Assessment of nuclear sclerosis after nonvitrectomizing vitreous surgery

An objective evaluation of lens transparency after vitrectomy surgery with different intravitreal tamponades

PURPOSE

To evaluate and compare the effects of different intraocular tamponade agents on lens density after vitrectomy.

METHODS

The participating patients were divided into four groups according to the tamponade agent used: a sulfur hexafluoride (SF₆) group, a perfluoropropane (C₃F₈) group, a silicone oil group, and a no tamponade group. Lens density measurements were performed preoperatively and two weeks, one month, and three months postoperatively using a Pentacam HR device with a Scheimpflug camera. The postoperative values were compared with the preoperative baseline values, also the values were compared between the four groups.

RESULTS

The study included 82 eyes (82 patients). In the SF₆ group, lens density significantly increased in all zones two weeks and one and three months postoperatively (all P < .05). In the C₃F₈ group, lens density significantly increased in all zones three months postoperatively (all P < .01). In the silicone oil group, the zone 1, zone 2, and average lens density (ALD) value significantly increased one and three months postoperatively (all P < .05). In the no tamponade group, the zone 1, zone 2, and ALD values significantly increased three months postoperatively (all P < .05). There were no significant differences between the four groups in any zone either preoperatively or postoperatively (all P > .05).

CONCLUSIONS

Although increases in lens density were observed earlier in the tamponade groups than in the no tamponade group, between the groups over the follow-up period were no differences. We need the development of new surgical methods and materials to prevent post-vitrectomy lens damage in the future.

Local dry vitrectomy combined with segmental scleral buckling and viscoelastic tamponade for rhegmatogenous retinal detachment with vitreous traction

AIM

To demonstrate local dry vitrectomy combined with segmental scleral buckling and viscoelastic tamponade for the treatment of partial rhegmatogenous retinal detachment (RRD) with local vitreous traction in patients at high-risk for proliferative vitreoretinopathy (PVR).

METHODS

Eleven eyes of 11 patients were retrospectively studied, including 5 retinal dialysis and 6 retinal detachment (RD; 5 eyes with peripheral retinal hole and 1 eye with giant tear). All patients exhibited partial RD and local vitreous traction. Combined local dry vitrectomy without conventional infusion and segmental scleral buckling was performed. Viscoelastic fluid was injected into the vitreous cavity if needed. Demographic information, preoperative and post-operative complications, and outcomes were recorded.

RESULTS

The mean age of the patients at presentation was 26.55±13.52y. All 11 patients obtained retinal reattachment after a single surgical intervention. Postoperative visual acuities were improved or remained stable in all patients. None of them developed complications, except for temporary mildly increased intraocular pressure in 3 cases.

CONCLUSION

Combined local dry vitrectomy and segmental scleral buckling are effective for patients of RRD with local vitreous traction. The technique avoids many complications associated with regular surgery and was minimally invasive to both the external and internal eye.

International Board Members of the American Journal of Ophthalmology

This year marks the 100th anniversary of the "modern" American Journal of Ophthalmology (AJO). International influence has been present since the beginnings of the journal, and the AJO had boasted a number of foreign editorial board members and collaborators over the years. Within the article we present sketches of the deceased international board members of the AJO, particularly of Sir Stewart Duke-Elder, Pierre Amalric, Joaquin Barraquer, and Yasuo Tano. Although the AJO is American by name and with respect to the majority of contributions and readers, the international board members and collaborators have helped to maintain its international character and worldwide level of recognition. As the United States is a competitive society that values progress and success partially owing to foreign influence and immigrants, similarly the international contributions help to support and provoke the dynamic development of the AJO.

Modified Vitrectomy Technique for Phakic Rhegmatogenous Retinal Detachment with Intermediate Break

Purpose

To evaluate the effects of a modification of the traditional 25-gauge pars plana vitrectomy technique in the treatment of uncomplicated macula-on rhegmatogenous retinal detachment (RRD) with intermediate retinal break(s) and marked vitreous traction in the phakic eye.

Methods

Prospective, noncomparative, and interventional case series. All consecutive phakic eyes with primary uncomplicated macula-on RRD with intermediate retinal break(s) and marked vitreous traction, with at least 1 year of postoperative follow-up, were enrolled. In all eyes, "localized 25-gauge vitrectomy" under air infusion with localized removal of the vitreous surrounding the retinal break(s), in association with laser photocoagulation and air tamponade, was performed. The primary end point was the rate of primary retinal attachment. Secondary end points were cataract progression and assessed by digital Scheimpflug lens photography (mean change of nuclear density units) and the rate of complications.

