will regain vision of 6/60 or better. Visual outcomes remain unpredictable.

Vitreoretinal surgery after childhood ocular trauma.

AIM: In adults modern vitreoretinal surgery allows many traumatised eyes to be salvaged. However, one third of serious eye injuries occur in the paediatric age group and trauma is a leading cause of monocular blindness in childhood. This study aims to report the indications, complications and outcomes for vitreoretinal surgical intervention after childhood ocular trauma. METHODS: Retrospective case note review of 61 children (age 16 years or less) undergoing vitreoretinal surgical procedures following ocular trauma at a tertiary referral centre. RESULTS: Twenty-eight children (45.9%) had open globe injuries (OGI) and 33 closed globe injuries (CGI, 54.1%). The mean age of children with OGI was 9.5 years and with CGI 12.3 years (P=0.0068). Forty-seven children had traumatic retinal detachments (77.1%), which in 17 cases were treated with conventional scleral buckling surgery and in 30 by vitrectomy. Retinal re-attachment was achieved after one procedure in 70.6% with scleral buckling and 46.7% with vitrectomy. Fourteen children (22.9%) had attached retinas but required vitrectomy for other reasons. After a mean follow-up of 19.6 months, the median visual acuity (VA) of the children improved from counting fingers at presentation to 6/36 at final review (P=0.0031). Traumatic retinal detachment requiring vitrectomy was associated with poor visual outcome (P=0.0003). CONCLUSION: Vitreoretinal intervention resulted in an improvement in vision in 32 children (57.1%) and stabilised 11 at their presenting acuity (19.6%). Two thirds of the children attained a final VA of 6/60 or better. Proliferative vitreoretinopathy was the cause of redetachment in 68.2% of cases and was significantly associated with a poor outcome (P<0.0001).

Clinical features and surgical management of retinal detachment secondary to round retinal holes.

AIMS: The majority of rhegmatogenous retinal detachments result from pathological posterior vitreous detachment (PVD) and secondary horseshoe or giant retinal tears. Retinal detachment without PVD is usually associated with either retinal dialysis or round retinal holes. This study characterises the features, surgical outcome, and incidence of bilateral involvement of detachment associated with round retinal holes. METHODS: In all, 110 retinal detachments from 96 consecutive patients with retinal detachment secondary to round retinal holes were studied. Analysis of patient age, sex, refraction, preoperative visual acuity, presented symptoms, position and extent of detachment, number and distribution of holes present, posterior hyaloid membrane status, surgical management, outcome of surgery, and postoperative visual acuity were studied. RESULTS: The mean age for patients was 34 years with a marked female preponderance (64%) and myopia (83%). The posterior hyaloid membrane remained attached in 95 eyes (86%). In all, 45% patients had bilateral pathology, of which 33% had 'mirror image' distribution. Detachments were predominantly shallow (93%) and slow in progression (17%). A total of 100 detachments were repaired with cryotherapy and scleral buckling, eight with cryotherapy alone, and one with laser retinopexy. In all, 99% detachments were successfully reattached with a single procedure. The mean follow-up period was 2 years. There were no instances of redetachment. CONCLUSIONS: Round hole detachments are slowly evolving detachments with attached vitreous gel in young, predominantly female myopes. Examination of the fellow eye should be mandatory as there is a high incidence of bilateral pathology. Scleral buckling procedures remained highly effective in this selected group of patients.

A prospective study of the effect of a unilateral macular hole on sensory and motor binocular function and recovery following successful surgery.

