5.TITLE of the TOPIC : “ASTUDY OF ASTIGMATISM FOLLOWING SMALL INCISION CATARACT SURGERY COMBINED WITH TRABECULECTOMY COMPARED TO ASTIGMATISM POST SMALL INCISION CATARACT SURGERY ALONE.”
6. BRIEF RESUME OF THE INTENDED WORK:
6.1: NEED FOR THE STUDY:
The control of postoperative astigmatism is an important challenge which has received great interest especially in the recent years. When a patient suffers from co-existing cataract and glaucoma, the choice of surgery may be a combined procedure of cataract extraction and trabeculectomy as a one-stage procedure to restore visual rehabilitation and to prevent progressive optic nerve damage. It is well known that post-operative astigmatism after a seemingly well performed cataract extraction with intraocular lens implant can result in a degraded quality of vision often leading to patient dissatisfaction.
The major determinants of such post-operative astigmatism include the site and size of incision, the type of suture used and suturing technique and thereby the corneal distortion induced. Small incisions induce less astigmatism and thereby enhance visual recovery following SICS. Thus SICS is an answer to the problems related to post-operative astigmatism.
Another important determinant of post operative astigmatism is the site of incision. The closer the incision is to the limbus, the greater the post- operative astigmatism.
There are differing schools of thought regarding the surgical management when cataract is complicated by the presence of glaucoma. Some surgeons prefer to operate the cataract and trabeculectomy separately as compared to a single stage combined procedure. Both the one stage and two stage procedures have their own adherents. A combined single stage technique offers early visual restoration and prevents the early post-operative intra ocular pressure rise that may result from cataract surgery alone while undergoing surgical insult only once. A two stage procedure however allows the surgeon to implement newer astigmatically neutral techniques for incision placement and determining the size of incision to be done.
Whether the benefit of a small incision holds good in a combined surgery with trabeculectomy remains undetermined. The likelihood of postoperative astigmatism following a trabeculectomy is considered to be less of a problem since the scleral incision is placed well behind the limbus although the anterior chamber entry is anterior in the clear cornea. A clear corneal incision approach provides increased safety, decreased inflammation and pain as well as reduced post operative astigmatism. It would be of great benefit to know the amount of post-operative astigmatism induced following a combined cataract and trabeculectomy procedure and efforts can then be made to minimize this problem.
Very few studies have been undertaken in this regard. The present study is undertaken to compare the amount of induced astigmatism following Small Incision Cataract Surgery combined with Trabeculectomy compared to Small Incision Cataract Surgery alone.
6.2 REVIEW OF LITERATURE:
Cataract is the leading cause of blindness all over the world followed by glaucoma, age related macular degenerations, diabetic retinopathy and trachoma1. In many instances patients suffer from cataract with co-existing glaucoma. The only treatment to date for cataracts is surgical removal of the cataractous lens with implantation of an IOL to counter the resultant aphakia. Till the middle of the last century the favoured surgical technique was Extra Capsular Cataract Extraction (ECCE). Although it was replaced by Intra Capsular Cataract Extraction (ICCE) techniques in the second half of the twentieth century, the post operative complications of ICCE such as Retinal Detachment and Endophthalmitis caused the procedure to fall into disrepute and there was a return to ECCE. Today the technique of ECCE has seen many refinements in the form of improved instrumentation, equipments and modified surgical steps.
Corneal Astigmatism has been a by-product of cataract surgery as well as trabeculectomy since the first corneal incision was made. Patients with post operative corneal astigmatism account for a large number of such refractive errors and suffer from delayed visual rehabilitation and limited visual outcome thus reducing the effectiveness of the procedure. Symptoms such as glare, monocular diplopia, asthenopia and distortion are accompaniments. Even when corrected with glasses, astigmatism may cause off-axis blur eyestrain and visual field restriction. Both cataract extraction and trabeculectomy are known to cause mild to moderate degrees of changes in corneal curvature leading to post - operative astigmatism, each producing one or the other kind of astigmatism. It is now well known that cataract surgery produces an increase in vertical corneal radius of curvature and owes it to the wound gape or wound compression and also may be related to the size of the incision. In contrast, in trabeculectomy there occurs a reduction in the corneal radius in the vertical meridian. This difference may be the result of the partial thickness scleral flap created during trabeculectomy. The surgically produced gap is overlaid by a scleral flap, which spreads support from the sutures inserted into it over the whole of wound gape; the more posterior placement of the incision may also explain the difference in behaviour in comparison with cataract extraction2, 3. Following a combined procedure there may occur an increase or reduction of the vertical corneal radius of curvature.