Results

Thirty-two phakic eyes were included in the final analysis. At 12 months, the primary outcome of anatomical success was achieved in 94% of eyes. The mean nuclear density units did not change significantly at any time point during the follow-up. After localized vitrectomy, one eye developed an epiretinal membrane, and one eye developed cystoid macular edema; no other significant complications were reported.

Conclusions

"Localized vitrectomy" has a high anatomical success rate in phakic eyes with primary uncomplicated macula-on RRD with intermediate retinal break(s) and marked vitreous traction, without causing progression of cataract.

The quantitative assessment of alterations in lens transparency after transconjunctival 27-gauge microincision vitrectomy surgery

PurposeTo evaluate the baseline and post-vitrectomy lens densitometry values by a Scheimpflug camera in eyes with epiretinal membrane that were treated with 27-G microincision vitrectomy surgery (MIVS) without tamponade and to compare the results with those in fellow healthy eyes.Patients and methodsProspective case series. The lens densitometry measurements of 24 patients, who underwent 27-G MIVS without any tamponade for the treatment of epiretinal membrane, were taken preoperatively and on the first week, first month, and third month postoperatively with Pentacam HR-Scheimpflug imaging system.ResultsThe mean lens densitometry values at Zone 1 and average lens densitometry values significantly increased in the study eyes on the first month when compared with the preoperative values (P=0.011, P=0.033, respectively). Additionally, there were statistically significant differences regarding the mean lens densitometry values of Zone 1 and Zone 2, and also average lens densitometry values between the preoperative and third month postoperative values (P=0.003, P=0.021, P=0.009, respectively). However, the densitometry values of fellow eyes were similar at preoperatively and all the postoperative follow-up periods (P>0.05 for all).ConclusionsThis study suggests that 27-G MIVS might cause post-surgical lens density changes even in early postoperative months and vitreous may play an important role in protecting the transparency of the lens.

Refractive changes after lens-sparing vitrectomy for macular hole and epiretinal membrane

Purpose

Cataract progression after lens-sparing vitrectomy might differ according to original posterior segment diseases. Our objective was to analyze the refractive values after lens-sparing vitrectomy for macular hole (MH) and epiretinal membrane (ERM).

Materials and methods

We reviewed the medical records of 25 MH patients (25 eyes) and 23 ERM patients (23 eyes) who underwent lens-sparing vitrectomy. Refractive changes in both groups were compared. All patients underwent 20-gauge three-port pars plana vitrectomy. Fluid–air exchange was performed during vitrectomy only in the MH group. The results were analyzed using the unpaired t-test, chi-square test, or Fisher exact probability test, and multivariate analysis.

Results

There were no significant differences in the patient’s age (P=0.45). The myopia progression rate (D/month) was higher in the MH group after surgery than that in the ERM group (P=0.035). MH group had more females (P=0.043), longer surgical time (P<0.001), and higher frequencies of surgical adjuvants use (triamcinolone acetonide, P=0.019; brilliant blue G, P<0.001). The myopia progression rate in the MH group (R=0.568, P<0.001) correlated with female gender. However, no correlation was observed between longer surgical time and the use of surgical adjuvants.

Conclusion

The rate of myopia progression was higher in the MH group. Fluid–air exchange and gender may affect the rate of myopia progression.

Change in refraction after lens-sparing vitrectomy for rhegmatogenous retinal detachment and epiretinal membrane

The aim of this study was to compare changes in refraction following lens-sparing vitrectomy between patients with rhegmatogenous retinal detachment (RRD) and epiretinal membrane (ERM) and to investigate factors associated with the change in refraction.We reviewed medical records of 49 eyes of 49 patients with RRD (53.6 ± 7.8 years, mean ± standard deviation) and 24 eyes of 24 patients with ERM (50.9 ± 15.7 years) who underwent lens-sparing vitrectomy. Spherical equivalent refractive power was evaluated before and up to 18 months after surgery. The relationship between the change in refraction and several parameters was evaluated.A significant progressive myopic shift in refractive power was observed after vitrectomy in operated RRD and ERM eyes (P < 0.001, P = 0.016, respectively), with no significant difference in fellow eyes. The refraction values observed at ≥3 and ≥12 months following vitrectomy were significantly different as compared with those observed at baseline in the RRD group (P < 0.001) and the ERM group (P < 0.05), respectively. The change in refraction between the RRD and ERM groups was significant (P = 0.030). The multiple linear regression analysis showed that only age was significantly correlated with the change in refraction in RRD (P = 0.018) and ERM (P < 0.001) groups. The change in refraction was significantly and positively correlated with age in RRD (r = -0.461, P = 0.001) and ERM (r = -0.687, P < 0.001) groups. Following lens-sparing vitrectomy, cataract surgery was performed on 30 eyes after 0.89 ± 0.26 years in the RRD group and on 10 eyes after 1.11 ± 0.14 years in the ERM group; there was a significant difference in time to cataract surgery between the groups (P = 0.007). Kaplan-Meier survival analysis demonstrated that there was a significant difference in the rate of cataract surgeries between the RRD and ERM groups (P = 0.022).Following lens-sparing vitrectomy for RRD and ERM, a progressive myopic shift in refraction owing to nuclear sclerosis was observed. Core vitrectomy itself would cause a myopic shift of refraction. The only risk factor associated with cataract progression following lens-sparing vitrectomy is age for both types of patients.