AIMS: To examine the effect of a unilateral full thickness macular hole on sensory and motor binocular function and to study recovery after successful surgical closure. METHODS: Twenty eight consecutive patients undergoing surgery for a unilateral macular hole underwent orthoptic examination, including measurements of Titmus and TNO stereoacuity and motor fusion range before surgery. Twenty three patients had successful anatomical closure. Fifteen of these patients, who had both improved acuity in the operated eye following surgery and were available for further testing, underwent repeat orthoptic assessment 2-7 months after surgery. RESULTS: In all patients stereoacuity was reduced before surgery, but few patients were subjectively aware of a deficit of depth perception affecting their everyday life. In those patients with improved Snellen acuity after surgery, stereoacuity measured by the Titmus stereotest also improved significantly, but not that measured by the TNO test. Two patients were aware of a subjective improvement in depth perception. Motor fusion was markedly reduced compared to normal before surgery, with only limited recovery after surgery. CONCLUSION: A unilateral macular hole notably reduced both stereoacuity and motor fusion. Successful closure improved the deficit in stereoacuity associated with the hole when measured by a stereotest using contoured stimuli. The majority of patients were not subjectively aware of the deficit in stereoacuity or its improvement following surgery.

Clinical, histological and ultrastructural studies of the posterior hyaloid membrane.

AIMS: To investigate the histological, immunohistochemical and ultrastructural features of the posterior hyaloid membrane (PHM) in its naturally separated state in patients without previous surgery and slit-lamp documentation of antemortem posterior vitreous detachment (PVD). METHODS: A prospective study was commenced in 1992 to recruit patients with physiological PVD from an unselected group of general medical inpatients and ascertain the prevalence of PVD. Postmortem specimens subsequently available were studied to analyse the clinicopathological correlation and processed using standard techniques for histology, immunohistochemistry and electron microscopy. RESULTS: Eighty-five patients were examined with ages ranging from 68 to 98 yrs (mean 83.4 yrs). The posterior hyaloid membrane had clearly separated from the retina in 66% of eyes. Twenty-nine eyes from 15 patients were subsequently studied pathologically. The posterior hyaloid membrane exhibited a uniform cellular component, most densely populated around the Weiss' ring. The cells were characterised by oval or round nuclei, indistinct cytoplasm and were only seen within, or abutting, the weakly eosinophilic posterior hyaloid membrane. The posterior aspect of the posterior hyaloid membrane showed a convoluted appearance staining lightly with haematoxylin and eosin. The detached posterior hyaloid membrane exhibited focal positivity for GFAP and type IV collagen. Electron microscopy demonstrates both fibres and basement membrane associated with the cellular component including hemi-desmosome attachment plaques between the cells and basement membrane. CONCLUSIONS: This study illustrates some of the structural differences between the posterior hyaloid membrane and the cortical vitreous gel it envelopes and demonstrates the presence of cells intimately associated with the posterior hyaloid membrane in its naturally separated state. We propose the cellular population integral to the PHM to be designated as laminocytes in order to emphasise their type IV collagen/basement membrane association and planar array within the membrane which separates at posterior vitreous detachment.

Silicone plate-haptic lens injection without prior incision enlargement.

Injection devices are routinely used to implant silicone plate-haptic intraocular lenses (IOLs). The injector cannula is normally introduced directly into the anterior chamber prior to injection, either after deliberate wound enlargement or by forcible entry with significant wound stretching. We present a technique for injecting the lens through the wound in which apposition is maintained between the injector tip and the unenlarged phaco incision. In 25 eyes, the wound enlarged after IOL implantation by a mean of 0.13 mm +/- 0.05 (SD), representing a 4.0% increase in width. We have found this modified technique to be safe, effective, and reproducible.

The Kropp-onlay procedure (Pippi Salle procedure): a simplification of the technique of urethral lengthening. Preliminary results in eight patients.

OBJECTIVE: To lengthen the urethra to increase bladder outlet resistance in adolescent girls with a neurogenic bladder. PATIENTS AND METHODS: During a 2-year period (1992-94), eight girls (mean age 13.5 years, range 9-19) underwent a Kropp-onlay urethral lengthening associated, for six of them, with a bladder augmentation. Seven of the eight patients patients were spina bifida and confined to a wheelchair. One patient had had a previous transverse myelitis. A Benchekroun hydraulic value (in three cases) and a Malone procedure (in two cases) were performed at the same stage. The technique of Kropp-onlay urethral lengthening, which creates a flap value mechanism which leaks when the bladder is too full, is described and illustrated. RESULTS: Seven of eight patients were dry during the day and four were occasionally damp during the second part of the night. One could not be dry for more than 2 h during the day but had a very hyperactive detrusor. She developed two bladder stones which required an open vesicotomy. One developed a urethral fistula requiring a second Kropp-onlay procedure and became dry afterwards. Two patients, who did not undergo a bladder augmentation, needed oxybutinin therapy to obtain a satisfactory result. Post-operative urodynamic measurements are discussed. CONCLUSION: The Knopp-onlay urethral lengthening is easier to perform than the original Kropp procedure. The preliminary results are similar to those of alternative techniques (e.g. urethral suspension) but long-term reliability of this technique remains unknown.