In order to minimize the post operative astigmatism, the length and architecture of the incision, site of incision, types of suture and suture materials have all been modified over the years. A prime example being the change of surgical techniques from ICCE to ECCE to SICS to Phacoemulsification. The advent of improved instrumentation (better blades, canulas and needles) as well as better pre-operative and intra-operative measurements of astigmatism has led to a series of improvements, which promise to solve or greatly reduce the problem of induced astigmatism following cataract surgery and trabeculectomy, in the majority of patients.
It therefore becomes imperative to study the surgically induced astigmatism following the various techniques in order to offer the best corrected visual acuity post surgically.
CORNEAL ANATOMY AND OPTICS:
The eye acts as an optical instrument in which the Cornea and the lens act as focusing system of the eye. Cornea is a highly transparent structure of meniscus form, approximately 12mm in diameter and slightly smaller vertically than horizontally. The centre thickness is usually between 0.5 – 0.6mm. The thin pre-corneal tear film covering the anterior surface is too thin to affect the power appreciably. Both the surfaces of the cornea are regarded as spherical, the anterior radius of curvature being +7.7mm and posterior radius of curvature being +6.8mm. The refractive index of the corneal substance may be taken as 1.376 and that of the aqueous humour, in contact with the back surface of cornea as 1.336.
Since the shape of the corneal surface determines its refractive power, even a minor modification of its surface can lead to a significant alteration of the image formed on the retina. Consequently efforts have been made to detect and monitor this important refractive surface. The techniques frequently used to measure the anterior corneal curvature are Keratometry and Corneal Topography.
SALIENT FEATURES OF CORNEA:
The anterior surface of the cornea is elliptical with an average horizontal diameter of 11.5mm and vertical diameter of 10.6mm. The posterior surface of the cornea is circular with an average diameter of 11.5mm. The corneal thickness varies from 0.52mm at centre to 0.8mm peripherally increasing to about 1.2mm at the limbus. Thus the cornea has different radii of curvature at different points along the same meridian with central steepening and peripheral flattening. The central zone occupies the central 4mm of the cornea and is responsible for forming image at the fovea. The cornea is divided into three peripheral zones, namely – the Para central zone which is 4 – 8mm in diameter, peripheral zone of 8-11mm diameter and a limbal zone of 11- 12mm diameter. The light entering the eye as a whole is refracted markedly at the anterior corneal surface for two reasons- the corneal curvature and the difference in refractive indices of air and cornea.
The aspherical shape of the cornea’s anterior surface is responsible for baseline astigmatism of 0.25 – 0.5D in almost every human eye.
Astigmatism is a type of refractive error wherein the refraction varies in different meridian. As a result of which, the rays of light entering the eye cannot focus on a point focus but form multiple focal lines.
Sir Isaac Newton, who himself had been astigmatic, first considered the question of astigmatism in 1727. This optical error received its first detailed investigation from the scientist, Thomas Young, in 1801discovered that his astigmatism of 1.7D remained unchanged on his immersing his head in water and thus eliminating the influence of the corneal refraction, and so he attributed this defect to the lens. Although Cambridge astronomer, Airy in 1827, was the first to correct the defect by cylindrical lens it was largely the work of Donders in 1864, which impressed the ophthalmic society with the prevalence and importance of Astigmatism.
About 50% of full term infants in their first year of life have astigmatism of over 1D. The incidence of astigmatism decreases as the child grows and by adulthood about 15% of the people have astigmatism > 1D and only 2% have astigmatism > 3D.