TRANSCONJUNCTIVAL NONVITRECTOMIZING VITREOUS SURGERY VERSUS 25-GAUGE VITRECTOMY IN PATIENTS WITH EPIRETINAL MEMBRANE: A Prospective Randomized Study

PURPOSE

To compare the clinical outcomes and the rate of complications of 27-gauge transconjunctival nonvitrectomizing vitreous surgery (NVS) and of 25-gauge transconjunctival sutureless vitrectomy surgery for idiopathic epiretinal membrane removal.

METHODS

In this prospective randomized study, 83 phakic eyes of 83 consecutive patients with an idiopathic epiretinal membrane were randomized to receive 27-gauge NVS (NVS-group) or 25-gauge vitrectomy (Standard-group). Main outcome measures were best-corrected visual acuity, central retinal thickness, nuclear density units' changes, and rate of complications.

RESULTS

Thirty-nine eyes of the Standard-group and 40 of the NVS-group were considered in final analysis. Mean best-corrected visual acuity improved significantly in both groups, with a significant better result at 12 months in NVS-group (P = 0.039; t-test). Central retinal thickness decreased significantly in both groups (P < 0.001, Tukey test), without significant difference between the two groups at any time point. At 12 months, nuclear density increased significantly in the Standard-group (analysis of variance, P < 0.001), and it did not change in the NVS-group (analysis of variance, P = 0.537). Epiretinal membrane recurred in 5.1% of eyes in the Standard-group and in 7.5% of eyes in the NVS-group (Fisher's exact test, P = 1.000).

CONCLUSION

The 27-gauge NVS is an effective surgical procedure in eyes with epiretinal membrane and it induces less progression of nuclear sclerosis than 25-gauge vitrectomy.

[The role of the vitreous body in diseases of neighboring structures]

BACKGROUND

The vitreoretinal interface is not merely the space between the vitreous body and the retina but it is also a site for highly complex pathologies with the vitreous body exerting an influence on all the neighbouring structures.

METHODS

A literature search was performed in Pubmed and current book articles

RESULTS

This review article highlights the role of the vitreous body in vitreomacular adhesion and traction, in the development of macular holes and epiretinal membranes as well as its role in age-related macular degeneration. In the retinal periphery the vitreous structures play a pivotal role in retinal tears and detachment as well as in diabetic and other proliferative vitreoretinopathies. The role of the vitreous bodyin the emergence of various forms of cataract is often underestimated.

DISCUSSION

Vitreo-etinal surgeons should thoroughly understand the pathophysiological relationship between the vitreous body and the neighboring structures, especially in the era of medical vitreolysis.

Cataract formation following vitreoretinal procedures

Purpose

To evaluate the incidence and prevalence of cataract formation, progression, and extraction in patients that underwent vitreoretinal procedures and to evaluate factors that can potentially predispose patients to postoperative cataracts.

Materials and methods

The medical records of consecutive patients who underwent vitreoretinal surgery at the Yale Eye Center with at least 6 months of follow-up and no prior intraocular surgery were obtained. Preoperative, intraoperative, and postoperative data were recorded and analyzed in this retrospective observational study. The main outcome measures were defined as cataract extraction, formation, and progression after vitreoretinal procedures. The lens status of the surgical eye was recorded preoperatively and at 1 month, 3 months, 6 months, 12 months, 24 months, and 36 months postoperatively.

