Ординатура / Офтальмология / Английские материалы / Textbook of Vitreoretinal Diseases and Surgery_Natarajan, Hussain_2008

Textbook of Vitreoretinal Diseases and Surgery

Disadvantages

Both 23 and 25 gauge vitrectomy involves risks inherent to 20 gauge PPV, including cataract progression, iatrogenic retinal breaks, inadvertent lens touch, and postoperative ocular hypertension.

In 25 gauge vitrectomy the instruments are too flexible and many are too small to be sufficiently effective.4 Although next generation vitrectomy systems are stiffer, increased flexibility of 25 guage instruments do not allow as much torsion of the eye itself. By placing a finger on the instrument shaft just above the collar of the microcannula during surgery can help to partially overcome this. Also, due to the smaller port size and inner diameter, the 25 gauge vitrector has a lower aspiration rate by a factor of 6.6 compared with the 20 gauge cutter; the infusion rate in the 25 gauge system is similarly decreased by a factor of 6.9.

Hypotony during aspiration is rarely encountered, but maximum cut settings and increased aspiration power must be employed to achieve reasonable cutting and aspiration rates. This will minimize occlusion of the vitreous cutter with large or dense fragments of fibrous or other intraocular tissue. Flow rates through a tube is related to the radius to the fourth power and so any small increase in the diameter of the “tube” will make a big increase in the flow rates.3,4,8

Many problems with 23 G vitrectomy relate to the larger wound required. Unlike 25 G, conjunctival displacement is not sufficient to prevent wound leaks. Many surgeons have observed that 23 G wounds leak if the scleral tunnel is too short. Some surgeons have noted intra operative scleral folds extending into the posterior pole if the scleral tunnel is too long.4,10,8,12 Although tools and technique changes have attempted to address this problem, many surgeons still have difficulty in locating the sclerotomy made with the stiletto when subsequently inserting the cannula.

Open sclerotomies or leaking tunnels at the end of surgery can create other complications such as early postoperative hypotony, which develops when the opening is not plugged internally with vitreous or externally by conjunctiva. Hypotony itself will produce more wound gaping in case of the tunnel incisions. This may occur more frequently with significant intraocular manipulation or removal of peripheral vitreous gel. As oblique insertion requires adequate scleral tissue, patients with a history of severe ocular trauma, high myopia, or multiple intraocular surgeries may not be ideal candidates.

A suggested potentially more devastating complication in small gauged vitrectomy is endophthalmitis. Endophthalmitis in transconjunctival sutureless vitrectomy may occur secondary to several mechanisms.

•Direct cannula insertion may inoculate the vitreous with conjunctival flora during trocar insertion.

•Open sclerotomies and wound leaks may allow for increased influx of bacteria.

•Decreased infusion during vitrectomy itself may decrease the amount of fluid that dilutes or flushes out organisms within the eye.

To decrease these risks,

•Carefully prepare and sterilize the surgical field with povidone iodine.

•Ensure purposeful conjunctival displacement prior to cannula insertion to misalign the conjunctival and scleral openings in 25 gauge surgeries.

•Good oblique cannula insertion in 23 gauge surgeries to facilitate scleral wound closure.

•Suture any wound leaks seen following cannula removal.

Postoperative retinal detachment following 25 gauge vitrectomy has been reported, in rates

that appear comparable to 20 gauge surgery. 3, 4 The open sclerotomies are plugged by small amounts of vitreous that usually do not exert significant traction to produce subsequent retinal detachment.

198 If there minimal leakage through the sclerotomy, it may lead to formation of a small conjunctival bleb.

Microincision Vitrectomy

There are few limitations that are common to both 23 and 25 gauge vitrectomy.

Currently, there is no fragmatome smaller than 20 gauge. Even though cortical and small nuclear lenticular fragments can be removed with a 23 gauge cutter, large nuclear pieces require at least one 20 gauge sclerotomy. The cannulae are more difficult to insert than in 25 gauge systems because of the additional steps required. Lastly, there are fewer 23 gauge instruments commercially available than 25 gauge, as the system has been more recently introduced, although any 25 gauge instrument can be used in 23 gauge surgery, but not vice versa.3, 11

Conclusion

Recent advances and successful clinical experience have ushered in a new era of sutureless vitrectomy. As 25 and 23 gauge vitrectomy has evolved, we have seen further improvements in instrument design and function, which in turn have expanded the indications for its use. New innovations in technique, such as oblique insertion of microcannulae to facilitate sclerotomy healing, may help to minimize complications such as hypotony. Certain issues still remain and need to be addressed, like limitations on types of available instruments and probably, a slightly increased rate of postoperative endophthalmitis. When used for appropriate cases, however, these systems allows for less invasive and more efficient surgery. Decreased surgical time, less trauma and inflammation, faster patient recovery all have served to enhance patient care and satisfaction. It is likely that indications for the sutureless, small-incision vitrectomy technique will expand and postoperative outcomes will improve.

