RGP CL
Rigid gass permealbe contact lens
Parents: Why my child sees blur?
Feb 27th
Parents: Why my child sees blur?
First you should tell how long, which eye, simultaneous symptom such as eye pain, red eye etc. to doctor about your child’s complain. After excluded congenital cataract, glaucoma, fundus abnormalities and nervous disease, the most common reason for it are optometric problems, such as myopia, hyperopia and astigmatism, sometimes keratoconus.
Follow the instructions according to your child’s age:
Myopia
1. 0~2 years old. Recommend using powerful cycloplegica, then exam the refractive status carefully. If there is no existed strabismus or high myopia, it is no necessary to prescribe glass wear, just observe. If high myopia, it is necessary to correct partial myopia.
2. 3~6 years old. Also recommend using powerful cycloplegica to correct partial myopia. As to less than -1.5D, observation is the treatment. The aim of this stage is to cure and prevent amblyopia.
3. 6~18 years old. The principle of wearing glass is MPMVA(maximum plus to maximum visual acuity). You should avoid accommodation of the eyes when in optometry. Avoid overcorrection. Generally, the refractive error would increase -0.5D to -0.75D per year. If exceeds, go to ophthalmologist to exclude eye disease such as glaucoma or wear RGP to prevent the hyper-increase. When the refractive error diopter is less than -3.0D, just wear the glass for distant seeing, if more than, wear all day.
Hyperopia
1. 0~3 years old. Also recommend using powerful cycloplegica to correct partial hyperopia which is more than 5.0D. If less than 5.0D, just observe. If amblyopia and strabismus, fully correct the refractive error.
2. 3~6 years old. If with amblyopia, strabismus and high AC/A, fully correct the refractive error. Mild hyperopia need no treatment.
3. 6~18 years old. Mild hyperopia need no treatment. Prescribe glass to child with visual fatigue and tell this kind of patient for wear for distance. If with amblyopia, strabismus and high AC/A, fully correct the refractive error.
Astigmatism
1. 0~2 years old. If with high astigmatism, amblyopia and strabismus, fully correct the astigmatism. Mild astigmatism need no treatment.
2. 3~6 years old. Fully correct the astigmatism.
3. 6~18 years old. Child always like see in wryneck and squint Fully correct the astigmatism. If have adaption problem, just correct insufficiently, then add gradually to full. As to the irregular astigmatism, RGP is the preference.
Astigmatism treatment methods
Feb 7th
Astigmatism treatment methods
How to make a success with refractive lens exchange? It depends on the patient’s education, expectation, surfacial status of the eye, such as tear film, fundus of the eye and the rate of posterior capsule opacification. The most important is to reduce residual refracive error, especially the astigmatism.
Treatment methods:
1. Spectcles. Wear toric glasses.
2. Toric contact lens. Such as soft contact lens and RGP.
3. Corneal surgery.
Incision:
AK: Aracuate keratotomy
LRI: Limber relaxing incision
RK: Radial keratotomy
Incisional modification: 0.5-1.0D
Excimer Laser:
PRK: Photorefractive keratectomy
Lasik: Laser in situ keratomileusis
Lasek: Laser Epithelial Keratomileusis(Laser sub-epithelial )keratotectomy
Sbk-lasik: Sub-Bowman-Keratomileusis
Epi-lasik: Epipolis laser in situ keratomileusis
4. RLE: Refractive lens exchange
PIOL: Phakic intraocular lens
IC-PIOL:Toric Verisyse
AS-PIOL: Phakic6
TICL: Implantable Collamer Lens（Visian）
IOL: Toric IOL
There are four misconceptions regarding corneal incision: unpredictable, only useful for low astigmatism, regress and dangerous and difficulty of learn curve. There are also keys to overcome it: proper centration, periph clear cornea, perpendicular, cut deep and clean.
The pricinple of laser correction is bioptics. PRK is more excellent than Lasik as it is safe as soon as four weeks. So, what is the best in so many methods? It needs time.
Am I suitable for contact lens?