Results

A total of 193 eyes of 180 patients fulfilled the inclusion criteria. The percentages of eyes with mild lens change were 96% after 20-gauge pars plana vitrectomy (PPV), 72% after small gauge (23- and 25-gauge) PPV, 38% after scleral buckle (SB), 38% after pneumatic retinopexy (PR), and 91% after PPV plus SB (PPV+SB). Posterior subcapsular and nuclear sclerotic cataracts were the most common with almost all developing within 24 months. There was no statistically significant difference (P=1.00) between the rate of cataract extraction after 20-gauge (41%) and small gauge PPV (42%), but there was a statistically significant difference between PPV and non-PPV (SB, 6%; PR, 7%; P<0.001) and PPV and PPV+SB groups (69%; P=0.0063).

Conclusion

Cataracts were common following PPV regardless of the gauge. SB and PR led to the lowest while PPV+SB led to the highest risk of postoperative cataracts.

Small-gauge vitrectomy does not protect against nuclear sclerotic cataract

PURPOSE

To determine whether the gauge of vitrectomy instrumentation is associated with the progression of nuclear sclerotic cataract.

METHODS

A prospective interventional and observational study of patients undergoing vitrectomy surgery for various retinal conditions. Patients had Scheimpflug lens photography in the operated and fellow eye at baseline and at 6 months and 12 months after vitrectomy surgery.

RESULTS

Of 42 eyes included in the analysis, 11 had 20-gauge surgery, 22 had 23-gauge surgery, and 9 had 25-gauge surgery. In all operated eyes, vitrectomy surgery led to the significant progression of nuclear sclerotic cataract, compared with the fellow, unoperated eye. This small study was unable to detect a difference in nuclear sclerotic progression when comparing small-gauge surgery (23 and 25 gauge) with standard 20-gauge surgery.

CONCLUSION

Removal of the vitreous gel using any-gauge vitrectomy surgery leads to significant progression of nuclear sclerotic cataract at 6 months and 12 months. The findings are consistent with the hypothesis that the vitreous gel is important in protecting the lens from increased exposure to oxygen that leads to the formation of nuclear sclerotic cataract. This increased exposure to oxygen occurs as a result of removing the vitreous gel and is independent of the gauge of vitrectomy instrumentation.

Maintaining transparency: a review of the developmental physiology and pathophysiology of two avascular tissues

The lens and cornea are transparent and usually avascular. Controlling nutrient supply while maintaining transparency is a physiological challenge for both tissues. During sleep and with contact lens wear the endothelial layer of the cornea may become hypoxic, compromising its ability to maintain corneal transparency. The mechanism responsible for establishing the avascular nature of the corneal stroma is unknown. In several pathological conditions, the stroma can be invaded by abnormal, leaky vessels, leading to opacification. Several molecules that are likely to help maintain the avascular nature of the corneal stroma have been identified, although their relative contributions remain to be demonstrated. The mammalian lens is surrounded by capillaries early in life. After the fetal vasculature regresses, the lens resides in a hypoxic environment. Hypoxia is likely to be required to maintain lens transparency. The vitreous body may help to maintain the low oxygen level around the lens. The hypothesis is presented that many aspects of the aging of the lens, including increased hardening, loss of accommodation (presbyopia), and opacification of the lens nucleus, are caused by exposure to oxygen. Testing this hypothesis may lead to prevention for nuclear cataract and insight into the mechanisms of lens aging. Although they are both transparent, corneal pathology is associated with an insufficient supply of oxygen, while lens pathology may involve excessive exposure to oxygen.

Functional outcome and patient preferences following combined phaco-vitrectomy for macular hole without prone posturing

BACKGROUND

Macular hole surgery varies widely regarding the duration of gas tamponade, the use of patient posturing post-operatively, and whether or not cataract extraction is undertaken at the same time.

AIM

To analyse anatomical and functional success rate following macular hole surgery and to examine patient preferences regarding posturing and length of gas tamponade.

MATERIALS AND METHODS

Study design. Prospective, interventional and non-comparative case series.

PARTICIPANTS

Thirty patients with stage III and IV full-thickness macular hole who underwent macular hole repair during the period April 2005-January 2006.Intervention. All eyes underwent a standard three-port pars plana vitrectomy, removal of posterior vitreous, internal limiting membrane (ILM) peel, C3F8 gas tamponade, and cataract extraction with IOL implantation. Patients did not posture post-operatively.Outcome measures. Post-operative anatomic results, visual acuity, complications, patient preferences regarding surgical protocol, and subjective improvement in visual function.

RESULTS

Patients were followed up post-operatively for 6 months. Primary anatomical hole closure was achieved in 96.7% eyes. Visual acuity improved in 83.8% patients. Two patients had raised intraocular pressure following surgery. A total of 96.9% of patients were happy with no posturing and a 2-month gas bubble.