The Stenstrom’s study from Uppsala, Sweden, proposed a rough estimate on the incidence of Astigmatism:
Almost all individuals have a minor degree of physiological astigmatism.
About 60% cases of refractive errors have astigmatism which needs to be corrected.
Astigmatism occurs with equal frequency in males and females.
The approximate distribution according to degree of astigmatism is:
0.25- 0.5D 50%
0.75- 1.0D 25%
1.0 - 4.0D 24%
> 4.0D 1%
The most common type of astigmatism is compound myopic, followed by compound hypermetropic, mixed, simple myopic and simple hypermetropic.
With the rule 38%
Against the rule 30%
Symptoms of Astigmatism include transient blurring of vision, asthenopic symptoms, tilting of the head, and squinting, burning and itching sensation in the eyes. When the astigmatism shows a steeper vertical corneal meridian, it is termed with-the-rule and a steeper horizontal corneal meridian; it is called against-the-rule. Corneal astigmatism is usually with-the-rule in young eyes and there is a shift toward against-the-rule with advancing age.4
a) Retinoscopy – it is the time tested method of estimating the optical state of the eye. An illuminated area of the retina serves as an object and the image is formed at the far point of the eye by moving the illumination across the fundus and noting the behavior of the luminous reflex in the pupil. Conclusions can be drawn regarding the refractive status of the eye by studying the nature of the rays, emanating from the fundus to form an illuminated area of the pupil. If the image is formed between the patient and the observer, the movements of the reflex and the external light are in opposite directions. If it falls outside the region, either behind the patient’s eye or behind the observer’s eye, the two move in the same direction. When the far point of the patient’s eye corresponds to the nodal point of the observer’s eye, a neutral point is reached. The rationale of the method is to add lenses to the diopteric system of the patient’s eye until the point of reversal is seen by the observer.
In Astigmatism, the refractionist has to determine, not only the neutralization points of the principal meridians but also the orientation of the meridia.
The various retinoscopes used nowadays are reflecting retinoscopes – may be a plane mirror or a combination of plane and concave mirrors like the Priestley- Smith’s mirror or self illuminating ones like spot or streak retinoscopes.
b) Keratometry-the keratometer is used to determine the different corneal curvature in the two different meridians which may or may not be orthogonal. It is the measurement of the curvature of the anterior surface of cornea across a fixed chord length, usually 2-3mm, which lies within the optical spherical zone of the cornea. An ideal keratometer must be able to measure the radii in various meridia about the axis of the cornea. To this end, instruments are designed that can be rotated with respect to a particular axis. The objects are called mires. Various keratometers have been designed such as Helmholtz keratometer, Bausch and lomb keratometer, Javal – schiotz keratometer and today there are also Surgical keratometers and Automated keratometers.
BAUSCH AND LOMB KERATOMETER: The working of the Reichert (Bausch and Lomb) keratometer is based on the principle of constant image size and variable image size.in order to avoid error due to constant motion of the eyes, this doubling device has been introduced.
Optical system and parts of Bausch and Lomb Keratometer:
The object is circular mire with two plus and two minus signs.light from the mire strikes the patient’s cornea and produces a diminished image behind it. This image then becomes the object for the remainder of optical system.
The objective lens focuses the light from the image of the mire along the central axis.
Diaphragm and doubling prisms
Procedure of Keratometry involves the adjustment of the instrument and patient, focusing of the mires and the measurement of corneal curvature. The findings in case of astigmatism are a difference in the power between two principal meridian, horizontally oval mires in with- the – rule astigmatism and vertically oval mires in against- the – rule astigmatism.In oblique astigmatism, the principal meridian are between 3-600 and 120- 1500
d) Jackson cross cylinder test- confirms the power and axis of cylindrical lenses and is mostly useful for refining the spectacle prescription.
Treatment of Astigmatism includes prescribing appropriate cylindrical lens after accurate refraction. Modalities include spectacle correction, hard contact lens and in cases of higher astigmatism, toric lenses. Astigmatism nowadays is increasingly being tackled surgically with procedures like Astigmatic keratotomy, Photo astigmatic refractive keratotomy, Astigmatic epi-LASIK, Astigmatic LASIK and Astigmatic C- LASIK.