References

1.Fujii GY, de Juan E Jr, Humayun MS, et al. A new 25 gauge instrument system for transconjunctival sutureless vitrectomy surgery. Ophthalmology 2002;109:1807-13.

2.Jain V, Kar D, Natarajan S, Shome D, Mehta H, Mehta H, Jayadev C, Borse N. Phacoemulsification and pars plana vitrectomy: A combined procedure. Indian J Ophthalmol 2007;55:203-6

3.Howard F. Fine, MD, MHSc,1,2 Reza Iranmanesh, MD,1,2 Diana Iturralde, MD,3 Richard F. Spaide, MD. Outcomes of 77 Consecutive Cases of 23 gauge Transconjunctival Vitrectomy Surgery for Posterior Segment. Ophthalmology Volume 114, Issue 6, June 2007.

4.Lakhanpal RR, Humayun MS, de Juan E, Jr, et al. Outcomes of 140 consecutive cases of 25 gauge transconjunctival surgery for posterior segment disease. Ophthalmology 2005;112:817-24.

5.Chen JC. Sutureless pars plana vitrectomy through self-sealing sclerotomies. Arch Ophthalmol 1996;114:1273-5.

6.Chang CJ, Chang YH, Chiang SY, Lin LT. Comparison of clear corneal phacoemulsification combined with 25 gauge transconjunctivalsuturelessvitrectomyand standard20gaugevitrectomyforpatientswithcataractandvitreoretinal diseases. J Cataract Refract Surg 2005;31:1198-207.

7.Theelen T, Verbeek A, Tilanus MAD, van den Biesen PR. A novel technique for self-sealing, wedge-shaped pars plana sclerotomies and its features in ultrasound biomicroscopy and clinical outcome. Am J Ophthalmol 2003;136:108592.

8.Williams DF. Complications of 25 Gauge Vitrectomy. American Academy of Ophthalmology, Subspecialty Day. Retina Las Vegas, Nevada, 2006.

9.RahmanR,RosenPH,RiddellC,TowlerH.Self-sealingsclerotomiesforsuturelessparsplanavitrectomy.Ophthalmic Surg Lasers 2000;31:462-6.

10.RizzoS,Genovesi-EbertF,MurriS,etal.25gauge,suturelessvitrectomyandstandard20gaugeparsplanavitrectomy in idiopathic epiretinal membrane surgery: A comparative pilot study. Graefe’s Arch Clin Exp Ophthalmol 2006; 244:472-9.

11.RichardH.Roe,MD,MHSandArthurD.Fu,MD.SmallgaugeVitrectomy:TheFutureisNow,Reviewofophthalmology. Vol. No: 14:06 Issue: 6/1/2007.

12.Eckardt C. Transconjunctival sutureless 23 gauge vitrectomy. Retina 2005;25:208-11.

Textbook of Vitreoretinal Diseases and Surgery

Introduction

Retinopathy of prematurity (ROP) is a potentially blinding eye disorder that primarily affects premature infants weighing 1250 grams or less ,that are born before 31 weeks of gestation (A fullterm pregnancy has a gestation of 38–42 weeks). The smaller an infant is at birth, the more likely that infant will develop ROP. This disorder develops in both eyes and is among the leading causes of childhood blindness and is recognized as a priority by the VISION 2020: The Right to Sight. 1-5 In its more severe form it results in severe visual impairment or blindness, both of which carry a high financial cost for the community but also a high individual cost by affecting the normal motor, language, conceptual, and social development of the child which are amplified when a child commences formal education.

There exist a total of 50 million blind people worldwide. Four percent of these are constituted by children i.e. a figure of 2 million. Twenty two percent cases of blindness in children have cause attributable to retinal disease due to Retinopathy of prematurity (ROP). Preventable blindness in children exists in 57% of cases because of ROP.