CONCLUSIONS

There is a high rate of anatomical and functional success in patients undergoing macular hole surgery without prone posturing. In our study, most patients preferred long-acting gas tamponade with no posturing over the option of posturing with short-acting gas tamponade.

Lower intraocular oxygen tension in diabetic patients: possible contribution to decreased incidence of nuclear sclerotic cataract

PURPOSE

To report intraocular oxygen tension in eyes of diabetic and nondiabetic patients.

DESIGN

A prospective, interventional consecutive case series.

METHODS

Oxygen was measured with an optical oxygen sensor in patients who were undergoing vitrectomy. Before turning on the infusion fluid, intraocular oxygen tension was measured in two locations: adjacent to the lens and in the mid vitreous cavity.

RESULTS

Fifty eyes from 50 patients were included in the study. Twenty-one eyes were from diabetic patients and 29 eyes were from nondiabetic patients. The mean oxygen tension adjacent to the lens was significantly lower in diabetic than in nondiabetic patients (8.4 +/- 0.7 mm Hg vs 10.7 +/- 0.8 mm Hg; P < .05). Similarly, the mean oxygen tension in the center of the vitreous cavity was lower in diabetic than in nondiabetic patients (5.7 +/- 0.7 mm Hg vs 8.5 +/- 0.6 mm Hg; P < .001). In subgroup analyses, previous panretinal photocoagulation or cataract surgery did not affect oxygen levels significantly in the vitreous of diabetic or nondiabetic patients.

CONCLUSION

Eyes from diabetic patients have significantly lower intraocular oxygen tension than in eyes from nondiabetic patients. Because oxidative damage to the lens nucleus and increased intraocular oxygen tension have been associated with nuclear sclerotic cataract, these findings may help explain recent reports of an apparent protective effect of diabetes mellitus against nuclear sclerotic cataract.

Development of Microelectromechanical Systems (MEMS) forceps for intraocular surgery

AIM

To develop silicon microforceps for intraocular surgery using Microelectromechanical Systems (MEMS) technology, the application of microchip fabrication techniques for the production of controllable three dimensional devices on the micrometre scale.

METHODS

Prototype MEMS forceps were designed and manufactured for intraocular surgery. Scanning electron microscopy was used to evaluate device tip construction. Designs using both thermal expansion actuators and conventional mechanical activation were tested in human cadaver eyes and in vivo rabbit eyes to assess functionality in standard vitreoretinal surgery.

RESULTS

MEMS forceps were constructed with various tip designs ranging from 100 mum to 2 mm in length. Scanning electron microscopy confirmed accurate construction of micro features such as forceps teeth as small as tens of micrometres. In surgical testing, the silicon forceps tips were effective in surgical manoeuvres, including grasping retinal membranes and excising tissue. The mechanical actuator design on a 20 gauge handle was more operational in the intraocular environment than the thermal expansion actuator design. While handheld operation was possible, the precision of the forceps was best exploited when mounted on a three axis micromanipulator.

CONCLUSION

MEMS microforceps are feasible for conventional vitreoretinal surgery, and offer advances in terms of small scale, operating precision, and construction tolerance.

25-gauge, sutureless vitrectomy and standard 20-gauge pars plana vitrectomy in idiopathic epiretinal membrane surgery: a comparative pilot study

BACKGROUND

The aim of the study was to evaluate the safety and functional outcome of a small incision, sutureless vitrectomy in the treatment of idiopathic epiretinal membranes (ERM) compared with a standard 20-gauge vitrectomy system.

METHODS

Forty-six consecutive patients with idiopathic ERM were recruited for this study and prospectively evaluated. In group 1 (n=26) we used a transconjunctival sutureless 25-gauge vitrectomy system (TSV), patients in group 2 (n=20) were operated on using a standard 20-gauge vitrectomy system. The ERM was removed and the internal limiting membrane (ILM) was peeled in all eyes. Surgery-related complications, operating time, intraoperative balanced salt solution (BSS) consumption, postoperative discomfort, postoperative intraocular inflammation, lens opacification, and long-term visual outcome are reported and compared.

RESULTS

No surgery-related complications were observed in either group. Operating time was shorter in group 1 compared with group 2 (mean 15.6 and 29.6 min respectively). Intraoperative amount of BSS consumption was less in group 1 (mean 28 ml in group 1 and 42 ml in group 2). Postoperative discomfort and intraocular inflammation were significantly reduced in the 25-gauge group. In the 20-gauge group cataract formation requiring surgery was observed in two eyes. Visual acuity improved significantly in both groups. The 25-gauge group improved on average by more lines of vision and the improvement in vision was more rapid.