Any opacity in the lens or its capsule, whether developmental or acquired, is termed a cataract. Cataract is caused by the degeneration and opacification of the lens fibres or deposition of other materials in their place.
Specific investigations include slit lamp examination for grading the cataract and when the fundus cannot be seen – macular function tests namely detection of projection of rays, Maddox rod test, entoptic phenomenon and two-point discrimination test and colour vision needs to be tested.
Cataract surgery or removal of the crystalline lens is performed if the lens is causing visual loss by virtue of opacification, subluxation or dislocation, defects in shape or any lens induced complications. The various strategies include:
Intracapsular cataract extraction
Conventional Extracapsular cataract extraction
ECCE by small incision cataract surgery or
Small incision manual nucleus fragmentation
SMALL INCISION CATARACT EXTRACTION WITH PCIOL IMPLANTATION:
In developing countries, manual small incision cataract surgery is becoming very popular because of its merits over conventional ECCE as well as Phacoemulsification. In this technique, ECCE with intraocular lens implantation is performed through a sutureless self-sealing valvular sclera corneal tunnel incision under local anesthesia preferably.
Surgical steps include:
Superior rectus (bridle) suture is passed to fix the eye in a downward gaze.
Conjunctival flap and exposure of sclera. A small fornix based conjunctival flap is made with the help of sharp tipped scissors along the limbus from 10 to 2 o’clock positions. Conjunctiva and the Tenon’s capsule are dissected, separated from the underlying sclera and retracted to expose about 4mm strip of sclera along the entire incision length.
Haemostasis is achieved by applying gentle and just adequate wet field cautery.
Sclera- corneal tunnel incision. A self sealing sclero-corneal tunnel incision is made in manual SICS. It consists of the following components:
External sclera incision
internal corneal incision
A Side port entry of about 1.5mm valvular corneal incision is made at 9 0’clock position. This helps in aspiration of the sub- incisional cortex and deepening the anterior chamber at the end of the surgery.
Delivery of the nucleus by irrigating wire vectis method/ Blumenthal technique/ phacosandwich technique/phacofracture technique/fishhook technique.
Aspiration of cortex
Removal of viscoelastic material
Ensuring a sealed wound.
In many patients cataract co-exists with glaucoma. Glaucoma is a chronic, progressive optic neuropathy caused by a group of ocular conditions which lead to damage of the optic nerve with loss of visual function. The most common risk factor known is raised intraocular pressure. Specific investigations include tonometry to access the iop either digitally or by applanation tonometry, optic nerve head changes to be detected by direct and indirect ophthalmoscopy, gonioscopy to grade the degree of glaucoma and perimetry to access the visual field defects in relevant cases.
Although, in adults, several surgical options like Peripheral iridectomy, Goniotomy, Trabeculotomy, Artificial drainage shunt operations and Cyclo- destructive procedures are available, filtering procedures like trabeculectomy is the most preferred.
Trabeculectomy, first described by Carain in 1980, is the most frequently performed partial thickness filtering surgery till date.
Mechanisms of filteration:
A new channel fistula is created around the margins of sclera flap, through which aqueous flows from anterior chamber into the conjunctival space.
If the tissue is dissected posterior to the sclera spur, a cyclodialysis may be produced leading to increased uveoscleral outflow.
Initial steps of anaesthesia, cleansing, draping, exposure of eyeball and fixation with superior bridle suture is done
Conjunctival flap. A fornix based or limbal based conjunctival flap is fashioned and the underlying sclera is exposed. The Tenon’s capsule is cleared away using a Tooke’s knife and haemostasis is achieved using cautery.
Sclera flap. A partial thickness limbal based sclera flap of 5mm x 5mm size is reflected down towards the cornea.
Excision of trabecular tissue. A narrow strip of the exposed deeper sclera near the cornea containing the canal of Schlemm and the trabecular meshwork is excised.
Peripheral iridectomy is performed at the 12 o’clock position with de Wecker’s scissors.