Impact and shear resistance of turf grass racing surfaces for Thoroughbreds.

The 2 dominant processes involved in the horse hoof-to-racing surface interaction are the shock loading of the horse's leg upon impact with the racing surface and rotation of the horse's hoof into the racing surface. These processes were measured as impact resistance (ie, the peak deceleration of a moving body upon impact with the test surface) and as resistance to shear. The objective of the present study was to measure physically (under a variety of conditions) those soil and turf factors related to the 2 processes. It was concluded that thatch accumulation and mowing height of the turf did not have a significant (P less than 0.05) effect on racing surface hardness (therefore, turf management should optimize turf growth and recovery), that turf roots were responsible for an increase in impact resistance and in resistance to shear, that control over soil moisture through irrigation and drainage allowed modification of racing surface hardness, and that soil materials tend to have lower impact resistance (ie, lower shock loading of the horse's leg) and higher resistance to shear (ie, greater resistance to hoof rotation) than do sand materials.

Differential effect of irradiance and nutrient nitrate on the relationship of in vivo and in vitro nitrate reductase assay in chlorophyllous tissues.

Growth at increasing continuous irradiance (at high nutrient nitrate) and nutrient nitrate concentrations (at high continuous irradiance) furnished increases in the in vivo and in vitro nitrate reductase activities of corn (Zea mays L.), field peas (Pisum arvense L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and globe amaranth (Gomphrena globosa L.) leaves and of marrow (Cucurbita pepo L.) cotyledons. Ratios of in vivo to in vitro activity declined exponentially in all species with increasing nitrate reductase levels promoted by nutrient nitrate. The ratios were more nearly independent of nitrate reductase levels generated by adjusting the irradiance; major exceptions were marrow and wheat at low (1.5 klux and less) irradiances and peas throughout the irradiance range, where decreases in the ratio were accompanied by increases in in situ nitrate concentration. The ratio also increased at the highest irradiance (39.2 klux) in wheat and barley, associated with a decline of in vitro nitrate reductase. These differences in response to irradiance and nutrient nitrate indicate that the in vivo assay does not provide a simple measure of nitrate reductase but rather yields a more composite measure of nitrate reduction, possibly related both to nitrate reductase level and to the supply of reductant for in vivo activity.

Phytochrome, nitrate movement, and induction of nitrate reductase in etiolated pea terminal buds.

The role of phytochrome in the induction of nitrate reductase of etiolated field peas (Pisum arvense L.) was examined. Terminal bud nitrate concentration increased in darkness, and the increase correlated with induction of nitrate reductase following brief exposure of intact plants to red, blue, far red, and white lights. Brief light exposure of intact plants stimulated nitrate uptake and induction of nitrate reductase by terminal buds subsequently excised and incubated on nitrate solution in darkness; exposure of excised buds in contact with nitrate led to less uptake but more induction. Nitrate and nitrate reductase activity both declined during incubation with water, irrespective of light treatment. Nitrate enrichment of intact terminal buds and uptake into excised buds and increases in nitrate reductase activity were all red/far red reversible. Dimethyl sulfoxide (1%, v/v) and sugars (sucrose 0.5%, glucose 1, w/v), although stimulating nitrate uptake into excised tissue in darkness, failed to enhance nitrate reductase activity over dark controls. Phytochrome may regulate nitrate reductase via both nitrate movement and a general mechanism such as enhancement of protein synthesis.