CONCLUSION

The TSV system is a safe and efficient surgical technique for ERM surgery. Operating time is significantly reduced, minimizing surgery-induced trauma, and reducing postoperative intraocular inflammation and the patients' discomfort. The incidence of cataract formation may be less using TSV. Postoperative recovery is accelerated.

Nonvitrectomizing vitreous surgery for epiretinal membrane long-term follow-up

PURPOSE

To report the long-term follow-up results of nonvitrectomizing vitreous surgery for idiopathic epiretinal membrane (ERM).

DESIGN

Nonrandomized comparative case series.

PARTICIPANTS

Thirty patients were followed up for at least 5 years after nonvitrectomizing vitreous surgery.

INTERVENTION

Epiretinal membranes were peeled without infusion of balanced salt solution and removal of the vitreous. The data from the fellow eye was the control data.

MAIN OUTCOME MEASURES

We examined the visual acuities (VAs), objective refractions, and slit-lamp and Scheimpflug photographs from the preoperative and the final examinations of both eyes. Quantitative assessment of the progression of nuclear sclerosis was performed by densitometry analysis using Scheimpflug photography. The recurrence rate of ERM was determined.

RESULTS

The follow-up periods ranged from 60 to 102 months (mean+/-standard deviation, 72.2+/-11.0 months). The patient ages ranged from 52 to 76 years (68.8+/-6.3 years). The final VA improved or stabilized within 2 lines in 29 of 30 eyes (96.7%). No unilateral progression of nuclear sclerosis occurred in any cases. The mean preoperative and postoperative refractions without additional surgery were -0.4+/-2.9 diopters (D) and -0.2+/-3.0 D in the operated eyes, respectively, and -0.2+/-2.5 D and 0.1+/-2.4 D, respectively, in the unoperated fellow eyes. The mean differences in the refractive error between both eyes (operated eye data minus fellow eye data) were -0.2+/-0.7 D before surgery and -0.3+/-0.8 D after surgery (P = 0.319, paired t test). The mean preoperative and postoperative nuclear densities in 16 patients were 69+/-14 nuclear density units (NDUs) and 76+/-12 NDUs in the operated eyes and 71+/-14 NDUs and 78+/-14 NDUs in the fellow eyes, respectively. The mean preoperative and postoperative differences in nuclear densities in both eyes were -2+/-2 NDUs and -2+/-5 NDUs, respectively (P = 0.836, paired t test). The ERM recurred in 10 eyes (33%), and 3 eyes underwent conventional vitrectomy combined with cataract surgery.

CONCLUSIONS

Unilateral nuclear sclerosis did not progress for at least 5 years after nonvitrectomizing vitreous surgery. The recurrence rate of ERM appeared to be higher than that after conventional vitreous surgery.

Electrophysiological and histological studies of chronically implanted intrapapillary microelectrodes in rabbit eyes

PURPOSE

To determine the safety and efficacy of transsclerally placed intrapapillary wire microelectrodes implanted chronically into the optic nerve head of rabbit eyes.

METHODS

Four platinum wire microelectrodes were passed through the sclera and implanted into the optic nerve head of five rabbit eyes for 4-6 months. Color fundus photography, fluorescein angiography, electroretinograms (ERGs), and visually evoked potentials (VEPs) were used to monitor the retina. Electrically evoked potentials (EEPs) were elicited by bipolar electrical stimulation of the optic nerve axons by different combinations of the four electrodes immediately after the implantation and at 1-month intervals thereafter. The effects of the chronic implantation of the electrodes on the morphology of the optic nerve were evaluated by histological and immunohistochemical examinations at 4 and 6 months after the implantation.

RESULTS

All of the electrodes remained stable in the implanted sites throughout the post-implantation period, except for one electrode that had pulled out of the optic nerve head at 1 month after implantation. No intraocular infection, inflammation, or vitreoretinal proliferation was observed in any eye. EEPs could be elicited from each pair of electrodes at all testing times. The mean threshold currents (charge densities) to evoke EEPs increased from 19.3 +/- 9.2 microA (6.0 +/- 2.9 microC/cm2) on the implantation day to 78.8 +/- 31.9 microA (24.6 +/- 10.0 microC/cm2) at 1 month after implantation, but did not change significantly thereafter. The implicit time and amplitude of the a- and b-waves of the ERGs and of P1 of the VEPs did not change significantly throughout the post-implantation period. Histological evaluation of the optic nerve head revealed slight tissue encapsulations surrounding the electrode and increased expression of glial fibrillary acidic protein near the surface of the optic nerve.