Closure: the sclera flap is replaced and 10-0 nylon sutures are applied. Then the conjunctival flap is reposited and sutured with two interrupted sutures or continuous sutures.
Sub conjuctival injection of dexamethasone and gentamicin is given.
The sclera flap can be tested for adequate flow resistance, before closing the conjunctival flap, by injecting balanced salt solution into the anterior via a paracentesis.
CO-EXISTING CATARACT AND GLAUCOMA:
In the management of a patient with a cataract with coexisting glaucoma, the options for surgical correction include:
A cataract extraction alone
Combined cataract and glaucoma surgery as a one stage procedure.
As compared to cataract surgery alone, combined procedures have a greater risk of complications such as increased inflammation, hyphema, hypotony, shallow anterior chamber, and choroidal detachments, but they have an advantage of less early IOP rise. For these reasons the operating surgeon should consider each of the basic surgical options and select the approach that seems to be most appropriate for each individual.
COMBINED CATARACT EXTRACTION AND
Between the two extremes i.e those patients with good glaucoma control and those with uncontrolled glaucoma which poses an immediate threat to vision, there is a third group of patients with borderline glaucoma status for whom combined procedure may be indicated. There is often a fine line of judgement involved in selecting these cases, although the following situations are some in which such an approach might be preferred.
Glaucoma under borderline control despite maximum tolerable medical therapy,
Adequate IOP control, but significant drug induced side effects
Adequate IOP control on well tolerated medical therapy, but advanced glaucomatous optic atrophy,
Uncontrolled glaucoma, but an urgent need to restore vision or when two operations are not feasible.
The rationale for a combined procedure, as opposed to cataract surgery alone, in eyes with good IOP control but advanced damage, is the risk of a transient pressure rise in the early post operative period. Studies have shown that the early post operative pressure rise is significantly less after a combined procedure than after cataract extraction alone5, 6.
Modifications in the combined surgery:
A soft eye is necessary which can be achieved by a mercury bag or oculo-compression or mercury bag or by digital pressure. After retrobulbar injection of anesthesia, a superior rectus bridle suture is placed. A limbus or fornix based conjunctival flap can be used. A lamellar scleral flap is incorporated into the 10mm chord length incision. It is outlined in a square, trapezoidal or half moon shape with a sharp knife. Grooves are made on both sides of the sclera flap along the posterior limbal border to the desired extent of the corneoscleral incision. A two-planed incision in which the entry incision is beveled is preferred and the anterior chamber is entered anterior to the schwalbe’s line, at the proximal extension of the sclera flap.
An anterior capsulectomy is performed. An iridoplasty may be required if the pupil dilates poorly. A rectangular trabeculectomy site is outlined with four incisions, two parallel to and perpendicular to the limbus. The small rectangular piece of deep sclera is excised. A punch can be inserted to cut a hole in the sclera and a peripheral iridectomy is formed. The nucleus is expressed using the standard bimanual technique and sutures are put to form a relatively closed eye. The centre suture is cut and a PCIOL is inserted after the capsular bag is inflated with a viscoelastic material. The incised iris is not usually sutured and the larger pupil permits evaluation of the retina and the optic nerve. The scleral flap is loosely sutured and the conjunctival flap is closed with absorbable or non absorbable sutures.
Normally, the vertical corneal meridian is more steeply curved than the horizontal meridian in with-the-rule and is corrected by a plus cylinder whose axis is at 90 degrees. While in against-the-rule astigmatism, the horizontal corneal meridian is more steeply curved than the vertical meridian and is corrected by a plus cylinder whose axis is at 180 degrees.
In the recent times, post-operative astigmatism has given rise to a lot of concern as it interferes with the final outcome of a well performed ocular surgery and thereby delays the visual rehabilitation. There still exists considerable confusion and difference in opinion regarding the pathophysiology of postoperative astigmatism following SICS, Trabeculectomy and combined procedures due to the differing techniques employed in the various studies undertaken. Post-operatively, patients can develop either a with–the-rule astigmatism or against-the-rule astigmatism.