Jan 31st
Indications
1. Age from 16 to 38
2. Myopia or hyperopia more than 1.5D, astigmatism less than 1.5D
3. Corneal curvature arranges from 41D to 46D
4. BUTs test time more than 15 second, Schirmer test is negtive
Contraindication
1. Refractive error less than 1D
2. Health habits are not good, like smoking, dirty
3. Ocular allergy, Chronic blepharitis, Arthritis, Exophthalmos, Ptosis, Psychological factors
4. Occupational environment
5. Wearing with cautious: swimming, once failure to wear
Particularly suitable for soft contact lens
1.Need to adapt to rapid or intermittent wear
2. Comfort
3. Low refractive errors(<1.5D)
4. Can not wear RGP
5. Athletes
6. Children (such as iris defects, amblyopia treatment, Albinism, nystagmus)
7. Big blepharophimosis
Particularly suitable for rigid gass permeable contact lens(RGP)
1. Those who need good vision
2. Those who have corneal astigmatism (sphere RGP can correct astigmatism within 2.5D)
3. Irregular astigmatism (corneal, keratoconus)
4. Require higher oxygen conductivity (hyperopia, aphakia, a high degree of astigmatism)
5. Children (children’s myopia progress can be delayed)
6. Those who need to simplify the lens operation, care
7. Those who need durable lens (RGP’s average life span is 2 years)
Optical characteristics of contact lens
Jan 31st
Optical characteristics of contact lens
1. Thick Lens Optics
F = F1 + F2-(t / n) F1F2
The key refractive power of a contact lens depends on FOZR(front optical zone radius of curvature).
2. Vertex distance effect
F = Fs / (1-dFs)
s = spectacle diopter
3. Tear lens
LL = BC-K
LL = tear lens
BC = Base Curve
K = corneal front surface curvature
4. ORv + CLP + LL = SRv
5. Magnification vs. spectacle
Think magnification change of myopia and hyperopia with contact lens?
6. Accommodation and convergence
Minus lens more than spectacle
Positive lens less than spectacle
A=1/s(1-2dP)
7. Others factors: temperature, moisture content, bending
Material properties of contact lens
Jan 31st
General nature
1. Transparency
2. Hardness and toughness
3. Tensile and strength
4. Elastic modulus
5. Relative density
6. Refractive index
7. Wettability (surface tension, wetting angle, water absorption)
Special nature
1. Moisture content
2. Ion charge
3. Permeability (Dk value, Dk/L or Dk/t, EOP)-3.0D
Am I suitable for orthokeratology?
Jan 29th
Who is suitable for orthokeratology?
Indications
1. Get the understanding of the mechanism of the correction, potential problems and limitation of the correction.
2. Good motivation and compliance
3. Myopia arrange from -0.75d to -6.00D, astigmatism lower than 1.75D, with rule.
4. Corneal curvature arranges from 37D to 52D.
Contraindication
1. Have unrealistic expect.
2. Ocular diseases such as infection and so on.
3. Refractive error more than -6.00D, anti rule, astigmatism more than 2.0D
4. Age less than 12.
5. Not compliance.
RGP lens wearers show eye blink variations with 3 o’clock, 9 o’clock staining
Sep 16th
While experiencing 3 o’clock and 9 o’clock staining, rigid gas permeable contact lens wearers exert more eye blinking attempts and demonstrate fewer complete eye blinks and more incomplete eye blinks compared with lens wearers with minimal staining and non-lens wearers, according to a study. Contact lens fit and corneal coverage may influence these incomplete eye blinks.
Eef van der Worp, BSc, FAAO, and colleagues evaluated variations in frequency and completeness of eye blinks during a 5-minute period among 30 rigid gas permeable contact lens wearers experiencing 3 o’clock and 9 o’clock corneal fluorescein staining. They compared results with variations observed in 25 RGP lens wearers with less than grade 1 corneal staining and 26 controls who were not lens wearers.
All eye blinks were categorized as either complete, incomplete or an attempt. The investigators also assessed type of lens fit, lens-to-cornea fit, spherical equivalent of refraction and corneal coverage. The study results are published in the September issue of Optometry and Vision Science.
The investigators found no differences in eye blink frequencies between the three groups.
However, they observed fewer complete eye blinks, more incomplete eye blinks and more eye blink attempts in eyes experiencing 3 o’clock and 9 o’clock staining (P < .01) than in eyes without substantial staining (P = .03) and in non-lens wearers (P < .01).
Eyes with interpalpebral lens fits demonstrated fewer complete eye blinks while exerting more eye blink attempts than eyes with lid attachment lens fits (P < .01 for both).
In addition, eyes wearing large or optimally sized lenses demonstrated fewer complete eye blinks (P = .02) and more incomplete eye blinks (P = .03) than eyes wearing small lenses, according to the study.
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