CONCLUSIONS

Implantation of transscleral intrapapillary microelectrodes appears to be safe and effective. These findings indicate that the implantation of microelectrodes in the optic nerve head should be considered for an optic nerve-based prosthesis.

Visual outcomes following vitrectomy and peeling of epiretinal membrane

BACKGROUND

Visual outcomes of patients following vitrectomy and peeling of visually significant epiretinal membranes were assessed to determine the influence of specific perioperative factors and surgical complications on final visual acuity and functional vision.

METHODS

In an unmatched, consecutive surgical series, vitrectomy and membrane peeling were performed on 125 eyes of 123 patients with visually significant macular epiretinal membranes. Patients were followed for 6-36 months. Visual outcome measures included postoperative logMAR visual acuity, change in visual acuity and functional vision tasks evaluated by questionnaire. Perioperative factors including duration of symptoms, preoperative visual acuity, aetiology, membrane type and leakage on fundal fluorescein angiogram were correlated with final visual outcomes.

RESULTS

Visual acuity improved by a mean of 0.31 A+/- 0.21 units (three lines of vision). In 104 cases (83%), visual acuity improved in patients by two lines or more, with 20 cases (16%) having unchanged acuity and one case (1%) having worse acuity. Ninety-three per cent of interviewed cases reported improvement in functional vision, especially reduction of distortion. Cataract was observed in 52 cases (52% of phakic eyes) postoperatively compared with 19 cases (19%) preoperatively. Postoperative visual acuity correlated with preoperative visual acuity. Patients with worse preoperative vision recorded greater visual improvement following surgery. No other perioperative factors were found to have a prognostic value in this study.

CONCLUSION

Epiretinal membrane peeling improves vision in the majority of patients with significant symptoms, even if preoperative visual acuity is not substantially reduced. Surgery improves functional vision including metamorphopsia not measurable by visual acuity, and thus assessment of functional vision should be included in surgical case planning.

Vitrectomy surgery increases oxygen exposure to the lens: a possible mechanism for nuclear cataract formation

PURPOSE

To report vitreous oxygen tension before, immediately after, and at longer times after vitrectomy.

DESIGN

A prospective, interventional consecutive case series.

METHODS

Oxygen was measured using an optical oxygen sensor in patients undergoing vitrectomy. Intraoperatively, oxygen measurements were taken before and after vitrectomy in two intraocular locations: adjacent to the lens and in the mid-vitreous.

RESULTS

Sixty-nine eyes underwent oxygen tension measurements at the time of vitrectomy. In baseline eyes, oxygen tension in the vitreous was low, measuring 8.7 +/- 0.6 mm Hg adjacent to the lens and 7.1 +/- 0.5 mm Hg in the mid-vitreous. The difference between the two locations was statistically significant (P < .003), indicating that vitreous gel maintains an intraocular oxygen gradient. Immediately after vitrectomy, oxygen tension in the fluid-filled eye was higher, measuring 69.6 +/-4.8 mm Hg adjacent to the lens and 75.6 +/- 4.1 mm Hg in the mid-vitreous. There was no statistically significant oxygen gradient between the two locations. The difference in oxygen tension pre- and postvitrectomy is highly statistically significant (P < .0001 lens, P < .0001 mid-vitreous). In eyes with a history of vitrectomy and previous removal of the vitreous gel, the intraocular oxygen tension was significantly higher than in eyes with a formed vitreous gel undergoing a first vitrectomy (P < .02 lens, P < .003 mid-vitreous).

CONCLUSION

Vitrectomy surgery significantly increases intraocular oxygen tension during and for prolonged periods after surgery. This exposes the crystalline lens to abnormally high oxygen and may lead to nuclear cataract formation.