ASTIGMATISM POST CATARACT EXTRACTION:
The size, architecture and location of the incision together influence the post-operative astigmatism following a cataract extraction. The incision is more than a port of access into the anterior chamber as it represents an important step of the operation thereby affecting ocular integrity and corneal stability.7
Satoperformed a posterior half incision the midpoint of which was placed on the steeper meridian of the cornea in which the refractive power of the eye is greatest8. The effectiveness of this procedure was maximal when the incision was made tangential to the pupil. This was later corroborated by Corcostegui Moliner, who alsoreported that the reduction of refraction in the meridian of greatest curvature is greater the larger the amplitude of the keratotomy, the more tangential the incision is to the cornea and the closer it is to the pupil9. The studies undertaken by N S Jaffe showed that the smaller the amplitude of the incision, the less the effect there is on the horizontal meridian. Incisions ending at or beyond the horizontal meridian tend to neutralize some of the changes in the vertical meridian10, 11.
Small incisions are beneficial as they induce less corneal distortion, promote more rapid wound healing and provide more control of the anterior chamber during surgery12-14. The best incision for cataract surgery ensures no leakage and has minimal influence on corneal shape. Drews found that 2.0 mm wounds had essentially no effect on corneal astigmatism, showing almost no shift over 5 years12. In their study in 60 patients, Beltrame et al. found a mean induced astigmatism of 0.7D with 3.5mm incisions13. Steinert et al. found an induced astigmatism of 1D with 4mm incisions and Naesser et al reported astigmatism of 0.6D averaged across 59eyes with 4 mm incisions14, 15.
The effect of location of the incision on the corneal curvature is related to the delayed wound healing observed with anterior incisions.Kohnen et al and barequet et al in their respective studies have both reported a statistically significant reduction in astigmatism in a temporal approach when compared to a nasal incision16, 17. A similar study was undertaken by Nikhil.S.G where he similarily reported that induced astigmatism was lower in groups where temporal and superotemporal incisions were made when compared to the group with a superior incision18.
Using non-absorbable sutures material (nylon) leads to with-the-rule astigmatism at 6 weeks whereas using absorbable or removable suture (chromic catgut or silk) leads to against-the-rule astigmatism. In an effort to reduce the progression of this against-the-rule astigmatism usually seen following extracapsular cataract extraction, 10-0 monofilament polypropylene sutures and 10-0 monofilament polyester sutures were introduced as they tend to remain in the eye longer before degrading19. However with the advent of Phacoemulsification, the beveled nature of the incision ensures a sutureless closure of th incision. In his study Masket found that the sutureless incisions skip the with-the-rule phase and at once demonstrate against-the-rule astigmatism even on the first post-operative day20. Thus, sutures tend to cause with-the-rule astigmatism and both sutured as well as un-sutured incisions move towards against-the-rule astigmatism over time.
ASTIGMATISM POST TRABECULECTOMY:
Trabeculectomy affects the corneal curvature but the post-operative astigmatism following trabeculectomy does not follow a similar trend as of post cataract astigmatism. In majority of patients undergoing this procedure, the vertical corneal radius of curvature is reduced with a trend towards with-the-rule astigmatism. The horizontal radius of curvature is increased and thus there is a steepening in the vertical meridian. In the various studies undertaken the above trend was marked in the first 3 months of early postoperative period and decreased by the third post-operative month.
Hugkulstone was one of the first to undertake a study regarding astigmatism post trabeculectomy3. He found similar changes of reduction in vertical corneal radius of curvature following trabeculectomy. Rosen et al found that 5 out of 8 eyes developed 1.5 – 2.0D of steepening in the vertical meridian following trabeculectomy21. Cunliffe IA et al discovered that the change in vertical corneal curvature after trabeculectomy is consistent with the with-the-rule change in corneal astigmatism22. Similar studies conducted by several
others23-27 show that trabeculectomy causes certain with-the-rule astigmatism which in most of the cases may decrease as time passes by, though a statistically insignificant small number of patients developed a superior corneal flattening.
