Contact lens pre fitting evaluation and Examination

Contact lens pre fitting

1. Name:-Ayan Das
University Roll No.:-16401722005
Stream:-Bachelor of Optometry
Semester:-5
th
Subject:-Contact Lens
Paper Code:-BO-502

2. Introduction
•Aroutinepreliminaryexaminationshouldbedoneforeachpatient
beforefittingcontactlenses.Thepurposeofdoingthisisto:
1.Determineifthecontactlensesareindicatedorcontraindicated.
2.Tocollectthebaselineinformation.
3.Toadvicethebestoptionforthepatient.
4.Toeliminatepostfittingcomplications.

3. Steps
Thepreliminaryexaminationconsistsoffollowingsteps:
•Assessingreasonsforwantingcontactlensesandthe
motivation
•Takingdetailedhistoryofpatient’sgeneralcondition,ocular
condition,medicationandpreviousvisioncorrection,
occupationalandenvironmentalfactors.
•Evaluatingpatientsrefractiveerrorandbestcorrected
vision.
•Examiningtheocularstructuresofthepatient.

4. Patient Screening
•History Taking
✓History taking reveals the ocular status of patient.
✓It helps in recommending suitable lens as per Occupational
needs of patient. Patients engaged in sports need very
sharp vision and less moving lenses like soft contact lens,
similarly patients in dusty environments may not adapt to
RGP lenses.
✓The examiner gets to know about patient’s previous contact
lens history, if any.

5. Patient Screening
•Identifying why the patient needs Contact lenses?
✓Cosmetic purpose
✓Therapeutic purpose
✓Occupational requirements
✓Pathological condition
✓Myopia control
•It will help in choosing the best contact lenses for the patient.

6. Refraction
•Baseline refraction
✓It includes both subjective and objective findings
(autorefractor, retinoscopy)
•Vertex distance
✓Vertex distance compensation should be made in case of
the power are above +/-4.0 diopters.
•Accommodation and Convergence
✓Myopes have to converge and accommodate more in
wearing contact lenses than in spectacles so they require
less minus power
✓Conversely, hyperopes have to accommodate and converge
less when wearing contact lens so they require more plus
power than spectacles.

7. Anterior segment examination
•Slitlampbiomicroscopeisusedforexaminingtheanterior
segmentofeye.
•Biomicroscopyisnecessaryasithelpsindiagnosingany
anomaliespresentthatmaycausecomplicationsincontactlens
wear.
•Siltlampbiomicroscopyisperformedbeforeanytriallensfitting
toidentifypossiblecontra-indications.
•Itisrepeatedduringandafterthetrialfittingtoassessthefit
anddetectanyanteriorsegmentchangesinducedbylenses.

8. Cont..
Aslitlampexaminationisperformedtoassesstheconditionof:
•Eyelids
•Conjunctiva
•Cornea
•Tears
•Anteriorchamber

9. Ocular Measurements
•Corneal Curvature
✓Keratometry
✓Corneal topography
✓Horizontal Visible Iris Diameter (HVID)
✓Vertical Visible Iris Diameter (VVID)
HVID and VVID are measured using torch
and ruler
•Pupil Measurements
✓Under low illumination
✓Under standard room illumination

10. Ocular Measurements
•Palpebral Aperture
✓The shape and size of Palpebral aperture varies in races
specially the Asian versus Caucasian eyes. Measurements
are done by millimeter scale.
•Lid Tension
✓It is a subjective method of measuring the tightness of eyelid,
there is no specific instrument available.
✓The patient looks down and the examiner pulls down the
upper lid outward by grasping the eyelashes gently.
✓Subjectively grading the resistance to pulling from +3 (very
tight) to -3 (very loose).
Lid tension affects lens centration and movement. Higher lid
tensions cause greater displacement on blinking.

11. Ocular Measurements
•Blink Rate
✓An adequate blink rate is necessary to
prevent desiccation of the ocular surface.
✓Partial blinking may result in superficial
punctate staining of the cornea.
✓An average blink rate of approximately 15
blinks per minute is considered normal.

12. Tear Layer Assessment
•It is performed to assess the proper functioning of lacrimal system.
•Patients with DRY EYES are not suitable for soft contact lens
candidates.
•The following tear layer measurements should be undertaken:
✓Schirmer test, Phenol red thread test
✓Break-up time
✓Lipid layer evaluation

13. •Schirmer test
✓This test measures the volume of the tears. Special filter strips
are bend over the notch and hooker over the nasal lower lid
margin.
✓Patient is asked to blink normal during the measurements, the
wet area of the strip is measured after 5 minutes of insertion.
✓Reading above 10 mm is taken as normal.
•Phenol Red Thread test
✓This test can be done similarly by using a 70 mm thread dipped
in phenol red dye.
✓The wet length is noted as colour change from yellow to red.
Tear Layer Assessment

14. •Break-up time
✓This test measures the stability of the tear film. Fluorescein
dye is instilled in the eye and patient is asked to blink. The
tear layer is observed with the cobalt blue filter of slit
lamp.
✓The first appearance of dye spot of cornea is seen and BUT
less than 10 seconds is suspicious of dry eye or unstable
tear film.
•lipid layer evaluation
✓This is done by using Tearscope.
✓Different colour fringes patterns are seen depending upon
the thickness of the tear layer.
✓Thicker layer means better stability and less evaporation
while it may lead to lipid deposits problems.
Tear Layer Assessment