Oxygen tension in the rabbit lens and vitreous before and after vitrectomy

Oxygen is believed to be one of the potential causative agents for the development of nuclear cataract following vitrectomy. The aim of this study was to determine the partial pressure of oxygen (pO2) in different compartments of the rabbit eye, and to describe the changes following vitrectomy. Twenty-six rabbits (3.5-5.3 kg) were anesthetized and oxygen tension was probed using a fiber-optic oxygen sensor system (optode). A micromanipulator was employed to ascertain the exact position of the probe within the eye. Measurements were taken pre- and post-vitrectomy at several defined positions within the vitreous, the lens and the anterior chamber. Follow-up measurements were performed 2 and 8 weeks after vitrectomy. The contralateral eye served as a control. Measurements in the normal rabbit eye showed that oxygen tension in the globe is asymmetrical with the lowest pO2 in the nucleus of the lens (10.4 mmHg+/-3.0). The region of the lens near the posterior capsule has an oxygen tension close to the values of the vitreous directly behind the posterior capsule (12.4 mmHg+/-3.1). The highest pO2 within the posterior compartment of the eye was measured close to the retinal surface (40-l60 mmHg) depending on neighboring large vessels. The tension drops off rapidly to 20 mmHg some 0.5 mm from the retina. From that position to the posterior surface of the lens there is a shallow gradient of decreasing pO2. Immediately following vitrectomy the pO2 in the BSS replacement varied from ca. 90-140 mmHg, and decreased over approximately 30 min. to levels that were 2-3 times that of normal vitreous. Two weeks after vitrectomy the pO2 values in the lens were 2-3 times as high as in the control eye (p < 0.05). In addition there is no longer a gradient in the vitreous cavity, except close to the retina. Eight weeks after vitrectomy, pO2 levels in the lens were decreased but still remained higher than in the normal eye (13.83 mmHg+/-0.02). The pO2 gradient in the vitreous was not detectable anymore. Overall the results provide evidence that oxygen levels in the lens increase significantly after vitrectomy in rabbits. If this occurs in humans it may contribute to cataract formation following surgery.

The role of patient age and intraocular gas use in cataract progression after vitrectomy for macular holes and epiretinal membranes

PURPOSE

To evaluate the rate of increase in nuclear sclerosis and posterior subcapsular cataracts in eyes as a function of patient age and use of intravitreal gas at the time of vitrectomy.

DESIGN

Observational case series.

METHODS

Nuclear sclerosis and posterior subcapsular cataracts were evaluated as a function of patient age and use of intravitreal gas at vitrectomy.

SETTING

A clinical practice.

STUDY POPULATION

The study population consisted of 301 consecutive eyes.

OBSERVATIONAL PROCEDURE

Nuclear sclerotic cataracts and posterior subcapsular cataracts were graded on a scale from 0 to 4.0 before and after vitrectomy.

MAIN OUTCOME MEASURE

Linear regression analysis was performed to measure and compare the rate of change in cataract score over time based on patient age and use of intraocular gas.

RESULTS

Nuclear sclerotic cataracts showed minimal increase in patients younger than 50 years of age after vitrectomy (0.13 grades/year). Nuclear sclerotic cataracts increased at a rate of 0.7 to 0.9 grades/year (mean, 0.812) in patients aged 50 to 60 years, 60 to 70 years, 70 to 80 years, and 80+ years, even though the baseline nuclear sclerosis scores were progressively greater for each decade. The increase in nuclear sclerotic cataracts in patients younger than 50 years of age was significantly less (P <.001) than in patients aged 50 years or older. Eyes with intraocular gas use had a higher rate of nuclear sclerosis progression (0.8 grades/year) compared with eyes without intraocular gas bubbles (0.5 grades/year; P <.001). Posterior subcapsular cataract scores showed minimal or no increases in all groups.

CONCLUSIONS

Patients older than 50 years of age have a similar rate of increase in nuclear sclerotic cataracts, independent of age. The rate is approximately sixfold greater than in patients younger than 50 years of age. Intravitreal gas bubbles are associated with a nuclear sclerosis increase of approximately 60% compared with eyes without use of a gas bubble.

Macular hole repair with minimal vitrectomy

PURPOSE

Conventional macular hole surgery usually involves removing 80% of the intraocular contents to repair a hole a few hundred micrometers in diameter. Although the success rate for conventional surgery is good, it may be possible to reduce the number of complications with less invasive surgery.

METHODS

A newly designed microspatula knife was used to dissect the connection between the vitreous and the retina previously delineated by optical coherence tomography. The posterior vitreous was not stripped from the retinal surface. Limited vitrectomy over the hole was performed to create a space for a gas bubble.

RESULTS

The macular holes in three eyes of three patients were closed with this technique with no operative or postoperative complications after a mean follow-up of 8.7 months. The mean change in visual acuity was 6.3 lines.

CONCLUSION

It is possible to repair macular holes by using optical coherence tomography to guide the dissection of the vitreous from the macular hole followed by limited vitrectomy. By using a less invasive approach, it may be possible to repair macular holes in less operative time and with fewer complications.