Ординатура / Офтальмология / Английские материалы / Jaypee Gold Standard Mini Atlas Series CORNEALTOPOGRAPHY_Agarwal, Jacob_2009

MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

FIGURE 9.6: Preoperative topography (picture on the left) of a patient before presbyopic lasik and picture on the right shows the postoperative topography of the patient after presbyopic lasik

presbyopic LASIK is not the end of it all. This technique needs further improvisations to become the technique of choice for one and all.

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CHAPTER 9: PRESBYOPIC LASIK

FIGURE 9.7: Preoperative and postoperative topography of a patient after presbyopic lasik shown in a 3 D pattern

REFERENCES

1.Guillermo A. Presbyopic LASIKthe PARM technique in Amar Agarwal’s Presbyopia : A surgical textbook. Slack Inc, USA, 2002.

2.Agarwal T, et al. Presbyopic LASIKthe Agarwal technique in Amar Agarwal’s Presbyopia : A surgical textbook. Slack Inc, USA, 2002.

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MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

INTRODUCTION

Conductive Keratoplasty® (CK®) from Refractec, Inc. is a non-laser, radiofrequency-based procedure for treating presbyopia. The mechanism of action of CK is through the application of high frequency (radiofrequency) energy that the cornea converts to heat in a controlled fashion. Conductive keratoplasty requires no ablation or incisions and does not invade the central cornea.

In April, 2002, the United States Food and Drug Administration granted approval of the ViewPoint® CK System (Refractec, Inc., Irvine, CA) for the treatment of mild to moderate (0.75 D to 3.00 D) previously untreated, spherical hyperopia in persons 40 years old or older.1-3

This was followed by the approval in March 2004 of CK to reduce the symptoms of presbyopia in presbyopic hyperopes (+1.00 to +2.25 D) or emmetropes through induction of a mild myopia in the non-dominant eye.4 Other potential uses of the CK technique under investigation include treatment of overor undercorrections following LASIK or other excimer laser procedures, enhancing outcomes of cataract surgery, and treating astigmatism (regular or irregular).

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CHAPTER 10: CONDUCTIVE KERATOPLASTY

HISTORY OF CONDUCTIVE KERATOPLASTY

Early Thermokeratoplasty Procedures (Second Level Section)

Thermokeratoplasty techniques aim to change corneal curvature through the application of heat, which shrinks corneal collagen. Although Lans attempted to shrink corneal collagen in rabbit eyes through thermal burns in the nineteenth century, it was not until the 1970s that various pathological conditions in humans, such as keratoconus and persistent corneal hydrops, were successfully treated with heated probes.5,6 Although initially successful, corneal curvature returned to preoperative status and the complication rate was unacceptable.7-9

The Russian surgeon, Fyodorov, was the first to use thermokeratoplasty to change corneal refraction in 1981. Using a retractable probe tip, he and other investigators applied controlled thermal burns to treat spherical hyperopia and hyperopic astigmatism. The tip was heated to 600° C, and corneal penetration depth was reported to be 95%.10-12 Although hyperopic corrections of up to 8.0 D were achieved, later studies showed lack of predictability and marked regression.13,14

Also in the early 1980s, Rowsey and colleagues developed the Los Alamos thermokeratoplasty probe. This

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MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

instrument heated stromal collagen by means of radiofrequency waves, rather than by direct thermal conduction from a heated instrument.

However, the topographical effect with this probe was short-lived, and testing was terminated.15-17

Following the report by Seiler and associates of stable corneal steepening achieved in blind eyes with a pulsed holmium:YAG laser used in the contact mode,18 Sunrise Technologies of Fremont, California began to develop a non-contact method of holmium:YAG laser treatment for

hyperopia. The clinical studies with two-year follow-up were published in 1996 and 1997.19,20 The US Food and

Drug Administration approved the Hyperion LTK device in June 2000, based on a study cohort of 612 eyes, with 80% available for analysis at 12 months and only 12% at 24 months postoperatively.21 The present Sunrise Hyperion LTK noncontact system provides three algorithms for pulse energy versus age of the patient. The physician must choose between an algorithm that substantially overcorrects initially but provides more long-term effect or one that overcorrects less but has less effect over time.

Laser Thermal Keratoplasty became unpopular because it lacked predictability and stability, and the device is no longer manufactured by Sunrise Technologies.

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CHAPTER 10: CONDUCTIVE KERATOPLASTY

Conductive Keratoplasty Technology (Second Level Section)

In the 1990s, Antonio Mendez, MD studied radiofrequency as an alternative to procedures that applied heat directly to the corneal surface.22 His success in denaturing collagen and steepening of the cornea led to the development of the Conductive Keratoplasty® procedure (CK®), performed with the ViewPoint® CK System (Refractec, Inc., Irvine, California).

Unlike previous thermokeratoplasty methods that used a laser to generate heat intrastromally, conductive keratoplasty uses radiofrequency energy to shrink corneal collagen. The procedure is performed with the ViewPoint® CK System, and is based on the delivery of a precise amount of radiofrequency energy through a fine tip inserted into the peripheral corneal stroma. Treatment is applied in a ring pattern outside of the visual axis at a defined number of treatment spots, with a greater number of spots applied to achieve a greater effect (Fig. 10.1).

A full circle of treatment spots acts like a belt tightening the cornea in the periphery so that the central cornea steepens (Fig. 10.2). During conductive keratoplasty treatment, corneal tissue is exposed to the same temperature at the bottom of the probe as at the top of the probe (corneal surface). This is in contrast to non-contact holmium LTK,

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MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

FIGURE 10.1: This shows the optical zone marks made by the marker to guide the surgeon in placement of the treatment spots. A circular mark is made on the 7 mm optical zone with the CK marker. An inner hatch mark lies on the 6 mm and an outer hatch mark on the 8 mm optical zone

FIGURE 10.2: The conductive keratoplasty technique cinches the peripheral cornea which increases the curvature of the central cornea

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CHAPTER 10: CONDUCTIVE KERATOPLASTY

which has a significant axial gradient and produces the highest temperatures at the corneal surface. The footprint after conductive keratoplasty is cylindrical and extends deep into the stroma to approximately 80% depth. This is in contrast to the conical stromal footprint made with the LTK technique.

The ViewPoint® CK® system (Fig. 10.3) consists of a portable console, corneal marker, lid speculum (choice of

FIGURE 10.3: ViewPoint™ CK System. The ViewPoint™ CK system from Refractec, Inc. consists of a portable console, a corneal marker, choice of lid specula, a handpiece that holds the Keratoplast™ Tip, and a foot pedal

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