Various explanations have been put forward to explain this effect of trabeculectomy on corneal curvatures. It may be related to the surgically produced gap in trabeculectomy is overlaid by a partial thickness scleral flap which is capable of spreading any support from the sutures inserted into it over the whole of wound gape. The more posterior placement of the incision and the use of cautery producing a scleral contraction in the meridian of surgery may also explain this trend of with-the-rule astigmatism following trabeculectomy.
ASTIGMATISM POST COMBINED SURGERY:
Studies on induced corneal astigmatism following combined cataract and trabeculectomy are few and comparison among the studies limited due to the different surgical techniques employed in these studies. Earlier studies have demonstrated a tendency to the development of against-the-rule astigmatism following a combined surgery, with an average induced cylinder of about 2D against-the-rule astigmatism 28-30. Hong et al reported a shift of astigmatism at the vertical meridian from +2.17 D to -1.72D over 12 months after a combined operation26. Choplin,in his study compared the amount of surgically induced astigmatism between eyes undergoing combined cataract- filteration surgery and cataract surgery alone and concluded that about 1.00D of the induced against-the-rule astigmatism was due to the filtering procedure itself31.
Hence, it is quite evident that very few studies have been undertaken to determine the post operative astigmatism induced by a combined procedure and the exact nature and explanation of the deviation remains to be elucidated.
6.3 OBJECTIVES OF THE STUDY:
The objective of this study is to compare the post-operative Astigmatism following combined Cataract extraction with Trabeculectomy to the post-operative Astigmatism following Cataract extraction alone.
7. MATERIALS & METHODS:
7.1 SOURCE OF THE DATA
Patients (maintaining inclusion & exclusion criteria) attending the ophthalmology outpatient department of the Yenepoya Medical College & Hospital.
7.2 METHODS OF COLLECTION OF DATA
This is a prospective study of the comparison of the postoperative astigmatism following cataract surgery to combined cataract and trabeculectomy surgery during a period of one and half years.
Study Type: Comparative Study.
Duration of Study: One and half years.
Sample Size: Forty patients (selected using purposive sampling technique), twenty of whom will undergo Small Incision Cataract Surgery with PCIOL implantation in one eye will be included in the study. Another twenty patients will undergo a combined Small Incision Cataract Surgery with PCIOL Implantation combined with Trabeculectomy. Data will be collected in accordance with the clinical Proforma.
These forty patients will be categorized into two age matched groups as follows:
Group A will comprise of 20 patients who will undergo Small Incision Cataract Surgery with PCIOL Implantation alone.
Group B will comprise of 20 patients who will undergo Small Incision Cataract Surgery
with PCIOL Implantation combined with Trabeculectomy.
INVESTIGATIONS: visual acuity tests
Slit lamp examination
Corneal topography (in relevant cases)
All cases of senile cataract without any other ocular disorder.
All cases of glaucoma with co-existing cataract with normal cornea.
Grossly altered corneal topography
Any history of previous ocular surgery
Post operative complications
Any preceeding eye disease other than cataract or glaucoma
Data will be collected in accordance with the inclusion-exclusion criteria and analysed by t-tests between the two groups- A and B. The sample size being 40 patients.
Sex: Age: Year:
Sex: Age: Year:
Relationship with the patient:
I ……………………………………… the undersigned GIVE CONSENT for timely investigations and for co-operating to be a part of the study undertaken by Dr. RAJNA.
The precise nature of the study and the investigations has been explained to me / my bystander in my own language and I have understood the procedure and give my consent willingly.
7.3 Does the study require any investigations or interventions to be conducted on patients or other humans or animals? If so please describe briefly.
The study will involve non invasive investigations on humans
Ethical clearance: Has ethical clearance been obtained from your institution in case of 7.3?
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Barequet IS, Yu E, Vitale S, Cassard S, Azar DT, Stark WJ.Astigmatism outcomes of horizontal temporal versus nasal clear corneal incision cataract surgery. J Cataract Refract Surg. 2004; 30:418-423.
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9.Signature of candidate:
10.Remarks of the guide :
An important study to know if Trabeculectomy combined with cataract surgery affects the corneal curvature differently from Cataract surgery alone.