RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES

KARNATAKA, BANGALORE

PROFORMA FOR REGISTRATION OF TOPIC FOR DISSERTATION

1 / Name of the candidate / Dr. Kishore Krishna Nyamagouder
Address of the candidate / Department of Ophthalmology
2 / Name of the institution / Vydehi Institute of Medical Science and Research Center Bangalore- 560066
3 / Course of the study and the subject / MS - Ophthalmology
4 / Date of admission to course / 30 May,2009
5 / Title of the topic / To evaluate the predictability of IOL power calculation using ultra sound biometry ( A-scan & B-scan) comparing SRK II and SRK/T formulas.
6 / Brief resume of intended work
Need for the study :
Various formulas are used t to calculate IOL power .The variables in IOL power calculation are
Keratometry - Corneal curvature in Dioptres
Central anterior chamber depth in millimeters
Axial length of the eyeball in millimeters
Effective IOL position – Anterior chamber / Iris fixated / Posterior chamber
Desired postoperative refractive status
Each formula has peak specificity at a particular range of axial length .Our study will determine the accuracy of the IOL power calculation formulas.
6.2 / Review of literature
IOL formulas are evaluated for emmetropes, hyperopes and myopes from time IOL implantation began Sanders 1 and Retzlaff 2
The formulas were subsequently improved by Retzlaff 3 ,Sanders4
Hoffer KJ 5 , Holladay JT6
First generation formulas assumed the effective lens position and Anterior chamber depth to be the same in all cases.Later formulas assumed them to differ from case to case and also took into account lens thickness . The SRK /T formula is thought to be more accurate than the SRK II formula in patients with axial length 22to 25mm and corneal power between 42and 46D.
Our study plans to assess the accuracy of IOL power calculation in terms of predicted and actual spherical equivalents using SRKII and SRK/T IOL formulas in emmetropes, hyperopes and myopes and compare data with other studies7 .
6.3 / Objective of the study
Ø  To compare and evaluate the IOL power calculation using SRK II and SRK/T formula .
Ø  To evaluate the post operative objective and subjective refractory status – spherical equivalents using both formulas
7 / Resources and Method
7.1 / Source of data
1.  Comparative clinical study in which the IOL power is calculated using the above SRK- II and SRK/T in all cataract patients (emmetropic hypermetropic and myopic) visiting ophthalmology department of Vydehi Institute of Medical Sciences & Research Center Hospital, Bangalore.
2.  Informed written consent of the participating patient shall be taken.
3.  A pre-structured proforma shall be used to collect the base line data.
4.  Routine clinical examination is performed for those who satisfy the inclusion and exclusion criteria.
5.  Keratometry( Average of three)and A-scan readings
(Average of three ) are taken . Any discrepancy in axial length of the two eyes greater than 0.2mm is rechecked .
6.  IOL is implanted using power calculated by SRK II formula. The actual refractive error/ spherical equivalent can be compared with the predicted refractive error / spherical equivalent using SRK/T formula .
7.2 / Method of collection of the data
Informed written consent of the participating patient is taken. Pre-structured proforma is used to collect the base line data.
Post – operative desired refractive status was decided on basis of his/her requirement. The post operative actual spherical equivalent was estimated on first post-operative day ,and thirtieth post-operative day and compared to the predicted spherical equivalent using both SRK II and SRK /T formulas.
B Scan is performed on all patients to compare the anterior and posterior segment ratio as disproportion between the two is known to occur. The study plans to determine if the anterior segment, posterior segment disproportion is more common in hypermetropes or myopes.
Statistical analysis used
1.  T- test
2.  Mean
3.  standard deviation
Sample size calculation :
To calculate the number of cases for the study the formula used is
n=Z2PQ/ d2
where
n= number of cases,
Z= 1.96 at 95% accuracy
P= prevalence of cataract
Q= 100- P
d= 20% of P
Inclusion criteria:
Ø  All men and women aged 40 years to 70 years with cataract
undergoing cataract extraction and IOL implantation irrespective of their axial length and pre-operative refractive status .
Exclusion criteria
Ø  History of ocular trauma
Ø  History of ocular surgery
Ø  Subjects who are blind due to causes other than cataract- glaucoma,keratoconus, diabetic retinopathy, hypertensive retinopathy,
corneal opacities /dystrophies,ARMD .
7.3 / Required investigation and intervention
Ø  Keratometry reading using auto-refractokeratometer (PRK- 5000)
Ø  Axial length using A-scan (AXIS- 11) ultrasound
Ø  Anterior segment and posterior segment length using calipers on
B-Scan ultrasound
Ø  Post operative refractive status is calculated using Heine streak retinoscopy , autorefractor and subjective refraction.
7.4 / Ethical clearance from Ethics committee of the Vydehi Institute of Medical Sciences & Research Centre was obtained .
8 / List of references
1.  Sanders DR, Kraff MC, improvement of intraocular lens power calculation using empirical data. JAM Intraocular implant Soc. 1980 Jul.6 (3):263-267
2.  Retzlaff.a new intraocular lens calculation formula.
J Am Intraocular Lens Implant Soc .1980 April 6 (2) : 148- 152
3 Retzlaff J A, Sanders DR, Kraff MC. Development of SRK/T intra-
ocular lens implant power calculation formula. J Cataract Refract Surg
1990:333-40.
4 Sanders DR, Retzlaff JA, Kraff MC, et al. comparison of the SRK/T formula and other regression formula. J Cataract Refract Surg 1990:16:341-6.
5 Hoffer KJ The Hoffer Q formula : a comparision of theoretical and
regression formulas J Cataract Refractive Surg 1993 : 19 : 700-712
6 Holladay JT , Prager TC , Ruiz RS et al Improving the predictability of intraocular lens calculations
Arch Ophthalmol 1986 104 : 539-541
7  Wang JK , Hu CY, Chang SW et al
Intraocular lens power calculation using IOL Master and various formulas in eyes with long axial length
J Cataract Refract Surg 2008 , Feb 34 (2 ) 262-267
9 / Signature of the candidate
10 / Remarks of the Guide
Only persons between 40 and 70 years of age were included in the study to avoid ocular morbidity due to extremes of age.
An attempt is made to determine the anterior segment to posterior segment ratio in hypermetropes, emmetropes, myopes in an rural Indian population .
11 / Name and designation of the guide : Dr.I.Vittal Nayak
M.S. Ophthalmology
Prof & HOD of Ophthalmology
VIMS & RC
B,Lore.-66
12 / Signature of guide
13 / Co-guide : Dr.Seema Channabasappa
M.S.Ophthalmology
Asso.Prof
VIMS & RC
B,lore.- 66
14 / Signature of Co-guide
15 / Head Of The Department’s signature
16 / Remarks of the principal
17 / Signature

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