The incidence and severity of ROP increases with decreasing birth weight and gestational age.6 In the past two decades, advances in neonatal intensive care have contributed to an increase in the survival of premature infants leading to a concomitant increase in ROP. 7-8 More than half of the infants with a birth weight of 700 grams survive.9 These extremely low-birth weight infants are at a greater risk of developing ROP. Not all infants who are premature develop ROP. The incidence of ROP worldwide ranges from 21.3% to 64.5%,10-13 and the estimated incidence in India is 38 - 42.3%.14,15

Of the 14,000–16,000, premature infants weighing less than 1250 grams born each year in United States, 9000 to 10,500 are affected by some degree of ROP. The disease improves and leaves no permanent damage in milder cases of ROP. About 90 percent of all infants with ROP are in the milder category and do not need treatment. However, infants with more severe disease can develop impaired vision or even blindness. About 1,100–1,500 infants annually develop ROP that is severe enough to require medical treatment. About 400–600 infants each year in the US become legally blind from ROP.16

Cause of ROP

ROP is a multifactorial disease. Low birth weight, low gestational age and supplemental oxygen therapy following delivery have been consistently associated with ROP.17

ROP occurs when abnormal blood vessels grow and spread throughout the retina. These abnormal blood vessels are fragile and can leak, scarring the retina and pulling it out of position. This causes a retinal detachment. Retinal detachment is the main cause of visual impairment and blindness in ROP. Two overlapping phases are known to occur in ROP: (a) an acute phase in which normal vasculogenesis is interrupted and a response to injury manifests in the retina and (b) a chronic or late proliferation of membranes into the vitreous wherein detachments of the retina, and scarring of the macula occurs resulting in significant visual loss.18 Several complex factors may be responsible for the development of ROP. The eye starts to develop at about 16 weeks of pregnancy, when the blood vessels of the retina begin to form at the optic nerve in the back of the eye. The blood vessels grow gradually toward the edges of the developing retina, supplying oxygen and nutrients. During the last 12 weeks of a pregnancy, the eye develops rapidly. When an infant is born full-term, the

202 retinal blood vessel growth is mostly complete (The retina usually stops growing a few weeks to a

Update on Retinopathy of Prematurity: Concept and Management

month after birth). But if an infant is born prematurely, before these blood vessels have reached the edges of the retina, normal vessel growth may stop. The edges of the retina—the periphery—may not get enough oxygen and nutrients.

Scientists believe that the periphery of the retina then sends out signals to other areas of the retina for nourishment. As a result, new abnormal vessels begin to grow. These new blood vessels are fragile and weak and can bleed, leading to retinal scarring. When these scars shrink, they pull on the retina, causing it to detach from the back of the eye.

ROP Classification

An International Classification of Retinopathy of Prematurity (ICROP)19 is the work of 23 ophthalmologists from 11 countries and is today followed world wide for documentation of ROP findings. They described various aspects of the disease. The anteroposterior extent or the location was divided into 3 zones (zones 1-3), the circumferential extent into clock hours (1-12) and severity of the disease in 5 stages (stage 1-5). The presence of dilated and tortuous vessels denotes an aggressive, potentially sight threatening component and is called the PLUS disease.19

LOCATION OF THE DISEASE (ZONES)

The normal blood vessels of the retina progress from optic nerve posteriorly to the edge of the ora serrata anteriorly. The location of ROP is a measure of how far this normal progression of blood vessels have reached before the disease takes over (Figures 18-1A to C). Three circular zones are defined with the optic disc at the center.

Zone I: This is the area around the optic nerve and the macula. The radius of zone I is equal to two times the distance between the disc and the fovea.

Zone II: This is up to ora serrata on the nasal side and up to the equator temporally.

Zone III: This is the remaining crescent of retina from the equator to the ora serrata temporally.

EXTENT OF THE DISEASE (CLOCK HOURS)

The eye is divided into twelve sectors similar to a clock. The extent of ROP is defined by how many clock hours of the eye circumference is diseased.

Plus Disease

Plus disease is characterised by abnormal dilated vessels on the iris and/or engorgement and tortuosity of the blood vessels in the retina. Additional findings include retinal haemorrhages, poorly dilating pupil and hazy media.